Windows
Windows are used to hide layers from regions of the screen. On a per-scanline basis, they can be used to cut out areas of:
- Background layers (BG1, BG2, BG3, BG4)
- The Sprite layer (OBJ)
- The main screen
- The sub screen (color math)
Registers
| Name | Address | Bits | Type | Notes |
|---|---|---|---|---|
| W12SEL | $2123 | DdCc BbAa | W8 | Enable (ABCD) and Invert (abcd) windows for BG1 (AB) and BG2 (CD). |
| W34SEL | $2124 | DdCc BbAa | W8 | Enable (EFGH) and Invert (efgh) windows for BG3 (EF) and BG2 (GH). |
| WOBJSEL | $2125 | LlKk JjIi | W8 | Enable (IJKL) and Invert (ijkl) windows for OBJ (IJ) and color (KL). |
| WH0 | $2126 | LLLL LLLL | W8 | Window 1 left position. |
| WH1 | $2127 | RRRR RRRR | W8 | Window 1 right position. |
| WH2 | $2128 | LLLL LLLL | W8 | Window 2 left position. |
| WH3 | $2129 | RRRR RRRR | W8 | Window 2 right position. |
| WBGLOG | $212A | 4433 2211 | W8 | Window mask logic for BG layers (00=OR, 01=AND, 10=XOR, 11=XNOR). |
| WOBJLOG | $212B | .... CCOO | W8 | Window mask logic for OBJ (O) and color (C). |
| TMW | $212E | ...O 4321 | W8 | Main screen layer window enable. |
| TSW | $212F | ...O 4321 | W8 | Sub screen layer window enable. |
| CGWSEL | $2130 | MMSS ..AD | W8 | main/sub screen color window black/transparent regions (MS), fixed/subscreen (A), direct color (D). |
Window
The SNES has two window devices.
Each window has a left and right pixel position (WH0/WH1/WH2/WH3) where the window should hide the affected layers. The window effect (1 output) is at left <= X <= right. If left > right then the window is disabled (all 0 output). HDMA can be used to create shapes by adjusting the left/right position for each scanline.
If the window is inverted (W12SEL/W34SEL), the left/right position instead defines where the window should not hide the affected layers. Invert has no effect if the window is not also enabled.
Additionally if two windows are enabled for the same layer, boolean logic can be applied between them (WBGLOG/WOBJSEL). An individual window is 0 when showing the layer, and 1 when hiding it. This logic will combine the effect of both windows in the chosen way.
The windows can be selectively applied to the main screen and sub screen layers (TMW/TSW).
Finally, the color window can be used to black areas of the main screen, or create a transparent region on the sub screen to mask color math (CGWSEL).
