public bool hit(ray r, float t_min, float t_max, hit_record rec)
{
vec3 oc = r.Origin - center;
float a = vec3.dot(r.Direction, r.Direction);
float b = vec3.dot(oc, r.Direction);
float c = vec3.dot(oc, oc) - radius * radius;
float discriminant = b * b - a * c;
if (discriminant > 0)
{
float temp = (-b - (float)Math.Sqrt(discriminant)) / a;
if (temp < t_max && temp > t_min)
{
rec.t = temp;
rec.p = r.point_at_parameter(rec.t);
rec.normal = (rec.p - center) / radius;
return(true);
}
temp = (-b + (float)Math.Sqrt(discriminant)) / a;
if (temp < t_max && temp > t_min)
{
rec.t = temp;
rec.p = r.point_at_parameter(rec.t);
rec.normal = (rec.p - center) / radius;
return(true);
}
}
return(false);
}
static vec3 GetColor(ray r, hitable world)
{
hit_record rec = new hit_record();
//float value = -1;
//bool hit = HitSphere(new vec3(0, 0, -1), 0.5f, r, out value);
if (world.hit(r, 0.0f, float.MaxValue, rec))
{
return(new vec3(1 + rec.normal.x, 1 + rec.normal.y, 1 + rec.normal.z) * 0.5f); //[-1,1]-->[0,2]-->[0,1]
}
else
{
vec3 Normal = (r.point_at_parameter(value) - new vec3(0, 0, -1)).Normalize(); //normal:[-1,1]
return(new vec3(1 + Normal.x, 1 + Normal.y, 1 + Normal.z) * 0.5f); //[-1,1]-->[0,2]-->[0,1]
}
vec3 normalizedDir = r.Direction.Normalize();
float y = normalizedDir.y + 1; //[-1,1]-->[0,2]
float t = 0.5f * y; //[0,2]-->[0,1]
vec3 color_start = new vec3(1, 1, 1); //white
vec3 color_end = new vec3(0.5f, 0.7f, 1); //light blue
return(color_start * (1 - t) + color_end * t); //linear interpolate
}