GSoC/GCI Archive
Google Code-in 2012 BRL-CAD

Add a command-line option that sets an object color temporarily

completed by: javamonn

mentors: Sean

This task involves adding probably less than 10 lines of code.

BRL-CAD has a raytracer / renderer command-line application called "rt" that generates pretty pictures.  It has a whole slew of command-line options, and this task entails adding support for one more that sets an object's color.

This task is meant to be proof-of-concept, so here's a crash-course:

  • Run "mged -c test.g"
  • Say 'y' for yes when it asks whether to create a new database
  • Select "nu" on the attach prompt so we stay in command-line mode
  • Run "make sph sph" to create a sphere
  • Run "r sph.r u sph" to make a solid region out of the sphere
  • Run "mater sph.r plastic 255 0 0 ." to make the sphere red
  • Run "quit" to exit mged
Next, render:
  • Run "rt -s1024 -C255/255/255 test.g sph.r" to render the sphere in a 1024x1024 window with a white background specified.

Now your task is to make it so that we can override that sphere's red color (just temporarily) during rt.  Make something like this work:

rt -s1024 -C255/255/255 -O0/0/255 test.g sph.r

That will set the 0/0/255 color on the specified sph.r object and it should render blue.  That is it!


  • src/rt/opt.c
  • src/rt/view.c
  • src/rt/do.c
  • src/rt/worker.c
  • src/rt/main.c

You won't necessarily need to modify all of those (I did claim this was probably <10 lines after all), but the code you add will probably be to one of those five files.  A hint to get you started, look for bu_getopt() and find where -C is getting processed.  That may help creating a -O (or similar option if -O is already taken).

Submit your work as a single patch file.  See for help.