After tediously calculating layouts for resizable components and using the setBoundsRelative method for resizing, I discovered the relative modes of layout in the Jucer. But they don’t appear to work correctly.
For example, suppose I’ve got a component with width 600 and height 400 and place a button (width: 100, height:24) so that it’s centered using absolute coordinates at x=250, y=188. I then set the mode for the x position to “percentage of width of parent, anchored at left, relative to the parent component” and the mode for the y position to “percentage of height of parent, anchored at top. relative to the parent component”. It puts the percentages at 18.222% for the x position and 20.324% for the y position. Now these percentages should 41.667 (250/600100) and 47.0 (188/400100) respectively. Putting these latter numbers (and similar modes for the button width and height) in a setBoundsRelative call works as expected.