This is a simple narrative description of the fire application included with the Lumen library as a demo.

The fire demo requires no command-line parameters, so you just invoke it by typing its name, like ./fire if you're sitting in the bin directory, or bin/fire if you're in the lumen directory.

When run, fire creates a black window with a "fire" at the bottom, created using a particle system and blending of carefully selected colors. Terminate it by pressing any key, or closing the window.

The fire demo uses a custom event loop instead of any of the canned mainloop procedures. It runs as fast as possible, "flat out" in Lumen terms, reporting the effective frame rate in the window's title bar.

Here is the author's description of the process the app uses to create its image:

It's point sprites [textured quads in screen space] (lots of them) and additive blending and a tricky color choice.

Here's how it works:

All particles have a life time of 2 s. And they are initialized with different ages, so as to uniformly "fill" 2 seconds. This means: When updating the age per frame, some particles "die" and are respawned, which means that the spawning frequency and the number of particles never change.

They respawn at (0.0, -0.5) and their velocity is initialized to a uniform random square [-spread, spread] x [-spread, spread]. And the respawn is the same as the initialization.

Global lift (or inverse gravity) is applied to the velocity per frame. This causes the particles to rise.

That's all there is to it regarding the dynamics.

Last Updated: 14 Dec 2011 09:32:32