Sprite
Sprites are used to display things on the screen using the SNES's "objects". All sprites are made of a number of 16x16 objects. There can be up to 32 sprites displayed at a time.
Sprite data structure
Sprites in the sprite table ($7E:185E) have the following format:
| Offset | Length | Type | Description |
|---|---|---|---|
| 0x00 | 2 | bit field | Sprite properties |
| 0x02 | 2 | int16 | X position |
| 0x04 | 2 | int16 | Z position |
| 0x06 | 2 | int16 | Y position |
| 0x08 | 4 | pointer32 | Pointer to sprite tile data |
| 0x0C | 2 | uint16 x2 | Parent entity ID |
| 0x0E | 2 | uint16 | Sprite type |
| 0x10 | 2 | uint16 | Alternate palette (shifted 9 bits left to align with the tile properties palette) |
| 0x12 | 2 | optional pointer16 | Pointer to next sprite |
The "pointer to next sprite" value creates a linked list of all sprites. The first element of the list is set by $7E:1B5E. The sprites are ordered in the list from front-most to back-most. That is, sprites earlier in the list will appear in front of sprites later in the list. See "display ordering" for details.
Sprite properties
| Bit mask | Description |
|---|---|
| 0x0001 | Sprite entry is used |
| 0x0002 | Flip horizontally |
| 0x0004 | Flip vertically |
| 0x0008 | Background priority |
| 0x0010 | Use alternate palette |
| 0x0020 | Appear on top of other sprites |
| 0x4000 | Absolute positioning |
| 0x8000 | Visible |
Sprite Tile Data
Sprite tile data is generally located in the ROM, and contains the arrangement of 16x16 tiles used to make up the full sprite.
Header
| Offset | Length | Type | Description |
|---|---|---|---|
| 0x00 | 1 | byte | Tile count (also see extended sprite tile data) |
Tile data
This data is repeated for each tile (up to "Tile count" from the header)
| Offset | Length | Type | Description |
|---|---|---|---|
| 0x00 | 2 | int16 | X position |
| 0x02 | 2 | int16 | Y position |
| 0x04 | 2 | bit field | Tile properties |
| 0x06 | 2 | uint16 | Tile number |
The sprite graphics are located at $84:8000 and each is 0x80 bytes long, so the address of the graphics for a given tile number can be calculated as "0x20000 + TileNumber * 0x80".
Tile properties
| Bit mask | Description |
|---|---|
| 0x0E00 | Palette |
| 0x4000 | Flip horizontally |
| 0x8000 | Flip vertically |
Sprite types
| Type | Description |
|---|---|
| 0x0000 | None. Sprites set to this type will have no collision. |
| 0x0001 | Victim |
| 0x0002 | ? |
| 0x0003 | Monster |
| 0x0004 | ? |
| 0x0005 | Zeke |
| 0x0006 | Julie |
| 0x0007 | ? |
| 0x0008 | ? |
| 0x0009 | Giant baby milk |
| 0x000A | Giant baby |
| 0x000B | Bubble shot by martian |
| 0x000C | Squirt gun item pickup |
| 0x000D | Fire extinguisher item pickup |
| 0x000E | Martian bubble gun item pickup |
| 0x000F | Weed-eater item pickup |
| 0x0010 | Ancient artifact item pickup |
| 0x0011 | Bazooka item pickup |
| 0x0012 | Soda pop cans item pickup |
| 0x0013 | Tomatoes item pickup |
| 0x0014 | Ice pops item pickup |
| 0x0015 | Bananas item pickup |
| 0x0016 | Plate item pickup |
| 0x0017 | Silverware item pickup |
| 0x0018 | Football item pickup |
| 0x0019 | Flamethrower item pickup |
| 0x0021 | Key item pickup |
| 0x0022 | Speed shoes item pickup |
| 0x0023 | Monster potion item pickup |
| 0x0024 | Ghost kid potion item pickup |
| 0x0025 | Random potion item pickup |
| 0x0026 | Grey potion item pickup |
| 0x0027 | Hamburger item pickup |
| 0x0028 | First aid kit item pickup |
| 0x0029 | Pandora's box item pickup |
| 0x002A | Skeleton key item pickup |
| 0x002B | Decoys item pickup |
| 0x002C | Pile of keys |
| 0x002D | Secret item |
| 0x002E | 1up |
| 0x002F | Gold |
| 0x0030 | Dollar bills |
| 0x0031 | ? |
| 0x0032 | ? |
| 0x0033 | ? |
| 0x0034 | Jelly blob shot |
| 0x0035 | Football player |
| 0x0036 | ? |
| 0x0037 | Exit door |
| 0x0038 | Decoys |
| 0x0040 | Victim insta-killer used by Debug.asm |
| 0x005C | Squirt gun shot from Zeke |
| 0x005D | Fire extinguisher shot from Zeke |
| 0x005E | Martian bubble gun shot from Zeke |
| 0x005F | Weed-eater shot from Zeke |
| 0x0060 | Ancient artifact shot from Zeke |
| 0x0061 | Bazooka shot from Zeke |
| 0x0062 | Soda pop cans/Flamethrower shot from Zeke |
| 0x0063 | Tomatoes shot from Zeke |
| 0x0064 | Ice pops/Bananas shot from Zeke |
| 0x0065 | Unused, but damages fire |
| 0x0066 | Plate shot from Zeke |
| 0x0067 | Silverware shot from Zeke |
| 0x0068 | Football shot from Zeke |
| 0x0069 | Pop-up wall |
| 0x006A | Unused |
| 0x006B | Unused |
| 0x006C | Unused |
| 0x006D | Unused |
| 0x006E | Unused |
| 0x006F | Pandora's box shot from Zeke |
| 0x0070 | Monster potion punch from Zeke |
Weapon shots from Julie are the same type as those from Zeke, except with the high bit set.
Display ordering
Sprites are sorted in order to have the correct sprites display on top of each other. The criteria used is as follows:
- Sprites with the "Appear on top of other sprites" property set will appear on top of those that don't.
- If two sprites have the same above value, the one with the greater value for "Y position" will appear on top.
Positioning
There are two positioning options for sprites, which is determined by the "Absolute positioning" property.
If absolute positioning is not enabled, the camera position ($7E:1B6A and $7E:1B6C) is subtracted from the X and Y positions . Then the Z position is subtracted from the Y position. This has the effect of shifting the sprite upwards on the screen without changing the display ordering.
If absolute positioning is enabled, the X and Y positions are treated as absolute screen positions, and the camera position is not used. Sprites with this setting enabled are also always considered on-screen, thus will always be processed. The Z position is also not used in this mode.
Necrofy enhancements
Extra sprite graphics
The ROM only includes space for 2982 sprite tiles. In order to allow for more graphics, tiles with a tile number greater than or equal to this value are located in a second section of sprite graphics. The location and size of this is specified in the Necrofy properties. The total number of sprite tiles still can't exceed 0x1000 (4096) or it would overflow the table at $7E:2128.
Extended sprite tile data
In order to allow extra tiles to be added to existing sprite tile data, the format was extended. In the extended format, if the high bit of the "Tile count" is set, then following the tile data is a 4 byte pointer to additional sprite tile data (and the high bit is removed from the tile count). There is also 4 zero bytes following the pointer. The data located at the pointer contains the full sprite tile data including the header.
Related RAM addresses
| Address | Length | Type | Description |
|---|---|---|---|
| $7E:185E | 0x280 | byte[0x14][0x20] | Sprite table. 0x14 bytes for each of 0x20 sprites. |
| $7E:1B5E | 2 | pointer16 | Pointer to first sprite in sprite table ($7E:185E). |