pBounce

pBounce sits inside a particle chain between a source or other particle tools and pRender. It does not create or render particles; it receives an existing particle stream, tests contact with the selected Region and recalculates eligible particle motion after impact.

Elasticity is the central energy control. A value of 1.0 leaves a particle with approximately the same speed magnitude after impact as it had before impact. At 0.1 it loses about 90 percent of its velocity. The slider normally covers 0–1, but values above 1 can be entered manually to make particles gain momentum after impact. Negative values are accepted but the reference explicitly notes that they do not produce a useful result.

Variance and Roughness both keep the rebound from looking perfectly uniform, but they are useful to diagnose separately. Variance introduces variation into the reflection angle relative to the Region, while Roughness slightly randomizes post-impact direction to suggest a less perfect surface. Start with small values and change one at a time.

Spin modifies particle orientation at collision. Positive values impart forward spin, negative values impart backward spin, and larger magnitudes apply faster rotation. It is easiest to judge on oriented particles such as shards, leaves or elongated bitmap sprites.

Surface Motion makes the collision surface behave as though it were moving and transferring motion to particles. Surface Motion Direction sets the angle of that motion relative to the bounce surface. This is part of the contact response, not a separate force node and not the same thing as animating the Region transform itself.

Conditions decides which particles are eligible for pBounce. Probability is evaluated for each particle on every frame. A value of 0.6 therefore means a 60 percent chance on a given frame, not one permanent lifetime subset containing 60 percent of the particles.

Start/End Age restrict pBounce to a normalized portion of particle lifespan from 0 to 1. A range of 0.8–1.0 applies collision behavior only during the final 20 percent of a particle's life, which is useful for phased simulations.

Set Mode operates on Sets that were already assigned upstream by particle-creation or set-changing tools. Ignore Sets disregards the Set checkboxes, Affect Specified Sets limits pBounce to checked Sets, and Ignore Specified Sets excludes those Sets. The pBounce checkboxes do not create new groups.

Region defines the collision surface. Built-in All, Bezier, Cube, Line, Rectangle and Sphere Regions are generated by pBounce itself and need no additional data cable. Line is useful as a floor or wall, Rectangle as a plane, Cube/Sphere as volumetric surfaces and Bezier as a custom contour.

pBounce does not have a permanent blue Region/Mask input. By default the only physical input is the orange particle socket. Selecting Region = Bitmap creates a dynamic Region input for a 2D image/selectable channel; Region = Mesh uses the same logical socket for 3D mesh data. Its connector can appear green or magenta depending on the active mode/order.

Bitmap and Mesh are therefore not Effect Masks. They define the actual collision geometry. Built-in Line/Rectangle/Sphere Regions work without an external Region branch, while Bitmap/Mesh requires data of the correct 2D or 3D type from another branch of the Flow.

Node order matters when appearance should change at the collision event. Blackmagic's particle reference demonstrates pChangeStyle before pBounce while both use the same Region: pChangeStyle changes the particle at the intersection before pBounce reflects it. Placing pChangeStyle after the bounce can mean the particle no longer intersects the style-change Region.

pBounce is fundamentally different from pAvoid. pAvoid creates steering/desire before contact and can be overpowered by particle momentum; pBounce is intended for collision and rebound at the Region. Judge final behavior in playback through pRender because velocity, age, Probability and neighboring forces evolve over time.