Hello,
I'm writing something similar to a particle engine, where I have a bunch of quads in a vertex buffer, and modify each quad via two transform structures, child and parent, in the vertex shader.
struct SpriteParent
{
float4 mtxParentRS; // Parent sprite rot/scl
float4 fParentPosAlpha; // Parent position and alpha
};
struct SpriteChild
{
float4 mtxChildRS; // Child primitve rot/scl
float4 fTextureUVAlpha; // UV offset (pattern) and alpha
};
So I can reference them easily in HLSL, I define a couple of arrays in the shader file as well.
SpriteParent g_SpriteParents[30];
SpriteChild g_SpriteChildren[90];
The number of "child" primitives per "parent" sprite is variable, so the ratio of SpriteParent to SpriteChild structures that I actually use changes per DrawIndexedPrimitive call. Although I define 90 children in the shader, I may not use them all, or may actually need more if the ratio of Children:Parent is quite high.
I keep track of which structures to reference for each quad primtive via blend indicies in the vertex data, and upload batches of the SpriteParent and SpriteChild structures via ID3DXConstantTable::SetFloatArray.
The problem is I run into trouble when I need to access more Parent or Child structures than I define as above in the shader file; I get a D3D error telling me that the handle to the structure element is not defined. If I define the structure arrays to have the maximum possible amount utilized in any configuration, the collective size is larger than can fit in constant register memory, and the shader doesn't compile.
Is there a way to manage the allocation of these structures in the shader more dynamically so I can get the optimal packing I'm calculating on the game engine side? Or do I have to abandon user-defined structures then and write my shader in terms of pure constant registers and address offsets? (Never done this before, a little leery.)
Thank you for the advice!
