tiles.md

scroll/tiles.asm

Manages a scrollable tilemap consisting of raw uncompressed tiles (see tilemap.asm for more information about the tile data format). This builds on the API provided by tilemap.asm.

Importing the handler and setting the metatile size

The module isn't included by default so will need to be included:

.include "scroll/tiles.asm"

1. Initialise the map

Initialise the map and draw the initial view using scroll.tiles.init. This should be performed when the display is off.

.define tilemapData ... ; the tilemap data (pointing to the top left of the map)
.define mapCols 64      ; the number of columns in the map (width in tiles); Max 127
.define mapRows 64      ; the number of rows in the map (height in tiles); Max 255
.define colOffset 0     ; columns to offset the initial view by
.define rowOffset 0     ; rows to offset the initial view by

scroll.tiles.init tilemapData mapCols mapRows colOffset rowOffset

If needed you can use registers for this, though you'll need to handle the initial view offsetting yourself in the top left pointer.

ld a,  mapCols * 2      ; number of bytes per row (columns * 2)
ld b,  mapRows          ; the number of rows in the tilemap
ld d,  1                ; column offset (1-based; 1 = none)
ld e,  1                ; row offset (1-based; 1 = none)
ld hl, tilemapData      ; pointer to our tilemap (top-left corner)

scroll.tiles.init       ; initialise and draw

2. Adjust once per frame

Adjust the x and y pixels by up to 8 pixels each per frame (-8 to +8 inclusive). This limit isn't enforced so ensure you stay within it for correct results.

; Negative x values move left, positive move right
ld a, 1                         ; move right 1 pixel
scroll.tiles.adjustXPixels

; Negative y values move up, positive move down
ld a, -2                        ; move up 2 pixels
scroll.tiles.adjustYPixels

After adjusting these, use scroll.tiles.update to apply the changes to the RAM buffers.

3. Transfer changes to VRAM (during VBlank)

scroll.tiles.render will apply the scroll register changes to the VDP, and write the new row and/or column to the tilemap if required.