It probably was fine for your Cataclysm spell because it was all red, but for animations with less red such mask is less accurate than needed.
No... you (possibly) still misunderstand the concept.
Same movie works for cataclysm (as movie and mask) because it is mostly red! There are channels in most movie formats (called RBG):
- Red
- Green
- Blue
Some, like webm, have another channel, Alpha (but there are precious few players that can read it, like Google Chrome browser).
Your first, normal movie, is just a normal webm. With three RGB channels with each pixel encoded to a value between 0 and 255 resulting in millions of variation. Second movie (mask movie), is used to handle transparency. In that movie, Green and Blue channels are ignored while Red channel is being used to determine alpha (which is an alias for transparency) for every pixel.
Now, PNG image format, supports four channels (RGBA):
- Red
- Blue
- Green
- Alpha
That last channel, also ranging from 0 - 255 (0 being fully transparent and 255 being fully opaque) determines transparency of every pixel in the image which would become a frame in the movie as you convert.
So:
As you convert PNG to webm to be used in Ren'Py, you will be using .png frames and got to do the following:
Movie one (normal webm movie):
- PNG Red ==> WEBM Red
- PNG Blue ==> WEBM Blue
- PNG Green ==> WEBM Green
Movie Two (Special ("mask") webm movie)
- PNG Alpha ==> WEBM Red(This second movie's red channel will be used by C decoder as Alpha channel and send the final frame, made up from both movies to the Python land and Ren'Py will be able to render it using the same process it renders everything else).
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The reason Cataclysm works is that Red channel is so distinct there so it can pretty much be used as an alpha channel without messing with channels for the second (mask) movie.What you said you were doing is setting PNG Alpha channel to every channel of the "mask" movie but Ren'Py will ignore all channels of that Movie except Red, so you're basically adding information there which will not be used. Unless you're doing something else that accidentally works... As you claimed, you're making the first movie a normal webm and doing this for the mask (which obviously works because Red channel is exactly what it needs to be):
Movie Two (Special ("mask") webm movie)
- PNG Alpha ==> WEBM Red
- PNG Alpha ==> WEBM Blue
- PNG Alpha ==> WEBM GreenYou don't need it, real alpha value ranges from 0 - 255, there can not be any merit of setting all three channels because every pixel has just one Alpha value, not three (like not one per color). If you get different results when using three channels, you're doing something weird, like custom/proprietary algorithms that Abode is using that accidentally works out but is not necessary or even has any sort of advantage.
What lamoli was doing is setting:
- PNG Red ==> WEBM Red
- PNG Blue ==> WEBM Blue
- PNG Green ==> WEBM Green
- PNG Alpha ==> WEBM Alphain a single file but Google Chrome Browser video player might be the only thing that can decode that, although some other soft may have caught on by now... Ren'Py will play this incorrectly...