Render Realistic Fire Using Particle Systems

The unique nature of fire is tricky to reproduce in a computer environment.

One of the greatest challenges to a game or video designer is to design special effects to enhance a scene or tell a story. Of these challenges, creating realistic fire on your computer may feel the most daunting process. Superimposing images or video of live fire over a scene looks artificial and unrealistic; particle systems, however, offer a more sophisticated possibility. These include tools that emulate the way fire moves across a scene and interacts with the various comprised elements.


Particle Generation

1. Map out the area in which the fire should initially appear. If the fire is supposed to spread, a path for that effect will later be necessary. Because fire is a complex process which does not fit well into strict boundaries, define a soft boundary for the effect. Place one or more particle emitters as needed within this domain.

2. Define a particle size. Start with a scale that is a few pixels in diameter, expecting it to change later. Smaller particles can create more realistic fire, but they also add considerable complexity to the rendering process, as more of them are necessary than when working with large particles. Most computers vary in terms of speed and memory capability, and experimentation is required to find the tradeoff between rendering time and acceptable quality.

3. Define an initial color and texture for your particles. Different flames require different tonal sets. Look at various reference fire images and videos to pick a palate that will suit your flame or to create a texture to apply to your particles. Fires with incomplete combustion, toxic ingredients or low-temperature fire will also produce more smoke; add black or sooty gray colors for fires of this type.

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4. Set an initial velocity and acceleration to your fire particles. Roaring fires will require a high particle acceleration, while gentle fires should comprise slow-moving particles with low acceleration.

5. Set the opacity for your particles. A wispy fire should have low opacity components, while dense or smoky fires should be comprised of particles of higher opacity.

6. Set a lifespan for the particles. Defining how long a particle can “live” inside your model you frees up resources for new generation of particles to continue the effect. If the lifespan is too short, the particles do not have an opportunity to generate the entire process needed to create a flame effect.

Particle Motion and Interaction

7. Apply a script to the particle generator to emulate the various changes that the particles will undergo as they progress through the stages of the effect. Find scripts online for several types of fire for various software packages like Adobe Flash or Unity. These scripts will alter the initial attributes of the particles and change them as the particles mature.

8. Add particle collision elements to the scene. These allow you to set aside certain areas of the “world” that reflect or deflect particles when the particles impact them. In Unity, for example, these elements are called “particle colliders.” For situations in which the flame is forced into a confined area or shaped by the environment, minimize the dampening effect of these components by setting the dampening slider to zero.

9. Define conditions for particle extinction and insert them into the script. These should include things such as the particle running out of bounds, growing too dark or transparent to be seen in the scene or colliding with an entity that would extinguish the flame, such as hitting the ground.

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10. Pre-render the scene. This allows you to see the dynamics of your fire in the scope of the environment. Use a lower resolution than you will utilize in your final project so that this rendering step takes place quickly.

11. Tweak your settings. Using the appearance of your fire from the pre-rendered scene, change the initial settings of your particle emitters, the tone or textures of your particles or the values in the scripts that move your particles until they more closely resemble what you are looking for in the final product.