View Full Version : faking glow or speedup bloom ?

08-12-2004, 08:56 AM
Does anyone know how they did the glow-effect in
doom3 ? It seems they just use additive blending, but I'm not sure. It looks very nice, that's for sure :-)

Our engine uses a 4-pass bloom.
- downsize rendered scene ( and multiply with alphachannel )
- gaussian blure vertical
- gaussian blure horizontal
- add to original scene
we use the main framebuffer for each pass ( with glCopyTexSubImage2D ).
But this is very slow:
- 80fps without bloom
- 30fps with bloom
Does it make sense to use a pbuffer instead of glCopyTexSubImage2D ?

I don't know if it's possible to speedup the bloom effect( to 60/70fps ). What would u do ?
Try to speedup the bloom or try to fake it.

thx :-)

08-12-2004, 09:11 AM
Where does D3 have a glow effect? If you think that theres a glow effect on the lights, there isnt. It's just a special kind of 'billboard'. Just turn on wireframe and have a look at one of them and you will see how it will always turn to you and adjust it's size

08-12-2004, 01:49 PM
By "downsize rendered scene" do you mean that you render the scene full size, copy it, then resize it?

With my engine I just render the elements I wish to add a glow to (to the frame buffer, at a reduced size) and then I copy just the area I have rendered each object to, to create a texture for the glow. This way I can tile multiple objects on the frame buffer, I don't have to read more data than I'll end up using. I don't blur the result as such but I do draw multiple billboards to get the final result.

I could use pbuffers for this but with the number of context switch's (each object also has it's own dynamic cube map) it tends to slow things down.