|SCHG: VDP Documentation|
This article is a work in progress.
One of the capabilities of the VDP is shadowing and highlighting (often shortened as S/H, from hereafter named that way). In this mode, each pixel can have either one of three states, depending on a specific set of rules: normal, shadowed or highlighted. The set of rules defining this is simple, however it isn't explained well in the official documentation.
In order to enable S/H, you need to set bit S/TE in mode register #3. This is bit 3 from VDP register $0C, also used to set the horizontal resolution and interlaced mode.
move.w #$8C08, ($C00004) ; Enable S/H (H40 and interlace ignored)
The rules that define the status are shown in the list below. The pixel status depends on the combination of whatever is to be shown by the tilemaps there and also the sprites covering that pixel.
Indices 14 and 15 of palette 3 only have special meaning on sprites. In any other case, colors are shown normally (with the S/H effect, of course). Priority rules still apply, so if a low priority sprite would get obscured by a high priority sprite, it won't be able to affect the light status. Also it's possible for the special S/H colors in a sprite to hide a sprite below it, despite the fact they aren't opaque.
|Sonic Community Hacking Guide|
|Sonic Music Hacking Guide | SonED2 Manual|
|Sonic the Hedgehog (16-bit) | Sonic the Hedgehog (8-bit) | Sonic Eraser | Sonic CD (prototype 510) | Sonic CD | Sonic CD (PC) | Sonic CD (2011) | Sonic 2 (Nick Arcade prototype) | Sonic 2 (Simon Wai prototype) | Sonic 2 (16-bit) | Sonic 2 (8-bit) | Sonic 2 & Knuckles | Dr. Robotnik's Mean Bean Machine | Sonic Triple Trouble | Sonic 3 | Sonic & Knuckles | Sonic 3 & Knuckles | Sonic & Knuckles Collection | Sonic Crackers | Sonic 3D: Flickies' Island | Chaotix | Sonic R PC | Sonic Jam 6 | Sonic Advance | Sonic Advance 2 | Sonic Advance 3 | Sonic Battle | Sonic Adventure | Sonic Adventure DX: Director's Cut | Sonic Adventure DX: PC | Sonic Adventure (2010) | Sonic Adventure 2 | Sonic Adventure 2: Battle | Sonic Adventure 2 (PC) | Sonic Heroes | Shadow the Hedgehog | Sonic Riders | Sonic the Hedgehog (2006) | Sonic & Sega All-Stars Racing | Sonic Unleashed (Xbox 360/PS3) | Sonic Colours | Sonic Generations | Sonic Lost World | Sonic Forces|
|The Nemesis Hacking Guides||The Esrael Hacking Guides|
|ROM: Sonic 1 | Sonic 2 | Sonic 2 Beta | Sonic 3||Sonic 1 (English / Portuguese) | Sonic 2 Beta (English / Portuguese) | Sonic 2 and Knuckles (English / Portuguese)|
|Move to Sega Retro|
|Number Systems (or scrap) | Assembly Hacking Guide | Subroutine Equivalency List | 68000 Instruction Set | 68000 ASM-to-Hex Code Reference | VDP Documentation | Official Sega 32X Documentation | Official Mega-CD Documentation | Official Sega Mega Drive Documentation|