Easy way to have shader create red outline around sprite?

[ItsMeAlan]

In my game I want to indicate that the player is able to interact with an object by having a glowing red outline appear around it, pulsating in color. I want to do this with code so I can slap it on different objects with several frames of animation without having to come up with a ton of new art assets. Is there an easy way to do this with shaders?

[unikronsoftware]

If you place multiple copies of the sprite behind the main one, with a shader that draws a solid colour but uses the alpha channel, you should get an outline. You don't want to do this on big sprites though, as there will be a fair bit of increased overdraw there.

[ItsMeAlan]

Yeah, I do have some pretty big sprites with several lengthy different animation clips, and this is a mobile game so I'm striving to keep everything optimized. Do you think it's possible to do with just a custom shader?

[unikronsoftware]

Not just with a shader. You could do it as I suggested above, shader + multiple copies of the sprite. I don't know how bad the impact will be on perf.