MOV/transparency decolorization bug

[xonoma]

Description of bug / unexpected behavior

1. I run Manim Community v0.17.3 on 3 separate machines: a Macbook Air, a Mac Studio, and Linux/Pop OS 22.04.

2. Manim by default works well all 3 machines for generating MP4 files.

3. However when I generate MOV files with transparency, a bug appears that decolours all non-transparent regions.

Expected behavior

1. Consider this sample code. It generates a non-transparent MP4 file, of a rectangle stroked in RED. This code behaves similarly on all 3 of my machines:

       self.play(FadeIn(Rectangle(stroke_color=RED, stroke_width=10)))
       self.wait(2)

   red-stroked-rectangle.mp4

2. I then add transparency to the config dict: "transparent": True.

3. On my Macbook Air, the above code renders correctly. It generates the same contents in a MOV file, and with transparency. This is expected rendering behaviour.

4. But on my Mac Studio/Linux, the code behaves wrongly. It generates a MOV file with transparency, but where the red stroke (or any region that is non-transparent) is decoloured to cyan. Such is unexpected output:

   red-stroked-rectangle.mov

   

Additional comments

1. What puzzles me: my Macbook Air and the Mac Studio are virtually similar in every respect. If only the Linux had a different output, I could perhaps chalk it to a local machine's dependencies issue. But if I can generate transparency with MOV files on my Mac Air, then I should be able to do so too with the Mac Studio.

2. The cyan colour makes me suspect a compositing issue.

3. I am also inclined to believe it's a Cairo or a Pango issue, traced into Manim's settings, since there's a Stack Overflow comment which mentions the decolorization phenomenon.

   But if I reduce the code, and generate a transparent image:

       self.add(Rectangle(stroke_color=RED, stroke_width=10))

   

   ... then I get a PNG file that is transparent, and is correctly stroked RED (not decoloured).

   Which means that my Linux/Mac Studio's Cairo installation is able to generate transparency correctly for PNG images. (Yet Manim somehow cannot build transparent MOV files with it.) So I am no longer sure that this is strictly a Cairo issue.

System specifications

1. Machines are as above.

2. Python 3.10

3. Modules (in a virtual environment): Manim v.0.17.3 only

4. I installed the main dependencies, Cairo/Pango, on my Linux with the official apt commands:

    sudo apt install build-essential python3-dev libcairo2-dev libpango1.0-dev ffmpeg
   

5. I installed the dependencies on my Macbook Air/Mac Studio with these official commands:

    brew install py3cairo ffmpeg
    brew install pango scipy
    pip3 install manim