Ray Tracing Performance and Practice Part 2

In this post, we shall explore creating a scene worth rendering.  In my prior work, my ray tracers were creating simple assemblages of spheres and triangles, with some having textures and others mirrored surfaces, etc.  This time, I wanted to have a scene that others might enjoy.  So for my first step, I turned to the Stanford 3D Scanning Repository and selected the angel model, Lucy.

The first problem in rendering is that the model is about 116 million triangles, or over 500MB in size.  Perhaps slightly more detail than is required for all but the largest of images.  Some time was spent searching for a tool that would provide a simplified model, and I settled on MeshLab.  However, the GUI version would crash trying to load the initial model, so I had to create a script of the required transformations and have the command-line application create the reduced model.  This reduced down to a 250k model, and subsequent transformations in the GUI gave a 50k triangle model and oriented appropriately for the ray tracer.

The second problem in rendering is that the model is stored in the ply file format.  I extended my scene parser to handle ply files without really understanding them. While I would like to have a generalized parser, I confined my work to the specific format that MeshLab was generating and did not worry about whether there were triangles or rectangles, normals present, colors specified, etc.  Yet, even this single format took some work.

Initially, the parser took in a text version of the ply file; however, the time to parse 100k lines of text and convert to the appropriate representations was approaching the time to render the scene.  Switching to a binary representation seemed a reasonable step; however, how does one take a stream of bytes and convert to a specific type?  In C, you could do the following:

Vec3f v;  // Struct of three floats

fread(&v, sizeof(float), 3, sceneFile);

But in C#?  I eventually settled on reading each value and converting via the "BitConverter" class.

Support.Assert(4 == pFile.BaseStream.Read(data, 0, 4), 
    "INVALID Ply - Fail to parse vertex");
newV.x = BitConverter.ToSingle(data, 0);

Great!  The statue is now in the tracer.  However, 50k triangles is too much for my naive ray tracer.  So there was performance work to be done.  At the time, I would render a 5k triangle version as a test model, as seen below (pending while in flight).