I'm working to address the shortcomings of melonDS's OpenGL renderer.

Namely, if you've already used upscaling in melonDS, you may have noticed that it doesn't work right when the game renders 3D graphics to both screens: they flicker between the high-resolution render and a low-resolution copy. Technically, the DS can only render 3D graphics to one screen at a time, and games use a feature called display capture to work around that limitation.

Display capture records video output to VRAM (where it can later be reused). Hence the issue in melonDS: the upscaled framebuffer needs to be scaled back down to 256x192 so it can fit in VRAM. So instead, we need to detect when a given VRAM region contains a display capture and when it gets reused elsewhere, and replace it with a high-res version.

The original renderer was a bit of a hack. It did its job well, allowed for 3D upscaling with good performance, but the approach was simple and limited. As I tried to expand upon it to support high-res capture, it became clear that I was reaching the limits.

So instead, I decided to start building a proper OpenGL-based 2D renderer.

The advantage is that this opens up a lot of fun possibilities. Not only is it easier to integrate high-res 3D graphics, but even 2D graphics can be improved upon. For example: high-res rotation/scale. You can see it in action in that Super Mario 64 screenshot: look at that bottom screen minimap.

Filtering, too! I had attempted to add a xBRZ filter before, even made some videos of it, but never released it. The reason was that it was beyond the limits of what the old renderer could allow, it was a massive pain to work with and it never worked right, there were always oddball issues and glitches. But now, with this new renderer, it should be way easier to implement filtering for 2D elements.

There's still a bunch of things to be taken care of, but so far this is looking pretty promising.