pixie

Ray-tracer implementation as specified by the awesome The Ray Tracer Challenge book.

Pixie is designed to be used from the API level. That means there is no scene description language support for now. Although Pixie isn't designed for speed for speed first, it is not a slouch. It will hapilly put all your cores to full use.

reference image

The reference image below is rendered using the latest Pixie features. It shows off focal distance on the new FocalBlurSampler implementation.

The image below is one of the scenes from the book rendered with focal blur.

getting started

In order to create a World you need to create some shapes. Let's start with a simple Sphere with radius 1.0 positioned at the origin.

var sphere = new Sphere();

Next we need a light source, we'll offset this a bit so it shines from a nice angle.

var light = new PointLight(
    Vector4.CreatePosition(10, 10, -10),
    Color.White);

Our world will this sphere and the light so we get:

var world = new World()
{
    objects = new [] { sphere },
    lights = new [] { light },
};

In order to actually render something we need a camera. Since our objects are all in unit size and centered around the origin by default we just need to position our camera a few units back.

var cam = new Camera(
    Vector4.CreatePosition(-2, 1, -5),
    Vector4.CreatePosition(0, 0.5, 0),
    Vector4.CreateDirection(0, 1, 0));

And with a camera we can render and save the image as follows.

var img = cam.Render(world);
img.SavePpm(@".\out.ppm");

geometry

Pixie does not really distinguish between points and vectors on a low level. This allows for some freedom but also for some mishaps. For instance, it is very much possible to perform an addition operation on two points even though this makes little sense from a math perspective.

Both points and vectors are represented as instances of Vector4 structures. In the case of points, the w component equals one and otherwise zero. It is recommended to use the Vector4.CreateDirection and Vector4.CreatePosition factory methods to create values of these kinds.

Points and vectors in Pixie support all the operations that you would expect to perform on them (and a little bit more as mentioned above).

Such as for example:

var p0 = Vector4.CreatePosition(0, 0, 0);
var p1 = Vector4.CreatePosition(1, 0, 1.5);
var v = p1 - p0;
var v2 = v * 2;
var vn = v2.Normalize();
var vv = v.Dot(v);

shapes

Pixie supports all the usual suspects:

• sphere
• plane
• cube
• cylinder
• cone
• triangle

As well as composites such as constructive solid geometry (CSG) and group shapes.

shapes

To create a shape, we just invoke its constructor:

var sphere = new Sphere();
var box = new Cube();
var plane = new Plane();

Note that in general, these shapes do not take any arguments. In order to scale or translate them into place we need to apply a transformation matrix to them.

var plane = new Plane();
var sphere = new Sphere()
{
    Transform = Transform.Translate(0, 1, 0),
};

Since all these shapes are of unit dimension and centered around the origin we can easily transform them to the place where we want them to sit in the world. The matrix above will lift the sphere (with radius 1) above the plane.

light

Pixie has PointLight and AreaLight sources but can be easily extended using the ILightSource and ILight interfaces.

var light = new PointLight(
    Vector4.CreatePosition(10, 10, -10),
    new Color(1, 1, 1));

Area lights are still pretty much experimental, undocumented and their API is subject to change.

world

A World is nothing more than a container for lights and objects. Now that we have a plane and a sphere it's easy to create one. In fact, we could have created an empty one but there is usually not much point for that.

var world = new World()
{
    Lights = new [] { light },
    Objects = new Shape[] { plane, sphere },
};

materials

Materials are implemented based mostly on Phong shading whith some extensions for reflection, transparency and refraction.

Every new material will have have a white color and defaults that make sure it shows up. If you are going to use a particular material multiple times you probably should cache it but otherwise it is probably better to set it inline.

var s = new Cube()
{
    Material = new Material()
    {
        Specular = 0,
        Ambient = 0.3,
        Diffuse = 0.5,
        Color = new Color(0.8, 0.2, 0.8),
    },
};

patterns

Patterns are basically procedural textures. They support transformations as well. All of the classics such as stripe, gradient and checkers are included. Pixie supports nested and blended patterns as well.

samplers

Pixie includes a few samplers but many more can be implemented using the ISampler interface.

• DefaultSampler functions like a pin-hole camera. It shoots a single ray for each pixel right trough the center.
• RandomSuperSampler shoots a bunch of rays in but around the origin of a pixel. This sampler is not very smart but it can help with anti-aliasing.
• FocalBlurSampler takes a focal distance and an aperture size and creates an effect known as focal blur. Since this samper is also multi-sampling per pixel, it tends to create an anti-aliasing effect as well.

ideas

• Bezier curves
• L-systems
• More shapes & patterns
• Texture mapping
• Improve area lights
• Polynomial support
• Normal pertubation (smoothed triangles still todo)