Camera

The camera applies a global pixel offset to all subsequent draw calls. Integer only - pass Vector2i, never floats.

BT.cameraSet(new Vector2i(scrollX, scrollY)); // apply offset
BT.camera; // Vector2i - current offset
BT.cameraReset(); // set back to (0, 0)

// Clamp a camera origin so the viewport stays within a world:
const clamped = BT.cameraClamp(desired, worldSize);

// Optional third argument overrides the viewport size (default: BT.displaySize):
const clamped2 = BT.cameraClamp(desired, worldSize, new Vector2i(160, 120));

Camera persists across zero-update frames

BT.cameraSet()'s offset persists across render frames automatically, including frames where update() does not run - common on high refresh-rate displays where render() outpaces the fixed update rate (see Render frames with zero update() steps in API: Game Loop). Call cameraSet() once per update() tick and cameraReset() at the end of render() to switch to screen space for UI overlays, as the demos below do; the engine re-applies the last offset before the next render pass begins, so as long as update() keeps calling cameraSet(), the reset never leaks into a later frame's world draw.

cameraReset() itself persists the same way, on a one fixed-update-tick delay: if nothing calls cameraSet() again by the next tick, the camera offset becomes (0, 0) for every following frame, not just the rest of the current one - so a screen that stops touching the camera altogether (a menu, a world map after a scrolling level) starts clean instead of inheriting whatever offset the previous screen last scrolled to.

Standalone helper (same math as BT.cameraClamp):

const clamped = clampCameraToWorld(desired, worldSize, viewSize);

Two more camera-driven demos: parallax scrolling and a scrolling tile grid.

API history

See also

Last updated on October 18, 2026