#version 330 core

#define FOV 90

#define EPSILON 0.01
#define MAX_STEPS 64
#define NEAR_D 0.
#define FAR_D 20.

#define GRAD_EPSILON 0.0001

#define saturate(x) clamp(x, 0, 1)

uniform vec2 u_Resolution;
uniform vec4 u_Mouse;
uniform float u_Time;

out vec4 color;

#include "utils.glsl"
#include "march_prolog.glsl"
#include "hg_sdf.glsl"
#include "colormap_cool.glsl"

vec3 ray_dir(float fov, vec2 uv) {
	float z = 1./tan(radians(fov)/2.);
	return normalize(vec3(uv, z));
}

SceneResult scene_f(vec3 p) {
	SceneResult box = SceneResult(fBox(p, vec3(1)), 1.);
	SceneResult sphere = SceneResult(fSphere(p + vec3(1), 1.0), 2.);

	return min_sr(box, sphere);
}

vec3 estimate_scene_normal(vec3 p) {
	vec3 dx = vec3(GRAD_EPSILON, 0, 0);
	vec3 dy = vec3(0, GRAD_EPSILON, 0);
	vec3 dz = vec3(0, 0, GRAD_EPSILON);

	return normalize(vec3(
		scene_f(p + dx).d - scene_f(p - dx).d,
		scene_f(p + dy).d - scene_f(p - dy).d,
		scene_f(p + dz).d - scene_f(p - dz).d
	));
}

vec3 raymarch(vec3 o, vec3 d, float start, float end) {
	float t = start;
	for (int i = 0; i < MAX_STEPS; i++) {
		float dist = scene_f(o + d*t);
		if (dist < EPSILON || t > end)
			return vec3(t, i, 0.);

		t += dist;
	}
	return vec3(end, MAX_STEPS, 0.);
}

vec4 shade(vec3 p) {
	vec3 normal = estimate_scene_normal(p);
	return vec4((normal + vec3(1.0))/2.0, 1.0);
}

void main() {
	vec2 mouse_uv = u_Mouse.xy * 2.0 / u_Resolution.xy - 1.0;
	
	vec2 uv = gl_FragCoord.xy * 2.0 / u_Resolution.xy - 1.0;
	uv.x *= u_Resolution.x/u_Resolution.y;

	vec3 eye = vec3(0., 0., -5.);
	mat3 lookAt = calcLookAtMatrix(eye, vec3(0., 0., 0.), u_Time);
	vec3 dir = normalize(lookAt * ray_dir(FOV, uv));

	color = vec4(0.);

	vec3 result = raymarch(eye, dir, NEAR_D, FAR_D);
	float depth = result.x;
	float iters = result.y;
	if (depth >= FAR_D) {
		color = vec4(1.0, 0.5, 1.0, 1.0);
		return;
	}

	color = colormap(iters/MAX_STEPS+0.5);
	vec3 p = eye + dir * depth;
	color = shade(p);
}