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OpenGL Static lighting with GL_COLOR_ARRAY

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Hello ! I have a terrain with normals at each vertex. And I have a light source which is the sun in my case. The light source has ambient and diffuse light. Now I want to make the terrain rendering a little bit faster by precalculating the lighting colors for all vertices so that I don't need the normals anymore. So instead of the GL_NORMAL_ARRAY I want to use GL_COLOR_ARRAY. But how can I easily precalculate the color value for each vertex to be stored in the GL_COLOR_ARRAY ? I know I can calculate the angle between vertex normal and lightvector from the light source, but I think I also have to bring the ambient AND diffuse calculations in and I don't really know how to exactly do it. Is there an OpenGL function which calculates for a given vertex and a coresponding given normal vector and a light source with position, ambient light factors and diffuse light vectors a final color value which I can use in the GL_COLOR_ARRAY for the given vertex ? Or do I really have to calculate this vertex color myself ? If yes, please can you explain me how to bring the ambient and diffuse part in ? Thanks very much for any suggestions or help ! Greetings Megelan

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You have to do it yourself,but its not hard.

L: (normalized) Light Vector
N: Normal
Ma: Material ambient reflectance
Md: Material diffuse reflectance
La: Light ambient value
Ld: Light diffuse value


Diff=(L dot N)*(Ld*Md);
Ambient=(Ma*La);
VertexColor=Diff+Ambient;

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Quote:
Original post by mikeman
You have to do it yourself,but its not hard.

L: (normalized) Light Vector
N: Normal
Ma: Material ambient reflectance
Md: Material diffuse reflectance
La: Light ambient value
Ld: Light diffuse value


Diff=(L dot N)*(Ld*Md);
Ambient=(Ma*La);
VertexColor=Diff+Ambient;


Thx a lot ! It doesn't look hard but I thought the
VertexColor only holds the result of the light color
information combined with the vertex normal vector.

In the calculation above I already calculate the final
color from light source color AND material properties.
Shouldn't I only calculate the vertex color from the
light source vector and vertex normal vector and still use

glMaterialfv(GL_FRONT, GL_AMBIENT, MaterialAmbient);
glMaterialfv(GL_FRONT, GL_DIFFUSE, MaterialDiffuse);

for the material reflectance ?

Thx a lot !
Greetings Megelan

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If you're going to pre-calculate the lighting yourself and fake lighting with GL_COLOR_ARRAY,you will have to take into account the whole lighting equation when calculating the vertex colors.glMaterialfv works only when normal GL lighting is enabled,so it's useless in your case.

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Ah I forgot to ask somehting.

Doesn't the global ambient light of the ambient lighting model
also have to be used in this calculation ? I know the light
source has an ambient factor but also the global lighting model
has a global ambient factor.

MSDN says :
In RGBA mode, the lighted color of a vertex is the sum of the material emission intensity, the product of the material ambient reflectance and the lighting model full-scene ambient intensity [...]

So what changes need to be made on the above calculation
to bring also the lighting model full-scene ambient
intensity in ?

Thanks :)

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Just add together the global ambient with the one(s) from the light source(s) to get an ambient value which you can multiply by the ambient property of the material.

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alright, but I think the specular calculation isn't that
easy especially for point lights where the position of
the light source AND the direction plays a role, right ?

I think it would be a nice addition to the glu functions
if there would be a function which calculates for a given
vertex and light sources + global light parameters the
final vertex color which includes ambient, diffuse and
specular stuff :)

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Quote:
Original post by Megelan
alright, but I think the specular calculation isn't that
easy especially for point lights where the position of
the light source AND the direction plays a role, right ?

I think it would be a nice addition to the glu functions
if there would be a function which calculates for a given
vertex and light sources + global light parameters the
final vertex color which includes ambient, diffuse and
specular stuff :)


Specular lighting is usually computed this way:
V:normalized eye-to-vertex vector


H=normalize(L+V)
Spec=((H dot N)^exp)*(Mat_Spec*Light_Spec);

However,specular lighting cannot be precalculated,because it is view-depedent.If you want specular lighting,you need to switch to GL lighting,or do your own lighting using shaders.

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Again I've forgotten to ask something ^^
In case of a positional light source (point light) not
only the direction is important also the position should
play a role in the above calculation. But I can't the
a factor there which has something to do with the position
or have I missed something ? =|

I know my light source for the terrain is not positional
cause it's the sun and not a point light but would be nice
to know also the computation if
1. global light-model ambient is present
2. directional light source (ambient and diffuse) is present
3. positional light source (ambient and diffuse) is present

This should be the last thing I need to know about this
static lighting stuff with vertex colors...I hope *g*
Thx =)

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The equation is the same for directional(infinite)lights like the sun and for point lights.The difference is that,while for the sun the Light vector is fixed,for point lights you have to calculate it:

L=normalize(Light_pos-Vertex_pos);

All of the vectors I mentioned in this post and my earlier ones will be in world coordinates,of course.

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Well, in mikeman's post there's the light vector L, which points in the direction of the light source. If you have a directional source, all vertices would have the same L, but in the case of a positional one you would calculate different ones for each vertex (as light position - vertex position).

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Quote:
Original post by mikeman
The equation is the same for directional(infinite)lights like the sun and for point lights.The difference is that,while for the sun the Light vector is fixed,for point lights you have to calculate it:

L=normalize(Light_pos-Vertex_pos);


And how do I determine in case of directional light the
Light Vector L ? I mean I only have the position of the
directional light source and also OpenGL does not want
any direction vector so how does OpenGL compute directional
light without any direction vector just with the position ?
It must be a constant vector but I don't have one.

For the point lights, I think there must be another difference,
cause the attenuation is needed. I do not only need the
direction I also need the distance in the computation or
I won't be able to get any attenuation ?

Isn't it like this that the directional light source stuff has
also to be computed with L= normalize(Light_pos-Vertex_pos)
like the point light but the point light also has attenuation
and the directional has not ?

Well I just read in MSDN:
-----------------------------------------------------
The position is transformed by the modelview matrix when glLight is called (just as if it were a point), and it is stored in eye coordinates. If the w component of the position is 0.0, the light is treated as a directional source. Diffuse and specular lighting calculations take the lights direction, but not its actual position, into account, and attenuation is disabled. Otherwise, diffuse and specular lighting calculations are based on the actual location of the light in eye coordinates, and attenuation is enabled.
-----------------------------------------------------

So your right, directional light does not care about the
position but how is the Lightvector L computed ? I don't
have any direction I only have the position =|

And to the point lights, I also need the attenuation in
the computation =/

[Edited by - Megelan on August 26, 2004 2:53:50 PM]

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If you supply the position with a zero w-coordinate, OpenGL interprets the light as directional (with the position you gave as the direction.)
A directional light doesn't have any attenuation (attenuation=1 in the below equation.)
For a positional light, multiply the light contribution by attenuation=1/(c+l*d+q^2)
Here c is constant, l is linear and q is quadratic attenuation.
d is the distance between the light's position and the vertex.

Expanding on the earlier post:
Diff=(L dot N)*(Ld*Md);
Ambient=(Ma*La);
Globalambient=Global ambient multiplied by material ambient.
VertexColor=GlobalAmbient+attenuation*(Diff+Ambient);

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Quote:
Original post by TomasH
If you supply the position with a zero w-coordinate, OpenGL interprets the light as directional (with the position you gave as the direction.)
A directional light doesn't have any attenuation (attenuation=1 in the below equation.)
For a positional light, multiply the light contribution by attenuation=1/(c+l*d+q^2)
Here c is constant, l is linear and q is quadratic attenuation.
d is the distance between the light's position and the vertex.

Expanding on the earlier post:
Diff=(L dot N)*(Ld*Md);
Ambient=(Ma*La);
Globalambient=Global ambient multiplied by material ambient.
VertexColor=GlobalAmbient+attenuation*(Diff+Ambient);


ah ok =))) Thank you very much.
And how is the fixed LightVector L computed for directional
light ? OpenGL computes it if the w-coordinate is zero which
indicates directional light as you already mentioned. But
how is this fixed L computed if it's the same for ALL
vertices ? =/

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Oh, sorry, I wasn't very clear there.
If you supply (x,y,z,0) to OpenGL, as a light position, OpenGL will interpret it as a direction - i.e. that L is (x,y,z) for that light.

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Quote:
Original post by Megelan

And how do I determine in case of directional light the
Light Vector L ? I mean I only have the position of the
directional light source and also OpenGL does not want
any direction vector so how does OpenGL compute directional
light without any direction vector just with the position ?


Directional lights don't have position,all they got is direction.And the direction is not computed,you just supply it.In your case(the sun),the direction would be parallel to the y-axis.I think it is:LightVector=(0,1,0).

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Quote:
Original post by TomasH
Oh, sorry, I wasn't very clear there.
If you supply (x,y,z,0) to OpenGL, as a light position, OpenGL will interpret it as a direction - i.e. that L is (x,y,z) for that light.


ahhhhhhhhhhhhh yes of course that's it !!!! =D

Thank you so much ! You both helped me a lot :)
With this knowledge I'll try tomorrow to write
a function which returns me the desired vertex color
for given global light parameters, positional and
directional light sources.

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Quote:
Original post by TomasH
For a positional light, multiply the light contribution by attenuation=1/(c+l*d+q^2)
Here c is constant, l is linear and q is quadratic attenuation.
d is the distance between the light's position and the vertex.


I'm just implementing the whole static lighting stuff
and recognized a little error in the attenuation.
It has to be

attenuation= 1 / (c + l*d + q*d^2)

:)

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Quote:
Original post by TomasH
Expanding on the earlier post:
Diff=(L dot N)*(Ld*Md);
Ambient=(Ma*La);
Globalambient=Global ambient multiplied by material ambient.
VertexColor=GlobalAmbient+attenuation*(Diff+Ambient);


I just read somewhere else that I have to catch the cases
where the dotproduct (L dot N) results in a negative value.
So it has to be

Diff= Max(L dot N, 0) * (Ld * Md);

right ?

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Correct. Otherwise shadowed parts would get a negative diffuse color. Though negative colors don't make any sense, that is a thing that's easy to miss in the calculations.

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      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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