A Ray Tracer in C#3.0

A Ray Tracer in C#3.0

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Ray tracers are a lot of fun.  When I was in middle school, I discovered POV-Ray and was so excited about the cool graphics it could create that I would often leave my 286 on overnight rendering ray-traced scenes and movies.  When I was in high school, I discovered Computer Graphics: Principles and Practice and spent weeks working through it's ray tracing algorithms trying to implement my own ray tracer in C++.  When I was in college, taking an introductory course which used Scheme, I re-wrote the raytracer in Scheme to show some friends that you really could write programs longer than 20 lines in Scheme!  And then when I joined the C# team 3 years ago, I of course had to re-write my raytracer in C#. 

More recently, I took a pass through the code to update it to use C#3.0.  It's not a particularly fancy or efficient ray tracer - but then again, it's only 400 lines of code.  Below are a few of the interesting uses of C#3.0 from the ray tracer code.

C#3.0 Without the Databases and XML

Although we often demo C#3.0 using databases and XML to show off LINQ - it turns out that the new language features really are also great for applications which have little to do with querying.  Ray tracing, for example, is certainly not one of the prototypical scenario for query and transformation of data.  Nonetheless, I found quite a few places in the code where C#3.0 and LINQ to Objects really improved the code - making it easier to express what the program was doing.

LINQ to Objects

Here's one example of the method which computes the intersections of a ray with the objects in a scene.   

        private IEnumerable<ISect> Intersections(Ray ray, Scene scene)
            return scene.Things
                        .Select(obj => obj.Intersect(ray))
                        .Where(inter => inter != null)
                        .OrderBy(inter => inter.Dist);

The method intersects each object in the scene with the ray, then throws away those that didn't intersect, and finally orders the rest by the distance from the source of the ray. The first object in this result is the closest object hit by the ray.  If there are no elements in the result, there were no intersections.  The LINQ to Objects query methods provide a nice way to describe this, and lambdas make it easy to write the code which processes the objects and intersections.

Object and Collection Initializers 

Here's the code that describes the scene rendered in the image above.

        internal readonly Scene DefaultScene =
            new Scene() {
                    Things = new SceneObject[] { 
                                new Plane() {
                                    Norm = Vector.Make(0,1,0),
                                    Offset = 0,
                                    Surface = Surfaces.CheckerBoard
                                new Sphere() {
                                    Center = Vector.Make(0,1,0),
                                    Radius = 1,
                                    Surface = Surfaces.Shiny
                                new Sphere() {
                                    Center = Vector.Make(-1,.5,1.5),
                                    Radius = .5,
                                    Surface = Surfaces.Shiny
                    Lights = new Light[] { 
                                new Light() {
                                    Pos = Vector.Make(-2,2.5,0),
                                    Color = Color.Make(.49,.07,.07)
                                new Light() {
                                    Pos = Vector.Make(1.5,2.5,1.5),
                                    Color = Color.Make(.07,.07,.49)
                                new Light() {
                                    Pos = Vector.Make(1.5,2.5,-1.5),
                                    Color = Color.Make(.07,.49,.071)
                                new Light() {
                                    Pos = Vector.Make(0,3.5,0),
                                    Color = Color.Make(.21,.21,.35)
                    Camera = Camera.Create(Vector.Make(3,2,4), Vector.Make(-1,.5,0))

The scene consists of a collection of things, a collection of lights, and a camera, all of which are initialized in one statement using object and collection initializers.  This makes it quite a bit easier to describe the scene.  This format also helps to make the structure of the scene clear.


Here's the code describing the two surface textures used in the image above:

    static class Surfaces {
        // Only works with X-Z plane.
        public static readonly Surface CheckerBoard  = 
            new Surface() {
                    Diffuse = pos => ((Math.Floor(pos.Z) + Math.Floor(pos.X)) % 2 != 0) 
? Color.Make(1,1,1)
: Color.Make(0,0,0), Specular = pos => Color.Make(1,1,1), Reflect = pos => ((Math.Floor(pos.Z) + Math.Floor(pos.X)) % 2 != 0)
? .1
: .7, Roughness = 150 }; public static readonly Surface Shiny = new Surface() { Diffuse = pos => Color.Make(1,1,1), Specular = pos => Color.Make(.5,.5,.5), Reflect = pos => .6, Roughness = 50 }; }

These two static fields are initialized with the surface styles for the checkerboard and shiny textures on the objects in the scene above.  The surfaces are created with object initializers, and lambda expressions are used to provide the functions to compute diffuse, specular and reflection values based on the position on the surface.  The combination makes it possible to do something similar to prototype objects.

Try Out the Code

Want to try it out yourself?  Just compile RayTracer.cs with the Orcas C# compiler.  Then run.

File iconRayTracer.cs

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  • Recently my time has been taken up with a series of internal issues involving Beta1, C# Samples and various

  • C# PM Luke Hoban has posted a simple C# Ray Tracer code that utilizes the new C# 3.0 language capabilities.

  • I'm really impressed. Another msdn.com blogger just showed up a really nice example of how to use LINQ

  • I have been wanting this kind of thing in C++ for ages (well, at least a year). I think it will be useful in terms of writing AI programs and games where you don't keep your game characters in a database. An AI program could first load an entire common-sense database into memory. This is what I will use it for when LINQ comes out.


    print "Watch out! There are "+

    (select X from gameObjects where X.type==enemyTroll && X.pos.isNearTo(GamePlayer1.pos) ).length

    + "trolls near to you!"

    which is really easy to read.

    Here is another example that prints prime numbers less than 1000:

    foreach n in range(2,1000){

     if( (select d from range(2,sqrt(n)) where n%d==0).length ==0 ) print n+" is a prime\n"  


    How about using LINQ with OpenGL or DirectX where you could use it with vertex lists and things. Or how about using it with pixels in bitmaps:

    foreach PIXEL in BITMAP



    is this possible? This could be accelerated by DirectX10 shaders.


    What are the ideas for c# 4.0? With the idea that the computer should work out the best way to do things it sounds like it is turning into something like Maple, or Mathematica. Or how about using ideas from PROLOG?

  • On connaissait LinQ et ses possibilits pour du requtage type base de donnes, mais voici une application de RayTracing qui met en vidence les possibilits de LinQ dans un contexte compltement inhabituel :

  • how about a C# 2.0 version?  I'm not allowed to run beta applications at my employer.  Thanks!

  • Luke, a member of the c# team, created a Ray Tracer in c#. What is ray tracing exactly? Well, Wikipedia

  • Neat syntax, but... I'd rather see MS finally invest some effort in building decent .NET compilers, making use of the specific processor capabilities so we can do fast vector/matrix math *sigh*.

  • Paulsta - In principle there are places where LINQ could make sense with OpenGL or DirectX.  There was one specific topic related to leveraging pixel shaders from C# discussed on the forums recently http://forums.microsoft.com/MSDN/ShowPost.aspx?PostID=1533657&SiteID=1 - which may be relevent here.

  • Hi, I have a little different question:

    Diffuse = pos => ((Math.Floor(pos.Z) + Math.Floor(pos.X)) % 2 != 0)                                        ? Color.Make(1,1,1)                                        : Color.Make(0,0,0)

    Is it possible to generate functions / lambdas at runtime other way than emitting IL instructions? I mean a simple way to let user specify a string describing a material(per-pixel basis) and then

    render that material without parsing the string?

    Btw, in

    return scene.Things

           .Select(obj => obj.Intersect(ray))

           .Where(inter => inter != null)

           .OrderBy(inter => inter.Dist);

    I don't think the final OrderBy clause is a good approach since you only need the nearest intersection from the camera, so a linear loop over filtered Things would be quicker.

  • inv -

    It is in fact possible to generate functions at runtime.  In .NET2.0, the CLR added a feature called Lightweight Code Generation to REflection.Emit which allows defining DynamicMethods by providing an IL stream.  The API then allows you to capture a delegate to this newly created method.  This would enable the kind of thing you are suggesting - but it would be a lot of work.

    In .NET3.5 and C#3.0 we've added Expression Trees, which actually make this a lot easier.  You can use static factory methods on the Expression class to create the body of the expression and then use the ".Compile()" method to get a delegate back.  Under the hood this also uses LCG - but you can avoid mucking around with IL.  

    If I can find some time I'll write a post with a few examples of what this looks like.

    Also - you are right - the OrderBy is a bad idea - I should have used .Min().  Luckily there are only three objects in my scene - so the algorithmic complexity doesn't rear its head here :-)

  • Not too long ago I blogged about a C# raytracer which took advantage of a lot of C#3.0 language constructs.

  • Not too long ago I blogged about a C# raytracer which took advantage of a lot of C#3.0 language constructs

  • Multi-cpu systems and multicore processors are becoming ever more common, but writing code that actually

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