1920x1080 then reducing windows size at runtime?

I am set to crop at 1920x1080 as starting size. The viewport get wrong when i am reducing the windows size.

The problem seem to be the starting windows size.. if its 1920x1080 and that i am reducing the windows size.. the viewport doesn't fellow! it is still positionned as if it was 1920x1080.

Any ideas how to fix this ? i need a way to reduce the screen size without affecting the viewport.

I've noticed that with some devices. Mostly Android. It scales up great, but a few refuse to scale down. (not all Android)

I've take to making the games smaller, usually 800x450. (16x9)

It's the full size graphics scaled down, so when displayed at 1920x1080 they appear full quality.

Plus since the games are smaller than 800, they can be uploaded to the Scirra arcade.

After it's already built however, can be difficult. I re-scaled 3 games like that, some more difficult than others.

Someone was working on a scaling Program to assist doing a lot of it for you, but I lost track of that thread.

Even though you scale the graphics down, don't you still have to deal with the full image in memory? That could get large for mobile devices with a lot of sprites.