nuclear@3: struct Ray {
nuclear@3: 	vec3 origin;
nuclear@3: 	vec3 dir;
nuclear@3: };
nuclear@3: 
nuclear@3: struct AABBox {
nuclear@3: 	vec3 vmin, vmax;
nuclear@3: };
nuclear@3: 
nuclear@3: struct HitPoint {
nuclear@3: 	bool hit;
nuclear@3: 	float t0, t1;
nuclear@3: 	vec3 pos, normal;
nuclear@3: 	vec4 color;
nuclear@3: };
nuclear@3: 
nuclear@3: vec3 shade(Ray ray, HitPoint hit);
nuclear@3: HitPoint intersect_voxels(Ray ray);
nuclear@3: HitPoint intersect_aabb(Ray ray, AABBox aabb);
nuclear@3: Ray get_primary_ray(float x, float y);
nuclear@3: 
nuclear@3: #define RAY_STEP	0.001
nuclear@3: 
nuclear@3: #define FOV		camprop.x
nuclear@3: #define ASPECT	camprop.y
nuclear@3: uniform vec4 camprop;
nuclear@3: uniform vec3 volsize;
nuclear@3: uniform sampler3D voltex;
nuclear@3: 
nuclear@3: //const vec3 worldsize = vec3(4.0, 4.0, 2.0);
nuclear@3: const vec3 worldsize = vec3(1.0, 1.0, 0.5);
nuclear@3: 
nuclear@3: void main()
nuclear@3: {
nuclear@3: 	Ray ray = get_primary_ray(gl_TexCoord[0].x, gl_TexCoord[0].y);
nuclear@3: 
nuclear@3: 	vec3 color = vec3(0.0, 0.0, 0.0);
nuclear@3: 	HitPoint hit = intersect_voxels(ray);
nuclear@3: 	if(hit.hit) {
nuclear@3: 		color = shade(ray, hit);
nuclear@3: 	}
nuclear@3: 
nuclear@3: 	gl_FragColor = vec4(color, 1.0);
nuclear@3: }
nuclear@3: 
nuclear@3: vec3 shade(Ray ray, HitPoint hit)
nuclear@3: {
nuclear@3: 	const vec3 light_pos = vec3(-2, 3, 2);
nuclear@3: 	vec3 ldir = normalize(light_pos - hit.pos);
nuclear@3: 
nuclear@3: 	vec3 vdir = normalize(-ray.dir);
nuclear@3: 	vec3 hvec = normalize(vdir + ldir);
nuclear@3: 
nuclear@3: 	float ndotl = max(dot(hit.normal, ldir), 0.0);
nuclear@3: 	float ndoth = max(dot(hit.normal, hvec), 0.0);
nuclear@3: 
nuclear@3: 	vec3 diffuse = hit.color.xyz * ndotl;
nuclear@3: 	vec3 specular = vec3(0.4, 0.4, 0.4) * pow(ndoth, 60.0);
nuclear@3: 
nuclear@3: 	return diffuse + specular;
nuclear@3: }
nuclear@3: 
nuclear@3: vec4 fetch_voxel(vec3 pt)
nuclear@3: {
nuclear@3: 	pt *= 1.0 / worldsize;
nuclear@3: 	return texture3D(voltex, pt * 0.5 + 0.5);
nuclear@3: }
nuclear@3: 
nuclear@3: vec3 calc_voxel_normal(vec3 pt)
nuclear@3: {
nuclear@3: 	vec3 offs = 1.8 / volsize;
nuclear@3: 	float dfdx = fetch_voxel(pt + vec3(offs.x, 0.0, 0.0)).w - fetch_voxel(pt - vec3(offs.x, 0.0, 0.0)).w;
nuclear@3: 	float dfdy = fetch_voxel(pt + vec3(0.0, offs.y, 0.0)).w - fetch_voxel(pt - vec3(0.0, offs.y, 0.0)).w;
nuclear@3: 	float dfdz = fetch_voxel(pt + vec3(0.0, 0.0, offs.z)).w - fetch_voxel(pt - vec3(0.0, 0.0, offs.z)).w;
nuclear@3: 
nuclear@3: 	return -normalize(vec3(dfdx, dfdy, dfdz));
nuclear@3: }
nuclear@3: 
nuclear@3: HitPoint intersect_voxels(Ray ray)
nuclear@3: {
nuclear@3: 	HitPoint hit;
nuclear@3: 	//AABBox aabb = AABBox(vec3(-1.0, -1.0, -1.0), vec3(1.0, 1.0, 1.0));
nuclear@3: 	AABBox aabb = AABBox(-worldsize.xzy, worldsize.xzy);
nuclear@3: 
nuclear@3: 
nuclear@3: 	hit = intersect_aabb(ray, aabb);
nuclear@3: 	if(!hit.hit) {
nuclear@3: 		return hit;
nuclear@3: 	}
nuclear@3: 
nuclear@3: 	/* start tracing from the first intersection, or if it's behind
nuclear@3: 	 * the viewer, start from 0.
nuclear@3: 	 */
nuclear@3: 	float dist = max(hit.t0, 0.0);
nuclear@3: 	float end_dist = hit.t1;
nuclear@3: 
nuclear@3: 	while(dist < end_dist) {
nuclear@3: 		vec3 pt = ray.origin + ray.dir * dist;
nuclear@3: 		vec4 voxel = fetch_voxel(pt.xzy);
nuclear@3: 
nuclear@3: 
nuclear@3: 		if(voxel.a > 0.5) {
nuclear@3: 			hit.t0 = dist;
nuclear@3: 			hit.pos = pt;
nuclear@3: 			hit.normal = calc_voxel_normal(pt.xzy).xzy;
nuclear@3: 			hit.color = voxel;
nuclear@3: 			return hit;
nuclear@3: 		}
nuclear@3: 
nuclear@3: 		dist += RAY_STEP;
nuclear@3: 	}
nuclear@3: 
nuclear@3: 	hit.hit = false;
nuclear@3: 	return hit;
nuclear@3: }
nuclear@3: 
nuclear@3: HitPoint intersect_aabb(Ray ray, AABBox aabb)
nuclear@3: {
nuclear@3: 	HitPoint res;
nuclear@3: 
nuclear@3: 	vec3 invR = 1.0 / ray.dir;
nuclear@3:     vec3 tbot = invR * (aabb.vmin - ray.origin);
nuclear@3:     vec3 ttop = invR * (aabb.vmax - ray.origin);
nuclear@3:     vec3 tmin = min(ttop, tbot);
nuclear@3:     vec3 tmax = max(ttop, tbot);
nuclear@3:     vec2 t = max(tmin.xx, tmin.yz);
nuclear@3:     float t0 = max(t.x, t.y);
nuclear@3:     t = min(tmax.xx, tmax.yz);
nuclear@3:     float t1 = min(t.x, t.y);
nuclear@3: 
nuclear@3: 	if(t0 <= t1) {
nuclear@3: 		res.hit = true;
nuclear@3: 		res.t0 = t0;
nuclear@3: 		res.t1 = t1;
nuclear@3: 	} else {
nuclear@3: 		res.hit = false;
nuclear@3: 	}
nuclear@3: 	return res;
nuclear@3: }
nuclear@3: 
nuclear@3: Ray get_primary_ray(float x, float y)
nuclear@3: {
nuclear@3: 	vec3 dir;
nuclear@3: 	dir.x = ASPECT * (2.0 * x - 1.0);
nuclear@3: 	dir.y = 2.0 * y - 1.0;
nuclear@3: 	dir.z = -1.0 / tan(FOV / 2.0);
nuclear@3: 
nuclear@3: 	Ray ray;
nuclear@3: 	ray.origin = (gl_ModelViewMatrix * vec4(0.0, 0.0, 0.0, 1.0)).xyz;
nuclear@3: 	ray.dir = gl_NormalMatrix * normalize(dir);
nuclear@3: 	return ray;
nuclear@3: }