[sfml] Multiply blend mode + non-PMA doesn't look correct on Celestial Circus

[jabuwu]

Switching to "data/celestial-circus.atlas" here (removing -pma):

spine-runtimes/spine-sfml/c/example/main.cpp

Line 789 in da05fb8

testcase(celestialCircus, "data/celestial-circus-pro.json", "data/celestial-circus-pro.skel", "data/celestial-circus-pma.atlas", 0.2f);

And setting this to false:

spine-runtimes/spine-sfml/c/example/main.cpp

Line 724 in da05fb8

drawable->setUsePremultipliedAlpha(true);

The mouth, nose, and eyes render with white outlines:

Any insight why this might be happening? Blend modes are a source of great confusion for me. I generally use PMA and encourage others to do the same, so it's not a big deal, just curious if it might be a bug or some interaction I'm not familiar with.

Thanks for your time!

[badlogic]

The two slots in question use BlendMode:additive, which is defined like this in SFML

sf::BlendMode additive = sf::BlendMode(sf::BlendMode::SrcAlpha, sf::BlendMode::One);

This is correct in theory, however, for some reason, the rendering is not. I can only guess that this is a bug in SFML itself that is sadly outside our control.

TL;DR: keep using PMA :p