static bool HitSphere(vec3 sphereCenter, float sphereRadius, ray r, out float value)//r = A+B*t
{
vec3 oc = r.Origin - sphereCenter;
float a = vec3.dot(r.Direction, r.Direction); //dot(B,B)
float b = 2.0f * vec3.dot(oc, r.Direction); //2*dot(A-C,B)
float c = vec3.dot(sphereCenter, sphereCenter) - sphereRadius * sphereRadius; //dot(C,C)-R*R
float discriminant = b * b - 4 * a * c;
if (discriminant < 0)
{
value = -1;
return(false);
}
value = (-b - (float)Math.Sqrt(discriminant)) / (2.0f * a);//closest(smallest) hit point
return(true);
}
static void Main(string[] args)
{
int nx = 200;
int ny = 100;
float u, v;
ray r;
vec3 color;
int nr, ng, nb;
string dir = Directory.GetCurrentDirectory();
string fileName = @"\out.ppm";
StreamWriter sw = File.CreateText(dir + fileName);
sw.WriteLine("P3");
sw.WriteLine(nx.ToString() + " " + ny.ToString());
sw.WriteLine("255");
vec3 lower_left_corner = new vec3(-2, -1, -1); //offset
vec3 horizontal = new vec3(4, 0, 0); //total width
vec3 verticle = new vec3(0, 2, 0); //total height
vec3 origin = new vec3(0, 0, 0); //camera position
for (int j = ny - 1; j >= 0; j--)
{
for (int i = 0; i < nx; i++)
{
u = (i * 1.0f) / nx;
v = (j * 1.0f) / ny;
r = new ray(origin, lower_left_corner + horizontal * u + verticle * v);
color = GetColor(r);
nr = (int)(255.99 * color.r);
ng = (int)(255.99 * color.g);
nb = (int)(255.99 * color.b);
sw.WriteLine(nr.ToString() + " " + ng.ToString() + " " + nb.ToString());
}
}
sw.Flush();
sw.Close();
}
static vec3 GetColor(ray r)
{
float value = -1;
bool hit = HitSphere(new vec3(0, 0, -1), 0.5f, r, out value);
if (hit)
{
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
}