7 replies to this topic

[schupf]

Hello!

I made some tests but I am still not sure about this:
If I set a certain shader register (i.e. register c4 with mDevice->SetPixelShaderConstantF(4, data, 1))
Will register c4 now contain this value also the next frames or do I have to update c4 every frame even if the value never changes?

In other words: Should I upload everything every frame or upload all uniforms ONCE and then only update the ones that have been changed?

[MJP]

It's definitely persistent for the duration of a frame, but I'm not sure if the state will survive across frames. PIX should be able to tell you really quickly.

[schupf]

So whats best practice? Lazy updating or uploading everything every frame?

[mhagain]

Updating everything every frame would seem better to me; it's more in line with the way constant buffers are used in D3D10/11 which would be more likely to be the optimal path on current and future hardware. But this is just a personal hunch - as usual, benchmark.

[MJP]

I would just update constants every frame. Setting something once a frame shouldn't matter at all...it's setting constants many times during a frame that can hurt performance.

[Hodgman]

In D3D9, I treat the shader constants as if they were a global cbuffer. When you set a constant, you're writing into that global cbuffer. The value will persist there until you write a new value over the top of it.

[Nik02]

...unless the device is lost.

[mhagain]

...or you're using the Effects framework, in which case one constant may overwrite another.

Not relevant with SetPixelShaderConstantF of course, but something that the OP should be aware of nonetheless.