Post render filtering

Which is ‘the way’ of doing post render filtering like adjusting the brightness and blur of a frame? Suppose I
want to make the display brighter when the camera is looking to a lamp or to the sun, how would you do this? Is
there a way of doing this in hardware?

The right way is to draw with the correct brightness. Blur is harder but you can use the accumulation buffer. That is not hw accelerated on consumer cards so it is not realtime.

For the brightening effect, most people adjust the hw gamma ramp. The fastest way to blur the sceen (besides doing it on the CPU, which would probably be slower) I can think of is to render in a lower resolution, copy to a texture (with automaticaly generated mipmaps if you feel like it) and then draw that on a scrren aligned quad. If you use trilinear mip mapping and the texture lod bias extension you could even make it blur out gradually. Should look pretty good.