10-04-2024, 02:57 PM
To understand what's happening, take a closer look at individual particles in your flow:
In your source flow your particle is being born at some frame (ex: frame 0), then it travels through space and at some other frame it enters your surface and is deleted (ex: frame 1).
In your reference flow your Birth Flow operator births the particle at frame 0. However, the Birth Flow operator does not do any deleting - it just births new particles it finds in your source flow. So at frame 1 when your source flow particle is deleted, the Birth Flow operator takes no action.
In your reference flow your Flow Update operator doesn't take any action on deleted particles (by default) either - at frame 0 it finds the particle in the source flow and updates its properties. However, at frame 1 the particle was deleted in your source flow, so Flow Update does nothing (by default) either - it can't find the particle with the matching ID in the source flow so it takes no action. However, as noted at the bottom of the Flow Update operator, if a particle has no matching ID in the source flow it will test TRUE in the Flow Update operator. If you use this to delete particles then the Flow Update operator will take action and delete the particle at frame 1 because it has no matching ID in the source flow.
Birth Flow and Flow Update are working as expected and are not birthing/affecting deleted particles in the source flow.
In your source flow your particle is being born at some frame (ex: frame 0), then it travels through space and at some other frame it enters your surface and is deleted (ex: frame 1).
In your reference flow your Birth Flow operator births the particle at frame 0. However, the Birth Flow operator does not do any deleting - it just births new particles it finds in your source flow. So at frame 1 when your source flow particle is deleted, the Birth Flow operator takes no action.
In your reference flow your Flow Update operator doesn't take any action on deleted particles (by default) either - at frame 0 it finds the particle in the source flow and updates its properties. However, at frame 1 the particle was deleted in your source flow, so Flow Update does nothing (by default) either - it can't find the particle with the matching ID in the source flow so it takes no action. However, as noted at the bottom of the Flow Update operator, if a particle has no matching ID in the source flow it will test TRUE in the Flow Update operator. If you use this to delete particles then the Flow Update operator will take action and delete the particle at frame 1 because it has no matching ID in the source flow.
Birth Flow and Flow Update are working as expected and are not birthing/affecting deleted particles in the source flow.