Progressive Jittered Sample Sequence

jitter.cpp

static float rnd()
{
	return drand48();
}

float2 generate_sample_point(float i, float j, float xhalf, float yhalf, float n)
{
	float2 pt;
	pt.x = (i + 0.5f * (xhalf + rnd())) / n;
	pt.y = (j + 0.5f * (yhalf + rnd())) / n;
	return pt;
}

void extend_sequence(float2 points[], int N)
{
	int n = sqrtf(N);
	for(int s = 0; s < N; ++s) {
		float2 oldpt = points[s];
		float i = floorf(n * oldpt.x);
		float j = floorf(n * oldpt.y);
		float xhalf = floorf(2.0f * (n * oldpt.x - i));
		float yhalf = floorf(2.0f * (n * oldpt.y - j));
		xhalf = 1.0f - xhalf;
		yhalf = 1.0f - yhalf;
		points[N + s] = generate_sample_point(i, j, xhalf, yhalf, n);
		if(rnd() > 0.5f) {
			xhalf = 1.0f - xhalf;
		}
		else {
			yhalf = 1.0f - yhalf;
		}
		points[2 * N + s] = generate_sample_point(i, j, xhalf, yhalf, n);
		xhalf = 1.0f - xhalf;
		yhalf = 1.0f - yhalf;
		points[3 * N + s] = generate_sample_point(i, j, xhalf, yhalf, n);
	}
}

float2 *generate_pj(int M)
{
	float2 *points = new float2[M];
	return points;
}

void progressive_jitter_generate_2D(float2 points[], int size)
{
	points[0].x = rnd();
	points[0].y = rnd();
	int N = 1;
	while(N < size) {
		extend_sequence(points, N);
		N = 4 * N;
	}
}