Hi,

I have an openGL app that can switch from window/fullscreen,and when
switching i need to resize my openGL viewport to match the new window resolution
(which will be the screen res as i don't change mode), so I need to find
out the screen resolution, any idea ?

I checked SWAP_AREA or RECT_AREA etc but they're not returning the
correct values ...

1) Don't write new code in Carbon. Carbon is all but dead. Cocoa is easier and better documented. Even if you have a cross-platform codebase.

2) Is your viewport actually wrong? It seems to be set correctly when you attach the first drawable to a context...

3) The code you need is neither Carbon nor Cocoa, but CoreGraphics. CGGetActiveDisplayList and CGDisplayCurrentMode are the functions you need.