I want to create a bump map that will give the impression of a wake trailing behind a ball. I first did this here.

For the sake of efficiency, I will first create it as a B&W luminance channel. I find this to be an easier way to visualize the bump map as I develop it, rather than working with it directly in the bump channel. Once we get it to where we want it, we’ll copy paste it into the bump.

Start by moving a ball along a path, and setting an emitter as child of the ball. Set the emitters speed to zero, and set the particles to not render. Name the emitter "wake"

We get this.

Now create a material with proximal in the luminance channel. Set Proximal to target "wake", and check both ExludeParent and IncludeSubobjects. This will essentially draw a sphere for each particle.

We get this trail.

This is essentially the same as a technique first suggested by Toshio Fuji.
http://www.c4djug.com/SLA/writing2.mov
http://www.c4djug.com/SLA/review.html

side view

We want the trail to taper off as the ball moves along. If we set the emitter speed to send the particles downward, we get this.

This has two problems:
When the particles are first generated they pop in, creating a jittery effect around the ball.
We'd also like for the wake to spread out as the ball movers away.

If we set the emitter above the ball (140 m) the particles are born above the planes and move down through it.

If we reset the Proximal radius to match this distance (140 m), the particles are born just out of range of the planes Proximal setting. We have eliminated the jittery problem, because the particles are born above the plane, out of Proximals range.

As they move through the plane, they draw the familiar increasing/decreasing circle.

The particles collectively create this.

Now nest Proximal into a Colorizer channel shader and create a gradient similar to this.

Getting closer, but I would like to get rid of the circular form of the trail.

Copy the Colorizer shader and place it into the base layer of a Fusion shader.

Set the mode to Multiply.

Creat a Proximal shader for the blend layer, and have it target the ball. Set a wide falloff to effectivly erase the far end of the wake.

Getting very close, but I'd like to add some extra detail to trail the wake.

Dulpicate the wake emitter and rename it "trail". Then set it's speed to a bit slower and lower it down to around 90 m.

We now have 2 distinct particles sets, each with their own behavior.Notice that the trail one (yellow) is falling more slowly, thus staying "on stage" longer. This will define our extra detail.

Now duplicate the wake material (which now contains all those nested shaders) and reset the deepest Proximal to target "trail" instead of "wake".

Stack the materials in the ObjectManager and set trail to MixTextures.

Good enough.

Now copy the luminance channels of both materials and paste them into their respective bump chanels.

Create a simple water material, and add the wake and trail material onto it.

Not bad.

I'd like to add a faint trail of red to give the impression that the ball is leaking color.

Create a Colorizer with Proximal, with Proximal targeting "trail".

This is a Fusion in the trany channel of the water material. The blend channel contains the above Colorizer.

HTH.

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