Whenever drawing_area needs to redraw, this function will be called.
drawing_area
This function should exclusively redraw the contents of the drawing area and must not call any widget functions that cause changes.
the GtkDrawingArea to redraw
GtkDrawingArea
the context to draw to
the actual width of the contents. This value will be at least as wide as GtkDrawingArea:width.
the actual height of the contents. This value will be at least as wide as GtkDrawingArea:height.
Whenever
drawing_areaneeds 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.