map-overlay

Overlay simple polygons on a rastermap instance

Initialization

mapOverlay.init takes a parameters object with the following properties:

• canvas: an HTML canvas element
• map: a rastermap instance (or equivalent). MUST have a method named xyToMapPixels, for converting x/y coordinates in the map's projection to pixel indices from the top left corner of the map
• width, height: the pixel dimensions of the rastermap drawingbuffer

API

Initialization returns an object with the following methods:

• draw(polygon, mapChanged): Draws polygon on the overlay canvas.
  • polygong must be an array of points, where each point is a two-element array containing floating point numbers.
  • mapChanged is a flag indicating whether the underlying map coordinates have changed since the last draw call.
• reset(): Clears the canvas and the stored polygon

Note that the .draw method will do nothing if all of the following conditions are true:

• polygon is the same as the last call
• overlay canvas has not changed size
• mapChanged is false

If the supplied polygon contains exactly two points, they will be treated as the top left and bottom right corners of a rectangle, and drawn using the Canvas2D strokeRect method.