Skill: Scroll with a camera

Written for blit386 1.8.0. The rest of blit386.dev documents the newest engine, so an API you find there may be missing from a game pinned to 1.8.0.

Move a single global offset so a world larger than the screen scrolls, then keep it inside the world's edges.

When to use

Use for side-scrollers, top-down maps, or any level bigger than the 320x240 screen that should follow the player.

How to do it

update() {
    // Center the camera on the player, then clamp so it never shows past the world edge.
    const worldSize = new Vector2i(1280, 960);
    const half = new Vector2i(BT.displaySize.x / 2, BT.displaySize.y / 2);
    const wanted = new Vector2i(this.player.x - half.x, this.player.y - half.y);

    BT.cameraSet(BT.cameraClamp(wanted, worldSize)); // clamp to world, then set
}

render() {
    BT.clear(2);
    // Draw in WORLD coordinates - the camera offset is applied for you.
    BT.drawRectFill(new Rect2i(this.player.x, this.player.y, 16, 16), 1);
}

Key calls

• BT.cameraSet(offset) (method) - set the global scroll offset (Vector2i).
• BT.camera (getter) - the current offset.
• BT.cameraReset() (method) - back to (0, 0).
• BT.cameraClamp(camera, worldSize, viewSize?) (method) - return an offset kept inside the world bounds.

Notes

• Draw everything in world coordinates; the camera shifts the whole frame.
• For a fixed HUD or mini-map, call BT.cameraReset() (or draw before setting the camera) so it does not scroll.
• Offsets are whole numbers.

See docs/input.md for moving the player.