Sprites: Difference between revisions

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Sprites on the NeoGeo aren't like those on other systems.
Sprites on the NeoGeo aren't like those on other systems.


They're made of tiles (sometimes called characters) coming from the C ROMs, or from the .SPR files on the NeoGeo CD. Those tiles are always 16x16 pixels in size and can contain 15 colors (the color index 0 is used for transparency).
They're made of tiles (sometimes called characters) coming from the [[C ROM]]s, or from the .SPR files on the NeoGeo CD. Those tiles are always 16x16 pixels in size and can contain 15 colors (the color index 0 is used for transparency).


Sprites are vertical strips of tiles, with a fixed width of 1 tile (16 pixels), and an adjustable height (up to 32 tiles, 512 pixels).
Sprites are vertical strips of tiles, with a fixed width of 1 tile (16 pixels), and an adjustable height of up to 32 tiles (512 pixels).
Each sprite has its own tilemap, defining which tile number goes in which place.
Each sprite has its own tile and attributes map, defining which tile goes in which place, how is it flipped, and which palette to use.
Sprites can be stuck together horizontally to make huge moveable objects.
Sprites can be stuck together horizontally to make huge moveable objects.


== Limitations ==
== Limitations ==


*No more than 96 sprites can be rendered by scanline. Any others will be ignored (priority: 1 is in the back ?).
*No more than 96 sprites can be rendered by scanline. Any others won't be displayed (priority: 1 is in the back ?).
*Even if the VRAM has space for 448 sprites, only 381 can be displayed per frame (without [[sprite multiplexing]] tricks).
*Even if the VRAM has space for 448 sprites, only 381 can be displayed per frame. This is imposed by the GPU's architecture.
*Contrary to common belief, sprites can't be zoomed. They can only be shrinken. Graphics for sprites then have to made to the biggest size needed.
*Contrary to common belief sprites can't be zoomed, they can only be shrunk. Graphics for sprites then have to be drawn to the biggest size needed.
A lot of games contain pre-stretched graphics for sprites which are seen scaled down most of the time ("crashing" logos in title screens for example).
A lot of games contain pre-stretched graphics for sprites which are seen scaled down most of the time ("crashing" logos in title screens for example).
*$100000 tiles can be addressed (20 bits, 128MiB of graphics), if more tiles are needed then the sprites graphics need to be bankswitched.
*1048576 tiles can be addressed (20 bits, 128MiB of graphics), if more tiles are needed then the sprites graphics need to be bankswitched.


== Graphics format ==
== Graphics format ==


Sprite tiles are 16x16 pixels in a 4BPP planar format, handled as 8x8 tiles by the [[GPU]]. See [[sprite graphics format]].
Sprite tiles are 16x16 pixels in a 4BPP planar format, handled as four 8x8 tiles by the [[GPU]]. See [[sprite graphics format]].


A sprite tile is 128 bytes.
A sprite tile is 128 bytes.
==Horizontal reduction==
See [[Sprite shrinking]].


= Sprite control blocks =
= Sprite control blocks =


There are 4 Sprite Control Banks located in VRAM: SCB1 to SCB4.
There are 4 Sprite Control Blocks located in VRAM: SCB1, SCB2, SCB3 and SCB4.
They respectively start at adresses $0000, $8000, $8200 and $8400. They aren't mirrored in any way.
They respectively start at VRAM addresses $0000, $8000, $8200 and $8400. They aren't mirrored in any way.


Please see [[VRAM]] to learn more about read/writing to these locations.
Please see [[VRAM]] to learn more about read/writing to these locations.


Sprites wrap around the screen on a 512 pixels boundary.
Sprites wrap around the screen on a 512 pixels X or Y boundary.


<center>[[File:spriteex.png]]</center>
<center>[[File:spriteex.png]]</center>
(All sprites are mapped with tiles $01~$21)
(All sprites are mapped with tiles $01~$21)
Unused bits in SCB2 and SCB4 can be used for any purpose, they can be written and read back like the others.


== SCB1 (VRAM $0000~$6FFF): Tilemaps ==
== SCB1 (VRAM $0000~$6FFF): Tilemaps ==
SCB1 is used to store the tilemaps and tile attributes of each sprite.
SCB1 is used to store the tilemaps and tile attributes of each sprite.


(Note that the $7000~$7FFF locations in VRAM are used for the [[Fix layer]]).
(Note that the $7000~$7FFF range in VRAM is used for the [[Fix layer]]).


Each sprite has a 64 words table, organized as a linear up to down tile/attributes pairs. This means even locations are the tile numbers, and odd ones are attributes.
Each sprite has a 64-words table, in which each pair of words correspond to a tile in the sprite, top to bottom.
 
Even locations are the tile number's 16 lower bits:


{{16BitRegister|Tile number LSBs|16}}
{{16BitRegister|Tile number LSBs|16}}


Odd locations contain the remaining tile number bits, palette index and attributes:


{{16BitRegister|[[Palettes|Palette]]|8|Tile number MSBs|4|3bit Auto-anim|1|2bit Auto-anim|1|Vertical flip|1|Horizontal flip|1}}
{{16BitRegister|[[Palettes|Palette]]|8|Tile number MSBs|4|3bit Auto-anim|1|2bit Auto-anim|1|Vertical flip|1|Horizontal flip|1}}


The 8-frame [[auto animation]] bit has priority over the 4-frame one.
The 8-frame [[auto animation]] bit has priority over the 4-frame one.


== SCB2 (VRAM $8000~$81FF): Shrinking coefficients ==
== SCB2 (VRAM $8000~$81FF): Shrinking coefficients ==


SCB2 is used to specify the shrinking values of each sprite.
SCB2 is used to specify the shrinking value of each sprite.


The lower byte is the vertical shrinking. $FF is full size.
The lower byte is the vertical shrinking. $FF is full size.
Line 65: Line 73:
== SCB3 (VRAM $8200~$83FF): vertical positions ==
== SCB3 (VRAM $8200~$83FF): vertical positions ==


SCB3 is used to specify the sprites's Y position, its([[Sticky bit]] and its size (height in tiles).
SCB3 is used to specify the sprite's Y position, its [[sticky bit]] and its size (height in tiles).
The actual position is 496-Y, from the top border of the screen.
The actual position is 496-Y, from the top border of the screen.


A sprite size of 33 makes it 32 tiles high, and loops borders when shrinking (see example sprite 6).
A special sprite size of 33 makes it 32 tiles high, and loops borders when shrinking (see example sprite 6).


The sprite's height is actually the "window" size in which the sprite will be drawn. Shrinking isn't calculated from this.
The sprite's height is actually the "window" size in which the sprite will be drawn. Shrinking isn't calculated from this.

Latest revision as of 23:54, 7 March 2018

"Sprites" as defined by SNK

File:Mutnatsprite.png
Structure of a grouped sprite. The red sprite drives the other 3.

Sprites on the NeoGeo aren't like those on other systems.

They're made of tiles (sometimes called characters) coming from the C ROMs, or from the .SPR files on the NeoGeo CD. Those tiles are always 16x16 pixels in size and can contain 15 colors (the color index 0 is used for transparency).

Sprites are vertical strips of tiles, with a fixed width of 1 tile (16 pixels), and an adjustable height of up to 32 tiles (512 pixels). Each sprite has its own tile and attributes map, defining which tile goes in which place, how is it flipped, and which palette to use. Sprites can be stuck together horizontally to make huge moveable objects.

Limitations

  • No more than 96 sprites can be rendered by scanline. Any others won't be displayed (priority: 1 is in the back ?).
  • Even if the VRAM has space for 448 sprites, only 381 can be displayed per frame. This is imposed by the GPU's architecture.
  • Contrary to common belief sprites can't be zoomed, they can only be shrunk. Graphics for sprites then have to be drawn to the biggest size needed.

A lot of games contain pre-stretched graphics for sprites which are seen scaled down most of the time ("crashing" logos in title screens for example).

  • 1048576 tiles can be addressed (20 bits, 128MiB of graphics), if more tiles are needed then the sprites graphics need to be bankswitched.

Graphics format

Sprite tiles are 16x16 pixels in a 4BPP planar format, handled as four 8x8 tiles by the GPU. See sprite graphics format.

A sprite tile is 128 bytes.

Horizontal reduction

See Sprite shrinking.

Sprite control blocks

There are 4 Sprite Control Blocks located in VRAM: SCB1, SCB2, SCB3 and SCB4. They respectively start at VRAM addresses $0000, $8000, $8200 and $8400. They aren't mirrored in any way.

Please see VRAM to learn more about read/writing to these locations.

Sprites wrap around the screen on a 512 pixels X or Y boundary.

(All sprites are mapped with tiles $01~$21)

Unused bits in SCB2 and SCB4 can be used for any purpose, they can be written and read back like the others.

SCB1 (VRAM $0000~$6FFF): Tilemaps

SCB1 is used to store the tilemaps and tile attributes of each sprite.

(Note that the $7000~$7FFF range in VRAM is used for the Fix layer).

Each sprite has a 64-words table, in which each pair of words correspond to a tile in the sprite, top to bottom.

Even locations are the tile number's 16 lower bits:

Bit 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
Def Tile number LSBs

Odd locations contain the remaining tile number bits, palette index and attributes:

Bit 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
Def Palette Tile number MSBs3bit Auto-anim2bit Auto-animVertical flipHorizontal flip

The 8-frame auto animation bit has priority over the 4-frame one.

SCB2 (VRAM $8000~$81FF): Shrinking coefficients

SCB2 is used to specify the shrinking value of each sprite.

The lower byte is the vertical shrinking. $FF is full size.

The lower nibble of the upper byte is the horizontal shrinking. $F is full size.

Bit 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
Def HorizontalVertical


SCB3 (VRAM $8200~$83FF): vertical positions

SCB3 is used to specify the sprite's Y position, its sticky bit and its size (height in tiles). The actual position is 496-Y, from the top border of the screen.

A special sprite size of 33 makes it 32 tiles high, and loops borders when shrinking (see example sprite 6).

The sprite's height is actually the "window" size in which the sprite will be drawn. Shrinking isn't calculated from this.

Bit 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
Def Y position Sticky bitSprite size


SCB4 (VRAM $8400~$85FF): horizontal positions

SCB4 is used to specify the sprite's X position. The actual position is from the left border of the screen.

Bit 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
Def X position -