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Device Context and Vertex Buffer with Many Vertex and Pixel Shaders


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#1 e.s.   Members   -  Reputation: 110

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Posted 27 January 2013 - 09:49 PM

Hello!

 

I have tried to phrase my question in multiple ways, mostly because I don't think I understand the complexity of this particular topic, so thanks for your patience!

 

Yet another rephrase:

1. Can I write Vertex Data to the VertexBuffer for two different objects, (square, triangle), with either the same or different input layout?
2. Can they both use different vertex shaders, pixel shaders, and textures?

3. Could I write a sort of Shader Selector in HLSL that reads a parameter from the input element and dynamically chooses a different pixel shader or texture?

 

Related C++ Code

 

When I create an input layout, can I do this without specifying an actual Vertex Shader, or somehow specify more than one?

 

 

    NS::ThrowIfFailed(
    result = NS::DeviceManager::Device->CreateInputLayout(
    NS::ModelRenderer::InitialElementDescription,
    2,
    vertexShaderFile->Data,
    vertexShaderFile->Length,
    & NS::ModelRenderer::StaticInputLayout
    )
    );


 

When I set the VertexShader and PixelShader, how do I associate them with a particular model in my VertexBuffer?  Is it possible to set more than one of each?



  DeviceManager::DeviceContext->IASetInputLayout(ModelRenderer::StaticInputLayout.Get());

DeviceManager::DeviceContext->VSSetShader(ModelRenderer::StaticVertexShader.Get(), nullptr, 0);
DeviceManager::DeviceContext->PSSetShader(ModelRenderer::StaticPixelShader.Get(), nullptr, 0);

Edited by e.s., 28 January 2013 - 10:40 AM.


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#2 MJP   Moderators   -  Reputation: 10601

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Posted 28 January 2013 - 12:01 AM

To answer  all 3 of your questions, you can only ever have 1 shader bound for each stage. So 1 vertex shader, 1 pixel shader, etc. That same shader has to be used for all primitives rendered by any single Draw call. So in your case you need to use multiple Draw calls to draw all of your models if some of those models require different shaders.

 

EDIT: I missed your fourth question...you need to pass a pointer to the compiled bytecode of a vertex shader in order to create an input layout.


Edited by MJP, 28 January 2013 - 01:22 AM.


#3 e.s.   Members   -  Reputation: 110

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Posted 28 January 2013 - 10:35 AM

you need to pass a pointer to the compiled bytecode of a vertex shader in order to create an input layout.

 

Just a few* questions for clarification, if you don't mind:  (I also cleaned up my initial question.)

 

Are there any issues with passing in a null pointer?

 

If I use multiple draw calls for models that require different shaders, do I just release the buffer, bind all the new vertex instance data, and draw?  Or do I have to re-bind/re-set all of my shaders as well since the input layouts will be different?

 

DrawInstanced allows you to effectively point at a different model template in one buffer, and instance info for that model from another to render the model + instance data. 

 

Is it possible to have the VertexShader define multiple output types so that a different pixel shader could be called?

 

Thanks for your help!


Edited by e.s., 28 January 2013 - 11:35 AM.


#4 MJP   Moderators   -  Reputation: 10601

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Posted 29 January 2013 - 02:50 AM

You can't pass in a NULL pointer, you need to pass in a pointer to the bytecode. The whole point of an input layout is to create a binding between the contents of a vertex buffer and a vertex shader's input signature, if you didn't pass a pointer to the VS bytecode there would be nothing to bind to. There are certain cases where you don't need an input layout at all (basically whenever the vertex shader doesn't actually expect any inputs from a vertex buffer), but that's about it.

I'm not sure if I understand your second question..

 

Your vertex shader only has one set of outputs, which is the outputs that are declared in the shader when you compile it. If you need a different set of outputs, then you need to compile a different vertex shader.



#5 e.s.   Members   -  Reputation: 110

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Posted 29 January 2013 - 12:41 PM

Thanks, I am just trying to find the most efficient way to have different pixel shaders used by the same type of mesh, but colored differently.  For example, I would like square and triangle models in the vertex buffer, and for the pixel shaders to act differently based on instance data....

 

Is there a good way to accomplish this?


Edited by e.s., 29 January 2013 - 12:42 PM.


#6 MJP   Moderators   -  Reputation: 10601

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Posted 29 January 2013 - 01:50 PM

You could use the same pixel shader, and then in your instance data you could pass a color along with the transform. Then you can pass that color from the vertex shader to the pixel shader, and use that as the output color.



#7 e.s.   Members   -  Reputation: 110

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Posted 30 January 2013 - 12:07 PM

To answer  all 3 of your questions, you can only ever have 1 shader bound for each stage. ..

 

What do you mean by stage?  I was thinking that a Vertex Shader /was/ a stage.  I am trying to bind 3 vertex shaders via the input layout, (which apparently won't work), or at least 3 shaders into the DeviceContext, using VSSetShader .... Can there only ever be 1 shader "pipeline"  per DeviceContext?



#8 MJP   Moderators   -  Reputation: 10601

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Posted 30 January 2013 - 01:40 PM

"Stage" as in "vertex shader stage", "pixel shader shader stage", etc. In other words, you can only ever have 1 shader of each type bound to a context at any given time.






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