BigSprite

BigSprite is the beginnings of a library intended to make it easier to manipulate sprites. The purpose of BigSprite is:

• to easily combine up to 22 8x8 sprites into any size or shape you wish

• once combined, the 8x8 sprites can function as one BigSprite, which can be easily moved as a unit etc.

• BigSprite has built-in collision detection of other BigSprites and of background tiles using bounding boxes

You don't have to know how BigSprite works to make good use of it. Just follow these directions and use the functions as described. You can also look at hello-bs.asm as an example.

overview

• The BigSprite library reserves space for 32 BigSprites located from memory location $DC00 to $DFFF.

• Each BigSprite takes 32 bytes to describe. The bytes are as follows:

  • 1 byte: sprite ID

    • the ID can be any 1-byte number you want, but should be unique for each BigSprite

    • since there are a maximum of 32 BigSprites, it would be possible to use 2 extra bits in this byte as flags

  • 2 bytes: location of BigSprite in upper left hand corner on screen (x,y)

  • 4 bytes: bounding boxes (lowx, lowy, highx, highy)
  • 2 bytes: sprite dimensions in terms of 8x8 sprites (x # of sprites, y # of sprites)

  • 22 bytes: list of sprites used. (must be 22 bytes even if 22 sprites aren't used)

  • 1 byte: flags (not yet implemented)

• blank BigSprites are loaded with BSEMPTY (currently $ff)

• for simplicity, the BigSprite library creates 32 8x8 sprites numbered 0 through 31 and sets each of these sprites to its corresponding tile number i.e. sprite 0 is loaded with tile 0, sprite 1 with tile 1, etc.

usage

create your tiles

• create tiles for your sprite using GBDT or whatever
• design your tiles using any dimensions you wish, but for simplicity export them as 8x8

• it's easiest if you number your tiles for BigSprite starting with tile 0

• it is easiest if there is a unique tile for every part of every BigSprite

  • if a particular tile is needed more than once for your design, duplicate it

  • if a particular BigSprite will appear more than 1 time, duplicate all of its tiles

edit bigsprite.asm

• replace the example hardcoded BigSprite descriptions at the beginning of the file with your hardcoded BigSprite descriptions

  • each description needs to be 32 bytes and needs to follow exactly the byte layout described above (also shown in the example descriptions inside bigsprite.asm)

• edit the number of hardcoded BigSprite descriptions EQUed with HARDCODEDBSES

edit your code

• add INCLUDE "bigsprite.asm" in your code after a section statement.

  • One good place for it might be right after INCLUDE "memory.asm" if you have that line

  • bigsprite.asm requires hello-sprite.inc so have the most recent version of that in your path as well

• at the end of your main code initialization add

          INIT_BS

  • this calls a macro which sets up the BigSprite system

function calls and macros in the BigSprite library

•         INIT_BS

  Initialize the BigSprite system

  • initializes sprites 0-31 and assigns them to tiles 0-31

  • loads hardcoded BigSprites

  • initializes the remaining BigSprite list as empty

  • add to the end of your initialization code, after the tiles are loaded and before the main loop

•         SET_BS_LOC        <BS ID>,<X coord>,<Y coord>

  set the X and Y coords of a specified BigSprite

  • input:
    • BS ID can be any 8 bit number or any 8 bit register (a,b,c,d,e,h,l)
    • X coord and Y coord can be any 8 bit number or any 8 bit register except h or l

•         call              get_bs_param

  get coordinates of BigSprite location or of any corner of a bounding box

  • input:

    • a = BigSprite ID

    • b = specified parameter: one of the following constants:

      • BB_UPPER_LEFT: upper left corner of bounding box

      • BB_UPPER_RIGHT: upper right corner of bounding box

      • BB_LOWER_LEFT: lower left corner of bounding box

      • BB_LOWER_RIGHT: lower right corner of bounding box

      • BS_LOCATION: BigSprite screen location

  • output: d: x coordinate (pixels), e: y coordinate (pixels)

•         call              BSCheck4Clison

  test if 2 BigSprites are colliding

  • input: h = BigSprite 1 ID, l = BigSprite 2 ID

  • output: c flag is set if BigSprites are colliding, otherwise is reset

•         call              bs_get_background_tile

  return tile # of background tile touching specified corner of a bounding box

  • a = BigSprite ID

  • b = specified parameter: one of the following constants:

    • BB_UPPER_LEFT: upper left corner of bounding box

    • BB_UPPER_RIGHT: upper right corner of bounding box

    • BB_LOWER_LEFT: lower left corner of bounding box

    • BB_LOWER_RIGHT: lower right corner of bounding box

  • hl: Background tile map location in memory. Will always be either _SCRN0 ($9800) or _SCRN1 ($9C00)
  • output: a = tile number hitting specified corner

  • note: in its current implementation, this routine waits for VBLANK, since it cannot read video memory at any other time. This could (should?) be rewritten at some point to instead integrate with the VBLANK interrupt.

function calls and macros associated with the BigSprite library

•         SetSpriteTileNum    <sprite # or name>,<tile #>

  set tile # of a specified sprite

  • technically, SetSpriteTileNum is not part of the BigSprite library, but is instead part of sprite.inc, a dependency of BigSprite. It is mentioned here because of its obvious use with the BigSprite library. By design, the BigSprite library loads sprites 0-31 with corresponding tiles 0-31. This means that sprite 0 is automatically loaded with tile 0, sprite 1 is automatically loaded with tile 1, etc. However, using SetSpriteTileNum, the sprites can be loaded with other tiles instead.

  • always call this macro AFTER calling INIT_BS, since INIT_BS will redefine each sprite to be associated with its current tile # as explained above.

  • <sprite # or name> may be either a sprite # (0,1,2,etc.) or a name of a sprite as defined by SpriteAttr in sprite.inc