bsnes/docs/notes.md

The consoles that higan emulates are similar in many ways, but some of them do have particular quirks that you should be aware of.

Video Shaders and TV-based consoles

Video Shaders customize how higan scales the low-resolution video of the emulated console up to the high-resolution of the computer display. Simple shaders (like "None" and the third-party "AANN" shader) just blindly scale up the images they're given, but sophisticated shaders (such as the third-party "xBR" shader) try to produce higher-quality output by recognising particular patterns of pixel, like taking three diagonal pixels and turning that into a smooth diagonal line.

These shaders assume that each pixel drawn by the game's artists becomes a single pixel in the video output they analyze. Many of the consoles higan emulates can only output video at one specific resolution, so this "one pixel equals one pixel" rule holds true, and pattern-based shaders like "xBR" work just fine.

Unfortunately, this is not the case for the Super Famicom. The "normal" video mode draws 256 pixels across the width of the screen, but the "high resolution" mode draws 512. Since Super Famicom games can enable hi-res mode at any time (even halfway through a frame), higan always renders Super Famicom video output 512 pixels wide, just in case. This means that in "normal" mode, each pixel drawn by the game's artists becomes two pixels in the video output, breaking the assumption that pattern-based shaders are based on.

The Super Famicom has a similar issue in the vertical direction: normally, an NTSC-based Super Famicom draws about 240 rows of output every frame, sometimes referred to as "240p" video. When a game turns on "interlaced" mode, it draws the 240 odd-numbered lines of one frame, then the 240 even-numbered lines of the next, and so forth. This is sometimes referred to as "480i" video. Although interlaced mode cannot be enabled mid-frame like high-resolution mode, resolution switching is still complex, so higan always draws all 480 lines of video output. This means for a normal, non-interlaced game, each pixel drawn by the game's artists becomes four pixels in the video output (two horizontally and two vertically) making pattern-based shaders even less useful. It also breaks most scanline-emulation shaders, since they typically draw a scanline for each row of pixels in the video output.

The Mega Drive has similar problems to the Super Famicom. It has the same behaviour with interlacing, but its high-resolution mode switches from 256 pixels across to 320 pixels across. Therefore in normal mode, each pixel drawn by the game's artists becomes five pixels in the video output, while in high-resolution mode, each pixel drawn by the game's artists becomes four pixels in the video output (or 10 and 8 pixels in non-interlaced mode).

The PC Engine does not support an interlaced mode, but its horizontal resolution is much more flexible than the Super Famicom or Mega Drive, and so it has the same problems with shaders.

Music and Sound Effect Volume on the Mega Drive

The Mega Drive has two different audio-generating chips:

• the SN76489 or "PSG" chip, inherited from the Master System, mostly used for sound-effects like Sonic picking up rings
• the YM2612 or "FM" chip, mostly used for music

With two different sound sources, it's important that they have similar volumes, or the sound-effects will drown out the music, or vice-versa. Sega did not do this, and different hardware revisions used different relative volumes.

higan currently sets the PSG volume to 125% of the FM volume, based on a Sega Genesis model 1 VA6 that byuu owns. If you feel sound-effects in higan's Mega Drive core are too loud or too quiet, you may be comparing it to a Mega Drive calibrated to a different scale (or to an emulator tweaked to match such a Mega Drive).

Playing Game Boy Color games in Game Boy mode

Games for the original Game Boy came in solid grey cartridges, and only supported four-shade greyscale graphics. ROM files for these games typically have filenames ending in .gb.

The Game Boy Color played all the original Game Boy games, but extended the hardware to support colour graphics. Games that required the extra hardware in the Game Boy Color came in transparent cartridges, and had a slightly different shape to prevent them from being used in original Game Boys.. ROM files for these games typically have filenames ending in .gbc.

However, there were also some games that could use colour if it was available, but would stick to greyscale if it wasn't. These games came in black cartridges. ROM files for these games typically have filenames ending in .gbc (since they are genuinely designed for the Game Boy Color) or .gbb.

Sometimes people ask for higan to include these backwards-compatible Game Boy Color games when asking for a Game Boy game to load. However, this would make higan much more complex for not much benefit: it's just the same game as in Color mode, but with bits chopped off. You might as well play backward-compatible games in Game Boy Color mode and get the full experience the developers intended.

If you really, really want to see what a particular game's backward-compatible mode looked like, change the filename to end with .gb (instead of .gbc or .gbb) before importing it. If you want to experiment with loading in-game saves from colour-mode in monochrome mode or vice-versa, you can import the game once with .gb and once with .gbc, then manually copy files between the game folders in the "Game Boy" and "Game Boy Color" sub-folders of the Game Library folder.

Do not expect save-states to be compatible between Game Boy and Game Boy Color.

In-Game Saves and the Game Boy Advance

For most of the consoles that higan emulates, in-game saves are simple: the cartridge contains some battery-backed RAM that the game accesses like any other memory, and the game's internal header usually contains some hint about where in memory the save data appears and how large it is.

The Game Boy Advance is different. By the time of the GBA, many save-storage technologies were available, most with a more complex interface than plain memory. Frustratingly, the GBA's internal header does not describe which storage variant the game expects. Therefore, when importing a GBA game, higan must guess which storage type to use and sometimes it guesses incorrectly.

If higan guesses incorrectly for a game you want to play, you will need to turn on "Create manifests" in the Icarus settings dialog, turn off "Ignore manifests" in higan's Advanced settings, re-import the game, and edit manifest.bml in the game folder to describe the correct storage type. Try importing other GBA games to see what save types they use.

For more discussion of the GBA save type mess, see What's the deal with... GBA save files?

Rumble compatibility for Game Boy (Color)

The Game Boy and Game Boy Color did not natively support any kind of rumble or force-feedback system, but some game cartridges (such as Pokémon Pinball) included a rumble motor within the cartridge itself.

Because higan does not currently support game-specific controller features, to experience the rumble effect in higan you'll need to configure the console itself:

• Open higan's Input settings
• In the list of consoles, select Game Boy, or Game Boy Color depending on which console you want to use to play the game
• In the list of inputs, double-click "Rumble" or select it and press Enter
• Press any button on the gamepad that should shake when the game turns on the rumble effect.

Rumble compatibility for Game Boy Advance

The original Game Boy Advance and the Game Boy Advance SP did not support any kind of rumble or force-feedback system, but the Game Boy Player addon for the Gamecube allowed Game Boy Advance games to use the rumble feature in Gamecube controllers.

Because rumble is a feature of the Game Boy Player, to experience the rumble effect in higan you'll need to configure the console itself:

• Open higan's Input settings
• In the list of consoles, select Game Boy Advance
• In the list of inputs, double-click "Rumble" or select it and press Enter
• Press any button on the gamepad that should shake when the game turns on the rumble effect.

As well as the Game Boy Player rumble feature, some Game Boy Advance cartridges included a rumble motor within the cartridge itself. higan does not support this rumble technology, but that's not a big deal: the only two such games are Drill Dozer, which can use Game Boy Player rumble, and WarioWare: Twisted, which doesn't work anyway because it requires gyroscope hardware that higan does not yet emulate.

Game Boy Advance rotation

Some Game Boy Advance homebrew games, as well as a bonus mode in Dr Mario + Puzzle League, expect the player to physically rotate the device so the screen is tall rather than wide. higan supports this feature with a Rotate hotkey.

When the user presses the Rotate hotkey, the console's video output is rotated 90° anti-clockwise, and the directional-pad controls are also rotated so that (for example) pushing the button for "up" sends the signal "right" to the emulated console, so that the player character moves "up" on the rotated screen.

WonderSwan rotation

The WonderSwan hardware included multiple sets of buttons so the player could hold the device vertically or horizontally. Makaimura for WonderSwan includes a level that requires the player to repeatedly rotate the device as they play. higan supports this feature with a Rotate hotkey.

When the user presses the Rotate hotkey, the console's video output is rotated 90° anti-clockwise, and the X and Y button cluster mappings are adjusted to match.