Based on the 3 filters (1x (START+SELECT), 1.25x (default), and 1.5x (used only in GBA mode)) found inside TWL_FIRM, I reverse engineered most of the capture card's image processor (used to capture DS and GBA screens), and made my own filters to show that sharp upscaling can be done.

But that's not all! Since the initial patcher (which was only able to change the upscaling filter), a lot of work has been done:

Remove the DPAD input filter, so you can press LEFT+RIGHT and UP+DOWN without it being blocked, so you can enjoy glitches exclusive to this gameplay mechanic ;)
Blue light filtering thanks to CTR_Redshift
Screen swap for DS mode (the GBA only has a single screen, so it's not swappable)
Widescreen patching for both DS (4:3 --> 16:10) and GBA (15:10 --> 15:9) mode
ARM11 <--> ARM7 communication with rtcom (discovered by @Gericom)
- Currently only GBARunner2 utilizes this for gyroscope emulation when playing WarioWare Twisted!, but any developer and romhacker can use this for anything which needs 3DS hardware access
Use GPU for upscaling
- It looks much better than the default upscaling, but it's too blurry for some people
- It can also pose a health hazard for people with nervous system problems who get weird spazms and epilleptic effects, so use with care!

With a lot of help, love, and support from the community, there are useful use cases for the above patches:

TWiLightMenu++ lets you play games which have widescreen patches... in widescreen!
- It's also possible thanks to everyone who are actively making those patches!
GBARunner2 uses rtcom to enable us to be able to play WarioWare Twisted! utilizing the gyroscope built into the 3DS

There are also a few patches for developers too:

Possible to patch Process9, Kernel11Loader, and Kernel11
Includes a Kernel11 patch which reinstalls exception handlers, so you can debug your payloads easier

Spoiler: Widescreen SM64DS video (sorry for the 480p24 footage)

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Spoiler: Images

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If you want to see all scale matrixes, @Halvorsen has used a capture card to capture how it looks like on real hardware.

Spoiler: Scale matrix comparison

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Download stable [cia] 2021/02/21 Download outdated [3dsx (doesn't work)] 2021/01/12

Spoiler: Useful developer material

[upscale matrix matrix all possible resolution values] https://docs.google.com/spreadsheets/d/1kMbn1cBD5a7W9zalBLTN-ig1vgqS6fuuBGlm45FRN6M/ [upscale matrix research] [1] [2]

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