Tree Parallel Ulam Spiral

This fancy spiral is a mathematical doodle discovered by Stanislaw Ulam (who was bored during math class.) It demonstrates an apparent ordering within the primes (the white dots) in relation to quadratic polynomials. It also relates to other spirally things like the Droste Effect and Mobius Transformations which have recently demonstrated up and coming hipness.

I could not find any code for rendering it in parallel, so I wrote my own.
float ulam_spiral(vec2 p)
{
	float x = abs(p.x);
	float y	= abs(p.y);
	bool q	= x > y;
	
	x	= q ? x : y;
	y	= q ? p.x + p.y : p.x - p.y;
	y 	= abs(y) + 4. * x * x + 1.;
	x 	*= 2.;
	
	return q ? (p.x > 0. ? y - x - x : y) 
		 : (p.y > 0. ? y - x : y + x);	
}
Live Demo with Sourcecode