Writing computational algorithms in pixel shaders can be very difficult. Writing such algorithms for 9_3
target can be impossible. Too much restrictions. But, well, I think I know how to workaround your problems.
1. Shader repetition
First of all, it is unclear, what do you call "bottleneck" here. Yes, theoretically, draw calls in for loop is a performance loss. But does it bottleneck? Does your application really looses performance here? How much? Only profilers (CPU and GPU) can answer. But to run it, you must first complete your algorithm (stages 3 and 4). So, I'd better stick with current solution, and started to implement whole algorithm, then profile and than fix performance issues.
But, if you feel ready to tweaks... Common "repetition" technology is instancing. You can create one more vertex buffer (called instance buffer), which will contains parameters not for each vertex, but for one draw instance. Then you do all the stuff with one DrawInstanced()
call.
For you first stage, instance buffer can contain your D
value and index of target Texture3D
layer. You can pass-through them from vertex shader.
As always, you have a tradeof here: simplicity of code to (probably) performance.
2. Multi-pass rendering
CPU needs to be involved to pass results from temp texture (result of V pass) to the second pass (H pass)
Typically, you do chaining like this, so no CPU involved:
// Pass 1: from pTexture0 to pTexture1
// ...set up pipeline state for Pass1 here...
pContext->PSSetShaderResources(slot, 1, pTexture0); // source
pContext->OMSetRenderTargets(1, pTexture1, 0); // target
pContext->Draw(...);
// Pass 2: from pTexture1 to pTexture2
// ...set up pipeline state for Pass1 here...
pContext->PSSetShaderResources(slot, 1, pTexture1); // previous target is now source
pContext->OMSetRenderTargets(1, pTexture2, 0);
pContext->Draw(...);
// Pass 3: ...
Note, that pTexture1
must have both D3D11_BIND_SHADER_RESOURCE
and D3D11_BIND_RENDER_TARGET
flags. You can have multiple input textures and multiple render targets. Just make sure, that every next pass knows what previous pass outputs.
And if previous pass uses more resources than current, don't forget to unbind unneeded, to prevent hard-to-find errors:
pContext->PSSetShaderResources(2, 1, 0);
pContext->PSSetShaderResources(3, 1, 0);
pContext->PSSetShaderResources(4, 1, 0);
// Only 0 and 1 texture slots will be used
3. Resource data location
Does all textures resides in GPU memory all the time even between Draw() method calls and Pixel/Vertex shaders switching?
We can never know that. Driver chooses appropriate location for resources. But if you have resources created with DEFAULT
usage and 0
CPU access flag, you can be almost sure it will always be in video memory.
Hope it helps. Happy coding!