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OpenGL Virtual Visible Spectrum

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Hello all. New member here. I've just gotten into 3d programming. I am intermediate in C++ programming, and I know a bit of OpenGL. What I would like to do, is create an environment which functions like our own. I notice that a lot of 3d applications use polygons with image textures, and then there is application of shadows and highlights, based on the light source. Then again, that's just what I have noticed, when watching 3d movies, and playing 3d videogames. Perhaps I am wrong. I find this method to be flawed and limited, and I think I have a better way to simulate it. Let's say we create a lightsource. Let's imagine that the lightsource is the sun. I would assign an array of variables to this. These variables would be assigned to wavelengths on the electromagnetic spectrum. I would not limit the amount of wavelengths to the visible spectrum, because some other wavelengths, like ultraviolet are visible to some people and some creatures, and also because I would need these wavelengths for a project I would use this graphics theory for. There would be a few other variables, which measure distance between objects and the light source, the intensity, and so forth. I would create a formula, which calculates the value of the color at any given location. Objects would be anisotropic polygons, with colorless texture. The objects would have different polygons, for the distance of the viewpoint which is viewing it. This is something like Elder Scrolls IV: Oblivion's engine, where graphics become more detailed, as the distance between the player and the object becomes smaller. This would be to reduce the amount of computing power required to render the entire picture. Anyway, I would use the aforementioned formula, and assign variables which hold the values calculated by this formula, to areas on the object. Then, when the object appears under the light source, its local value will be that of which the color it emits when the wavelengths from the light source reach the object. Then, highlights and shadows would be assigned to the object (I haven't really thought about this part yet, but based on what I have learned in art school, I would use analogous colors and compliments, for a more accurate portrayal.) The atmosphere would actually be the color of the gases which make it up. Clouds would actually take form, and would not just be some background, atmospheric image. Copyright 2008, Nathan Jones, by the way. What I would like to know, is, would this be possible to do with the limitations of today's computing technology? Is it possible to program such an advanced system using OpenGL and C++? I know I could do the C++ part, but does OpenGL have any prohibiting boundaries? Does something like this already exist? I really doubt it, but I never completely throw away the possibility.

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Quote:
Original post by anachronistic89
I would create a formula, which calculates the value of the color at any given location.

Well, this equation already exists. It's called the general global illumination equation. In it's complete form (which is not yet 100% complete, because many parts of the equation are not yet fully understood and/or are not computable with todays technology), its complexity is beyond belief.

After applying several very aggressive optimizations, many approximate equation sets were developed over the last 30 or so years: Radiosity, photon mapping, Metropolis LT, and several others. They are still way beyond what current hardware can do in realtime at acceptable quality. Yet, you can use them to precalculate some data to your 3D scene that will later be reused while rendering (see lightmapping, precomputed radiance transfer, etc). These precalculations can take from a few minutes to several weeks depending on the complexity of your scenes. Most current 3D games do that to one extend or another.

Here is some more info to start.

Of course this method is very popular in highend offline rendering, such as for still images, architecture, movies, etc. Most current 3D software include it or can use through plugins (Mental Ray, V-Ray, Maxwell, etc).

Quote:

Copyright 2008, Nathan Jones, by the way.

You legally can't copyright an idea, BTW [wink]

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Original post by Yann L
Quote:
Original post by anachronistic89
I would create a formula, which calculates the value of the color at any given location.

Well, this equation already exists. It's called the general global illumination equation. In it's complete form (which is not yet 100% complete, because many parts of the equation are not yet fully understood and/or are not computable with todays technology), its complexity is beyond belief.

After applying several very aggressive optimizations, many approximate equation sets were developed over the last 30 or so years: Radiosity, photon mapping, Metropolis LT, and several others. They are still way beyond what current hardware can do in realtime at acceptable quality. Yet, you can use them to precalculate some data to your 3D scene that will later be reused while rendering (see lightmapping, precomputed radiance transfer, etc). These precalculations can take from a few minutes to several weeks depending on the complexity of your scenes. Most current 3D games do that to one extend or another.

Here is some more info to start.

Of course this method is very popular in highend offline rendering, such as for still images, architecture, movies, etc. Most current 3D software include it or can use through plugins (Mental Ray, V-Ray, Maxwell, etc).

Quote:

Copyright 2008, Nathan Jones, by the way.

You legally can't copyright an idea, BTW [wink]


I know that one cannot copyright an idea :P that's just to prevent the lazy people from copying and pasting my post.


Thank you for your reply. I know this will certainly help me along in the process.

Maybe I should study some graphics engines on the code-level.

Are the APIs for the big projects designed specifically for themselves, or do they use OpenGL and so forth?

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Original post by anachronistic89
Are the APIs for the big projects designed specifically for themselves, or do they use OpenGL and so forth?

If you're talking about realtime, it's either OpenGL or Direct3D.

For the global illumination (GI) calculations, that's either done on the CPU (or better on multiple CPUs, GI is particularly well suited for parallel computation models) or on one (or multiple) GPUs through CUDA or the upcoming OpenCL.

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As Yann L mentioned the FULL GI equation isn't known yet, but most important parts are known (on which are based some calculations, which are pretty correct for simulation - namely Photon mapping, radiosity, etc.).
And as was said there isn't enough computational power in PC to solve F.e. photon mapping in real time (Well, it might be possible with ray tracing ... on enough fast PCs (I'm talking about 8-core, or rather 16-core CPUs in that machines) even in real time).
But there are several paths how can be GI (not 100% correct) achieved in real time graphics using OpenGL or Direct3D. Real time dynamic radiosity (which can be seen in several demos made by me, and not just in them) ... it's pretty limited in scale, in which is used ... but in engine which are those demos running at (also made by me) you're able to set radiosity quality, and if you'd set it high enough it'd have enough quality to even simulate multiple light bounces and correct light accesability (But that probably wouldn't be in real time or close to real time on todays hardware). Link to engines web (not so good, I need to rebuild it ... don't kill me for that) Web
If you have any question about radiosity solution in those demonstrations, ask me on my e-mail or PM me.

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Yes, radiosity has already proved itself to me as a method worth considering. I will be checking out your demos. I'll be sure to contact you if I have questions. Thanks!


Hmm, has the fact that human vision is trichromatic been used to help simulate color?

Part of my project focuses on the idea of color vision, detail, and all of that. Could it be possible to render based on whether or not the character has pentachromatic/trichromatic/dichromatic color?

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Original post by anachronistic89
Hmm, has the fact that human vision is trichromatic been used to help simulate color?

Well, look at your screen (which is trichromatic) :)

But yes, of course the human eye is taken into account. Most higher end GI systems use SPDs (spectral power distributions) to calculate the lighting. Generally two types of engines exist: those that calculate everything in linear wavelength space (radiometric engines) and those that use the non-linear weighted visible spectrum (photometric engines). The former ones must convert the radiometric energies to photometric energies when they have completed the calculations. The latter directly operate on photometric units. In order to take the (non-linear) response of the human eye to colours into account (ie. convert from radiometric to photometric data), you need to use the CIE spectral weighting curves. See CIE colour space (or here).

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Most of the things you said are well-known in the graphics literature. I suggest you google "rendering equation", "spectral rendering", "atmospheric scattering" and "level of detail".

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Original post by Yann L
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Original post by anachronistic89
Hmm, has the fact that human vision is trichromatic been used to help simulate color?

Well, look at your screen (which is trichromatic) :)

But yes, of course the human eye is taken into account. Most higher end GI systems use SPDs (spectral power distributions) to calculate the lighting. Generally two types of engines exist: those that calculate everything in linear wavelength space (radiometric engines) and those that use the non-linear weighted visible spectrum (photometric engines). The former ones must convert the radiometric energies to photometric energies when they have completed the calculations. The latter directly operate on photometric units. In order to take the (non-linear) response of the human eye to colours into account (ie. convert from radiometric to photometric data), you need to use the CIE spectral weighting curves. See CIE colour space (or here).


I've just gotten a chance to read all that stuff. Finally on the CIE color link that you've supplied.

From what I read, this is going to make my project all the more fun that I thought it would be :)

It's going to be fun depicting ultra-violet light with the limitation of RGB. I could certainly work with available colors to help do this, because I am sure that bright-magenta colors and purple do not appear in the natural world.

I estimate that it will take a lot more computing to render what I originally wanted.

It will especially take a lot of computing to convert trichromatic into dichromatic, and trichromatic into monochromatic. This is the fun of programming, no? :)

By the way, if there are any projects on here that use dichromatic, monochromatic, and simulated tetrachromatic viewpoints, please link them to here. Also, motion-based vision, blurry vision, and anything like that. In the meantime I will be searching for such things, and working on the project.

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For a real tetrachromat for example, you would notice that a combination of red and blue is not equal to purple because they wouldn't excite your fourth sensor the same way (even if you could get the three first sensors right). So the real object and the photograph of that object (using three kind of color pigments, magenta blue yellow or red green blue on your screen) would never match to you. Your neighbor will tell you that they match.

Simulating that is kind of hard because you would need a point of reference to notice the mismatch (what if the object is REALLY painted red and blue ?). What you could do, is in the game world, having a person that you play see an object, take a polaroid (or digital photography) so you have the ability to compare. Then have the rendering of the photograph mismatch the regular rendering. And non player character in the game tell you that they match (in a perverse way ^_^).

Simulating dichromat would be a bit simpler (somehow), you could make for example a modified RGB value be a linear combination of original RGB values through a transform matrix with one of the vector of the matrix being a combination of one or both other columns. One of the simplest example would be to make a modified red channel = original computed green channel. Of course different types of mutation could make the effect more complex. To be complete you could also go the way of completely simulating the radio transmission of frequencies and their effect on cones and rods and try to approximate that with your red green and blue emitters. Having a real dichromat on hand to validate your model would help of course.

As a last example, I don't think I'm a tetrachromat but I have a particularity is that I wear corrective glasses. The matter they're made of is not totally achromatic, so on the edge of the glass in particular each frequency of light will follow a slightly different path. So this brings us to the internal representation of our colors. If a spot is shining red and blue, I see two distinct spots if observed through the edges of my glasses. If it was pure purple wavelength I would see one spot. This distinction is not something you can make with a traditional RGB representation.

LeGreg

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For a real tetrachromat for example, you would notice that a combination of red and blue is not equal to purple because they wouldn't excite your fourth sensor the same way (even if you could get the three first sensors right). So the real object and the photograph of that object (using three kind of color pigments, magenta blue yellow or red green blue on your screen) would never match to you. Your neighbor will tell you that they match.


Yes, you are right; in fact, no color would look the same, if one really thinks about the concept. To a trichromat, the color wheel is perfectly triadic. With the additional sensor, many new color combinations would become present, and things would not be the same color as they appear.

I read a bunch of things all day, and I've found that the trichromatic human's eye is particularly sensitive to greenish hues. This is because of the pigments in the cones of our eyes, which are greenish. I don't really understand how we can see reddish hues without reddish pigments though. Maybe you have some articles on hand I should read about color vision.

Quote:
Original post by LeGreg
Simulating that is kind of hard because you would need a point of reference to notice the mismatch (what if the object is REALLY painted red and blue ?). What you could do, is in the game world, having a person that you play see an object, take a polaroid (or digital photography) so you have the ability to compare. Then have the rendering of the photograph mismatch the regular rendering. And non player character in the game tell you that they match (in a perverse way ^_^).


Well, I, as the creator of the script will have the point of reference; I will have a standard view, which is trichromatic. The tetrachromatic view will show patterns and colors differently, and should give the tetrachromat visual advantages over the trichromat. For example, say you have a trichromat with camouflaging abilities, which it uses in order to prey on dichromats. A tetrachromat would be able to easily see the trichromat, because the tetrachromat's extra sensor would make the trichromat stand out in color.


Quote:
Original post by LeGreg
Simulating dichromat would be a bit simpler (somehow), you could make for example a modified RGB value be a linear combination of original RGB values through a transform matrix with one of the vector of the matrix being a combination of one or both other columns. One of the simplest example would be to make a modified red channel = original computed green channel. Of course different types of mutation could make the effect more complex. To be complete you could also go the way of completely simulating the radio transmission of frequencies and their effect on cones and rods and try to approximate that with your red green and blue emitters. Having a real dichromat on hand to validate your model would help of course.


Yes, I think the dichromat would be easier to create (by theory) because all I would have to do is reduce the perceived wavelengths of the missing color to zero (or whatever number is concluded as 'accurate').

I would really love to do all the mathematics with rods and cones and all, but that is probably not the best thing to do for a videogame. (I would like opinions on this) It would really be an extensive idea for producing images, though! I would like to eventually make both. Whichever comes first, I guess.

I would also like to simulate monochromats and rod-monochromats, but those are even simpler than dichromats.

I am thinking about brightness and nightvision. You know, we only see light at a certain intensity because our eyes block the rest of it out. Some animals can see even more light, and some much less.

Quote:
Original post by LeGreg
As a last example, I don't think I'm a tetrachromat but I have a particularity is that I wear corrective glasses. The matter they're made of is not totally achromatic, so on the edge of the glass in particular each frequency of light will follow a slightly different path. So this brings us to the internal representation of our colors. If a spot is shining red and blue, I see two distinct spots if observed through the edges of my glasses. If it was pure purple wavelength I would see one spot. This distinction is not something you can make with a traditional RGB representation.


What is the the reason for your wearing glasses? Perhaps this is why the material reflects light in the manner it does.

I had some trouble understanding everything (about the glasses part) you meant. Could you try explaining that once more? Or maybe share a video?



What about assigning achromatic textures to polygons, and then under the ray-tracing of the lightsource, or however I end up programming it, values are assigned (based on that magical formula, which would tell which frequencies hit where) and the object is given color the way it is supposed to be perceived (i.e. the character is trichromatic/dichromatic/tetrachromatic/monochromatic)

Do you think it is possible to to go such detail for a videogame? I have thought about making it online... then the programming could be done remotely, and the rendering locally. Hmm, I am not sure where to draw the lines on this one.

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      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 tutorials, sample applications, asteroids performance benchmark and an example Unity project that uses Diligent Engine in native plugin.
      Atmospheric scattering sample 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, Linux, Android, MacOS, and iOS platforms. Direct3D11, Direct3D12, OpenGL/GLES backends are now feature complete. Vulkan backend is coming next, and Metal backend is in the plan.
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