Here are some mockups (not code, just image editing) (using the TSF screen because the original ones have big black areas at the bottom and that would be confusing):

320x240

Stretch to both dimensions, and/or keep aspect ratio and stretch to either dimension

Draw at real size

800x600

Stretch to both dimensions, and/or keep aspect ratio and stretch to either dimension

Draw at real size

800x450

Stretch to both dimensions

Draw at real size

Keep aspect ratio and stretch to either dimension