Lag-less Gradient Function

void FillGradient(IDirect3DDevice9 * m_pD3Ddev,int x, int y, int h, int w, DWORD color1, DWORD color2)
{
DWORD a1 = (color1>>24)&0xFF;
DWORD r1 = (color1>>16)&0xFF;
DWORD g1 = (color1>>8)&0xFF;
DWORD b1 = color1&0xFF;
DWORD a2 = (color2>>24)&0xFF;
DWORD r2 = (color2>>16)&0xFF;
DWORD g2 = (color2>>8)&0xFF;
DWORD b2 = color2&0xFF;
float aDif,rDif,gDif,bDif;
aDif = ((float)a2-(float)a1)/h;
rDif = ((float)r2-(float)r1)/h;
gDif = ((float)g2-(int)g1)/h;
bDif = ((float)b2-(float)b1)/h;
DWORD DrawCol;
for(int i = 0;i<h;i++)
{
DrawCol = (a1+(int)(aDif*i) << 24) | (r1+(int)(rDif * i) << 16) | (g1+(int)(gDif * i) << 8) | (b1+(int)(bDif*i));
DrawRect(m_pD3Ddev,x,y+i,w,1,DrawCol);
}
}