HD emulation mode gives new look to SNES "Mode 7" games



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Older players probably remember being seduced by the smooth, fast rotation and scaling effects of Super Nintendo's stunning "Mode 7" graphics. In retrospect, these players might also notice how these background transformations could be large and pixelated, especially when viewed on current high-end screens.

Emulation to the rescue. DerKoun has released a patch "HD Mode 7" for the SNES emulator focused on precision. In their own words, the patch "performs 7 mode transformations … with a resolution up to 4 times the horizontal and vertical resolution" of the original material.

The results, as you can see in the gallery above and in the YouTube video below, are almost miraculous. Pieces of 7 mode cards that were once smears of very distant colors are now straight and crisp lines with distinct borders and distinctive features. It's like watching a new game.

What is perhaps most impressive about these effects is that they occur on original SNES ROMs and graphics; DerKoun said that "no work has been altered" in the games since the project was only a proof of concept a month ago. This makes this project different from the scale emulation efforts for the N64 console and other retro consoles, which often require hand-drawn HD texture packs for old works to look beautiful at higher resolutions. high.

How it works

Games using the SNES "Graph Mode 7" used backgrounds encoded in SNES memory as a field of 256 mosaics of 8 x 8 pixels. This was a "map" of 1026 × 1026 that can be manipulated en masse by basic affine transformations into linear algebra to rotate, resize, shear, and quickly translate the entire screen.

Some Mode 7 games also used an additional HDMA mode (direct access to horizontal erase memory) to simulate a "3D" plane extending into the horizon. These games would essentially draw each horizontal scan line into a single SDTV frame on a different scale, making the lower elements in the image appear "closer" than those that are far apart.

This is a clever effect, but one that can give the underlying map data an especially smudged, stain-like appearance, especially for parts of the map that are "far away". This fading is exacerbated by the implementation of the mathematical matrix of the SNES, which uses trigonometric and rounded search tables to reduce the time required to run all this linear algebra on consumer hardware for years. 90. Converting these transformation results to SNES-scale mosaics and a 420p SD display causes problems on the edges of objects, which may appear defocused and "defeated" by one or two pixels at certain points in the image. l & # 39; screen.

The HD Mode 7 mod corrects this problem by using modern computer hardware to perform its "at output resolution" matrix computations, enlarging the original mosaics before any transformation. This provides more accurate underlying subpixel data, which allows the emulator to effectively use the HD screen and fill in some of the spaces between these "boxy" pixels at the same time. ;ladder.

For these HDMA Mode 7 slant-shifted games, the HD mod also eliminates "some limitations in the calculation of whole numbers used by the SNES … by a more aggressive average calculation," says DerKoun. This removes round-off errors from real SNES hardware, straightens lines, and positions sloping background tiles more accurately.

Byuu, the main coder of the bsnes project, said The Mod Mode HD 7 from DerKoun will be integrated with the next major release of the emulator. Then, the project will officially join the growing list of other emulation efforts that actually enhance the performance of the original hardware, including WideNES, RetroArch's LAGFIX latency mitigation and the 4K upscaling for PS3 and Wii U games, to name a few.

Image announcement by DerKoun / FrameCompare

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