Grasshopper animation bugs involving transparency

[rhino19 (Henry Segerman)]

I’ve noticed a few strange problems with creating animations from sliders in grasshopper when transparency is involved.

Here’s a minimal setup to reproduce one of the issues:

(Here’s that setup as a grasshopper file: transparency_animation_bug.gh (8.7 KB))

This makes a box that rotates as you move the Angle slider. If I choose Animate from that slider’s menu I see the right thing on screen, looking something like this:

However, the saved bmp files are… strange. In Preview they look like this:

If I open it in Photoshop I just get a blank white square.
If I open it in Sublime Text, I get this:

It looks like it is a bmp file with transparency? In any case, my other Mac software seems to be very confused, and the output doesn’t look like what I see in the Rhino window.

If the transparency slider is below 0.5 then the animations behave much better. I also noticed that the ambient occlusion effect on the ground plane only appears for transparency below 0.5. Here it is at 0.4:

I have also had other buggy, inconsistent behaviour from animations with transparency. For example, I’m rotating some object around, and on some frames the transparency appears correct, and on others the appearance changes drastically. I don’t have a way to reproduce this. Running the exact same animation multiple times can give inconsistent output.

Any thoughts or workarounds?

[rhino19 (Henry Segerman)]

Finding my own workarounds: So far. setting the transparency below 0.5 and turning off shadows on the lights seems to be producing usable animations.

[rhino19 (Henry Segerman)]

I think I may have found a solution to another bug I’ve run into while making Grasshopper animations with transparency. I would frequently get output frames in which the transparency level would appear to flicker randomly as the animation progressed. No such flickering appeared on screen as the slider moves - it would only appear on the saved output frames.

The solution to this, or at least what worked for me just now, was disconnecting my external monitors before recording the animation frames.

I realised that his might have something to do with it because when I was making animations while travelling, I didn’t have any external monitors to plug into, and I didn’t get any flickering. For the record, I’m on Rhino 8, 8.10.24228.13002 on an M1 Macbook Pro, Sonoma 14.6.1.