Full screen stretching

[vnctdj]

If I understand correctly, you need to change "Rendering resolution" to "1x PSP"
This way PPSSPP will always display a 480x272 picture, no matter which display resolution you are using

The "Stretch to display" option does make a difference if it's enabled.
Here is an example :
480x272 is not exactly 16:9, it should be 480x270. Therefore, if your screen use 1920x1080, you might want to use "4x PSP" so PPSSPP will display 1920x1088, which is not 1920x1080.
When you enable "Stretch to display", PPSSPP will resize your 1920x1088 picture to 1920x1080.
If you disable "Stretch to display", PPSSPP will keep the aspect ratio of the PSP (multiples of 480x272). In our example, PPSSPP will crop the picture to 1920x1080, which mean we will lose 4 pixels at the top and 4 pixels at the bottom of the picture.