func ClearIndex(c float32) {
	syscall.Syscall(gpClearIndex, 1, uintptr(math.Float32bits(c)), 0, 0)
}
func ClearIndex(c float32) {
	syscall.Syscall(gpClearIndex, 1, uintptr(math.Float32bits(c)), 0, 0)
}
// specify the clear value for the color index buffers