I have gallery of images representing player's avatars that can be unlocked. Avatar is simple Phaser.Image with transparency. Locked avatars are displayed as darkened version of normal avatars. To avoid duplicate graphics, I would like to use some sort of overlay, but I can't figure it out. I tried to use overlay semi-transparent black rectangle with multiply blend mode in hopes that it would cover only non-transparent parts of avatar, but it just shows semi-transparent black rectangle on top. It is quite possible that I am using it wrong, I can't find any useful examples how to use blend modes and documentation is rather sparse.
On more generic term, is there any way how to use image with transparent background as a alpha mask for another image/sprite? From what I understand, you can only use Graphics object as a mask, but is there some hack? It can be slow, it will be used only on a screen with 5 such images and performance is not an issue in this case.