DrawingAreaDrawFunc   
    typealias DrawingAreaDrawFunc = (drawingArea: DrawingArea, <Error class: unknown class>, <Error class: unknown class>, <Error class: unknown class>) -> Unit(source)
Whenever @drawing_area needs to redraw, this function will be called.
This function should exclusively redraw the contents of the drawing area and must not call any widget functions that cause changes.
- param - drawingAreathe- GtkDrawingAreato redraw
- param - crthe context to draw to
- param - widththe actual width of the contents. This value will be at least as wide as GtkDrawingArea:width.
- param - heightthe actual height of the contents. This value will be at least as wide as GtkDrawingArea:height.