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n00body

Member Since 20 Oct 2006
Offline Last Active May 24 2015 02:21 PM

Topics I've Started

How to calculate Lumens?

14 May 2015 - 07:31 PM

I've seen the term being thrown around a lot lately when I read up on engines with their new PBR pipelines. Quite a few of them are saying that they now specify their light intensities in Lumens. I know that that is a term referring to output from real-world light source, but that's the extent of my knowledge. 

 

My questions are:

1.) How do they pertain to lights in shaders?

2.) Is there a specific formula for calculating the light intensity from them?

3.) Am I just over-thinking this, and Lumens is just another name for the light intensity scale value?

 

Any help would be most appreciated. Thank you.


[SOLVED] Detail mapping + Parallax = Texture Swimming?

31 December 2014 - 09:00 PM

So basically when I do heavily tiled detail mapping on a surface that is using Offset Bump Mapping or Parallax Occlusion Mapping, as I orbit around the surface the detail maps appear to swim across the surface.

 

Conditions

  1. Both the base and detail maps use UV0.
  2. The base maps are tiled 1x with no offset.
  3. The detail maps are tiled 10x with no offset.
  4. The parallax offset is generated from a heightmap tied to the base maps texture coordinates.
  5. I apply the parallax offset like so: (UV0 * Tile + Offset) + parallaxOffset.

 

Questions

  1. Is there any way to counteract this problem?
  2. Do I need to modify the parallaxOffset somehow before I apply it to the transformed detail texture coordinates?
  3. Are Detail mapping and Parallax just inherently incompatible?

Thanks. 


[SOLVED] Area Light, Representative Point, Blinn-Phong

26 August 2014 - 08:10 PM

Background

Okay, so I have seen Epic's paper that covers, among other things, how they did area lights in UE4 by the "representative point" method:
http://blog.selfshadow.com/publications/s2013-shading-course/karis/s2013_pbs_epic_notes_v2.pdf

 

Problem

They specifically talk about how they needed to come up with a modification to the normalization factor for their BRDF to make the intensity looks close to correct. However, the one they list is for GGX, and I am using Normalized Blinn Phong. Sadly, I don't understand the math behind normalization.

 

Question

Is there a nice simple way for me to find the normalization factor to use Normalized Blinn Phong with this area light trick?

 

Thanks. 


Toksvig AA and normal map precision issues

23 January 2014 - 08:23 PM

Background

I am working on a physically based shading system in Unity. Among the many components needed by this system is way to compensate for specular aliasing. Our chosen method involves calculating Toksvig AA from our normal maps, pre-correcting our specular powers, and storing the result for use at runtime.

 

Problem

We are dealing with ARGB32 precision normal maps as inputs, and are encountering the problem that some of our artists tools don't quite output unit length normals in this precision. Unfortunately, this has dramatic consequences when applied to our pre-correction of specular powers, even for "flat" normals. So materials that are supposed to be smooth end up getting dramatically more rough.

 

Questions

1.) Is there a way to deal with this besides just using higher precision storage for our normal maps? 

2.) One of our tactics to try to deal with this problem is offering the artist a bias factor that adjusts the calculated variance down slightly to compensate. Is this a valid solution, or will it break horribly down the line?

3.) Is there some other trick I could try that I have overlooked?

 

Thanks for any help you can provide.


[SOLVED] HDR PBR, exceeded FP16 range

09 January 2014 - 10:00 PM

Background

I've been developing a physically-based shader framework for Unity3D. I am using the Normalized Blinn Phong NDF, and an approximation to the Schlick visibility function. I am using an effective specular power range of [4,8192] for direct illumination. I have also developed a translucent shader that uses premultiplied alpha to only make the diffuse translucent while preserving the specular intensity based on fresnel.

 

For all my testing, I am doing everything in Linear HDR mode which affords me an FP16 render target for my camera.

 

Situation

So this is a highly contrived scenario, but my team's artist managed to make it happen. Basically he has a scene with a directional light whose intensity is effectively 1.0 (0.5 input for Unity)  shining on a glass bottle surrounding a smooth metallic liquid. As a result, the two substances' highlights overlapped and their combined intensity seems to have exceeded the range of the FP16 render target. This resulted in weird artifacts where the the highest intensity color component went to black, while the other two just looked really bright. (see example image below).

 
Attached File  ExceededPrescisionOfHDR.jpg   97.5KB   3 downloads

 

Upon further testing, I found I could remove the artifact by making the surface more rough, thus reducing the intensity of the highlight. However, I still found it having this visual error for even relatively rough overlapping materials.

 

Questions

1.) Is there any way to prevent this from happening programmatically without having to clamp the light values to an upper limit or otherwise harm the visual quality?

2.) Is it just something that falls to the artist to avoid doing?

3.) Even so, this means that I can't have multiple overlapping translucent objects or have to be careful about what objects pass behind them. Am I missing something here?

4.) Just for future reference, what is the actual upper limit value of FP16?

 

Thanks for any help you can provide.


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