I am making glyphs on a wall "glow", by changing how much of the overlay textures light intensity is blended into the diffuse map. The basic approach is to capture the diffuse map into a render target, and then
spritebatch.draw(additive) the light intensity texture on top of it.
This worked great for smaller textures. Now I want to do the same for a larger scene that has massive texture maps. It doesn't make sense to capture all of that just to make some portions "glow".
Is there a better way than to use render targets for a "glowing" effect?