How to get an acceptable aspect ratio with GRRLIB (NSTC only)

2022/08/01

If you are using GRRLIB for graphics in your Wii/GameCube homebrew, you may have noticed that by default, the aspect ratio is, quite frankly, atrocious. For some reason, even after a decade, no one has bothered to fix this issue. If you do like your squares not to be rectrangles, however, follow along to correct the aspect ratio to what I would call an "acceptable" level.

I found this patch on the WiiBrew Wiki. All credits go to "CarstenK". Whoever you are, I am indebted! They link to the GRRLIB forums and eventually propose this fix for GRRLIB:

f32 vcorrection = (rmode->xfbHeight-426)/2; //fudge factor
f32 hcorrection = 0.0f;
if( CONF_GetAspectRatio() ) {
    hcorrection = (rmode->xfbHeight-(9.0f*rmode->xfbHeight/16.0f))/2;
}
guOrtho(orthographic,0.0f-vcorrection,rmode->xfbHeight+vcorrection,
    0.0f-hcorrection,rmode->fbWidth+hcorrection,0.0f,300.0f); //tblr

I will not pretend to know what is going on here, but all I can tell you is how to actually apply this patch to GRRLIB, even the latest version (the patch was written in 2008, so 14 years ago -- yikes)

Go to the directory on your computer where the GRRLIB source code lives. This is usually C:\grr\GRRLIB\GRRLIB (Linux users, I expect you to know where your GRRLIB installation is).
On line 184 (or wherever it is in your version of GRRLIB), find the function call to guOrtho.
Replace the entire line with the code in the snippet above.

Congratulations! This should fix your aspect ratio issues. I have found that it is unfortunately still not quite perfect (some horizontal pixels are still missing), but it is still much better than the default code.

I have only tested this code using Dolphin set to NTSC-U. In the PAL setting, the vertical resolution is increased and the aspect ratio looks really weird. I will test the code on an actual GameCube once my SD Gecko arrives, and then I will update this article.