CS6620 Advanced Graphics 2 University of Utah
Prof: Peter Shirley Ray Tracing Sem: Spring 2002

Assignment 06 - Image Texture Mapping

On top of the framework I built for Assignment 05a - Specular Study, I've added the ability to use images as texture maps. I did this by expanding the set of channel classes I created for Assignment 05 - Solid Texture (Marble). I've created a new derived class called a ChannelImage that returns colors from an image depending on a parameterization of the surface. Here's where it got a little tricky. Each surface contains a material, but sometimes the material needs properties from the surface in order to compute the color at a point (for example, a (u,v) pair in this case). So, all the color functions in the Channel classes take a pointer to a surface as well as the original point on the surface now.

In the scene description file, you can now attach any image to a material, like so:

material "picture" {
  diffuse { image "image.tga" }

Targa (.tga), Portable Pixmap (.ppm) and PC Paintbrush (.pcx) files are the only image file types that are currently supported. The filtering is locked in to bi-linear right now, but I hope to expand that to use other filtering methods in the future.

Timings (MM:SS.S) are for 500x500 pixel images on a PentiumIII 733Mhz with 384MB SDRAM
(unless otherwise noted).

Image Texture Maps Texture Mapped Spheres
crustal-white crustal-orange texture-white texture-orange
crustal-green crustal-grey texture-green texture-grey
(click on each image for a larger view).

mercator-0 mercator-90
mercator-180 mercator-270
(click on each image for a larger view).

Here is another mercator projection image. I created a rendering of a sphere texture mapped with this image at 18 degree intervals around the y axis. This created 20 frames which I then composited into an animation. The lighting was always from the point of view of the camera, so that the texture map is visible in each frame.

Indeo Video (529 Kb)

sphere-16 sphere-32
sphere-64 sphere-128
(click on each image for a larger view).

Here is the same map on spheres composed of triangles. (You can tell the difference because the triangles are flat shaded.) There is a sphere of 16x16, 32x32, 64x64 & 128x128 triangles.

All of the images above can be regenerated by specifying the appropriate scene file on the command line of the rayn program rayn-06.zip (271 Kb). The source code is included in the zip file. Here is a description of the command line parameters for rayn.
usage: rayn [options] <scene_file>


             <scene_file>    file containing scene description


  -o         <output_file>   output image filename (output.tga)
  -w         <width>         width of output image (256)
  -h         <height>        height of output image (256)
  -shadows   <true/false>    generate shadow rays (true)
  -rgs       <true/false>    generate regular grid subdivision (true)
  -bvh       <true/false>    generate bounding volume hierarchy (false)
  -sort      <true/false>    sort (not split) the surface list (false)
  -cull      <true/false>    cull backfacing triangles (false)

Questions/comments to nate@pobox.com.

March 2002
© Nate Robins