I'm new to graphics and still wondering how do people set up their post processing passes.
so I draw all my object onto a render target texture. and then apply FXAA on that texture and output to the back buffer.
This takes 7-8ms every frame.

Then I added another post process shader which do nothing but pass through color. And the frametime goes up to 14-15ms.
Is it normal or did I do something wrong?

the pipeline is something like this:

draw objects onto a screen size texture -> render the same texture onto another screen size texture -> apply fxaa to this texture and output to backbuffer

thanks,

Yup, that's normal. PP is fillrate sensitive and even a "do nothing" pass still needs to write out everything in the framebuffer all over again.

got it, guess i need to squeeze more stuff in one pass then

[quote name='champloo' timestamp='1327877993' post='4907460']
Is it normal or did I do something wrong?

That depends on the hardware, your resolution, and what you're doing. Adding an addition 7-8ms just for one post-processing effect does sound wayyyy too high, unless the hardware is extremely weak (Intel integrated graphics) and/or you're doing something really complex. What kind of hardware are you running on?
[/quote]
it's a nvidia gt 525M. And the resolution is 1280x720.
and removing both post-processing effects causes my frametime drop to 1-2ms.