trace.glsl

#version 450

layout(location = 1) uniform float dt = 1.0 / 128.0;
layout(location = 2) uniform float target_z = 4.0;
layout(location = 3) uniform int limit = 1000;
layout(location = 5) uniform vec4 params;

float scale(vec3 p);

vec3 grad(vec3 p) {
	const float h = 1.0 / 1024.0;
	float Dx = scale(p + vec3(h, 0.0, 0.0)) - scale(p - vec3(h, 0.0, 0.0));
	float Dy = scale(p + vec3(0.0, h, 0.0)) - scale(p - vec3(0.0, h, 0.0));
	float Dz = scale(p + vec3(0.0, 0.0, h)) - scale(p - vec3(0.0, 0.0, h));
	return vec3(Dx, Dy, Dz) / (h / 2.0);
}

bool trace(inout vec3 p, inout vec3 d) {
	const float outer_radius = params.x;
	d = normalize(d);
	for (int k = 0; k < limit; k++) {
		if (p.x >= target_z)
			return true;
		float r = outer_radius;
// 		if (length(p.yz) > r) {
// 			float a = dot(d.yz, d.yz);
// 			float b = 2.0 * dot(p.yz, d.yz);
// 			float c = dot(p.yz, p.yz) - r*r;
// 			float D = b * b - 4.0 * a * c;
// 			if (D <= 0.0)
// 				return true;
// 			float t1 = (- b - sqrt(D)) / (2.0 * a);
// 			float t2 = (- b + sqrt(D)) / (2.0 * a);
// 			if (t2 < 0.0)
// 				return true;
// 			if (t1 > 2 * dt) {
// 				p += (t1 - dt) * d;
// 				continue;
// 			}
// 		}

		float c = scale(p);
		if (c != 1.0) {
			vec3 dc = grad(p);
			vec3 dd;
			dd.x = (0.5 / c) * (dc.x * d.x - dc.y * d.y - dc.z * d.z) * d.x;
			dd.y = 0.5 * dc.y * d.x * d.x;
			dd.z = 0.5 * dc.z * d.x * d.x;
			d += dt * dd;
		}
		p += dt * d;
	}
	return false;
}

bool trace2(inout vec3 p, in vec3 d) {
	bool ok = trace(p, d);
	p += (target_z - p.x) / d.x * d;
	return ok;
}

vec3 trace3(vec3 p, vec3 d) {
	trace(p, d);
	return d;
}