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..::automatic particle explosions::..

Note from the author: This article was written with 3ds max 3.x in mind. Due to software improvements, bug fixes, user interface amendments and added features, some items listed below may not apply to 3ds max after version 3.x...

Trying to set off explosions upon particle impact seems daunting with all the particle geometry flying around, but it need not be so. The initial thought is how to manually place every explosion when a particle hits. This can be done quite simply using particle spawn.The geometry that is to receive the barrage of impacts needs to have a UDeflector spacewarp assigned to it with a bounce value of 0. This therefore ensures that when any particle (weapon) impacts, they do not pass through or bounce off it. This also enables us to key off the explosion using particle spawn in the SuperSpray particle system.

After creating geometry for the explosion (normally a plane, but any geometry will do if it displays an animated map nicely), bind the UDeflector spacewarp to the particle system. Make instanced geometry (this has to be else particle spawn will not work) as the particle type, and choose the weapon geometry.

Under the Particle Spawn rollout, check on Spawn on Collision and increase the Multiplier value to about 3. Add a lifespan value of about 20 (this is an amendment of the initial particle's life, which should be set to a higher value) and pick the explosion geometry for the Object Mutation Queue. All this means that when the particle strikes a deflector that it is bound to (namely the geometry to receive the impacts), it amends the particle shape from the missile / laser to the explosion geometry, and keeps it stationary in the place where the impact occured.

The next step is to amend the material for the explosion. The main problem is that simply checking on Animation Offset Keying does not have the desired effect as it is a material that is the animation source, which uses global time; ie the animation will key off from frame 0.

As most stock explosion animations play only once then fades out, we need to create a looping explosion that has the mostly the same luminace throughout. Create this in a post application (or Video Post) by staggering three copies of the same animation, using an additive compositor as the transitions, and only rendering out the timeframe of the middle (second) copy, therefore resulting in a seamlessly looping anim. Assign this with 100% self-illuminace to the diffuse and opacity slots, or amend the levels of a copy of the anim slightly to make it more opaque to the explosion geometry. Assign the instanced materials to the particle system by checking on Instanced Geometry in Mat'l Mapping and Source and click on the Get Material From: button.

A quick test render should show the particles emitting, striking the target geometry and the particle type changing from the weapon geometry to the explosion geometry. To test fully, animate the position of the particle emitter over a number of frames to generate explosions in more than once place. Once tested, you will notice that the particles just appear and disappear (or even stay on). Set the fade for value to the same value as in the Lifespan Value Queue.

Another test render shows that everything should be well, but it all looks the same. One way to fix this is to have clones of the same particle system with amended seeds and explosion animations. Additionally, create clones of the particle system(s) (with no multiplier value in the particle spawn rollout) and create an impact bitmap to display an impact mark where the particles strike the target. Also, with more particle clones, create debris when the weapon hits. Finally, add a touch of blur and a glow or two. This should add more chaos and effect to the scene.

Enlarge ScreenshotBy adding additional particle system, smoke, debris, sparks and impact scorch marks can be easily overlaid.
Enlarge ScreenshotAssign glows and motion blur to the scene elements to add a touch more realism and to hide any imperfections in the repeating explosion animation.

Initially published: 3D World magazine, Issue 7, Xmas 2000.

Copyright Pete Draper, December 2000. Reproduction without permission prohibited.

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