Bug? Blend mode "SCREEN" does not work on transparent pixels
#1 019 ouverte le 5 juin 2021
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Description
Expected Behavior
I create a new Jimp with all pixels set to 0xFFFFFF00, then composite another image with all pixels set to 0x00000000 over it using Jimp.BLEND_SCREEN, then set the result to opaque, like so:
var pic = new Jimp(25, 25, 0xFFFFFF00).composite(new Jimp(25, 25, 0x00000000), 0, 0, {mode:Jimp.BLEND_SCREEN}).opaque();
This should yield an image with all pixels at 0xFFFFFFFF.
Current Behavior
The result is an image with everything set to 0x000000FF;
Failure Information (for bugs)
It looks like the algorithm simply nulls everything when the destination is at alpha 0? This makes it impossible, for example, to composite a blurred version of a picture that has transparency over itself using screen blending in order to create a halo of light - it will look like a drop shadow instead!
This also happens with ADD, by the way.
Steps to Reproduce
See above for code.
Context
- Jimp Version: 0.16.1 in a browser
- Operating System: win
- Node version: n/a