type sysSizeData struct {
	// windows
	baseX	int
	baseY	int
	// possibly also the HDWP
	// gtk, mac os x: nothing
}

func (s *sysData) beginResize() *sysSizeData {
	// windows: get baseX/baseY for window
	// gtk, mac: return nothing
}

func (s *sysData) endResize(d *sysSizeData) {
	// redraw
}

type allocation struct {
	x		int
	y		int
	width	int
	height	int
	this		Control
	neighbor	Control
}

func (s *sysData) translateAllocationCoords(allocations []*allocation, winwidth, winheight int) {
	// windows, gtk: nothing
	// mac
	for _, allocation := range allocations {
		// winheight - y because (0,0) is the bottom-left corner of the window and not the top-left corner
		// (winheight - y) - height because (x, y) is the bottom-left corner of the control and not the top-left
		allocation.y = (winheight - allocation.y) - allocation.height
	}
}

func (s *sysData) resizeWindow(width, height int) {
	d := s.startResize()
	allocations := s.resize(0, 0, width, height, d)
	s.translateAllocationCoords(allocations, width, height)
	for _, c := range s.allocations {
		c.this.doResize(c, d)
	}
	s.finishResize(d)
}

main widget sizing function
	get preferred size of all subwidgets
		windows: uses dialog base units
	produce map of which controls are next to which controls
	properly space controls
		windows: uses dialog base units
	return list of size allocations back to window sizer

each doResize on a control should just defer to sysData.doResize()

each widget adjustment
	mac: neighboring control baselines are aligned for labels
	gtk: vertical alignment of text changed to top if neighboring control is multi-line
		TODO - should it be center-aligned vertically or not
	windows: none