[Bug] PhotoStudio horking alpha channel for flame and for smoke in Save to .png

[jimmiedave]

Describe the bug

OpenRocket is not providing a clear alpha channel for flame or smoke it exports in an image with a transparent background. This means the flame or smoke is exported as part of the image, but not generally visible in the matted image when composited.

To Reproduce

1. Bring a rocket into OR's Photo Studio
2. Place on a color background, make background 0% opacity
3. Turn on Flame and Sparks. Adjust to taste.
4. Save file
5. Import into an image editing or compositing program
6. Place on a black background
7. Note that the sparks appear, but not the flame
   ...

Screenshots / .ork file

In this demo image, I've drawn a stripe of white across the alpha channel in the exhaust area to show that the flame is indeed in the image, but the alpha channel hasn't been composited with the alpha for the sparks in a way that lets the flame be seen.

Same OR file and setup, sparks turned off, composited on black

Prior setup but on OpenRocket black sky (image saved from within openrocket, not composited)

OR-exported alpha channel from a photo-editing program

Smoke is similarly affected:

OpenRocket version

23.09

What platform are you running on?

macOS

Additional context

Mac OS Sonoma, 2019 MacBook Pro Intel, 16GB RAM, plenty of free disk.

[jimmiedave]

First wondering about this: Could the OR image be premultiplied, but not tagged in such a way that compositors recognize that, and they matte it twice, shrinking the flame?

Don't really think that's it looking at the exported alpha channel and its direct correspondence to the puny flame.