Setting shader constants: Purpose of various functions

Graphics and GPU Programming Programming

Started by cdoubleplusgood October 11, 2013 08:43 AM

2 comments, last by cdoubleplusgood 10 years, 6 months ago

cdoubleplusgood

897

Author

October 11, 2013 08:43 AM

Hi Folks,

I have 2 questions regarding the various shader constant functions in IDirect3D9Device, e.g. SetVertexShaderConstantB/F/I.

1. Is my assumption correct that both SetVertexShaderConstantF and SetVertexShaderConstantI simply stuff a multiple of 128 bit into one or more constant registers, and there is not actual difference between them? That means, if I had a float[4] and cast a pointer to them to int*, I could use SetVertexShaderConstantI instead of SetVertexShaderConstantF with the same result. (No, I'm not actually going to do this; I just try to understand what goes on behind the scenes.)

2. What does SetVertexShaderConstantB do? How many bits in the constant register are taken for one BOOL? Both SetVertexShaderConstantF and SetVertexShaderConstantI take 4 values or a multiple of them; why is this different for SetVertexShaderConstantB?

Thanks!

Tordin

632

October 11, 2013 01:06 PM

As i understand it´s just a naming convention and probably has to do some with how the shaders compiles and optimize. but in the end everything is just bytes.

I Dx11, it´s not named F/B/I and just SetConstantBuffer. And thats also why i assume it´s the same here and more of a naming convention than anything.

and if you read on msdn, there is no real hints that it would be anydiffrent.

"There will be major features. none to be thought of yet"

Hodgman

52,717

October 11, 2013 02:15 PM

In DX9, the F version sets the c registers, the I version sets the i registers and the B version sets the b registers.

http://msdn.microsoft.com/en-us/library/windows/desktop/bb172963(v=vs.85).aspx

In HLSL SM2/3 (DX9), float, int and bool variables are all quite different, and are stored in these different types of registers.

As above, in SM4/5 (DX10/11) things have changed and you instead use SetConstantBuffer to bind constant buffers to b registers (b now == buffer, not bool), and ints/bools/floats exist inside these buffers.

. 22 Racing Series .

cdoubleplusgood

897

Author

October 11, 2013 02:24 PM

In DX9, the F version sets the c registers, the I version sets the i registers and the B version sets the b registers.

So I was completely wrong.

Thanks!

Setting shader constants: Purpose of various functions

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Setting shader constants: Purpose of various functions

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