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iigs-game-engine
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@ -30,11 +30,11 @@ qtRec adrl $0000
da $00
```
# Setting up the play field
## Setting up the play field
Once the engine is initialized, the play field must be set up. The play field defines a rectangular area of the physical graphics screen that is managed by the Tile Engine.
The size of the play field can be set directly by passing the width and height in the `x` and `y` registers. Also, there are 9 predefined[^1] screen sizes that correspond to well-known Apple IIgs software titles and hardware of the era which can be selected by the `x` register argument.
The size of the play field can be set directly by passing the width and height in the `x` and `y` registers. Also, there are 9 predefined screen sizes that correspond to well-known Apple IIgs software titles and hardware of the era which can be selected by the `x` register argument.
```asm
; Main code here...
@ -55,7 +55,6 @@ The size of the play field can be set directly by passing the width and height i
By default, the play field will be centered on the graphics screen. If a custom placement of the play field is desired, then the `SetScreenRect` subroutine can be used directly to set a specific area of the graphics screen as the managed area.
[^1]: Table of predefined `SetScreenMode` sizes
| Play Field Id | Width | Height | | Size (bytes) | Percent of Full Screen |
|---------------|-------|--------|-------------------|---|----|
| 0 | 320 | 200 | Full Screen | 32,000 | 100% |
@ -67,6 +66,113 @@ By default, the play field will be centered on the graphics screen. If a custom
| 6 | 240 | 160 | Game Boy Advanced | 19,200 | 60.0% |
| 7 | 288 | 128 | Ancient Land of Y's | 18,432 | 57.6% |
| 8 | 160 | 144 | Game Boy Color | 11,520 | 36.0% |
## Palettes
A simple `SetPalette` subroutine is provided in order to set any of the IIgs' 16 palettes.
```asm
ldy #PALETTE_NUMBER ; 0 - 15
lda #^PaletteData ; High Word of palette color array
ldx #PaletteData
jsl SetPalette
PaletteData dw $0000,$007F,$0090,$0FF0
dw $000F,$0080,$0f70,$0FFF
dw $0fa9,$0ff0,$00e0,$04DF
dw $0d00,$078f,$0ccc,$0FFF
```
## Tilemaps
Up to two tile layers are supported in GTE. Each layer can have its own tile map and origin set, independent of the other. This allows for a true parallax scrolling effect.
## Background 0
In order to enable a tile map on the first background, the width, height and pointer to tile data must be set by initializing the appropriate values on the GTE direct page. The direct page locations are defined in the `Defs.s` file and can be included in an application's main source file.
```asm
lda #NUMBER_OF_TILE_COLUMNS ; Set the tile map dimensions
sta TileMapWidth
lda #NUMBER_OF_TILE_ROWS
sta TileMapHeight
lda #TileMapBG0 ; Set the pointer to the tile map data
sta TileMapPtr
lda #^TileMapBG0
sta TileMapPtr+2
```
Once the tile map has been initialized, the camera view into the layer is set by defining the upper-left corner of the screen. The resolution of the tile map coordinates are byte-aligned, so each tile has a width of 4 and height or 8 even though each tile is 8x8 pixels.
```asm
lda #TileMapLeft
jsl SetBG0XPos
lda #TileMapTop
jsl SetBG0YPos
```
## Background 1
The second background is initialized in exactly the same manner as the first background.
```asm
lda #NUMBER_OF_TILE_COLUMNS ; Set the tile map dimensions
sta BG1TileMapWidth
lda #NUMBER_OF_TILE_ROWS
sta BG1TileMapHeight
lda #TileMapBG1 ; Set the pointer to the tile map data
sta BG1TileMapPtr
lda #^TileMapBG0
sta BG1TileMapPtr+2
lda #TileMapLeft
jsl SetBG1XPos
lda #TileMapTop
jsl SetBG1YPos
```
## Sprites
There are four subroutines that are available to provide sprite support in GTE: `AddSprite`, `MoveSprite`, `UpdateSprite` and `RemoveSprite`. GTE supports up to 8 sprites.
### Adding a Sprite
```asm
lda #SPRITE_FLAGS+SPRITE_TILE_ID
ldx #X_POSITION
ldy #Y_POSITION
jsl AddSprite
bcs error ; sprite could not be added
sta SpriteId ; Returns an opaque identifier
```
### Moving a Sprite
```asm
lda SpriteId
ldx #NEW_X_POSITION
ldy #NEW_Y_POSITION
jsl MoveSprite
```
### Updating a Sprite
```asm
lda SpriteId
ldx #NEW_SPRITE_FLAGS_AND_TILE_ID
jsl UpdateSprite
```
### Removing a Sprite
```asm
lda SpriteId
jsl RemoveSprite
```
# Rendering a Frame
There is a single `Render` subroutine that applies all of the frame changes and efficiently renders to the super hires screen. It bear repeating here that most of the GTE functions operate in a deferred manner; any expensive operation that involved updating internal data structures is delayed until the `Render` function in called.
```asm
jsl Render
```
# Advanced Usage
# API
GTE provides the following capabilities
@ -76,4 +182,7 @@ GTE provides the following capabilities
* [Apple IIgs Tech Note #70: Fast Graphics Hints](http://www.1000bit.it/support/manuali/apple/technotes/iigs/tn.iigs.070.html)
* [Super Merryo Trolls](http://garote.bdmonkeys.net/merryo_trolls/)
* [Coding Secrets of Wolfenstein IIgs](https://www.kansasfest.org/wp-content/uploads/2004-sheppy-wolf3d.pdf)
* [Apple IIgs Graphics and Sound College](https://www.kansasfest.org/wp-content/uploads/1992-heineman-gs.pdf)
* [Apple IIgs Graphics and Sound College](https://www.kansasfest.org/wp-content/uploads/1992-heineman-gs.pdf)
* [Adaptive Tile Refresh](https://en.wikipedia.org/wiki/Adaptive_tile_refresh)
* [A Guide to the Graphics of the Sega Mega Drive / Genesis](https://rasterscroll.com/mdgraphics/)
* [Jon Burton / Traveller's Tales / Coding Secrets](https://ttjontt.wixsite.com/gamehut/coding-secrets)