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 16x16 tile 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	Solid to players	Solid to monsters
0x0000	None. Sprites set to this type will have no collision.
0x0001	Victim		✓
0x0002	Monster that does no damage		✓
0x0003	Monster	✓	✓
0x0004	Ant that isn't holding an item pickup	✓	✓
0x0005	Zeke		✓
0x0006	Julie		✓
0x0007	Wall breaking from player punching it as a monster
0x0008	Unused type that damages evil doll axes
0x0009	Monster projectiles	✓	✓
0x000A	Giant baby flattening the player	✓	✓
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	Unused item pickup type
0x0032	Unused item pickup type
0x0033	Unused
0x0034	Jelly blob shot	✓	✓
0x0035	Football player	✓	✓
0x0036	Frozen monster	✓	✓
0x0037	Exit door		✓
0x0038	Decoys/Player who is invincible after dying	✓	✓
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/invincible after dying damage 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 weapon shot type		✓
0x006B	Unused weapon shot type		✓
0x006C	Unused weapon shot type		✓
0x006D	Unused weapon shot type		✓
0x006E	Unused weapon shot type		✓
0x006F	Pandora's box shot from Zeke		✓
0x0070	Monster potion punch from Zeke		✓
0x00FF	One-shot monster/victim went off screen

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:

1. Sprites with the "Appear on top of other sprites" property set will appear on top of those that don't.
2. 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.

Collision

Entities can call $80:8475 to set a collision handler for the sprites they own. When a sprite collides with another sprite, the collision handler of the parent entity of each sprite is called, with the type of the sprite it collided with provided in the accumulator. In addition, $7E:0076 and $7E:0078 can be used to access the two sprites involved in the collision. The collision handlers are set per entity, so even if an entity has multiple sprites, they must share the same collision handler. Collision handlers are run outside the context of the entity, so $80:8353 cannot be called to wait. However, the direct page will be set to the entity memory, so data from there can be accessed.

The collision handler returns a value in the carry flag. If this value is set, then the entity will be immediately resumed, regardless of how much was left in its current wait timer.

Sprites are considered collided if their X and Y positions are both less than 8 pixels apart, they are both on-screen (meaning they must be visible), they both have non-zero sprite type, and they have different sprite types. Collision can also triggered over an arbitrary area by calling $80:BF1B. The same restrictions on sprite type apply to this as well.

Solid sprites

Certain sprite types are considered solid. That is, players or monsters will not be able to move through them. Sprite types that are solid are shown in the sprite type table above. In addition, types 0x39 through 0x5B are solid to both players and monsters, and types 0x71 and greater are solid to monsters, but these types are not used in the original game.

Solid sprites are implemented in a different way from normal sprite collision. An entity must manually call $80:BFC8 to check if a given position is solid to players, or $80:BF67 to check if a position is solid to monsters.

The area for solid sprites is slightly smaller than for regular collision. A position is considered touching a solid sprite if it is within 6 pixels of the right or bottom, or within 5 pixels of the left or top. The area is smaller so that sprites will trigger regular collision before stopping due to running into a solid sprite.

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).