Converting 16 bit unsigned int array to 32 bit float array

Question

I am using directx 9 with 64bit render targets...I need to read the data on the render target surfaces. Each color component( a,r,g,b ) is encoded with 2 bytes( or 16bits x 4 = 64 ). How do I convert each 16 bit color component to a 32 bit floating point variable? Here is what I've tried:

BYTE *pData = ( BYTE* )renderTargetData;

for( UINT y = 0; y < Height; ++y )
{

   for( UINT x = 0; x < width; ++x )
   {
       // declare 4component vector to hold 4 floats
       D3DXVECTOR4 vColor;

       // convert the pixel color from 16 to 32 bits
       D3DXFloat16To32Array( ( FLOAT* )&vColor, ( D3DXFLOAT16* )&pData[ y + 8 * x ], 4 );
    }
}

For some reason this is incorrect...In one case after conversion, where the actual renderTargetData for one pixel is ( 0, 0, 0, 65535 ), I get this result: ( 0, 0, 0, -131008.00 ).

Answer 1

In general, converting an integer v from integer in range [0..n] to float in range [0.0..1.0] is:

float f = v/(float)n;

So, in your case, a loop that does:

vColor.x = (pData[ y + 4 * x ])/65535.0f; 
vColor.y = (pData[ y + 4 * x + 1 ])/65535.0f; 
// ... etc. 

should work, if we change the BYTE *pData = ( BYTE* )renderTargetData; into WORD *pData = ( WORD* )renderTargetData;

But there may be some clever way for DX to do this for you that I don't know of since I