Parallax 2D

What it is

Parallax2D is a modifier that moves a layer at a depth relative to a camera.
A far layer follows less of the camera movement than the world, a near layer follows more.
It writes the Transform of the entity, the same way physics moves a body.
It also scales the layer with the camera zoom, and can wrap the layer so it repeats.
It runs after the other modifiers each tick (#phase(after, tick)).

Basic use

Make a root entity for the layer, with a Transform.
Link the layer content (sprites, tiles, anything with a transform) under the root.
Attach Parallax2D to the root.
The layer looks the way it was placed when seen from the camera start position at zoom 1.

import "luxe: world" for Entity, Transform
import "luxe: system/parallax2D.modifier" for Parallax2D

var layer = Entity.create(world)
Transform.create(layer)
Parallax2D.create(layer)

Depth

mode is background, foreground or custom.
distance is 0 to 1 and means how far the layer is from the gameplay layer.
0 moves with the world in both modes.
A background at 1 stays with the camera (a sky).
A foreground at 1 moves at foreground_ratio times the world (default 2).
axes limits the parallax to x or y, the other axis moves with the world.

Camera

camera is a link to the camera the layer follows.
Left empty, the layer follows the default camera of the world.
A camera change does not move the layer, the new camera becomes the reference.
Parallax2D.get_camera(entity) returns the camera in use, or null.

Zoom

zoom is follow or custom.
follow zooms the layer at the same depth as its movement.
A background at distance 1 does not zoom, a layer at distance 0 zooms with the world.
custom uses zoom_distance instead, with the same meaning as distance.
The layer scales around the camera, so it stays in place on screen.

Repeating

span is the length one repeat covers, per axis, in the local space of the layer.
Each direct child is kept within half a span of the view center by moving it a whole span.
A layer with no children wraps itself.
0 on an axis does not wrap that axis.
The children have to cover the view plus one repeat at the widest zoom out used.

Drift

autoscroll adds a constant movement in world units per second.
It uses the world delta, so the world rate and pausing apply.

Raw values

mode custom shows ratio, the movement factor per axis.
1 moves with the world, 0 stays with the camera, above 1 passes faster than the world.
With mode custom, zoom_distance is a raw zoom factor.
Parallax2D.get_factor(entity) returns the movement factor as [x, y].
Parallax2D.get_zoom_factor(entity) returns the zoom factor.

Advanced

foreground_ratio (under advanced) sets the movement factor of a foreground at distance 1.
Parallax2D.rebase(entity) takes the current camera position as the new reference.
Parallax layers inside parallax layers add their movement together.
Gameplay moves on a layer stay, the parallax adds to them.
Transform snap is respected, small moves accumulate until they reach a snap step.