Here's a thread you missed which has an official response in it:
http://steamcommunity.com/app/221410/discussions/2/846939071101757140/#c846939854332957006
I'm not saying that mentioned problem is not a bug since indeed it is a bug, but keep in mind that using native display resolution gives better performance than using lower ones. I've noticed that in few games like FarCry, PlanetSide, Tribes. This is because scaling has to be done by your graphics card and not by your flat panel... (Can someone confirm if I am I right or wrong?)
In general I think I would suggest to Valve that this problem is low priority thing. Windowed mode works fine, but I can't understand why in windowed mode one cannot choose any arbitrary resolution he likes, or even resize window on the run... and this really sux.
@Dragonsbrethren: Thanks for the missing link, admittedly I am having issues with the Steam Forum search functionality. I am including your suggestion that you made in the thread of using mat_viewportscale.
Added mat_viewportupscale and mat_viewportscale to enable rendering the
world at a reduced resolution. ("mat_viewportupscale 1" and
"mat_viewportscale 0.5" will downscale world rendering by 50%.
I haven't tried it yet, but will when I have the time.
Koolas, GPUs don't have a native resolution, LED/LCD monitors do. And running a game at the native resolution of the monitor is always going to be more resource demanding than running at a lower resolution.
If you run a full screen game at a lower than native resolution of the monitor, the monitor is going to be doing the image scaling internally to make it fit the screen, the GPU has nothing to do with this.
GPU's don't, displalys do, and scaling can be done either by display (it is always true for analog VGA signal), or by GPU (it might be the case for DVI/HDMI signal - and it probably depends on hardware and drivers)
I could finally play TF 2 after AMD released the legacy Catalyst 13.1 (I have a Radeon HD 4290 onboard) and I am having the same issue with screen resolution (I am only reporting the bug with my hardware, I know changing the desktop resolution is a good fix and I can play perfectly like this at the moment).
Here are my specs:
You should be able to pick different resolutions in the options tab now when going fullscreen now. If this isn't the case with the legacy Catalyst drivers (or other), please reopen a new bug specific to that with all hardware information and we can pester AMD (or whoever). Thanks.
The problem is the resolution doesn´t change, I pick the one I want (1280x720), click apply and then ok, but I doesn´t change and, when I go back to video it is set to 1600x900 (my native desktop resolution). As this happens with TF 2 and it is in Beta, I presume this is an issue with the game, right? I am not having this problem with any other game.
@Lord-Avallon ‘please reopen a new bug specific to that with all hardware information and we can pester AMD (or whoever).’ :)
Nothing extracted yet.
Attempting to adjust the screen resolution is ignored and can only be set to the native resolution. Forcing the user to adjust the resolution for the whole X windows system.
This has been brought up several times already over at the forums and remains an issue: