/* Rule: when a picture of size (x1,y1) with aspect ratio r1 is rendered
* on a picture of size (x2,y2) with aspect ratio r2, if x1 grows to x1'
/* Rule: when a picture of size (x1,y1) with aspect ratio r1 is rendered
* on a picture of size (x2,y2) with aspect ratio r2, if x1 grows to x1'