Direct X & HLSL - Normal ReCalculation - c++

Question

I'm using HLSL and DirectX 9. I'm trying to recalculate the normals of a mesh so that HLSL receives updated normals as a result of transforming the mesh. What method is best to do this...also...D3DXComputeNormals will not work for me because I do not use FVF_NORMAL as a vertex declaration...I declare vertex format like so:
const D3DVERTEXELEMENT9 dec[4] =
{
{0, 0, D3DDECLTYPE_FLOAT3, D3DDECLMETHOD_DEFAULT, D3DDECLUSAGE_POSITION,0},
{0, 12, D3DDECLTYPE_FLOAT3, D3DDECLMETHOD_DEFAULT, D3DDECLUSAGE_NORMAL, 0},
{0, 24, D3DDECLTYPE_FLOAT2, D3DDECLMETHOD_DEFAULT, D3DDECLUSAGE_TEXCOORD,0},
D3DDECL_END()
};
I know how to access the adjacency data and vertex buffers but I'm not sure what method to use in order to properly associate a vertex and its normal with a face...Any help would be greatly appreciated. Thanks!

Answer 1

It's not a good idea to update the normals on CPU and send it to GPU each frame. That would ruin the performance. What you really should do is to calculate the transformed normals in the vertex shader, just like you do with the positions. HLSL code would look like this:
float4x4 mWorldView; // World * View
float4x4 mWorldViewProj; // World * View * Proj
struct VS_OUTPUT
{
float4 position : POSITION;
float2 tex : TEXCOORD0;
float3 normalVS : TEXCOORD1; // view-space normal
};
// Vertex Shader
VS_OUTPUT VS(float3 position : POSITION,
float3 normal : NORMAL,
float2 tex : TEXCOORD0)
{
VS_OUTPUT out;
// transform the position
out.position = mul(float4(position, 1), mWorldViewProj);
// pass the texture coordinates to the pixel shader
out.tex = tex;
// calculate the transformed normal
float3 n = mul(normal, (float3x3)mWorldView); // calculate view-space normal
// and use it for vertex lighting
// ... some shading calculations ...
// or pass it to the pixel shader and perform per-pixel lighting
out.normalVS = n;
// output
return out;
}