Limiting the Y value of the xpCellAuto Solver Size results in a 2D style animation.
This second animation has a 3D application of xpCellAuto, using the Mode setting of Diffuse Limited Aggregation.
Note: The way particles are generated when using this object is slightly different from normal particle emission.
Usually, the emitter will emit a particle then call any available modifiers to act on it.
With this object, the emitter does not emit particles until forced to do so by the xpCellAuto object.
This happens outside the normal sequence so, if using an xpScale modifier (for example), the particle would first appear with the radius as set by the emitter and only in the next frame will this be changed by the modifier.
This issue applies not only to the particle radius but to any modifiers which alter parameters set by the emitter (e.g. color, mass, temperature, etc).
To avoid this, simply set the initial value in the emitter to match the value expected from the modifier and there won’t be a sudden change in the parameter.
Note: If you increase the number of subframes in the X-Particles project settings from the default of 1, this may sometimes cause a problem.
More subframes would not normally benefit this object at all, since the particles are stationary.
But if you need them for other purposes, be aware that it will prevent the particle color mode Gradient (Parameter) from working correctly.
The particle will initially have the default particle color but, in the next frame, it will change to the color expected from the gradient according to the chosen parameter.
The solutions to this problem are either to choose another color mode or to reduce the subframes to the default of 1.