RT_GPU/shaders/intersect.glsl

bool intersectSphere(Ray ray, GPUObject obj, out hitInfo hit)
{
	vec3 oc = ray.origin - obj.position;
	
	float b = dot(oc, ray.direction);
	float c = dot(oc, oc) - obj.radius * obj.radius;
	float h = b * b - c;
	
	float t = -b - sqrt(h);
	float last_t = -b + sqrt(h);

	if (t > last_t)
	{
		float temp = t;
		t = last_t;
		last_t = temp;
	}

	hit.t = t;
	hit.last_t = last_t;
	hit.position = ray.origin + ray.direction * t;
	hit.normal = normalize(hit.position - obj.position);
	
	return (h >= 0.0 && t > 0.0);
}

bool intersectPlane(Ray ray, GPUObject obj, out hitInfo hit)
{
	float d = dot(obj.normal, ray.direction);
	float t = dot(obj.position - ray.origin, obj.normal) / d;
	bool valid = t >= 0.0 && d != 0.0;

	if (!valid) return (false);
	
	hit.t = t;
	hit.position = ray.origin + ray.direction * t;
	hit.normal = d < 0.0 ? obj.normal : -obj.normal;
	
	return (valid);
}

bool intersectQuad(Ray ray, GPUObject obj, out hitInfo hit)
{
	vec3 normal = normalize(cross(obj.vertex1, obj.vertex2));
	float d = dot(normal, ray.direction);

	if (d == 0.0) return (false);

	float t = dot(obj.position - ray.origin, normal) / d;

	if (t <= 0.0) return (false);
	
	vec3 p = ray.origin + ray.direction * t - obj.position;
	
	float e1 = dot(p, obj.vertex1);
	float e2 = dot(p, obj.vertex2);
	
	float l1 = dot(obj.vertex1, obj.vertex1);
	float l2 = dot(obj.vertex2, obj.vertex2);
	
	bool inside = e1 >= 0.0 && e1 <= l1 && e2 >= 0.0 && e2 <= l2;
	
	hit.t = t;
	hit.position = p + obj.position;
	hit.normal = normal * -sign(d);
	
	return (inside);
}
bool intersectTriangle(Ray ray, GPUObject obj, out hitInfo hit)
{
	vec3 vertex1 = obj.vertex1 - obj.position;
	vec3 vertex2 = obj.vertex2 - obj.position;

	vec3 pvec = cross(ray.direction, vertex2);
	float det = dot(vertex1, pvec);
	vec3 tvec = ray.origin - obj.position;
	
	float invDet = 1.0 / det;
	float u = dot(tvec, pvec) * invDet;
	vec3 qvec = cross(tvec, vertex1);
	float v = dot(ray.direction, qvec) * invDet;
	float t = dot(vertex2, qvec) * invDet;
	
	bool valid = abs(det) > 1e-8 &&
				u >= 0.0 && u <= 1.0 &&
				v >= 0.0 && (u + v) <= 1.0 &&
				t > 0.0;
	
	hit.t = t;
	hit.position = ray.origin + ray.direction * t;
	hit.normal = obj.normal * sign(-dot(ray.direction, obj.normal));
	
	return (valid);
}

// bool intersectTriangle(Ray ray, GPUObject obj, out hitInfo hit)
// {
//     vec3 pvec = cross(ray.direction, obj.vertex2);
//     float det = dot(obj.vertex1, pvec);
	
//     if (abs(det) < 1e-8) return (false); // det < 0.0
	
//     float invDet = 1.0 / det;
	
//     vec3 tvec = ray.origin - obj.position;
	
//     float u = dot(tvec, pvec) * invDet;
//     if (u < 0.0 || u > 1.0) return (false);
	
//     vec3 qvec = cross(tvec, obj.vertex1);
//     float v = dot(ray.direction, qvec) * invDet;
//     if (v < 0.0 || u + v > 1.0) return (false);
	
//     float t = dot(obj.vertex2, qvec) * invDet;
//     if (t <= 0.0) return (false);
	
//     hit.t = t;
//     hit.position = ray.origin + ray.direction * t;
	
//     vec3 normal = obj.normal;
//     hit.normal = dot(ray.direction, normal) < 0.0 ? normal : -normal;
		
//     return (true);
// }

bool intersectCube(Ray ray, GPUObject obj, out hitInfo hit)
{
	vec3 halfSize = obj.vertex1 * 0.5;
	vec3 rayOriginLocal = ray.origin - obj.position;
	
	vec3 invDir = 1.0 / ray.direction;
	vec3 t1 = (-halfSize - rayOriginLocal) * invDir;
	vec3 t2 = (halfSize - rayOriginLocal) * invDir;
	
	vec3 tMinVec = min(t1, t2);
	vec3 tMaxVec = max(t1, t2);
	
	float tMin = max(tMinVec.x, max(tMinVec.y, tMinVec.z));
	float tMax = min(tMaxVec.x, min(tMaxVec.y, tMaxVec.z));
	
	bool hit_success = (tMax >= tMin) && (tMax > 0.0);
	if (!hit_success) return false;
	
	hit.t = tMin > 0.0 ? tMin : tMax;
	
	vec3 hitPointLocal = rayOriginLocal + hit.t * ray.direction;
	hit.position = hitPointLocal + obj.position;
	
	vec3 distances = abs(hitPointLocal) - halfSize;
	
	const float epsilon = 1e-4;
	vec3 signs = sign(hitPointLocal);
	vec3 masks = step(abs(distances), vec3(epsilon));
	
	hit.normal = normalize(masks * signs);
	
	bool inside = all(lessThan(abs(rayOriginLocal), halfSize + vec3(epsilon)));
	hit.normal *= (inside ? -1.0 : 1.0);
	
	return true;
}

bool intersectCylinder(Ray ray, GPUObject obj, out hitInfo hit) 
{
	float radius = obj.normal.x;
	float height = obj.normal.y;
	
	vec3 rayOrigin = mat3(obj.rotation) * (ray.origin - obj.position);
    vec3 rayDir = mat3(obj.rotation) * ray.direction;
    
    float halfHeight = height * 0.5;
    float radius2 = radius * radius;
    
    vec2 oc_xz = rayOrigin.xz;
    vec2 rd_xz = rayDir.xz;
    float a = dot(rd_xz, rd_xz);
    float b = dot(oc_xz, rd_xz);
    float c = dot(oc_xz, oc_xz) - radius2;
    
    float h = b * b - a * c;
    if (h < 0.0) return (false);
    
    float t_cyl = (-b - sqrt(h)) / a;
    float y = rayOrigin.y + t_cyl * rayDir.y;
    
    t_cyl = mix((-b + sqrt(h)) / a, t_cyl, 
                float(abs(y) <= halfHeight && t_cyl > 0.0));
    y = rayOrigin.y + t_cyl * rayDir.y;
    
    float invRayDirY = 1.0 / rayDir.y;
    float t_cap = (-sign(rayDir.y) * halfHeight - rayOrigin.y) * invRayDirY;
    vec2 cap_xz = rayOrigin.xz + t_cap * rayDir.xz;
    bool cap_valid = (dot(cap_xz, cap_xz) <= radius2) && (t_cap > 0.0);
    
    bool cyl_valid = abs(y) <= halfHeight && t_cyl > 0.0;
    float t = mix(t_cap, t_cyl, float(cyl_valid && (t_cyl < t_cap || !cap_valid)));
    
    if (!cyl_valid && !cap_valid) return (false);
    
    vec3 p = rayOrigin + t * rayDir;
    
    vec3 n_side = normalize(vec3(p.x, 0.0, p.z));
    vec3 n_cap = vec3(0.0, -sign(rayDir.y), 0.0);
    vec3 normal = mix(n_cap, n_side, float(cyl_valid && (t_cyl < t_cap || !cap_valid)));
    
    hit.t = t;
    hit.position = ray.origin + ray.direction * t;
    hit.normal = normalize(transpose(mat3(obj.rotation)) * normal);
    
    return (true);
}

bool intersect(Ray ray, GPUObject obj, out hitInfo hit)
{
	if (obj.type == 0)
		return (intersectSphere(ray, obj, hit));
	if (obj.type == 1)
		return (intersectPlane(ray, obj, hit));
	if (obj.type == 2 || obj.type == 5)
		return (intersectQuad(ray, obj, hit));
	if (obj.type == 3)
		return (intersectTriangle(ray, obj, hit));
	if (obj.type == 4)
		return (intersectCube(ray, obj, hit));
	if (obj.type == 6) 
		return (intersectCylinder(ray, obj, hit));
	return (false);
}