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OpenGL Really Big Textures?

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I have some advanced models one in particular has a 14mb png texture which opengl does not like but being the only thing showing can handle the model just fine and I think can handle it with textures just not 1 big one.

I am far from a 3d modeler so have no clue about the best way to do this but I would assume there is a way to break the giant texture into smaller gpu friendly textures how can I do this? I use blender for tinkering although im up for anything.

Also is there a library that can do this on the fly?

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simple downsampling is not suitable? breaking texture into multiple pieces can be hard depending on how UV are mapped to the model. If you have only a terrain that's fine and simple, more complex models will make things harder if not impossible. You can split the texture into 4 textures and remap UV to 1 to 4 different sets of UVs. That will need a shader and 4 textures used at the same time. So input of the vertex is always a UV set (you don't need to change UV). But instead of using 1 texture unit you use 4 textures units (each one with 1/4 of the original image)

-------->U
0......0.5....1
. ...............
0.5...0.5....1
................
1......1.......1
V

When UV is in the first quad you scale it by 2 and use first texture newU= 2*U; newV=V*2;
when UV is in the second quad newU = U*2 -1; newV = V*2;
When UV is in the third quad newU=U*2; newV = V*2-1;
When UV is in the fourth quad newU=U*2-1; newV = V*2-1;

quads assumed in this order

1 2
3 4

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Hi DemonRad

Downsampling will work but im looking to get really good detail out of the object and downsampling to something like 1024x1024 will quickly deteriorate quality as its a big model. I do think that I will give it a try though just too see.

Hmm I dont think breaking it down manually is an option as its a mesh/model not something easier like terrain and its lots triangles so far out of my knowledge.

Theres no way something like blender or 3d studio max can take a max texture size and then break it up accordingly? It makes no difference how its broken up to me I just want to show it and fly through the model I dont need animation or anything.

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[quote]I have some advanced models one in particular has a 14mb png texture which opengl does not like but being the only thing showing can handle the model just fine and I think can handle it with textures just not 1 big one.[/quote]
What is the texture size? What does opengl does not like it mean? Are you using DXT compression?

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Hi jeff8j, do try to be as specific as possible about errors. The nature of the error affects what solutions people will offer. Is there a code error? The object appears black? The texture looks distorted? If there is a visual artefact, a screenshot of how it looks in your game vs in the modelling program may help.

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The texture is 12,000 by 12,000 right now and not using dxt just a raw rgba texture.

At the moment I broke everything I was trying to change from the old fixed pipeline to using shaders and made a horrible mess.

Does anyone have a drop in class for assimp with devil and opengl?

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You have a texture that is 12000x12000? ..........sigh

Kill whoever built it. max texture size is 8192x8192 unless it got bumped up even more that I dont know of. But that doesnt matter, no texture for an object needs to be that big.

[quote]Downsampling will work but im looking to get really good detail out of the object[/quote]
I've seen plenty of detail out of 2048 textures, most of the time not needed 4096 textures. I would post a pic because that doesnt make any sense. Unless you plan to in game hold a microscope and zoom it in 10x.

If for say a gigantic spaceship, then this should have been built with multiple uv textures/uv coordinate sets. So each section would be a separate model/texture. If you need tiny detail, multiply a tiled black and white detail map and blend that with the other lower res textures. Or do the same: tile a detail normal map over the object.

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Lol I would be surprised if my card could even do 8192x8192.

Ill post a pic as soon as I get it going again.

Its only used for specific scenes that will pan across the outside of the ship where the game itself takes place inside so no performance concern because at max were talking the ship and a few other smaller things in the scene at once. Im for the sections was hoping for an easy way to achieve them with software rather than me messing with the model.

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Chop your image up into square sections that are 2048x2048 with the end sections only carrying whatever is left.
Take the uv coords 0 to 1, and mutliply them by 12,000. Then convert them to 0 to 1 for each section. Do some math and convert pixel coordinate x = 2048, y = 2048 = 1,1 for tile 0,0. x= (2048 + 1024), y = (2048 + 512) = .5,.25 for the texture tile 1,1

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8192x8192 is REALLY large. Even modern games don't typically exceed 2048x2048, and most get by on MUCH less (shadowmaps, for instance, are often 512x512). I have seen demos (e.g. NVIDIA's human head) that produce very [i]very[/i] high quality results with 4096x4096, and that had a [i]lot[/i] of sampling.

The only excuse I can think of for a texture that large is raw medical or scientific survey measurements. And even that should be reduced before going on a screen. You don't have 12000x12000 pixels on a monitor, so it's just plain pointless to have that much data.

-G

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dpadam450 I am going to take my little knowledge and work with that, in my mind thats exactly what needs to be done and wouldnt be much processing either, although im not confident about my ability to pull it off lol.

Geometrain 12000x12000 is really large for a single image but not when it occupies 10 seconds or so of maneuvering from multiple points to and from multiple angles it can actually quite easily be alot more. Thanks for the concern but theres alot of data that we would like to have a 1to1 scale.

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jeff8j, the only way you can get 1:1 scale is if a single piece of geometry is 12000x12000 in area, otherwise, it'll be down sampled by the hardware anyway.

but, let's say you absolutely have to(although i'm doubtful you can provide an actual valid reason that each pixel absolutely must be seen(and again, the hardware will downsample via nearest/linear mapping based on MAG and MIN filters to screen space for your texture anyway),

what you need to do is what dpadman said:

upon loading the texture, split it into several tiles, let's say 4096x4096, this means a total of 9 tiles in a row major format, where the mapping between each tile is 0-4096/12000=0.3413.

so, in the pixel shader, you take the input uv, from the original modeal and do something like:

[code]
sampler2D TexTiles[9];
vec2 inputUV;
vec2 UVMap; //0.3413 for both u/v.

void main(void){
int xtile = floor(inputUV.x/UVMap.x);
int yTile = floor(inputUV.y/UVMap.y);
sampler2D MappedTile = TexTiles[xTile+yTile*3];
vec2 mappedUV = vec2((inputUV.x-xtile*UVMap.x)/UVMap.x, (inputUV.y-ytile*UVMap.y)/UVMap.y); //get the inputUV into the tile range, then divide by the maximum size to map between 0-1.
vec4 Texel = texture2D(MappedTile, MappedUV);
}
[/code]

anywho, that's what my pixel shader would probably look like, but i doubt i'd ever build a game that absolutely relied on such ridiculously sized textures. Edited by slicer4ever

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Well it should be 1:1 it just wont be all visible so not all 12000x12000 but 1920x1280 give or take would be visible and be 1:1 although still probably not exactly the same.

I havent yet started on the code to break the texture apart but that looks like it will help out alot thank you.

If you had a big structure that played a major role how would you go about building it then besides using such a huge texture? Would you break it down into levels or something arbitrary of that nature? For us that would make it harder to edit because its not like a building made of squares that can be equally separated. Thats why I was wondering if something could break it down in software not necessarily at run time.

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[quote name='jeff8j' timestamp='1343713146' post='4964722']
Well it should be 1:1 it just wont be all visible so not all 12000x12000 but 1920x1280 give or take would be visible and be 1:1 although still probably not exactly the same.

I havent yet started on the code to break the texture apart but that looks like it will help out alot thank you.

If you had a big structure that played a major role how would you go about building it then besides using such a huge texture? Would you break it down into levels or something arbitrary of that nature? For us that would make it harder to edit because its not like a building made of squares that can be equally separated. Thats why I was wondering if something could break it down in software not necessarily at run time.
[/quote]

it sounds like your doing a perspective projection setup for your camera, so again, how the texture is filtered before it reach's the screen means that you won't ever have a 1:1 projection:screen space, the only way is via ortho projection, and it doesn't sound like this is an ortho simulation.

for your question, you say this is a game, I wouldn't build my editor to be bound to loading a single huge model/texture, this is absolutely horrible in terms of performance, you would have practically no method of culling large piece's of offscreen geometry, because all of the geometry/level sounds like it's one huge model(although i could be wrong, but this is what i understand from what i've read). I would never build a game in such a way, instead, the level would be broken up into chunks, and managed in such a way that i can create a nice bsp tree. as such, i could then have my modeler break the 12000x12000 texture into several pieces, to be mapped over several objects.

either way, without more information about what you are doing, we can't suggest a better approach/method, all you have told us is that it's a large model and texture, it's still a game, and it's viewed from several viewpoints. what is it?, why is it so difficult to be broken down manually? what are you trying to accomplish? Edited by slicer4ever

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[quote name='Geometrian' timestamp='1343707161' post='4964696']
The only excuse I can think of for a texture that large is raw medical or scientific survey measurements. And even that should be reduced before going on a screen. You don't have 12000x12000 pixels on a monitor, so it's just plain pointless to have that much data.

-G
[/quote]

It is not pointless to have a lot of data. I regularly work with data that is dozens or hundreds of Gigabyte in size and all of it is needed. The important point is: not at the same time. The same goes for the OPs problem. If he just needs a wide shot from the distance of his ship, then, yes, he could just downsample his data. A lot. But if he needs detail images of his ship he will need the full resolution texture (or more accurately: small subsets of the full resolution image at any one time). That is what LoD concepts are about after all.

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[quote name='jeff8j' timestamp='1343713146' post='4964722']
If you had a big structure that played a major role how would you go about building it then besides using such a huge texture? Would you break it down into levels or something arbitrary of that nature? For us that would make it harder to edit because its not like a building made of squares that can be equally separated. Thats why I was wondering if something could break it down in software not necessarily at run time.
[/quote]

If an object is so big that it needs a texture of that resolution then the object will be too big to be seen on screen at once in all that detail.
Therefore your object is the problem because the object is too big.

Large structres in games are made up of smaller substructures so that we can cull the chunks which aren't visable at any given moment and only process those which are.

For example, lets say you had a huge castle in the world. This would not be made as a single model instead various walls, ramparts and turrets would be made seperately and then placed together to form the final world object.

If you built the model as one solid object then you can only visibility test against that one huge object. Lets say the castle is 3 million verts in size. Now lets say you can only see the tip of the top of a tower - in the 'huge model' method you now have to submit and run the vertex shader for all 3 million verts (give or take depending on reuse) where as with a broken up model you'll end up submitting only the tower segement which might only be a few thousand verts at most.

The long and the short of it is you are not going to need a single model of such a size that it will need a single texture map of that size; if you have a model of that size then you'll want to break it up.

Doing otherwise is going to cost you performance AND, as you've discovered, is physically impossible to do in many cases.

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I might sound a bit simple, but the way you described those specific scenes makes me guess that those are cutscenes. If it's so, and you really need a texture this size, you could consider prerendering the scene. With the right settings, you could even make it look similar to an engine render. It would add the hassle of using a video decoder and displaying it, but this might be still easier than getting a 12k*12k texture working properly on the desired range of machines.
Also, as written above, breaking the model itself can be a nice idea too. This could work best if you had reusable parts of your object. This way you could get over redundant mesh data ( only store each element once ). The texture issue would be realigned - you would have to texture the individual parts. You would have small individual textures that would easily fit into the GPU. Also, the clipping issue would be conveniently solved.

Edit.: Forgot to mention that rendering takes some time, depending on your cutscene's length, complexity and your rig. Expect it to be somewhere from a few hours ( for 10-30 sec ), to a few days ( for 10-20 minutes ). However, these were just guesses based on my experiences. I own a not too competent machine. Edited by TheUnnamable

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[quote name='BitMaster' timestamp='1343717965' post='4964740']
[quote name='Geometrian' timestamp='1343707161' post='4964696']
The only excuse I can think of for a texture that large is raw medical or scientific survey measurements. And even that should be reduced before going on a screen. You don't have 12000x12000 pixels on a monitor, so it's just plain pointless to have that much data.

-G
[/quote]

It is not pointless to have a lot of data. I regularly work with data that is dozens or hundreds of Gigabyte in size and all of it is needed. The important point is: not at the same time. The same goes for the OPs problem. If he just needs a wide shot from the distance of his ship, then, yes, he could just downsample his data. A lot. But if he needs detail images of his ship he will need the full resolution texture (or more accurately: small subsets of the full resolution image at any one time). That is what LoD concepts are about after all.[/quote]I should clarify, that's what I meant when I said "that should be reduced before going on a screen." If your data is too large to even fit on your graphics card, that's an excellent indication that you need to do CPU processing to transfer the relevant bits only. However, I maintain that, while over time a large amount of different data might be loaded and displayed, a large amount of data in a short time is almost always unnecessary.[quote name='jeff8j' timestamp='1343707765' post='4964701']Geometrain 12000x12000 is really large for a single image but not when it occupies 10 seconds or so of maneuvering from multiple points to and from multiple angles it can actually quite easily be alot more.[/quote]I think the absolute worst case scenario for something like this is a REALLY up-close fly-through of a REALLY detailed model. You can imagine a quad with your texture mapped onto it, and then looking along one of the diagonals. Nearly all the data is visible, but most of it is minified. The problem is that there's not really a hard distinction between levels of detail--you blend mipmap levels for this. Another worst case is looking at that quad from above as a scale of about 1:1, then rapidly panning around the texture area. Breaking up the model into pieces will help, but you can still get worst cases like these.

If you really need every part of a fully, 100% contiguous texture that doesn't fit in texture memory, by definition, you're out of luck. You can get "all" of that detail at once by paging mipmap level texels in as necessary. This makes things more complicated, and again makes filtering (e.g. mipmap blending, anisotropic filtering) hard if not impossible.

I still feel like we're asking the wrong questions, though. Seriously--you need a 12K texture for an object? The largest unpaged texture I have [i]ever[/i] seen in a game is 8K (the hardware limit), and that was a hack to demonstrate how ridiculously useless it was. It's OK to have smaller textures. Will a 2x or 3x reduction [i]really[/i] hurt that much? There ARE situations where that kind of resolution is warranted (offline rendering, maybe), but unless you need cinematic-quality rendering, you're barking up the wrong tree.

Maybe you DO need that much resolution. But do you really need [i]information[/i], or just [i]detail[/i]? Procedural texturing uses next to no memory, and because texture samples are into smaller images (for lookup tables), it's cache-coherent and faster than sampling the actual data. If the state is small enough, you don't even need (texture) lookup tables at all! You can make a hybrid approach where you sample a more reasonably-sized texture, and then add as much detail as you want with some noise. This works [i]so well[/i] that offline renderers often do [i]that[/i] instead of making huge textures (memory efficiency pays off on the CPU too!). [i]Every[/i] major renderer has procedural texture support for [i]this exact reason[/i]. Don't forget, Perlin noise was [i]invented[/i] to solve this problem!

Maybe you DO need that much resolution because your texture is broadband noise, doesn't have a nice Fourier decomposition, and so recreating it with noise is out, or maybe you just can't add noise instead because every single subpixel-sized texel must be exactly right for some reason. Maybe you just need to view five orders of magnitude of texture all at once. In these cases, even if you [i]can[/i] figure out a way to robustly figure out which texels are necessary, page them in from RAM and render them, you're still talking about processing and transferring up to hundreds of megabytes of texels every few frames--a gigabyte or so per second if you really have a bad case. It's possible, but that will start eating up a lot of your CPU and GPU time just on data transfer. Many applications fail--I have seen games where clumsily-paged textures lead to LOD jumps (not in geometry but in texture). This is [i]disconcerting[/i] and [i]distracting[/i]. Setting the texture resolution smaller fixes the problem. There are no jumps, and the game plays smoothly. Even if a pixel here or there [i]could[/i] be more detailed, it is [i]immensely better[/i] not to have the little pops all over the place.

So maybe you DO need all that resolution, and you can't recreate it with noise--now you've figured out a way to rapidly page texels in and out of CPU and GPU memory--maybe with PBOs so it's somewhat asynchronous and doesn't hurt too much, and it works robustly and is miraculously realtime. What have you gained? You can display so much information that it's silly--humans can't differentiate small changes in data changing at more than about two times per second. Your model is rendered with much more detail than is needed. If you paused the moving camera and looked closely, admittedly you could see a pixel or two that are different--the higher resolution one looks better, yes. Maybe you're zoomed in and huge sections of texture space are magnified. That would point to a LOD problem (which is beside the point)--but hey, the texture is maybe [i]twice[/i] as detailed in each direction, so you win, right?

In sum:
-I am almost certain that you don't need a 12000x12000 texel texture, even without knowing exactly what your application is.
-Even for the most demanding applications, you still almost certainly don't need that much--you can recreate it MUCH more efficiently (and often, better) using procedural/hybrid techniques.
-This problem occurs frequently in industry, because people want "higher resolution" everything. It's a natural desire, but it is almost always an insignificant one. In nearly all cases, there is [i]minimal perceptual difference[/i] in even large resolution improvements, simply because the display technology and the human eye can't keep up. [i]Even if you succeed[/i] in making most of your scene's textures more detailed, it usually doesn't even matter because you kill your framerate and you get LOD pops--which is just not an improvement.
-On modern graphics hardware, it is (usually) possible to page texels in and out of memory fast enough to keep up with non-pathological cases where textures don't fit into memory, assuming minimal other work is being done on both the CPU and GPU. If doing it is still somehow absolutely critical, you might be better off looking into realtime CPU raytracing.
-A texture about half the resolution in both dimensions (4096x4096) avoids all the above problems. For magnified pixels, of which there are usually none, it looks maybe half as good--but in return you get portability, high framerate, robustness, elegance, and simplicity--and it's still ultimately high-quality. I [i]strongly recommend[/i] using 4096x4096 as a [i]maximum[/i], and (for only the [i]most extreme[/i] of circumstances), add procedural noise. Edited by Geometrian

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      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.
      Creating Shaders
      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:
      SHADER_SOURCE_LANGUAGE_DEFAULT - The shader source language matches the underlying graphics API: HLSL for Direct3D11/Direct3D12 mode, and GLSL for OpenGL and OpenGLES modes. SHADER_SOURCE_LANGUAGE_HLSL - The shader source is in HLSL. For OpenGL and OpenGLES modes, the source code will be converted to GLSL. SHADER_SOURCE_LANGUAGE_GLSL - The shader source is in GLSL. There is currently no GLSL to HLSL converter, so this value should only be used for OpenGL and OpenGLES modes. There are two ways to provide the shader source code. The first way is to use Source member. The second way is to provide a file path in FilePath member. Since the engine is entirely decoupled from the platform and the host file system is platform-dependent, the structure exposes pShaderSourceStreamFactory member that is intended to provide the engine access to the file system. If FilePath is provided, shader source factory must also be provided. If the shader source contains any #include directives, the source stream factory will also be used to load these files. The engine provides default implementation for every supported platform that should be sufficient in most cases. Custom implementation can be provided when needed.
      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:
      ShaderCreationAttribs Attrs; Attrs.Desc.Name = "MyPixelShader"; Attrs.FilePath = "MyShaderFile.fx"; Attrs.SearchDirectories = "shaders;shaders\\inc;"; Attrs.EntryPoint = "MyPixelShader"; Attrs.Desc.ShaderType = SHADER_TYPE_PIXEL; Attrs.SourceLanguage = SHADER_SOURCE_LANGUAGE_HLSL; BasicShaderSourceStreamFactory BasicSSSFactory(Attrs.SearchDirectories); Attrs.pShaderSourceStreamFactory = &BasicSSSFactory; ShaderVariableDesc ShaderVars[] = {     {"g_StaticTexture", SHADER_VARIABLE_TYPE_STATIC},     {"g_MutableTexture", SHADER_VARIABLE_TYPE_MUTABLE},     {"g_DynamicTexture", SHADER_VARIABLE_TYPE_DYNAMIC} }; Attrs.Desc.VariableDesc = ShaderVars; Attrs.Desc.NumVariables = _countof(ShaderVars); Attrs.Desc.DefaultVariableType = SHADER_VARIABLE_TYPE_STATIC; StaticSamplerDesc StaticSampler; StaticSampler.Desc.MinFilter = FILTER_TYPE_LINEAR; StaticSampler.Desc.MagFilter = FILTER_TYPE_LINEAR; StaticSampler.Desc.MipFilter = FILTER_TYPE_LINEAR; StaticSampler.TextureName = "g_MutableTexture"; Attrs.Desc.NumStaticSamplers = 1; Attrs.Desc.StaticSamplers = &StaticSampler; ShaderMacroHelper Macros; Macros.AddShaderMacro("USE_SHADOWS", 1); Macros.AddShaderMacro("NUM_SHADOW_SAMPLES", 4); Macros.Finalize(); Attrs.Macros = Macros; RefCntAutoPtr<IShader> pShader; m_pDevice->CreateShader( Attrs, &pShader );
      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.
      Binding Shader Resources
      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.
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