The big picture: Playing retro games at their original resolutions in today's displays can feel a bit off due to the black bars on the sides and the incorrect proportions. Retro gaming in widescreen displays doesn't tend to live to the memories we have of older games, but there are some alternatives to fix this.
Certain apps for playing retro console games may give a better experience by using a general fix to play at widescreen resolutions, but this usually comes with some visual issues. The other option is for modders to adapt one game at a time, which takes longer but tens to come with superior quality.
One such example is Vitor Vilela's latest mod work. Vitor is a software engineer and ROM hacker that alongside his team, modded the Super Mario World for SNES by introducing widescreen compatibility. For now, it only supports 16:9 and 16:10 resolutions, with 2:1 and 21:9 ratios coming at a later date.
NEW RELEASE: Super Mario World Widescreen (SNES) is now available for download! Explore the new expanded adventure, natively enhanced to work with modern screens. The true 2021 gaming experience mixed with the wonderful 1990 gaming golden age!— Vitor Vilela (@HackerVilela) June 18, 2021
Download: https://t.co/UugJXT4Fvh pic.twitter.com/BDTMIECQhP
For this to work, Vilela expanded the horizontal resolution by 96 pixels, from the original 256x224 resolution to 352x224. Despite the increase in resolution, it doesn't alter the 8:7 pixel aspect ratio from the SNES, meaning "that the screen you will see is like how would you see on a real TV screen connected to the SNES."
If you're interested in playing Super Mario World in widescreen resolution, you'll have to download the patch built by Vitor and his team. The patch doesn't include the Super Mario World (USA) ROM. Moreover, you'll also need the bsnes_hd emulator and follow this guide about patching ROM files. Once the patch is applied, make sure the config file has the widescreen settings correctly configured.
Besides Super Mario World, Vitor Vilela's Laboratory has also optimized titles like Gradius III, Contra III, Super Castlevania IV, among others.