Adds a simple outline, with color (ported r0j0hounds c2 original).
I think this effect needs to deal w/ spritesheeting (e.g. if neigboring sprites go to the edge of their sub-image in the spritesheet). Here's a clamp fix I am trying (replicate for other lines): mediump float a0 = texture2D(samplerFront, clamp(vTex + vec2(-dx*diag, dy*diag), srcOriginStart,srcOriginEnd)).a;
The other option is to make sure you have a few pixels of transparency around the edges of all sprite images.