Start fleshing out the "console-specific notes" section.

docs/notes.md

@@ -1,15 +1,137 @@
-TODO
+The consoles that higan emulates
+are similar in many ways,
+but some of them do have particular quirks
+that you should be aware of.
 
-The WonderSwan rotates!
+Video Shaders and the Super Famicom (and Mega Drive)
+----------------------------------------------------
 
 Shaders look weird on Super Famicom because of interlace/hi-res
 
+[Video Shaders](guides/shaders.md)
+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
+is a single pixel in the video output they analyze.
+
+Most of the consoles higan emulates
+can only output video at one specific resolution,
+so this "one pixel equals one pixel" rule holds true,
+and shaders like "xBR" work just fine.
+Unfortunately,
+this is not the case for the Super Famicom.
+
+The "normal" video mode for the Super Famicom
+draws 256 pixels across the width of the screen,
+but it also supports a "hi-res" mode
+that draws 512 pixels on each line.
+Since Super Famicom games can enable hi-res mode at any time,
+even halfway through a frame,
+higan always renders Super Famicom video output at 512 pixels wide,
+just in case hi-res mode is enabled later on.
+This means that in "normal" mode,
+each pixel drawn by the game's artists
+becomes two pixels in the video output,
+breaking the assumption pattern-based shaders are based on.
+
+The Super Famicom has a similar issue in the vertical direction:
+normally,
+an NTSC-based Super Famicom draws 238 rows of output,
+~60 times per second.
+This is sometimes referred to as "240p" video.
+When a game turns on "interlaced" mode,
+it draws ~480 lines of output,
+~30 times a second;
+first the ~240 odd-numbered lines,
+then going back to the top and drawing the ~240 even-numbered lines.
+This is sometimes referred to as "480i" video.
+
+TODO: https://board.byuu.org/viewtopic.php?p=44758#p44758
+
+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][vol],
+based on [a Sega Genesis model 1 VA6][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).
+
+[vol]: https://board.byuu.org/viewtopic.php?p=42482#p42482
+[va6]: https://board.byuu.org/viewtopic.php?p=42195#p42195
+
 Playing Game Boy Colour games in Game Boy mode
 ----------------------------------------------
 
-GBA in-game saves are Difficult
+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`.
 
-PSG volume for the Mega Drive
+The Game Boy Color played all the original Game Boy games,
-(see https://board.byuu.org/viewtopic.php?p=42158#p42158 for info)
+but extended the hardware to support colour graphics.
+Games that required
+the extra hardware in the Game Boy Color
+came in transparent cartridges.
+ROM files for these games
+typically have filenames ending in `*.gbc`.
+
+TODO: Rename files before import!
+Or afterward.
+
+In-Game Saves and the Game Boy Advance
+--------------------------------------
+
+TODO: GBA in-game saves are Difficult
+
+Rumble compatibility for Game Boy (Color)
+-----------------------------------------
+
+TODO: Test Pokémon Pinball
+
+Rumble compatibility for Game Boy Advance
+-----------------------------------------
+
+TODO:
+Some GBA carts contained an actual rumble feature (which?),
+some only supported rumble via the GBA Player (which?).
+Which does higan support?
+
+WonderSwan rotation
+-------------------
+
+TODO: The WonderSwan rotates!
 
-Rumble for GB and GBA?