type sysSizeData struct {
	// for size calculations
	// all platforms
	margin	int	// windows: calculated
	spacing	int	// gtk+, cocoa: constants
	// windows
	baseX	int
	baseY	int
	// gtk, mac os x: nothing

	// for the actual resizing
	// windows
	// possibly also the HDWP
	// gtk
	shouldVAlignTop	bool
	// mac os x
	// neighbor control alignment rect/baseline info
}

func (s *sysData) beginResize() *sysSizeData {
	// windows: get baseX/baseY for window and compute margin and spacing
	// gtk, mac: return zero
}

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 _, a := 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
		a.y = (winheight - a.y) - a.height
	}
}

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

// setSize() becomes allocate()
// each allocate on a non-layout control should just return a one-element slice
// each doResize and getAuxResizeInfo on a control should just defer to sysData
type Control interface {
	// ...
	allocate(x int, y int, width int, height int, d *sysSizeData) []*allocation
	preferredSize(d *sysSizeData) (width, height int)
	doResize(c *allocation, d *sysSizeData)
	getAuxResizeInfo(d *sysSizeData)
}

// vertical stack: no concept of neighbor, but not too hard to add a vertical neighbor
// horizontal stack:
	var current *allocation
	// ...
	as := s.controls[i].allocate(...)
	if current != nil {
		current.neighbor = as[0].self
	}
	current = as[0]
	// append all of as
// grid:
	// same as above, except current is set to nil on each new row
	// adding a vertical neighbor would require storing an extra list

// windows
func (s *sysData) doResize(c *allocation, d *sysSizeData) {
	if s.ctype == c_label {
		// add additional offset of 4 dialog units
	}
	// resize
}
func (s *sysData) getAuxResizeInfo(d *sysSizeData) {
	// do nothing
}

// gtk+
func (s *sysData) doResize(c *allocation, d *sysSizeData) {
	if s.ctype == c_label && !s.alternate && c.neighbor != nil {
		c.neighbor.getAuxResizeInfo(d)
		if d.shouldVAlignTop {
			// TODO should it be center-aligned to the first line or not
			gtk_misc_set_align(s.widget, 0, 0)
		} else {
			gtk_misc_set_align(s.widget, 0, 0.5)
		}
	}
	// resize
}
func (s *sysData) getAuxResizeInfo(d *sysSizeData) {
	d.shouldVAlignTop = (s.ctype == c_listbox) || (s.ctype == c_area)
}

// cocoa
func (s *sysData) doResize(c *allocation, d *sysSizeData) {
	if s.ctype == c_label && !s.alternate && c.neighbor != nil {
		c.neighbor.getAuxResizeInfo(d)
		// get this control's alignment rect and baseline
		// align
	}
	// resize
}
func (s *sysData) getAuxResizeInfo(d *sysSizeData) {
	// get this control's alignment rect and baseline
}