GradientFill
The GradientFill function fills rectangle and triangle structures.
BOOL GradientFill(
HDC hdc, // handle to DC
PTRIVERTEX pVertex, // array of vertices
ULONG dwNumVertex, // number of vertices
PVOID pMesh, // array of gradients
ULONG dwNumMesh, // size of gradient array
ULONG dwMode // gradient fill mode
);