DiffImageResult

Field	Type	What it is
width	numberint	The frame both pictures were compared in.
height	numberint
before	DiffImageArea	Where the first picture sits in that frame.
after	DiffImageArea	Where the second one sits.
offset	{ x, y }DiffImageOffset	How far the second was moved to line the two up.
mask	Uint8List	What happened to each pixel of the frame, row by row.
regions	DiffImageRegion[]List<DiffImageRegion>	Where the changes are, in reading order.
stats	DiffImageStats	How much of the frame ended up where.
complete	booleanbool	Whether the list of regions holds all of them.

A byte of mask is an index into DIFF_PIXEL_KINDSkDiffPixelKinds, which is ['equal', 'changed', 'added', 'removed'][DiffPixelKind.equal, .changed, .added, .removed] — so 0 is a pixel that did not change and anything else is a pixel that did.

offset is where the move went rather than where the contents were: a picture drawn a pixel further to the right than the first is moved a pixel to the left, and x is -1.