• Advertisement
Sign in to follow this  

DX11 ID3dX11Effect constant buffer

This topic is 2131 days old which is more than the 365 day threshold we allow for new replies. Please post a new topic.

If you intended to correct an error in the post then please contact us.

Recommended Posts


I am investigating the use of constant buffers in effect files. Say, my effect file had buffer declarations like this:

cbuffer cbPerViewBuffer
matrix viewMatrix;

When initializing my shader, i would get a pointer to this effect variable by name, and store it in my object:


ID3DX11EffectMatrixVariable *p_view;
ID3DX11Effect* p_effect;

//... Compiling effect ...//

p_view = p_effect->GetVariableByName("viewMatrix")->AsMatrix();

On rendering, I do

//... doing the math on v ...//

p_view->SetMatrix( v);

There is no buffer mapping or else involved. So my question is, is this even using the advantages of constant buffers, or is this an absurdely abuse of mentioned features?
Should I instead create a custom buffer type, create a buffer of this type, bind it as dynamic to the effect, and use map on each render call?
Can the view buffer even be updated, I have seen no flag specifying it as DYNAMIC?

Thanks for your help.

Share this post

Link to post
Share on other sites
The effects framework does a Map or UpdateResource behind the scenes. It's been a while since I looked at the effect code, but it should flag a variable as "dirty" and only update the constant buffer if one of the values changed. So it is not really an abuse.

However, one example of an improvement is your "per-frame" constant buffer. You only need one of these and all your effects can share it. I use a header and always put the per-frame cb in slot 0. Then I use ID3DX11Effect::GetConstantBufferByName and set the per-frame CB for each effect; this is just a bind operation (when Apply() is called), as the per-frame CB is only updated once per-frame.

If you don't do this, then each effect will maintain its own per-frame cbuffer. This is still not likely to make a performance impact, but still.

Share this post

Link to post
Share on other sites
This is how it's done:

[source] // Retrieve the handles to the constant buffers
m_pD3DXEffectEveryFrameConstBuffer = m_pD3DXEffect->GetConstantBufferByName("CBEveryFrame"); // Constant buffer that changes every frame
return E_FAIL;
update constant buffer:
D3D11_MAPPED_SUBRESOURCE oD3DMappedSubresource;
CHECK_COM(pD3DDeviceContext->Map(m_pD3DMaterialConstbuffer, 0, D3D11_MAP_WRITE_DISCARD, 0, &oD3DMappedSubresource)); // Get a pointer to the data in the constant buffer
::memcpy(oD3DMappedSubresource.pData, pMaterialConstantBuffer, sizeof(SMaterialConstantBuffer)); // Copy the constant buffers
pD3DDeviceContext->Unmap(m_pD3DMaterialConstbuffer, 0);
CHECK_COM(m_pD3DXEffectMaterialConstBuffer->SetConstantBuffer(m_pD3DMaterialConstbuffer)); // Set material constant buffer in the shader
Assuming the constant buffer was created dynamic usage flag. If it's created with default usage flag then you have to use UpdateSubresource method to do so[/source]

Share this post

Link to post
Share on other sites
@ Quat: Your answer sounds good: it's easy, would not require me to do too much changes, and would not need me to do obscure things.

@ Asesh: It's quite the opposite to what Quat suggested: You tell me to actually take everything in my own responsibility, and actually mapping the buffer. In this case, would I have to create the buffers myself? As I see it, the effect creates the declared buffers within it on compilation(?) and I can just access it with the GetConstantBufferFunction. Where can I make it's usage DYNAMIC? Do I have to create the buffer myself and replace it with the one the shader generated?

Actually, now I'm as wise as before: It seems to me I have two concurring opinions on this topic, and (of course I am tempted to use the easier one for the time being) still can't decide which option to settle with.
Are there any more opinions?

Share this post

Link to post
Share on other sites
Sign in to follow this  

  • Advertisement
  • Advertisement
  • Popular Now

  • Advertisement
  • Similar Content

    • By AxeGuywithanAxe
      I wanted to see how others are currently handling descriptor heap updates and management.
      I've read a few articles and there tends to be three major strategies :
      1 ) You split up descriptor heaps per shader stage ( i.e one for vertex shader , pixel , hull, etc)
      2) You have one descriptor heap for an entire pipeline
      3) You split up descriptor heaps for update each update frequency (i.e EResourceSet_PerInstance , EResourceSet_PerPass , EResourceSet_PerMaterial, etc)
      The benefits of the first two approaches is that it makes it easier to port current code, and descriptor / resource descriptor management and updating tends to be easier to manage, but it seems to be not as efficient.
      The benefits of the third approach seems to be that it's the most efficient because you only manage and update objects when they change.
    • By evelyn4you
      until now i use typical vertexshader approach for skinning with a Constantbuffer containing the transform matrix for the bones and an the vertexbuffer containing bone index and bone weight.
      Now i have implemented realtime environment  probe cubemaping so i have to render my scene from many point of views and the time for skinning takes too long because it is recalculated for every side of the cubemap.
      For Info i am working on Win7 an therefore use one Shadermodel 5.0 not 5.x that have more options, or is there a way to use 5.x in Win 7
      My Graphic Card is Directx 12 compatible NVidia GTX 960
      the member turanszkij has posted a good for me understandable compute shader. ( for Info: in his engine he uses an optimized version of it )
      Now my questions
       is it possible to feed the compute shader with my orignial vertexbuffer or do i have to copy it in several ByteAdressBuffers as implemented in the following code ?
        the same question is about the constant buffer of the matrixes
       my more urgent question is how do i feed my normal pipeline with the result of the compute Shader which are 2 RWByteAddressBuffers that contain position an normal
      for example i could use 2 vertexbuffer bindings
      1 containing only the uv coordinates
      2.containing position and normal
      How do i copy from the RWByteAddressBuffers to the vertexbuffer ?
      (Code from turanszkij )
      Here is my shader implementation for skinning a mesh in a compute shader:
      1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 struct Bone { float4x4 pose; }; StructuredBuffer<Bone> boneBuffer;   ByteAddressBuffer vertexBuffer_POS; // T-Pose pos ByteAddressBuffer vertexBuffer_NOR; // T-Pose normal ByteAddressBuffer vertexBuffer_WEI; // bone weights ByteAddressBuffer vertexBuffer_BON; // bone indices   RWByteAddressBuffer streamoutBuffer_POS; // skinned pos RWByteAddressBuffer streamoutBuffer_NOR; // skinned normal RWByteAddressBuffer streamoutBuffer_PRE; // previous frame skinned pos   inline void Skinning(inout float4 pos, inout float4 nor, in float4 inBon, in float4 inWei) {  float4 p = 0, pp = 0;  float3 n = 0;  float4x4 m;  float3x3 m3;  float weisum = 0;   // force loop to reduce register pressure  // though this way we can not interleave TEX - ALU operations  [loop]  for (uint i = 0; ((i &lt; 4) &amp;&amp; (weisum&lt;1.0f)); ++i)  {  m = boneBuffer[(uint)inBon].pose;  m3 = (float3x3)m;   p += mul(float4(pos.xyz, 1), m)*inWei;  n += mul(nor.xyz, m3)*inWei;   weisum += inWei;  }   bool w = any(inWei);  pos.xyz = w ? p.xyz : pos.xyz;  nor.xyz = w ? n : nor.xyz; }   [numthreads(1024, 1, 1)] void main( uint3 DTid : SV_DispatchThreadID ) {  const uint fetchAddress = DTid.x * 16; // stride is 16 bytes for each vertex buffer now...   uint4 pos_u = vertexBuffer_POS.Load4(fetchAddress);  uint4 nor_u = vertexBuffer_NOR.Load4(fetchAddress);  uint4 wei_u = vertexBuffer_WEI.Load4(fetchAddress);  uint4 bon_u = vertexBuffer_BON.Load4(fetchAddress);   float4 pos = asfloat(pos_u);  float4 nor = asfloat(nor_u);  float4 wei = asfloat(wei_u);  float4 bon = asfloat(bon_u);   Skinning(pos, nor, bon, wei);   pos_u = asuint(pos);  nor_u = asuint(nor);   // copy prev frame current pos to current frame prev pos streamoutBuffer_PRE.Store4(fetchAddress, streamoutBuffer_POS.Load4(fetchAddress)); // write out skinned props:  streamoutBuffer_POS.Store4(fetchAddress, pos_u);  streamoutBuffer_NOR.Store4(fetchAddress, nor_u); }  
    • By mister345
      Hi, can someone please explain why this is giving an assertion EyePosition!=0 exception?
      _lightBufferVS->viewMatrix = DirectX::XMMatrixLookAtLH(XMLoadFloat3(&_lightBufferVS->position), XMLoadFloat3(&_lookAt), XMLoadFloat3(&up));
      It looks like DirectX doesnt want the 2nd parameter to be a zero vector in the assertion, but I passed in a zero vector with this exact same code in another program and it ran just fine. (Here is the version of the code that worked - note XMLoadFloat3(&m_lookAt) parameter value is (0,0,0) at runtime - I debugged it - but it throws no exceptions.
          m_viewMatrix = DirectX::XMMatrixLookAtLH(XMLoadFloat3(&m_position), XMLoadFloat3(&m_lookAt), XMLoadFloat3(&up)); Here is the repo for the broken code (See LightClass) https://github.com/mister51213/DirectX11Engine/blob/master/DirectX11Engine/LightClass.cpp
      and here is the repo with the alternative version of the code that is working with a value of (0,0,0) for the second parameter.
    • By mister345
      Hi, can somebody please tell me in clear simple steps how to debug and step through an hlsl shader file?
      I already did Debug > Start Graphics Debugging > then captured some frames from Visual Studio and
      double clicked on the frame to open it, but no idea where to go from there.
      I've been searching for hours and there's no information on this, not even on the Microsoft Website!
      They say "open the  Graphics Pixel History window" but there is no such window!
      Then they say, in the "Pipeline Stages choose Start Debugging"  but the Start Debugging option is nowhere to be found in the whole interface.
      Also, how do I even open the hlsl file that I want to set a break point in from inside the Graphics Debugger?
      All I want to do is set a break point in a specific hlsl file, step thru it, and see the data, but this is so unbelievably complicated
      and Microsoft's instructions are horrible! Somebody please, please help.

    • By mister345
      I finally ported Rastertek's tutorial # 42 on soft shadows and blur shading. This tutorial has a ton of really useful effects and there's no working version anywhere online.
      Unfortunately it just draws a black screen. Not sure what's causing it. I'm guessing the camera or ortho matrix transforms are wrong, light directions, or maybe texture resources not being properly initialized.  I didnt change any of the variables though, only upgraded all types and functions DirectX3DVector3 to XMFLOAT3, and used DirectXTK for texture loading. If anyone is willing to take a look at what might be causing the black screen, maybe something pops out to you, let me know, thanks.
      Also, for reference, here's tutorial #40 which has normal shadows but no blur, which I also ported, and it works perfectly.
  • Advertisement