Returns the internal scale factor that maps from surface coordinates to the actual device pixels.
On traditional systems this is 1, but on very high density outputs this can be a higher value (often 2).
A higher value means that drawing is automatically scaled up to a higher resolution, so any code doing drawing will automatically look nicer. However, if you are supplying pixel-based data the scale value can be used to determine whether to use a pixel resource with higher resolution data.
The scale of a surface may change during runtime, if this happens a configure event will be sent to the toplevel surface.
surface to get scale factor for
the scale factor