Transformations

Easel has a number of common parameters that are used to attach sprites, perimeters or colliders to a body at a particular position. This is the order they are applied:

1. We begin in shape space. The initial Polygon, for example Rectangle(width=5, height=1), is placed at the origin. Note that the Polygon may have a pos parameter that shifts it from the origin, e.g. Equilateral(pos=@(5, 5), numPoints=3) means the shape is already beginning at @(5, 5). An ImageSprite or TextSprite functions the same as a Rectangle with a width and height derived from the image or text.
2. scale - aligned to the axes of the shape.
3. angleOffset - this rotation occurs in shape space.
4. bodyOffset - now we enter body space.
5. bodyScale - aligned to the axes of the body.
6. heading - everything attached to the body is rotated to match its heading, unless noRotation=true.

The sprite is then drawn at the body's position, perhaps with a screenOffset if provided.

Functions that take transformation parameters

You will see these parameters on functions like:

• PolygonSprite, ImageSprite, TextSprite
• PolygonCollider
• PolygonPerimeter
• Spark

Not all parameters are used by all functions. For example, PolygonCollider does not use screenOffset as the concept of a "screen" or a "camera" does not exist for the physics engine.