UV Displacement Particles

UV Displacement, aka UV Distortion, aka Pixel Offset, etc..., is a fantastically useful real time vfx technique where the particle texture lookup is perturbed by another texture. Usually that distortion texture resembles a normal map, and is scrolling, scaling, or otherwise given additional motion. We found that by driving this displacement texture with a intensity curve, you could get very interesting visuals resembling fluids that break apart, or in this case, an approximation of the quickly moving gases that form a flame. See the Brutal Legend VFX Presentation from GDC 2010for more details.

Comparison of a flame, with and without uv displacement. This technique uses a normal map to perturb the texture lookup on a particle sprite. The normal map can be scrolled, scaled, and have its strength modulated over time.