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Flight Path

When animating a flying jet, diving eagle, or swinging cutlass, you can enhance the path and momentum of the moving object by adding a visible trail, which often appears as a ghostlike repetition of the original object. In the following section, we will make the swooping path of the biplane more dramatic with a striated trail.

Leaving a Trail

Open the max file lightning_begin.max on the accompanying DVD.

This scene contains a grouped biplane model that has been constrained to a spline path through the scene, beginning in the distance, approaching the camera, and then looping and diving away (Figure 18.1). Lightning will strike near the biplane several times and then strike it directly around frame 275, resulting in an explosion of sparks and a trail of fire and smoke.

Figure 18.1. The starting point for this tutorial—a biplane constrained to a flight path, and several lightning meshes. The biplane is based on an original mesh by Chris O'Riley.

If you scrub the Time Slider, you will note that the scene contains three lightning meshes. Two of them are placed vertically in the scene, and they animate identically. A third lightning bolt is keyed to always point to the biplane. These three objects will be used later in this chapter as helpers.

The first effect we will create is a motion trail caused by the passage of the biplane along its path. Examine the mesh object “trail emitter,” which is a child of the Plane group (Figure 18.2). This simple mesh will be used to emit trail particles from the biplane's wings and tail. The Renderable check box in this object's Properties dialog has been cleared to ensure that it does not appear in renders.

Figure 18.2. A simple mesh will be used to emit a motion-based trail effect as the biplane travels.

Open Particle View and create a new Standard Flow (right-click in the Event panel, and from the contextual menu, choose New > Particle System > Standard Flow). By default, the PF Source icon will be created at World coordinates (0,0,0). This is not significant, as the icon will not be used to position particles.

Rename the global source event Flight Path and the birth event Trail Birth.

The emission of particles from this source will be at high speed, so in order to avoid “puffing” from coarse frame evaluation, go to the icon's System Management rollout and set both the Viewport and Render Integration Steps to 1/4 Frame. These settings will now be automatically applied to newly created source icons during the current max session.

A high number of particles will be necessary for this effect, so set the Birth operator to generate 10,000 particles over frames 0–300.

Go to frame 0 to ensure that you won't have to wait for max to update the scene as you make changes. The particles need to be generated from the biplane's trailing edges, so replace the Position Icon operator with a Position Object operator. Check the Inherit Emitter Movement box to ensure that particles are always generated from the emitter's updated position.


It is a good practice to return to frame 0 whenever you're making changes to your particle flow, particularly if your setup is complex and/or deals with a high number of particles. This will reduce the lag as max recalculates the flow and will avoid possible crashes.

Add a trail emitter to the Emitter Objects list (Figure 18.3).

Figure 18.3. The beginnings of a particle setup to generate a motion trail.

If you scrub the Time Slider, you will see a continuous trail of nondecaying particles being emitted from the biplane as it flies through the scene (Figure 18.4).

Figure 18.4. A simple nondecaying trail follows the biplane's flight path.

Reduce the particle Speed to 130.

The default setting of the Rotation operator will randomly orient each particle, but that's not the effect we need. To have the trail particles aligned instead along the emitter geometry's surface normals (which will give the effect of following the flight path), set the Orientation Matrix to Speed Space.

The actual particles to be emitted will use instanced geometry, so replace the Shape operator with a Shape Instance. Assign the object “trail geometry” as the Particle Geometry Object. This mesh consists of two quad polys at right angles. Once mapped with a two-sided material, it will look like a volumetric object from most angles (Figure 18.5).

Figure 18.5. This particle shape is basically a pair of facing quad polys joined at right angles.


In complex scenes utilizing large numbers of particles, use the simplest particle shape possible to keep the scene from bogging down.

To preview the effect of using this instanced shape, change the Display type to Geometry and scrub the Time Slider. It may be difficult to see the particles unless you zoom in using a Perspective viewport.

Initially, the particles will not be aligned properly. They seem to be perpendicular to the flight path (Figure 18.6).

Figure 18.6. The trail particles are not following the path, due to the order of event operators.

To correct the particle orientation, move the Speed operator to a position in the event after the Rotation operator. Because the rotation of the particles is based on the vector at which particles are emitted, the rotation relationship needs to be established before the particle speed is determined (Figure 18.7).

Figure 18.7. Once the operators are reordered, the particles follow the path as expected.

To reduce the viewport complexity of these particles, set the Display type to Lines.

I've created a fading material for this effect, so append a Material Dynamic operator and assign the Trail Vapor material.

The opacity of this material is keyed to particle age (Figure 18.8), so specify a particle life span by appending a Delete operator. Select By Particle Age, with a Life Span of 50 and a Variation of 10 (Figure 18.9).

Figure 18.8. The trail now fades as the particles age.

Figure 18.9. The completed particle setup for the trail effect.



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