HLSL question

So you are basically loading a single pixel of a texture and then adding another pixel?

Then you could just pass a variable to the shader instead, I think?

Please correct me If I'm wrong...

Its an example to show what the general idea of the question is, the general idea is if there is a way to load texels one time so i dont have to load them every time there is a different vertex or different pixel.

"Then you could just pass a variable to the shader instead"

describe it more, passing a variable in wich way, from CPU to GPU?(that cant be done because the variable is in a texel in GPU, and passing it to CPU by mapping it and then again to GPU is not so good for performance)

Do it on the CPU side and pass it to the shader?

As you only "load texels one time"...

ok, then it can't be done.

what i am doing is creating a view matrix from some particles positions that are in a texture so i dont only have to load texels but make some rotations of vectors too and doing those operations again and again in every vertex shader is a waste in performance, the texture is big passing it to CPU and then again to GPU, i think it will be worse in performance and a pain because the texel of the texture is not in the same place, changes a lot and depends on the value of another texel of another texture.

PS. I will be gone for a while...

I assume that when you call TextureA.Load it basically loads a pixel at specific coordinates, BTW, can you post the shader to make it easier for us?

So let me just get this straight, you will ONLY get the color of one pixel in a whole execution of one shader? So the color is basically a constant throughout the process?

If this is the case, I would recommend getting the color of the pixel at the CPU side and then sending this color to the GPU / shader, that would generally do what you would wan't me to do.

So at the CPU:

D3DXCOLOR t = GetPixelAt(x, y); // your method here...

Send to GPU...

GPU: (PS. are you using FX?)

float4 t; // then use this value

Can anyone confirm if my suggestion is right?

If you don't know how to send a variable from the CPU to the GPU, you could read this:

http://msdn.microsoft.com/en-us/library/windows/desktop/bb509581(v=vs.85).aspx

Now if you're using FX, you could read this:

http://msdn.microsoft.com/en-us/library/windows/desktop/bb206299(v=vs.85).aspx

PS. I don't know if what you are trying to do can be done, but this method might be easier...

Don't try to second-guess the driver or GPU! Profile your code, determine if it actually is slow, and act accordingly. Right now you're just assuming that Loading the texture is going to be slower, but you may be surprised - it may not be. In this case it's quite likely that your GPU's texture cache is going to mean that only the first Load is going to have any meaningful performance loss, and subsequent Loads (assuming that the coords remain the same) will just be fetched from cache.

Presumably you have a lot less VS instances being run than PS, so at the very least you could do your texture sample in the VS and pass the result on through to the PS.