The linear scale factor for drawing this image at its intended size.
The scale factor applies to the width and the height.
For example, if this is 2.0, it means that there are four image pixels for every one logical pixel, and the image's actual width and height (as given by the dart:ui.Image.width and dart:ui.Image.height properties) are double the height and width that should be used when painting the image (e.g. in the arguments given to Canvas.drawImage).
final double scale;