Preset canvas aspect ratios

[tomcrane]

(from conversation with @sammeltassen)

When modifying canvas dimensions, as well as offering free-form width and height as in the image above, also offer a set of useful aspect ratios (configurable). E.g., 4:3, 16:9, 2:1 etc. This is a good option when creating a blank canvas too. When the canvas has yet to acquire content the w,h can be set to multiples of 1000 in the aspect ratio, for simplicity. If I select 4:3 I get a 4000x3000 canvas.

If the user selects one of these for a canvas that already has content, the ME could either:

• Adjust the canvas so that the content still fits but preserve whichever it can of the current dimensions
• Pick a rounded up pair of dimensions, e.g., 4000:3000.

Content, including content that previously targeted the whole canvas, should have its own aspect ratio preserved. So if a 2000x1500 image was targeting a 2000x1500 canvas (no xywh target required), and you changed the canvas aspect ratio to 16:9, the canvas could either change to 2667x1500 and the painting now specifically targets 333,0,2000,1500; or the canvas could change to 16000x9000 and the painting anno now targets 2000,0,12000,9000.

[stephenwf]

This will not work for canvas creation, unless there is an additional behaviour or other property to tell Manifest Editor not to resize automatically when you add an image to it. We could have this on the edit properties page. There is an editor that specifically shows when there are multiple piece of media on a canvas.