# OpenGL Linear color space

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I am trying to learn about when to use, and when to not use, linear and non-linear color space. This is how I understand it, please correct me where I am wrong or have incomplete understanding:

• Many texture manipulations need to be done in linear space, e.g. anti aliasing and light manipulations.
• Many tools, like Photoshop, save pictures in non-linear format by default.
• You can specify SRGB as a bitmap format (e.g. GL_SRGB in OpenGL to glTexImage2D), and the graphic drivers (or the hardware?) will automatically transform the bitmap you sample from non-linear to linear.
• If you transform it yourself, you do that by setting each color component to c^2.2. This would be an approximation of the SRGB.
• You can transform each color channel independently on the others.
• As a last step, outputting the pixels to the screen, you need to transform it back into non-linear space, using c^(1/2.2) for each channel.
• The value 2.2 depends on the display you use. It looks like Apple use 1.8.

I am not sure about the glGenerateMipmap() function. Will it take the linear/non-linear attribute (SRGB) into account when applying the filter functions?

Is the approximation above good enough, for showing pixels on the screen? Or is it that the exact SRGB encoding need to be used?

Is there any automatic support in the hardware for the final pixel transformation to show on screen?

In most example and tutorials "out there", you don't find any gamma correction being done. So either I don't understand this, or there is a general lack of understanding elsewhere (or something in between :-).

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It sounds like you understand
In most example and tutorials "out there", you don't find any gamma correction being done. So either I don't understand this, or there is a general lack of understanding elsewhere
Yes, "gamma correct rendering" has only become popular in real-time graphics over, maybe the past 5 or so years (guessing), along with the growth in popularity of HDR and physically-based lighting. A lot of older real-time rendering literature ignores gamma issues.
I am trying to learn about when to use, and when to not use, linear and non-linear color space[/quote]You can think of sRGB as a "compression" format for the number of bits required to store an image without colour banding. Humans are good at differentiating between different colours, especially dark colours. The sRGB curve allocates "more bits" to representing darker colours, which means it allows 8-bit images to have less noticeable colour-banding in dark areas.
I've seen it stated that to get the same precision in dark areas, a linear image would need 10-16 bits.
The bad thing is that doing math in curved spaces is difficult -- we're used to flat spaces, like the number-line, or the cartesian plane, but "gamma spaces" (like sRGB, or "gamma 2.2") aren't flat, they're curved.
I am not sure about the glGenerateMipmap() function. Will it take the linear/non-linear attribute (SRGB) into account when applying the filter functions?[/quote]OpenGL and Dx10/11 should do this correctly (convert to linear, downsample, convert to sRGB), but DX9 does not.
You can specify SRGB as a bitmap format (e.g. GL_SRGB in OpenGL to glTexImage2D), and the graphic drivers (or the hardware?) will automatically transform the bitmap you sample from non-linear to linear.[/quote]When you sample from the texture, the texture-fetch hardware will apply the inverse sRGB curve to convert it from 8-bit sRGB to floating-point linear.
As a last step, outputting the pixels to the screen, you need to transform it back into non-linear space, using c^(1/2.2) for each channel.[/quote]If your render-target is created as an sRGB texture, then when you write to it, the hardware will perform the linear->sRGB conversion when writing values from your pixel shader automatically.
It's common to just assume that the user's monitor is an sRGB monitor (because, it's pretty much *the* standard), but yes, a lot of monitors aren't actually sRGB -- I've seen gamma 2.4 and gamma 1.8 monitors before. To get the correct appearance on these monitors, it would be better to manually convert to e.g. gamma 1.8 rather than to convert to sRGB.
Many tools, like Photoshop, save pictures in non-linear format by default[/quote]If you're painting a picture in an application that doesn't do any "gamma correction", then the data in your file is in the same "gamma space" as your monitor.
That is to say -- the image will only look the way that I saw it (while painting it), if it's displayed on another monitor with the same gamma-curve. If I paint my artwork on a gamma-1.8 screen, and then view it on an sRGB screen, it will look different (because the original data was painted in the "gamma 1.8 space").
For this reason, it's common for games studios to buy expensive calibration equipment to make sure that all of their artists monitors are correctly calibrated to the sRGB curve. Edited by Hodgman

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Just wanted to clarify this one. For some reason, they have used "sRGB" to denote "linear color space" in DirectX and OpenGL, which are just two separate things.

Indeed, you can convert from linear to non-linear color spaces and vice-versa by using Gamma correction.

RGB color space by itself lacks any standard or definition, so sRGB was proposed as a standard, which is defined by specifying white point and three chromaticities. For instance, there is also Wide gamut RGB, Adobe RGB and so on.

Now, the conversion from one color space to another, where the color gamut is different, you would need to convert your initial color space to CIE XYZ by using linear transformation and then to the desired color space.

This is why it is simply wrong to call sRGB "linear" and non-sRGB "non-linear" and do the conversion between both using gamma correction. In reality, both typical RGB and sRGB may or may not be linear.

In fact, typically, you can assume that your RGB color space is actually linear. You don't need to voluntarily apply any gamma correction there. Since it lacks standard definition, you can simply assume that when you work with RGB, you work in sRGB, or in Adobe RGB - whatever your choice is. In order to properly standarize your color space, you would need to convert it to one of perceptually uniform (or supposedly) color spaces such as CIELAB, CIELUV, DIN99, ATD95, CIECAM, or at least CIE XYZ, which can actually represent all visible colors by human eye, unlike RGB, which is limited by triangle in CIE diagram.

Now, the problem is that most LCD displays apply huge gamma correction to the input image. Not only that, they may also pre-process images and oversaturate them too. Why? To sell better since higher contrast and crispier images appear prettier, but in the end you receive a very distorted image. This is not your problem, it is a problem of display's manufacturers and vendors! You simply can't make an application that will predict all of the monitors out there, so it's their responsibility to generate final image as accurate as possible.

I don't know why they introduced "sRGB" into DirectX and OpenGL - after all, suposedly, you are already working in sRGB and it's display's job to properly represent input sRGB data so that output strictly conforms to sRGB, or any other standard. If you do gamma correction in your application - well, you still don't know how display is going to re-transform your image data, so in the end you may actually get less accurate results.

My guess is that they introduced so-called "sRGB" in APIs just for the hype of it, e.g.: "We can now store textures and front-buffer in gamma-adjusted format! WOW!" (like we couldn't do it back in 1969).

You may check some of the following bibliography to figure out more about different color spaces (you can see by the dates that this is a very studied topic, yet it seems that people making changes in DirectX/OpenGL standards regarding sRGB have never read them):

1. Poynton, Charles. Digital Video and HDTV Algorithms and Interfaces. Morgan Kaufmann, 2003.
2. Poynton, Charles. "Frequently-Asked Questions about Color." http://www.poynton.com/ColorFAQ.html
3. Hill, Francis S. Computer Graphics using OpenGL. Prentice Hall, 2000.
4. Hearn, Donald, and Pauline M. Baker. Computer Graphics, C Version. Prentice Hall, 1996.
5. Luo, Ronnier M., Guihua Cui, and Changjun Li. "Uniform Colour Spaces Based on CIECAM02 Colour Appearance Model." Color Research & Application (Wiley InterScience) 31, no. 4 (June 2006): 320-330.
6. Lindbloom, Bruce J. "Accurate Color Reproduction for Computer Graphics Applications." Computer Graphics 23, no. 3 (July 1989): 117-126.
7. Brewer, C. A. "Color Use Guidelines for Data Representation." Proceedings of the Section on Statistical Graphics. Alexandria VA: American Statistical Association, 1999. 55-60.
8. MacAdam, David L. "Visual Sensitivities to Color Differences in Daylight." (Journal of the Optical Society of America) 32, no. 5 (May 1942): 247-273.
9. Schanda, Janos. Colorimetry: Understanding the CIE system. Wiley Interscience, 2007.
10. Pratt, William K. Digital Image Processing. 3rd Edition. Wiley-Interscience, 2001.
11. Keith, Jack. Video Demystified: A Handbook for the Digital Engineer. 5th Edition. Fremont, CA: Newnes, 2007.

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Just wanted to clarify this one. For some reason, they have used "sRGB" to denote "linear color space" in DirectX and OpenGL, which are just two separate things.
No, sRGB is not linear color space so your accusations levelled against DirectX/OpenGL are wildly inaccurate.

For why it was so important to add sRGB support to GPUs, read this primer: http://http.develope...gems3_ch24.html

Yes, the sRGB standard does define a standard linear RGB space (as an intermediate step) based on a standardized red/green/blue linear transform from CIE XYZ space...
...but sRGB is a curved "gamma corrected" transformation of these standard linear RGB values.
sRGB isn't even a simple "gamma correction" transform. It's similar to gamma correction of 2.2, but it's actually a piecewise transform with a linear toe at the bottom and a gamma of 2.4 at the top.
Linear RGB to sRGB = http://www.wolframal...31308 & x<=1}}]
sRGB to linear RGB = http://www.wolframal...04045 & x<=1}}]

It's the standard color space for the WWW, and it's being pushed as a standard color space for TVs, computer monitors, cameras, etc... If a display performs sRGB "gamma correction" on the signal, then that's a good thing -- they're supposed to assume that the input signal is sRGB (~gamma 2.2) and adjust voltages accordingly to produce the appropriate perceptually linear luminance response.

Yes it's true that different monitors will do different, wacky things to the input signal, but the world is getting saner in this regard thanks to most manufacturers agreeing to adopt a single gamma standard. The right thing™ to do these days is to perform all of your math in a linear color space, and then output an sRGB signal, unless otherwise asked not to. Edited by Hodgman

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No, sRGB is not linear color space so your accusations levelled against DirectX/OpenGL are wildly inaccurate.

No, my accusations against sRGB in DirectX/OpenGL are based on fact that conversion between RGB and sRGB is thought in terms of gamma correction, while in reality RGB and sRGB may actually be the same thing. In any case, you cannot convert between the two using gamma correction, so this SDK article, for instance, is misleading.

For why it was so important to add sRGB support to GPUs, read this primer: http://http.develope...gems3_ch24.html

Have you read the article yourself? The article you provided can be used as an exercise to find out logical fallacies. Begging the question and fallacy of composition are amongst the first ones visible.

Yes, the sRGB standard does define a standard linear RGB space (as an intermediate step) based on a standardized red/green/blue linear transform from CIE XYZ space...

So, you've repeated what I've said, then added phrase "as an intermediate step" (to what, by the way?) and now you are saying that:

...but sRGB is a curved "gamma corrected" transformation of these standard linear RGB values.
sRGB isn't even a simple "gamma correction" transform. It's similar to gamma correction of 2.2, but it's actually a piecewise transform with a linear toe at the bottom and a gamma of 2.4 at the top.

Nonsense. sRGB is just a color space, nothing more. It's not "gamma correction of 2.2", left alone "piecewise transform with linear toe at [gibberish]". Proof by verbosity is a logical fallacy (but you already know that), please don't do that.

It's the standard color space for the WWW, and it's being pushed as a standard color space for TVs, computer monitors, cameras, etc... If a display performs sRGB "gamma correction" on the signal, then that's a good thing -- they're supposed to assume that the input signal is sRGB (~gamma 2.2) and adjust voltages accordingly to produce the appropriate perceptually linear luminance response.

Two separate arguments. Yes, sRGB is a standard and popular color space. But starting from "display performs sRGB gamma correction" - just a senseless manipulation of words.

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So, you've repeated what I've said, then added phrase "as an intermediate step" (to what, by the way?) and now you are saying that
...
Nonsense. sRGB is just a color space, nothing more. It's not "gamma correction of 2.2",
No, you misread - the sRGB standard defines two colour spaces -- one is a linear RGB colour-space, which is used as an intermediate between CIE XYZ and sRGB-proper.
Once you've got colour data in this "linear RGB" space, you can perform the above transforms on it to get the values into the non-linear sRGB space.

Regarding sRGB being similar to "gamma 2.2" -- the above functions to convert to/from linear/sRGB (the "piecewise gibberish") can be approximated by x[sup]^2.2[/sup] and x[sup]^(1/2.2)[/sup] (i.e. the regular "gamma correction" process with a power of 2.2).

Linear RGB colour spaces can be used to describe physical quantities of energy, not just colours. If I've got 100 "units" of photons at the "red" wavelength and send them through a half-silvered-mirror so I end up with only half of them, then I've now got "50" units of red photons. This kind of math does not work in non-linear spaces like sRGB.

Likewise if I've got a black/white checker pattern (0 & 255) and mathematically average it, I get a "50% grey" image (127). In a linear color-space, this value is exactly half as bright as the original white squares. However, in non-linear spaces this math doesn't work. For example, in sRGB 127 is ~21% as bright as 255. If you down-scale an sRGB image of a black/white checkerboard, the resulting colour should be ~187 (which corresponds to "half as bright as white").

e.g. the left half of this image is resized by performing the naive math (averaging sRGB values directly resulting in 127).
The right half performs the math correctly (convert sRGB values to linear, average to 127, then convert back to sRGB, resulting in 187).
If I squint at the image from a distance (to manually average the black/white pattern in my eye), the right hand side all looks almost the same brightness, but the left hand side is obviously too dark.

The linked article from nVidia shows the disastrous consequences from trying to perform math in a non-linear colour space.
while in reality RGB and sRGB may actually be the same thing[/quote]Yes, RGB is a loose term so it could mean anything.
But in rendering we deal with linear-RGB spaces, and non-linear RGB spaces (such as "gamma 2.2" and sRGB).
I posted the equations to transform between "linear RGB" and sRGB above, so when we talk about them in rendering they're definitely not the same - one is mathematically linear and one is not!
Have you read the article yourself? The article you provided can be used as an exercise to find out logical fallacies. Begging the question and fallacy of composition are amongst the first ones visible.[/quote]Wow. That article describes the basics for achieving physically correct math in a renderer. What is your problem with it?
you cannot convert between the two using gamma correction, so this SDK article, for instance, is misleading
[/quote]What's your problem with that article?
Maybe if you're disagreeing with nVidia, Microsoft, Kronos, and the GL ARB (3Dlabs, Apple, ATI, Dell, IBM, Intel, SGI, Sun), the problem is actually that they know what they're doing and you're refusing to read wikipedia to catch up? (the argumentum ad verecundiam fallacy, I know -- but while I'm here, what does make you an expert over them?)
Yes, sRGB is a standard and popular color space. But starting from "display performs sRGB gamma correction" - just a senseless manipulation of words.[/quote]The display has to calibrate it's internal voltages so that when it receives a value of 255 it outputs at maxium luminosity, at 187 it outputs half-maximum luminosity, and at 127 it outputs at 21% maximum luminosity. That's the sRGB correction that the monitor must perform. Edited by Hodgman

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Maybe if you're disagreeing with nVidia, Microsoft, Kronos, and the GL ARB (3Dlabs, Apple, ATI, Dell, IBM, Intel, SGI, Sun), the problem is actually that they know what they're doing and you're refusing to read wikipedia to catch up?

This is Argumentum ad populum.

The articles I've mentioned in my post are verified and have been passed scientific review (by several council members), while you provide your opinions backed up by your own words, some stuff on Internet and popular belief.

So you are saying that the companies you have randomly selected and mentioned have something to do in decision-making regarding misleading usage of sRGB term? With this, you automatically decide that I'm wrong and you are right?

(Appeal to authority fallacy, I know -- but while I'm here, what does make you an expert over them?)

Yes, it's appeal to authority. You are moderator, so you are always right and if there is something you don't like, you rather attack the person (Appeal to the person fallacy) rather than provide sound arguments in discussion. While we're here - I don't consider myself authority and there are many things in the world that I don't know or understand, and I'm humble about it. Yes, my master's and doctoral thesis works were regarding practical applications in mobile systems of color theory and I have published 12 council-reviewed scientific works regarding different color spaces and applications, so this is why I have something to say about it. I could always be mistaken as well as people who review and judge my work, but while I try to base my points on proven facts, you try to prove something by use of Wikipedia, popular folklore and your Moderator badge.

Please, I know your intentions in answering OP's question was good, I just tried to clarify things as something that made its way to SDK does not necessarily mean it is correct. You don't have either to defend something blindly just because I've pointed out to a misconception in Microsoft manual.

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You don't have either to defend something blindly just because I've pointed out to a misconception in Microsoft manual.
You said "For some reason, they have used "sRGB" to denote "linear color space" in DirectX and OpenGL" which is absolutely 100% false, so is a statement that should be criticized. Which of your references backs up this statement of yours?

sRGB is defined as a non-linear transformation from a particular linear RGB colour space.

Also, you've said [brackets mine]:
Indeed, you can convert from linear [RGB] to non-linear [sRGB] color spaces and vice-versa by using Gamma correction.
And then:
In any case, you cannot convert between the two [RGB and sRGB] using gamma correction, so this SDK article, for instance, is misleading.

The above checkerboard image and the linked nVidia article explain why you cannot perform your shading math in curved spaces such as sRGB, and thus why sRGB values have to be decoded to linear values for shading (and possibly re-encoded to sRGB for display or storage).

Here's the short form of linear vs non-linear:
Math in sRGB: [font=courier new,courier,monospace](0+1)/2=0.22[/font]
Math in any linear space: [font=courier new,courier,monospace](0+1)/2=0.5[/font]

What errors or misleading statements are there in the Microsoft and nVidia links that you've accused?

So you are saying that the companies you have randomly selected and mentioned have something to do in decision-making regarding misleading usage of sRGB term? With this, you automatically decide that I'm wrong and you are right?
The companies I listed are responsible for the important nVidia page you've denounced and the design of D3D/GL, which you've denounced.

I decided that you're wrong because you're saying things that I know are wrong. I've worked on converting a lot of renderers from being "gamma ignorant" to performing proper gamma correction and linear-space lighting. You can't perform shading math in colour spaces like sRGB because of the non-linearity. This makes it fundamentally different from linear RGB colour spaces. This is the reason why it was so important to add them to D3D/GL.

You are moderator, so you are always right and if there is something you don't like, you rather attack the person[/quote]Moderators always being right is a ridiculous appeal to authority. We generally don't moderate threads that we've participated in either, so my ability to lock/hide abusive content is irrelevant.

I've explained where and why you were wrong, which you've brushed off as nonsense, gibberish and senseless words. I think I've been quite polite regarding such condescension.
Despite 'appeal to popularity' being a fallacy, you do have to consider that perhaps you're just wrong and you should go and re-read the sRGB wikipedia page -- Occam's razor and all that... but take it as a personal slight instead of reflecting on it if you must, or explain to me the flaw in the above math.

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sRGB is defined as a non-linear transformation from a particular linear RGB colour space.

You are wrong. sRGB is an application of standardization to RGB color space and it is defined by three primaries in CIE XYZ color space. The transformation between linear and non-linear color spaces is entirely different topic. I've already said this before.

[quote name='Hodgman' timestamp='1347898336' post='4980926']What errors or misleading statements are there in the Microsoft and nVidia links that you've accused?[/quote]
I've already said this in my earlier posts. The error is to mix gamma correction concepts along with RGB and sRGB color spaces together, trying to imply that at one point or another when you "convert" or "transform" (or similar term) from one to another, you need to do gamma correcion, or that at some point gamma correction is applied. My suggested correction is that there are separate topics and the introduction of sRGB texture format is poorly fundamented and sRGB color space name is misused.

I decided that you're wrong because you're saying things that I know are wrong.

Just because you think/decide/believe I'm wrong, it doesn't make you right. It just makes you superficial.

Moderators always being right is a ridiculous appeal to authority. We generally don't moderate threads that we've participated in either, so my ability to lock/hide abusive content is irrelevant.

I was not referring to actual thread moderation, rather than you feel that you are right because you are moderator. Perhaps I'm wrong and maybe there are other reasons why you think you are automatically right.

I've explained where and why you were wrong, which you've brushed off as nonsense, gibberish and senseless words.

You have said that I'm wrong and failed to give any reasonable evidence to support your points, other than referring to popular belief, your own belief, mixing my phrases with new words among others. I wouldn't mind if you only posted your own points, but copying my text and then adding stuff of your own with the purpose of misguiding the discussion is just uncool. I think you just don't like being seen as wrong on forums where you moderate.

Despite 'appeal to popularity' being a fallacy, you do have to consider that perhaps you're just wrong and you should go and re-read the sRGB wikipedia page -- Occam's razor and all that... but take it as a personal slight instead of reflecting on it if you must.

Why don't you follow your own advice? On that note, I might suggest that you don't limit your reading to [s]Facebook[/s]Wikipedia only.

P.S. you might want to read some earlier versions of Wikipedia sRGB entry. The end result is that when sRGB is viewed on CRT, the viewed gamma appears as 2.2, but again, this is CRT/Display issue, not the space itself. Coincidence and consequence are two different things. Just because gamma is mentioned, it doesn't mean (non-S)RGB has different gamma. In fact, I think mentioning gamma in sRGB discussion is not relevant.

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You are wrong. sRGB is an application of standardization to RGB color space and it is defined by three primaries in CIE XYZ color space. The transformation between linear and non-linear color spaces is entirely different topic. I've already said this before.
If you don't beleive wikipedia, check it's references.
In this case, the sRGB standard is defined by IEC 61966-2-1:1999, which you can view a draft copy of for free here. Yes, it's defined by three XYZ primaries, and a non-linear transformation of those primaries (which is similar to a "gamma 2.2" adjustment).

The OP was specifically asking about sRGB in OpenGL; you can read their definitions of the sRGB transform here and here.

Those three documents describe the same non-linear transforms that appear on wikipedia... but because I've linked to them on the internet instead of quoted an ISBN, you don't believe them?

So either you're saying these documents are wrong (and that when i sample from an sRGB texture in my fragment shader, no non-linear transform of the texture data will take place) or that these documents are wrong to call this colour space sRGB, and they've actually misappropriated the name.
If the former, you can be refuted by experiment, if the latter, then it's irrelevant as the OP was asking about the "sRGB" space that's used by GL/D3D, which is also known as IEC 61966-2-1:1999.

I don't know what "sRGB" you're talking about, but what you've described is definitely not IEC 61966-2-1.
Perhaps this whole time you've been describing the "linear RGB" space that's defined as an intermediate conversion between XYZ and sRGB, which sounds likely. The point is that we want to be doing our shading math in this linear RGB space (at a high bit depth), but usually our input and output formats are sRGB, so we require the non-linear conversion (which is approximate to "gamma 2.2" correction, as mentioned in the specification).

In fact, I think mentioning gamma in sRGB discussion is not relevant.[/quote]The fact is that in OpenGL and D3D sRGB and gamma are related concepts, because as described in the above specification, sRGB is similar to a gamma 2.2 curve...

When I read a texel from an OpenGL sRGB texture, a non-linear transform described on the wikipedia page (which can be approximated as x[sup]^2.2[/sup]) is applied to it automatically.
When I write a pixel to an OpenGL sRGB render-target, a non-linear transform described on the wikipedia page (which can be approximated as x[sup]^(1/2.2)[/sup]) is applied to it automatically.

So if I assume that my input textures were authored in the sRGB space (or on a CRT and are happy that CRT's are close enough to sRGB displays) and assume that the user's output display is an sRGB device, then by using sRGB textures an render-targets, I can perform all of my fragment-shading math in a linear colour space automatically (but still have non-linear inputs and outputs), thanks to GL natively supporting these transforms.

This is the purpose of sRGB formats in OpenGL, as shown by the above OpenGL specifications.

you feel that you are right because you are moderator[/quote]No, that's insulting. I'm quoting the sRGB standard, and you're saying I'm wrong, the standard is wrong, and nVidia, ATI and Microsoft are wrong too. That's pretty simple. Why are you so opposed to learning about sRGB?
P.S. you might want to read some earlier versions of Wikipedia sRGB entry.[/quote]That old version still describes the exact same linear transformation from XYZ followed by a non-linear transformation!!! How can you post this stuff up, and still argue that it's a linear space? Now I think you're just trolling...
You have said that I'm wrong and failed to give any reasonable evidence to support your points[/quote]The wikipedia page that I linked to contains proper references, shown above. Where is your evidence that sRGB is just a linear transform from XYZ with no non-linear part to it?
As well as this obviously false claim, you've attacked an nVidia and microsoft article without actually stating any actual points against them or providing evidence.
You've made claims about the purpose/usefulness of sRGB resources in GL/D3D without providing any evidence to back them up too.
The end result is that when sRGB is viewed on CRT, the viewed gamma appears as 2.2,[/quote]The display has nothing to do with it -- arguing about what a signal looks like when plugged into a display of a different colour space is irrelevant.
e.g. oh I sent the HSV bytes of [0,0,100] on my RGB CRT and it came out Blue!
Yes, CRT's often work in a vague "RGB gamma 2.2" colour space -- however, this is actually a good approximation of sRGB colour space (sRGB was inspired by CRT's), so sRGB images look almost correct when viewed on these displays... However, to display it correctly in theory you should correctly decode the sRGB signal and re-encode it in the monitor's colour space (but in practice with 8-bit inputs, this will do more harm than good), but I assume you already know this - e.g.
if(srgb < 0.04045) linear = srgb / 12.92; else linear = pow( ((srgb + 0.055)/1.055), 2.4 ); CRT = pow(linear, 1/2.2);

If you still don't believe that you can't do math in curved spaces, and that sRGB is a curved space, despite the specification saying so, try it for yourself:
* Pick any two XYZ colours, A[sub]xyz[/sub] and B[sub]xyz[/sub].
* Convert them to "linear RGB" (as defined in the first part of sRGB specification) to get A[sub]linear[/sub] and B[sub]linear[/sub].
* Compute their average C[sub]linear[/sub].
* Convert A[sub]linear[/sub] and B[sub]linear[/sub]. to sRGB following the full sRGB specification to get A[sub]srgb[/sub] and B[sub]srgb[/sub].
* Compute their average C[sub]srgb[/sub].
* Convert C[sub]srgb[/sub] back into "linear RGB" and compare against C[sub]linear[/sub] -- It will be very wrong in most cases.

The reason the GPU hardware supports sRGB as a native colour space now, is so we can use sRGB data for storage and display, while performing our math in a linear colour space, without having the pay the cost of transforming back and forth between the two colour spaces constantly (the hardware makes the conversion 'free'). This is a huge deal, because as the checkerboard image from earlier shows -- math in sRGB space makes no sense. Edited by Hodgman

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Thanks for the very detailed information!

If your render-target is created as an sRGB texture, then when you write to it, the hardware will perform the linear->sRGB conversion when writing values from your pixel shader automatically.

It seems to be easy to do this in (looking at OpenGL specifically now). Using a Frame Buffer Object with a target texture object of format GL_SRGB8_ALPHA8 (which is a required format). The only caveat is that the transformation to SRGB color space should be done last, and I would prefer not to have a dummy draw into a FBO just to get this transformation. I don't think it is possible to associate the attribute "SRGB" with the default frame buffer?

You can do glEnable(GL_FRAMEBUFFER_SRGB), but only if the value GL_FRAMEBUFFER_ATTACHMENT_COLOR_ENCODING of the destination buffer is GL_SRGB.

Of course, there is always the possibility of doing the transformation yourself, in the shader. But automatic built-in functionality is sometimes more optimized.

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It's possible in DX, so it should be possible in GL as well. Although typically in the very last step you want to do the transformation yourself, so that you allow the user to tweak the curve slightly in order to compensate for the gamma of their display.

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CRT = pow(linear, 1/2.2);

This would be an approximation of the sRGB algorithm, which is
 if (linear <= 0.0031308) CRT = linear * 12.92; else CRT = 1.055 * pow(linear, 1/2.4) - 0.055; 
For high values, they are near. For low values, they start to diverge, especially very low values. What is the reason for using this approximation? I suppose one reason can be that of shader performance.

Possibly, it may be that the lower values will not be noticed in games. But that would seem to be a contradiction to the purpose of having extra resolution in the low value interval of sRGB. Actually, my game has some banding problems when drawing the outer limits of a spherical fog in a dark environment (while still not taking sRGB color space into account).

Sampled values from 8-bit textures will only have a resolution of 1/255 = 0.0039, which would not be used in the sRGB conversion unless using some form of HDR.

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What is the reason for using this approximation?
In that code, I was assuming that the input values were in non-linear sRGB, but the desired output was "CRT RGB" (linear RGB with gamma 2.2) -- the code was decoding from sRGB to linear, and then re-encoding the linear values to "CRT RGB". i.e. it was an [font=courier new,courier,monospace]sRGB->CRT[/font] conversion function.
N.B. this isn't a very useful thing to do in practice, because if this operation is done with 8-bits inputs and outputs, you'll just be destroying information. If displaying 8-bit sRGB images on a CRT, it would be best to avoid doing the right thing™ (which is converting the data into the display's colour encoding) and just output the sRGB data unmodified, because "CRT RGB" and sRGB are so similar.

In a game, if you had sRGB textures and the user had a CRT monitor, the right thing to do would be to sRGB decode the textures to linear, do your shading in linear (at high precision, e.g. float/half) and then encode the result with x[sup]^(1/2.2)[/sup] to compensate for the CRT's natural response of x[sup]^2.2[/sup].
However, most user's don't have a CRT, so it's best to encode the final result with the standard sRGB curve instead of the CRT gamma 2.2 curve. Edited by Hodgman

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• ### Similar Content

• By EddieK
Hello. I'm trying to make an android game and I have come across a problem. I want to draw different map layers at different Z depths so that some of the tiles are drawn above the player while others are drawn under him. But there's an issue where the pixels with alpha drawn above the player. This is the code i'm using:
int setup(){ GLES20.glEnable(GLES20.GL_DEPTH_TEST); GLES20.glEnable(GL10.GL_ALPHA_TEST); GLES20.glEnable(GLES20.GL_TEXTURE_2D); } int render(){ GLES20.glClearColor(0, 0, 0, 0); GLES20.glClear(GLES20.GL_ALPHA_BITS); GLES20.glClear(GLES20.GL_COLOR_BUFFER_BIT); GLES20.glClear(GLES20.GL_DEPTH_BUFFER_BIT); GLES20.glBlendFunc(GLES20.GL_ONE, GL10.GL_ONE_MINUS_SRC_ALPHA); // do the binding of textures and drawing vertices } My vertex shader:
uniform mat4 MVPMatrix; // model-view-projection matrix uniform mat4 projectionMatrix; attribute vec4 position; attribute vec2 textureCoords; attribute vec4 color; attribute vec3 normal; varying vec4 outColor; varying vec2 outTexCoords; varying vec3 outNormal; void main() { outNormal = normal; outTexCoords = textureCoords; outColor = color; gl_Position = MVPMatrix * position; } My fragment shader:
precision highp float; uniform sampler2D texture; varying vec4 outColor; varying vec2 outTexCoords; varying vec3 outNormal; void main() { vec4 color = texture2D(texture, outTexCoords) * outColor; gl_FragColor = vec4(color.r,color.g,color.b,color.a);//color.a); } I have attached a picture of how it looks. You can see the black squares near the tree. These squares should be transparent as they are in the png image:

Its strange that in this picture instead of alpha or just black color it displays the grass texture beneath the player and the tree:

Any ideas on how to fix this?

• This article uses material originally posted on Diligent Graphics web site.
Introduction
Graphics APIs have come a long way from small set of basic commands allowing limited control of configurable stages of early 3D accelerators to very low-level programming interfaces exposing almost every aspect of the underlying graphics hardware. Next-generation APIs, Direct3D12 by Microsoft and Vulkan by Khronos are relatively new and have only started getting widespread adoption and support from hardware vendors, while Direct3D11 and OpenGL are still considered industry standard. New APIs can provide substantial performance and functional improvements, but may not be supported by older hardware. An application targeting wide range of platforms needs to support Direct3D11 and OpenGL. New APIs will not give any advantage when used with old paradigms. It is totally possible to add Direct3D12 support to an existing renderer by implementing Direct3D11 interface through Direct3D12, but this will give zero benefits. Instead, new approaches and rendering architectures that leverage flexibility provided by the next-generation APIs are expected to be developed.
There are at least four APIs (Direct3D11, Direct3D12, OpenGL/GLES, Vulkan, plus Apple's Metal for iOS and osX platforms) that a cross-platform 3D application may need to support. Writing separate code paths for all APIs is clearly not an option for any real-world application and the need for a cross-platform graphics abstraction layer is evident. The following is the list of requirements that I believe such layer needs to satisfy:
Lightweight abstractions: the API should be as close to the underlying native APIs as possible to allow an application leverage all available low-level functionality. In many cases this requirement is difficult to achieve because specific features exposed by different APIs may vary considerably. Low performance overhead: the abstraction layer needs to be efficient from performance point of view. If it introduces considerable amount of overhead, there is no point in using it. Convenience: the API needs to be convenient to use. It needs to assist developers in achieving their goals not limiting their control of the graphics hardware. Multithreading: ability to efficiently parallelize work is in the core of Direct3D12 and Vulkan and one of the main selling points of the new APIs. Support for multithreading in a cross-platform layer is a must. Extensibility: no matter how well the API is designed, it still introduces some level of abstraction. In some cases the most efficient way to implement certain functionality is to directly use native API. The abstraction layer needs to provide seamless interoperability with the underlying native APIs to provide a way for the app to add features that may be missing. Diligent Engine is designed to solve these problems. Its main goal is to take advantages of the next-generation APIs such as Direct3D12 and Vulkan, but at the same time provide support for older platforms via Direct3D11, OpenGL and OpenGLES. Diligent Engine exposes common C++ front-end for all supported platforms and provides interoperability with underlying native APIs. It also supports integration with Unity and is designed to be used as graphics subsystem in a standalone game engine, Unity native plugin or any other 3D application. Full source code is available for download at GitHub and is free to use.
Overview
Diligent Engine API takes some features from Direct3D11 and Direct3D12 as well as introduces new concepts to hide certain platform-specific details and make the system easy to use. It contains the following main components:
Render device (IRenderDevice  interface) is responsible for creating all other objects (textures, buffers, shaders, pipeline states, etc.).
Device context (IDeviceContext interface) is the main interface for recording rendering commands. Similar to Direct3D11, there are immediate context and deferred contexts (which in Direct3D11 implementation map directly to the corresponding context types). Immediate context combines command queue and command list recording functionality. It records commands and submits the command list for execution when it contains sufficient number of commands. Deferred contexts are designed to only record command lists that can be submitted for execution through the immediate context.
An alternative way to design the API would be to expose command queue and command lists directly. This approach however does not map well to Direct3D11 and OpenGL. Besides, some functionality (such as dynamic descriptor allocation) can be much more efficiently implemented when it is known that a command list is recorded by a certain deferred context from some thread.
The approach taken in the engine does not limit scalability as the application is expected to create one deferred context per thread, and internally every deferred context records a command list in lock-free fashion. At the same time this approach maps well to older APIs.
In current implementation, only one immediate context that uses default graphics command queue is created. To support multiple GPUs or multiple command queue types (compute, copy, etc.), it is natural to have one immediate contexts per queue. Cross-context synchronization utilities will be necessary.
Swap Chain (ISwapChain interface). Swap chain interface represents a chain of back buffers and is responsible for showing the final rendered image on the screen.
Render device, device contexts and swap chain are created during the engine initialization.
Resources (ITexture and IBuffer interfaces). There are two types of resources - textures and buffers. There are many different texture types (2D textures, 3D textures, texture array, cubmepas, etc.) that can all be represented by ITexture interface.
Resources Views (ITextureView and IBufferView interfaces). While textures and buffers are mere data containers, texture views and buffer views describe how the data should be interpreted. For instance, a 2D texture can be used as a render target for rendering commands or as a shader resource.
Pipeline State (IPipelineState interface). GPU pipeline contains many configurable stages (depth-stencil, rasterizer and blend states, different shader stage, etc.). Direct3D11 uses coarse-grain objects to set all stage parameters at once (for instance, a rasterizer object encompasses all rasterizer attributes), while OpenGL contains myriad functions to fine-grain control every individual attribute of every stage. Both methods do not map very well to modern graphics hardware that combines all states into one monolithic state under the hood. Direct3D12 directly exposes pipeline state object in the API, and Diligent Engine uses the same approach.
Shader Resource Binding (IShaderResourceBinding interface). Shaders are programs that run on the GPU. Shaders may access various resources (textures and buffers), and setting correspondence between shader variables and actual resources is called resource binding. Resource binding implementation varies considerably between different API. Diligent Engine introduces a new object called shader resource binding that encompasses all resources needed by all shaders in a certain pipeline state.
API Basics
Creating Resources
Device resources are created by the render device. The two main resource types are buffers, which represent linear memory, and textures, which use memory layouts optimized for fast filtering. Graphics APIs usually have a native object that represents linear buffer. Diligent Engine uses IBuffer interface as an abstraction for a native buffer. To create a buffer, one needs to populate BufferDesc structure and call IRenderDevice::CreateBuffer() method as in the following example:
BufferDesc BuffDesc; BufferDesc.Name = "Uniform buffer"; BuffDesc.BindFlags = BIND_UNIFORM_BUFFER; BuffDesc.Usage = USAGE_DYNAMIC; BuffDesc.uiSizeInBytes = sizeof(ShaderConstants); BuffDesc.CPUAccessFlags = CPU_ACCESS_WRITE; m_pDevice->CreateBuffer( BuffDesc, BufferData(), &m_pConstantBuffer ); While there is usually just one buffer object, different APIs use very different approaches to represent textures. For instance, in Direct3D11, there are ID3D11Texture1D, ID3D11Texture2D, and ID3D11Texture3D objects. In OpenGL, there is individual object for every texture dimension (1D, 2D, 3D, Cube), which may be a texture array, which may also be multisampled (i.e. GL_TEXTURE_2D_MULTISAMPLE_ARRAY). As a result there are nine different GL texture types that Diligent Engine may create under the hood. In Direct3D12, there is only one resource interface. Diligent Engine hides all these details in ITexture interface. There is only one  IRenderDevice::CreateTexture() method that is capable of creating all texture types. Dimension, format, array size and all other parameters are specified by the members of the TextureDesc structure:
TextureDesc TexDesc; TexDesc.Name = "My texture 2D"; TexDesc.Type = TEXTURE_TYPE_2D; TexDesc.Width = 1024; TexDesc.Height = 1024; TexDesc.Format = TEX_FORMAT_RGBA8_UNORM; TexDesc.Usage = USAGE_DEFAULT; TexDesc.BindFlags = BIND_SHADER_RESOURCE | BIND_RENDER_TARGET | BIND_UNORDERED_ACCESS; TexDesc.Name = "Sample 2D Texture"; m_pRenderDevice->CreateTexture( TexDesc, TextureData(), &m_pTestTex ); If native API supports multithreaded resource creation, textures and buffers can be created by multiple threads simultaneously.
Interoperability with native API provides access to the native buffer/texture objects and also allows creating Diligent Engine objects from native handles. It allows applications seamlessly integrate native API-specific code with Diligent Engine.
Next-generation APIs allow fine level-control over how resources are allocated. Diligent Engine does not currently expose this functionality, but it can be added by implementing IResourceAllocator interface that encapsulates specifics of resource allocation and providing this interface to CreateBuffer() or CreateTexture() methods. If null is provided, default allocator should be used.
Initializing the Pipeline State
As it was mentioned earlier, Diligent Engine follows next-gen APIs to configure the graphics/compute pipeline. One big Pipelines State Object (PSO) encompasses all required states (all shader stages, input layout description, depth stencil, rasterizer and blend state descriptions etc.). This approach maps directly to Direct3D12/Vulkan, but is also beneficial for older APIs as it eliminates pipeline misconfiguration errors. With many individual calls tweaking various GPU pipeline settings it is very easy to forget to set one of the states or assume the stage is already properly configured when in fact it is not. Using pipeline state object helps avoid these problems as all stages are configured at once.
While in earlier APIs shaders were bound separately, in the next-generation APIs as well as in Diligent Engine shaders are part of the pipeline state object. The biggest challenge when authoring shaders is that Direct3D and OpenGL/Vulkan use different shader languages (while Apple uses yet another language in their Metal API). Maintaining two versions of every shader is not an option for real applications and Diligent Engine implements shader source code converter that allows shaders authored in HLSL to be translated to GLSL. To create a shader, one needs to populate ShaderCreationAttribs structure. SourceLanguage member of this structure tells the system which language the shader is authored in:
When sampling a texture in a shader, the texture sampler was traditionally specified as separate object that was bound to the pipeline at run time or set as part of the texture object itself. However, in most cases it is known beforehand what kind of sampler will be used in the shader. Next-generation APIs expose new type of sampler called static sampler that can be initialized directly in the pipeline state. Diligent Engine exposes this functionality: when creating a shader, textures can be assigned static samplers. If static sampler is assigned, it will always be used instead of the one initialized in the texture shader resource view. To initialize static samplers, prepare an array of StaticSamplerDesc structures and initialize StaticSamplers and NumStaticSamplers members. Static samplers are more efficient and it is highly recommended to use them whenever possible. On older APIs, static samplers are emulated via generic sampler objects.
The following is an example of shader initialization:
Creating the Pipeline State Object
After all required shaders are created, the rest of the fields of the PipelineStateDesc structure provide depth-stencil, rasterizer, and blend state descriptions, the number and format of render targets, input layout format, etc. For instance, rasterizer state can be described as follows:
PipelineStateDesc PSODesc; RasterizerStateDesc &RasterizerDesc = PSODesc.GraphicsPipeline.RasterizerDesc; RasterizerDesc.FillMode = FILL_MODE_SOLID; RasterizerDesc.CullMode = CULL_MODE_NONE; RasterizerDesc.FrontCounterClockwise = True; RasterizerDesc.ScissorEnable = True; RasterizerDesc.AntialiasedLineEnable = False; Depth-stencil and blend states are defined in a similar fashion.
Another important thing that pipeline state object encompasses is the input layout description that defines how inputs to the vertex shader, which is the very first shader stage, should be read from the memory. Input layout may define several vertex streams that contain values of different formats and sizes:
// Define input layout InputLayoutDesc &Layout = PSODesc.GraphicsPipeline.InputLayout; LayoutElement TextLayoutElems[] = {     LayoutElement( 0, 0, 3, VT_FLOAT32, False ),     LayoutElement( 1, 0, 4, VT_UINT8, True ),     LayoutElement( 2, 0, 2, VT_FLOAT32, False ), }; Layout.LayoutElements = TextLayoutElems; Layout.NumElements = _countof( TextLayoutElems ); Finally, pipeline state defines primitive topology type. When all required members are initialized, a pipeline state object can be created by IRenderDevice::CreatePipelineState() method:
// Define shader and primitive topology PSODesc.GraphicsPipeline.PrimitiveTopologyType = PRIMITIVE_TOPOLOGY_TYPE_TRIANGLE; PSODesc.GraphicsPipeline.pVS = pVertexShader; PSODesc.GraphicsPipeline.pPS = pPixelShader; PSODesc.Name = "My pipeline state"; m_pDev->CreatePipelineState(PSODesc, &m_pPSO); When PSO object is bound to the pipeline, the engine invokes all API-specific commands to set all states specified by the object. In case of Direct3D12 this maps directly to setting the D3D12 PSO object. In case of Direct3D11, this involves setting individual state objects (such as rasterizer and blend states), shaders, input layout etc. In case of OpenGL, this requires a number of fine-grain state tweaking calls. Diligent Engine keeps track of currently bound states and only calls functions to update these states that have actually changed.
Direct3D11 and OpenGL utilize fine-grain resource binding models, where an application binds individual buffers and textures to certain shader or program resource binding slots. Direct3D12 uses a very different approach, where resource descriptors are grouped into tables, and an application can bind all resources in the table at once by setting the table in the command list. Resource binding model in Diligent Engine is designed to leverage this new method. It introduces a new object called shader resource binding that encapsulates all resource bindings required for all shaders in a certain pipeline state. It also introduces the classification of shader variables based on the frequency of expected change that helps the engine group them into tables under the hood:
Static variables (SHADER_VARIABLE_TYPE_STATIC) are variables that are expected to be set only once. They may not be changed once a resource is bound to the variable. Such variables are intended to hold global constants such as camera attributes or global light attributes constant buffers. Mutable variables (SHADER_VARIABLE_TYPE_MUTABLE) define resources that are expected to change on a per-material frequency. Examples may include diffuse textures, normal maps etc. Dynamic variables (SHADER_VARIABLE_TYPE_DYNAMIC) are expected to change frequently and randomly. Shader variable type must be specified during shader creation by populating an array of ShaderVariableDesc structures and initializing ShaderCreationAttribs::Desc::VariableDesc and ShaderCreationAttribs::Desc::NumVariables members (see example of shader creation above).
Static variables cannot be changed once a resource is bound to the variable. They are bound directly to the shader object. For instance, a shadow map texture is not expected to change after it is created, so it can be bound directly to the shader:
PixelShader->GetShaderVariable( "g_tex2DShadowMap" )->Set( pShadowMapSRV ); Mutable and dynamic variables are bound via a new Shader Resource Binding object (SRB) that is created by the pipeline state (IPipelineState::CreateShaderResourceBinding()):
m_pPSO->CreateShaderResourceBinding(&m_pSRB); Note that an SRB is only compatible with the pipeline state it was created from. SRB object inherits all static bindings from shaders in the pipeline, but is not allowed to change them.
Mutable resources can only be set once for every instance of a shader resource binding. Such resources are intended to define specific material properties. For instance, a diffuse texture for a specific material is not expected to change once the material is defined and can be set right after the SRB object has been created:
m_pSRB->GetVariable(SHADER_TYPE_PIXEL, "tex2DDiffuse")->Set(pDiffuseTexSRV); In some cases it is necessary to bind a new resource to a variable every time a draw command is invoked. Such variables should be labeled as dynamic, which will allow setting them multiple times through the same SRB object:
m_pSRB->GetVariable(SHADER_TYPE_VERTEX, "cbRandomAttribs")->Set(pRandomAttrsCB); Under the hood, the engine pre-allocates descriptor tables for static and mutable resources when an SRB objcet is created. Space for dynamic resources is dynamically allocated at run time. Static and mutable resources are thus more efficient and should be used whenever possible.
As you can see, Diligent Engine does not expose low-level details of how resources are bound to shader variables. One reason for this is that these details are very different for various APIs. The other reason is that using low-level binding methods is extremely error-prone: it is very easy to forget to bind some resource, or bind incorrect resource such as bind a buffer to the variable that is in fact a texture, especially during shader development when everything changes fast. Diligent Engine instead relies on shader reflection system to automatically query the list of all shader variables. Grouping variables based on three types mentioned above allows the engine to create optimized layout and take heavy lifting of matching resources to API-specific resource location, register or descriptor in the table.
This post gives more details about the resource binding model in Diligent Engine.
Setting the Pipeline State and Committing Shader Resources
Before any draw or compute command can be invoked, the pipeline state needs to be bound to the context:
m_pContext->SetPipelineState(m_pPSO); Under the hood, the engine sets the internal PSO object in the command list or calls all the required native API functions to properly configure all pipeline stages.
The next step is to bind all required shader resources to the GPU pipeline, which is accomplished by IDeviceContext::CommitShaderResources() method:
m_pContext->CommitShaderResources(m_pSRB, COMMIT_SHADER_RESOURCES_FLAG_TRANSITION_RESOURCES); The method takes a pointer to the shader resource binding object and makes all resources the object holds available for the shaders. In the case of D3D12, this only requires setting appropriate descriptor tables in the command list. For older APIs, this typically requires setting all resources individually.
Next-generation APIs require the application to track the state of every resource and explicitly inform the system about all state transitions. For instance, if a texture was used as render target before, while the next draw command is going to use it as shader resource, a transition barrier needs to be executed. Diligent Engine does the heavy lifting of state tracking.  When CommitShaderResources() method is called with COMMIT_SHADER_RESOURCES_FLAG_TRANSITION_RESOURCES flag, the engine commits and transitions resources to correct states at the same time. Note that transitioning resources does introduce some overhead. The engine tracks state of every resource and it will not issue the barrier if the state is already correct. But checking resource state is an overhead that can sometimes be avoided. The engine provides IDeviceContext::TransitionShaderResources() method that only transitions resources:
m_pContext->TransitionShaderResources(m_pPSO, m_pSRB); In some scenarios it is more efficient to transition resources once and then only commit them.
Invoking Draw Command
The final step is to set states that are not part of the PSO, such as render targets, vertex and index buffers. Diligent Engine uses Direct3D11-syle API that is translated to other native API calls under the hood:
ITextureView *pRTVs[] = {m_pRTV}; m_pContext->SetRenderTargets(_countof( pRTVs ), pRTVs, m_pDSV); // Clear render target and depth buffer const float zero[4] = {0, 0, 0, 0}; m_pContext->ClearRenderTarget(nullptr, zero); m_pContext->ClearDepthStencil(nullptr, CLEAR_DEPTH_FLAG, 1.f); // Set vertex and index buffers IBuffer *buffer[] = {m_pVertexBuffer}; Uint32 offsets[] = {0}; Uint32 strides[] = {sizeof(MyVertex)}; m_pContext->SetVertexBuffers(0, 1, buffer, strides, offsets, SET_VERTEX_BUFFERS_FLAG_RESET); m_pContext->SetIndexBuffer(m_pIndexBuffer, 0); Different native APIs use various set of function to execute draw commands depending on command details (if the command is indexed, instanced or both, what offsets in the source buffers are used etc.). For instance, there are 5 draw commands in Direct3D11 and more than 9 commands in OpenGL with something like glDrawElementsInstancedBaseVertexBaseInstance not uncommon. Diligent Engine hides all details with single IDeviceContext::Draw() method that takes takes DrawAttribs structure as an argument. The structure members define all attributes required to perform the command (primitive topology, number of vertices or indices, if draw call is indexed or not, if draw call is instanced or not, if draw call is indirect or not, etc.). For example:
DrawAttribs attrs; attrs.IsIndexed = true; attrs.IndexType = VT_UINT16; attrs.NumIndices = 36; attrs.Topology = PRIMITIVE_TOPOLOGY_TRIANGLE_LIST; pContext->Draw(attrs); For compute commands, there is IDeviceContext::DispatchCompute() method that takes DispatchComputeAttribs structure that defines compute grid dimension.
Source Code
Full engine source code is available on GitHub and is free to use. The repository contains two samples, asteroids performance benchmark and example Unity project that uses Diligent Engine in native plugin.
AntTweakBar sample is Diligent Engine’s “Hello World” example.

Atmospheric scattering sample is a more advanced example. It demonstrates how Diligent Engine can be used to implement various rendering tasks: loading textures from files, using complex shaders, rendering to multiple render targets, using compute shaders and unordered access views, etc.

Asteroids performance benchmark is based on this demo developed by Intel. It renders 50,000 unique textured asteroids and allows comparing performance of Direct3D11 and Direct3D12 implementations. Every asteroid is a combination of one of 1000 unique meshes and one of 10 unique textures.

Finally, there is an example project that shows how Diligent Engine can be integrated with Unity.

Future Work
The engine is under active development. It currently supports Windows desktop, Universal Windows and Android platforms. Direct3D11, Direct3D12, OpenGL/GLES backends are now feature complete. Vulkan backend is coming next, and support for more platforms is planned.
• By reenigne
For those that don't know me. I am the individual who's two videos are listed here under setup for https://wiki.libsdl.org/Tutorials
I also run grhmedia.com where I host the projects and code for the tutorials I have online.
Recently, I received a notice from youtube they will be implementing their new policy in protecting video content as of which I won't be monetized till I meat there required number of viewers and views each month.

Frankly, I'm pretty sick of youtube. I put up a video and someone else learns from it and puts up another video and because of the way youtube does their placement they end up with more views.
Even guys that clearly post false information such as one individual who said GLEW 2.0 was broken because he didn't know how to compile it. He in short didn't know how to modify the script he used because he didn't understand make files and how the requirements of the compiler and library changes needed some different flags.

At the end of the month when they implement this I will take down the content and host on my own server purely and it will be a paid system and or patreon.

I get my videos may be a bit dry, I generally figure people are there to learn how to do something and I rather not waste their time.
I used to also help people for free even those coming from the other videos. That won't be the case any more. I used to just take anyone emails and work with them my email is posted on the site.

I don't expect to get the required number of subscribers in that time or increased views. Even if I did well it wouldn't take care of each reoccurring month.
I figure this is simpler and I don't plan on putting some sort of exorbitant fee for a monthly subscription or the like.
I was thinking on the lines of a few dollars 1,2, and 3 and the larger subscription gets you assistance with the content in the tutorials if needed that month.
Maybe another fee if it is related but not directly in the content.
The fees would serve to cut down on the number of people who ask for help and maybe encourage some of the people to actually pay attention to what is said rather than do their own thing. That actually turns out to be 90% of the issues. I spent 6 hours helping one individual last week I must have asked him 20 times did you do exactly like I said in the video even pointed directly to the section. When he finally sent me a copy of the what he entered I knew then and there he had not. I circled it and I pointed out that wasn't what I said to do in the video. I didn't tell him what was wrong and how I knew that way he would go back and actually follow what it said to do. He then reported it worked. Yea, no kidding following directions works. But hey isn't alone and well its part of the learning process.

So the point of this isn't to be a gripe session. I'm just looking for a bit of feed back. Do you think the fees are unreasonable?
Should I keep the youtube channel and do just the fees with patreon or do you think locking the content to my site and require a subscription is an idea.

I'm just looking at the fact it is unrealistic to think youtube/google will actually get stuff right or that youtube viewers will actually bother to start looking for more accurate videos.

• i got error 1282 in my code.