/// <summary>
/// Shoot a ray into the scene and determine the colour at the impact point.
/// </summary>
/// <param name="ray">The ray to shoot into the scene.</param>
/// <returns>The colour of the impacted point in the scene.</returns>
private Colour ShootRay(Ray ray)
{
Colour finalOutput = new Colour(0.0f, 0.0f, 0.0f);
float coefficient = 1.0f;
uint count = 0u;
do {
Colour output = new Colour(0.0f, 0.0f, 0.0f);
IObject closestObject = null;
float closestDistance = float.MaxValue;
foreach (var o in Objects) {
float t = o.IntersectDistance(ray);
if (t > 0.001f && t < closestDistance) {
closestObject = o;
closestDistance = t;
}
}
if (closestObject == null) {
break;
}
// Calculate the point of intersection.
Point intersection = ray.Start + closestDistance * ray.Direction;
// Get normal of object surface at impact of ray.
Vector normal = closestObject.GetNormalAtPoint(intersection);
foreach (var l in Lights) {
Vector toLightSource = (l.Location - intersection).Normalise();
float cosineLightAngle = normal * toLightSource;
if (cosineLightAngle <= 0.0f) {
// The light is below the surface.
continue;
}
bool inShadow = false;
foreach (var o in Objects) {
if (o == closestObject) {
continue;
}
if (o.IntersectDistance(new Ray(intersection, toLightSource)) > 0.0f) {
inShadow = true;
break;
}
}
if (!inShadow) {
var lambertianReflectance = (Colour)closestObject.Material.Colour * (Colour)l.Colour * cosineLightAngle;
output += lambertianReflectance;
var halfwayVector = (toLightSource - ray.Direction).Normalise();
var halfwayNormalAngle = halfwayVector * normal;
var blinnTerm = (Colour)l.Colour * closestObject.Material.SpecularTerm * (float)Math.Pow(Math.Max(halfwayNormalAngle, 0.0f), closestObject.Material.SpecularPower);
output += blinnTerm;
}
}
finalOutput += output * coefficient;
var newRayDirection = (ray.Direction - 2 * normal * (normal * ray.Direction)).Normalise();
ray = new Ray(intersection, newRayDirection);
coefficient *= closestObject.Material.Reflectance;
} while (++count < MAX_ITERATIONS && coefficient > 0.0f);
return finalOutput;
}
/// <summary>
/// Renders the image.
/// </summary>
public void Draw()
{
float exposure = CalculateExposure();
float widthRatio = (float)Camera.Width / output.Width;
float heightRatio = (float)Camera.Height / output.Height;
ParallelOptions options = new ParallelOptions() {
#if DEBUG
//MaxDegreeOfParallelism = 1
#endif
};
Parallel.For(0, output.Height, options, (y) => {
for (var x = 0u; x < output.Width; ++x) {
float sampleWidth = 1.0f / SubSampling;
float weight = sampleWidth / SubSampling;
Colour outputColour = new Colour(0.0f, 0.0f, 0.0f);
uint countX = 0u;
for (float sampleX = x; countX < SubSampling; sampleX += sampleWidth, ++countX) {
uint countY = 0u;
for (float sampleY = y; countY < SubSampling; sampleY += sampleWidth, ++countY) {
Ray r = Camera.GetRay(sampleX * widthRatio, sampleY * heightRatio);
Colour c = ShootRay(r);
Colour exposedColour = new Colour(1.0f - (float)Math.Exp(c.Red * exposure),
1.0f - (float)Math.Exp(c.Green * exposure),
1.0f - (float)Math.Exp(c.Blue * exposure));
outputColour += exposedColour * weight;
}
}
Colour sRgbColour = outputColour.ToSrgb();
output.Write((uint)x, (uint)y, sRgbColour);
}
});
}
