I have a weird issue with particlesSourceColor input in particlesGpu. I created an example patch to illustrate the issue. For some reason particlesGpu renders black particles although the source image connected to particlesSourceColor does not contain them.
Here’s the network. Particle source is an UV square, color input is the banana, there’s a custom orthographic cam and the transform after render just adds a red background for showing the black particles.
I wonder if it’s somehow related to alpha values in the source image (although all the alpha values in the banana should be either 0 or 1?) as a circle with some softness as the color source looks like this:
I am using TD 2023.12120 and particlesGpu shows Version 2.2.11 and .tox Save Build 2023.12096. Also tested with TD 2023.11600 (particlesGpu version 2.2.10) with similar results.
I would greatly appreciate if someone has any ideas on how to get the banana example working without black particles in the render. Thanks a lot in advance!
I believe that the particle emission is more or less binary with regards to alpha, so if the alpha has any alpha at all above 0 it still gets emitted as a particle. Since many images may have a feathered or slightly soft edge of alpha going into a black background, you might still get dark particles emitted, maybe try a hard clipped object that has no softness or feathering around the edges of the alpha.
For my current use, making the particleSourceColor input alpha values binary is ok and that sort of resolves my issue.
However, if I set the the Fade Out value in particlesGpu something else than 0, the particles fade to black (Compositing options in particlesGpu don’t affect this). For me that’s not an issue right now but it’s probably not intended behavior?
So yeah, my initial issue is solved by the simple GLSL shader that sets alpha values to either 0 or 1 but I’d say there’s some issues with transparency that could be looked into if possible
These tests were with TD 2023.11600 / particlesGpu 2.2.11