Animating Fire

by Kathleen Marty

How to create fire?

• Implement the paper: Structural Modeling of Flames for a Production Environment, by Arnauld Lamorlette and Nick Foster.

• Emphasis: Total artistic and behavioral control.

• Basis: Physics and stochastic models. No intention to perfectly model real world.

Motivation

• Why not use a numerical simulation to model fire?– Numerical simulations scale poorly. Increase

in resolution = O(n3) increase in complexity.– Fire is chaotic. Initial conditions cause drastic

effects.– Unintuitive to control under different physical

circumstances.

Essential Model: 8 stages

(1) Flame Spine (2) Wind Field (3) Flicker / Separate (4) Profile

(5) Noise (6) Transform (7) Render (8) Procedural Controls

What I did: Flame spine

• Step 1: Created a B-spline that can interpolate through points that move in a wind field.

• Step 2: Windfield: modeled thermal bouyancy and diffusion. Did not model rotational wind. Solved using rk4.

• Step 3: Modeled flame flickering. Flickers when reaches a certain height. Did not model flame separation.

What I did: Flame profile• Step 4: Obtained flame

profile by thresholding a flame image and reading the boundary.

• Rotated the profile about the center and randomly sampled the volume to create particles.

• Step 5: Adding noise to the volumetric samples made it look bad. Paper uses “Flow Noise” [Perlin].

What I did: Profile Transformation

• Step 6: Transformed the flame from the profile space to corresponding points on the flame spine.

• Quaternoins worked perfectly for this step, I learned the hard way. (Rotation about an arbitrary axis).

What I did: Rendering

• Step 7: Rendered the flame only by mapping colors from original image to particles.

• Did not:– Apply density function to determine

incandescence.– Super-sample profile based on camera

position (flames are view-dependent).– Do Step 8: flame spread, object interaction,

smoke generation.

Some Results

Some Results

Getting into Maya

• Plugin: Got particles in but lost color mapping.

Given more time: