问题
I have a vertex shader (2.0) doing some instancing - each vertex specifies an index into an array.
If I have an array like this:
float instanceData[100];
The compiler allocates it 100 constant registers. Each constant register is a float4, so it's allocating 4 times as much space as is needed.
I need a way to make it allocate just 25 constant registers and store four values in each of them.
Ideally I'd like a method where it still looks like a float[] on both the CPU and GPU (Right now I am calling EffectParamter.SetValue(Single[]), I'm using XNA). But manually packing and unpacking a float4[] is an option, too.
Also: what are the performance implications for doing this? Is it actually worth it? (For me, this will save about one batch in every four or five).
回答1:
Does that helps?:
float4 packedInstanceData[25];
...
float data = packedInstanceData[index / 4][index % 4];
来源：https://stackoverflow.com/questions/2866778/hlsl-index-to-unaligned-packed-floats