func SampleCoverage(value float32, invert bool) {
	syscall.Syscall(gpSampleCoverage, 2, uintptr(math.Float32bits(value)), boolToUintptr(invert), 0)
}
func SampleCoverage(value float32, invert bool) {
	syscall.Syscall(gpSampleCoverage, 2, uintptr(math.Float32bits(value)), boolToUintptr(invert), 0)
}
// specify multisample coverage parameters