Maybe a horror for the real emulator enthousiasts but I like to play my games in fullscreen stretched to every corner! So far I have been unable to do so with the Stella core.
I must admit that this is (for me) also not possible with the original Stella emulator, but I’m still hoping somebody has found the trick.
BTW: a fall back solution could be working with an overlay, but I still prefer real fullscreen.
Tx in advance.
Cowilf emulation on a Surface Pro 4 (Windows 10)
Does video settings: aspect ratio get you anywhere?
NO. My “video aspect ratio” is now set at 16:9 like my screen (2560x1440=16:9).
actually sp4 is 2736x1824 at 3:2
Back on line. Sorry for the delay.
Oops, you’re right I mistook it for the the settings of my desktop computer. But there I have the same problem ! I tried the 16:9 setting on my desktop and the 4:3 for the Surface: same result. 
That’s odd I have no trouble getting 16:9 to display on my desktop corner-to-corner with Stella. I just put Aspect Ratio on 16:9. I haven’t tried with my surface pro 4 which I know can be tricky with corner-to-corner at non-native resolution. Here’s my config file in case you want to take a look and see if you notice anything: https://jpst.it/-TP4
I see a line that says video_force_aspect = “true” but I don’t know what it does
I’ll give it a try on both computers and let you know. Tx
Hemm, copy paste of the retroarch.cfg did not work. 
Do you know which parameters you changed?
As an example, I propose having a look at Riverraid. I always have a black strip to the left and bottom.
As I mentioned before, I also have this problem with the original Stella emulator, but I’m still hoping Retroarch can correct this.
Tx for your help (and patience).
Stretched to 16:9?! OH, THE HORROR!!!
Anyway, I think what you’re seeing as an issue is just how the original 2600 games are rendered. A lot of them are not correctly centered, even if you play them with original hardware in an old-school TV.
River Raid is a good example, just look at this picture:
Now I remember having read somewhere that the makers of Stella said that they wanted to emulate the Atari 2600 as close as possible to the original and they would not center the image. So maybe it is just not possible to have a fully stretched image with that core?
I mean, sorry i can’t help here. But I defeinitely stretched a 16:9 image on my desktop. Actually it was on my TV though, so maybe the TV did it.
Some 2600 games use the entire screen, some add black bars.
I have discovered that the black borders only occur with certain games like Riveraid !!
If you play on your widescreen TV you have to set the video aspect on 16:9. On my Surface laptop, I have to set it on 3:2 to have full screen. Still I wonder if there is no possibility to play Riveraid without that border…
Tx for your answer.