Effects in DirectX 11

Warning! Some information on this page is older than 5 years now. I keep it for reference, but it probably doesn't reflect my current knowledge and beliefs.

# Effects in DirectX 11

May 2010

I no longer believe Microsoft did a good job complicating new DirectX so much. Effects framework - the API that supported loading and using effect files that grouped HLSL code and render states into passes and techniques - is no longer intrinsic part of D3DX. Instead they provided source code for this library so you have to compile it by yourself!

To do this: Enter your DX SDK subdirectory "Samples\C++\Effects11", open a "Effects11_*.sln" solution file appropriate for your Visual C++ version and compile the project in both Debug and Release configuration.

Then to use effects API in your project you have to include this header: "YOUR_DX_SDK_PATH\Samples\C++\Effects11\Inc\D3dx11effect.h" and link with this lib: "YOUR_DX_SDK_PATH\Samples\C++\Effects11\Debug\D3DX11EffectsD.lib (Debug) or "YOUR_DX_SDK_PATH\Samples\C++\Effects11\Release\D3DX11Effects.lib" (Release), as well as with "d3dcompiler.lib" (in both configurations).

Here is example of how to load an effect from file. You need to first compile a source code from file or memory into a blob binary effect and then create real effect object from this blob.

// Compile effect from HLSL file into binary Blob in memory
ID3D10Blob *effectBlob = 0, *errorsBlob = 0;
HRESULT hr = D3DX11CompileFromFile(
  "Effect1.fx", 0, 0, 0, "fx_5_0", 0, 0, 0, &effectBlob, &errorsBlob, 0);
assert(SUCCEEDED(hr) && effectBlob);
if (errorsBlob) errorsBlob->Release();
// Create D3DX11 effect from compiled binary memory block
ID3DX11Effect *g_Effect;
hr = D3DX11CreateEffectFromMemory(
  effectBlob->GetBufferPointer(), effectBlob->GetBufferSize(), 0, g_Dev, &g_Effect);

The effect itself is not enough. You need to retrieve object that represents "pass" to use it. So you get a technique from the effect (by index or by name) and then the pass from the technique.

ID3DX11EffectTechnique *g_EffectTechnique; // No need to be Release()-d.
g_EffectTechnique = g_Effect->GetTechniqueByIndex(0);
assert(g_EffectTechnique && g_EffectTechnique->IsValid());

ID3DX11EffectPass *g_EffectPass; // No need to be Release()-d.
g_EffectPass = g_EffectTechnique->GetPassByIndex(0);
assert(g_EffectPass && g_EffectPass->IsValid());

Now when you have this object, you can apply settings from this pass to the device context during rendering:

g_EffectPass->Apply(0, g_Ctx);
g_Ctx->Draw(3, 0);

But still one problem reamins. In DirectX 11 you need to pass a pointer to the bytecode with compiled shader when creating input layout - a step that you probably cannot omit. Fortunately there is a way to access this pointer stored inside loaded effect. You just need to pass through two descriptors, just like this:

effectVsDesc.pShaderVariable->GetShaderDesc(effectVsDesc.ShaderIndex, &effectVsDesc2);
const void *vsCodePtr = effectVsDesc2.pBytecode;
unsigned vsCodeLen = effectVsDesc2.BytecodeLength;

ID3D11InputLayout *g_InputLayout;
D3D11_INPUT_ELEMENT_DESC inputDesc[] = { /* ... */ };
hr = g_Dev->CreateInputLayout(
  inputDesc, _countof(inputDesc), vsCodePtr, vsCodeLen, &g_InputLayout);

Luckily it looks like the effect framework doesn't add much functionality over pure HLSL shader supported by D3D11 itself, so you don't have to use it. Defining these techniques and passess is not so important after all...

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