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Simulate elastic collisions of marbles
C++ Makefile
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This produces videos simulating collisions between marbles. This was just a prototype to validate alogirhtms for Collide.

Demo on YouTube:

Demo on YouTube

Questions, remarks, suggestions? Open an issue!

Main properties:

  • we never accumulate lots of small floating point numbers in a larger one, to avoid floating point precision issues
  • the precision of the simulation doesn't depend on the frame rate
  • we don't use any O(n²) algorithm after initialization, so we can simulate a rather large number of marbles. The main issue is writing the frames to the hard drive.

Run-time to simulate marbles with random initial velocities during 1 minute:

  • 125 marbles: 1s
  • 241 marbles: 3s
  • 455 marbles: 17s
  • 704 marbles: 60s


  • generate a log of the events simulation
  • display the log of events on the video
  • read initial positions from a file
  • generate video in main program instead of writing each frame to disk and calling avconv (see
  • separate the frame generators from the video creator
  • read command-line options to know what kind of output must be generated, in which resolution, etc.
  • create an ouptut with velocity vectors (long as speed, thick as mass)
  • create a demo output combining the different types of outputs on different areas of the video
  • add sound on collision... "Spouich spouich" or "tick-tick-tick" :)
  • generate videos with two frame rates and compare them (visually) to prove the simulation doesn't depend on the frame rate
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