MeterRect typedef
A rectangle of the frame, in fractions — what a view occupies.
A record rather than ViewportRect, deliberately: this library knows
nothing about cameras, views or scenes, and that is what lets a test hand
it bytes and read an exposure with no device and no scene graph in the
room. The renderer converts at the one call site.
Implementation
typedef MeterRect = ({double x, double y, double width, double height});