Changed the new resizing code so that it uses the same allocated slice per window instead of making a new one to store all the resize requests each time.

area.go

@@ -121,14 +121,14 @@ func (a *Area) make(window *sysData) error {
 	return nil
 }
 
-func (a *Area) setRect(x int, y int, width int, height int) []resizerequest {
-	return []resizerequest{resizerequest{
+func (a *Area) setRect(x int, y int, width int, height int, rr *[]resizerequest) {
+	*rr = append(*rr, resizerequest{
 		sysData:	a.sysData,
 		x:		x,
 		y:		y,
 		width:	width,
 		height:	height,
-	}}
+	})
 }
 
 func (a *Area) preferredSize() (width int, height int) {

button.go

@@ -61,14 +61,14 @@ func (b *Button) make(window *sysData) error {
 	return nil
 }
 
-func (b *Button) setRect(x int, y int, width int, height int) []resizerequest {
-	return []resizerequest{resizerequest{
+func (b *Button) setRect(x int, y int, width int, height int, rr *[]resizerequest) {
+	*rr = append(*rr, resizerequest{
 		sysData:	b.sysData,
 		x:		x,
 		y:		y,
 		width:	width,
 		height:	height,
-	}}
+	})
 }
 
 func (b *Button) preferredSize() (width int, height int) {

callbacks_unix.go

@@ -42,8 +42,9 @@ func our_window_configure_event_callback(widget *C.GtkWidget, event *C.GdkEvent,
 	if s.container != nil && s.resize != nil {		// wait for init
 		width, height := gtk_window_get_size(s.widget)
 		// top-left is (0,0) so no need for winheight
-		resizeList := s.resize(0, 0, width, height)
-		for _, s := range resizeList {
+		s.resizes = s.resizes[0:0]		// set len to 0 without changing cap
+		s.resize(0, 0, width, height, &s.resizes)
+		for _, s := range s.resizes {
 			err := s.sysData.setRect(s.x, s.y, s.width, s.height, 0)
 			if err != nil {
 				panic("child resize failed: " + err.Error())

checkbox.go

@@ -68,14 +68,14 @@ func (c *Checkbox) make(window *sysData) error {
 	return nil
 }
 
-func (c *Checkbox) setRect(x int, y int, width int, height int) []resizerequest {
-	return []resizerequest{resizerequest{
+func (c *Checkbox) setRect(x int, y int, width int, height int, rr *[]resizerequest) {
+	*rr = append(*rr, resizerequest{
 		sysData:	c.sysData,
 		x:		x,
 		y:		y,
 		width:	width,
 		height:	height,
-	}}
+	})
 }
 
 func (c *Checkbox) preferredSize() (width int, height int) {

combobox.go

@@ -143,14 +143,14 @@ func (c *Combobox) make(window *sysData) (err error) {
 	return nil
 }
 
-func (c *Combobox) setRect(x int, y int, width int, height int) []resizerequest {
-	return []resizerequest{resizerequest{
+func (c *Combobox) setRect(x int, y int, width int, height int, rr *[]resizerequest) {
+	*rr = append(*rr, resizerequest{
 		sysData:	c.sysData,
 		x:		x,
 		y:		y,
 		width:	width,
 		height:	height,
-	}}
+	})
 }
 
 func (c *Combobox) preferredSize() (width int, height int) {

control.go

@@ -9,6 +9,6 @@ import (
 // A Control represents an UI control. Note that Control contains unexported members; this has the consequence that you can't build custom controls that interface directly with the system-specific code (fo rinstance, to import an unsupported control), or at least not without some hackery. If you want to make your own controls, embed Area and provide its necessities.
 type Control interface {
 	make(window *sysData) error
-	setRect(x int, y int, width int, height int) []resizerequest
+	setRect(x int, y int, width int, height int, rr *[]resizerequest)
 	preferredSize() (width int, height int)
 }

delegate_darwin.go

@@ -90,8 +90,9 @@ func appDelegate_windowDidResize(self C.id, sel C.SEL, notification C.id) {
 	r := C.objc_msgSend_stret_rect_noargs(wincv, _frame)
 	if sysData.resize != nil {
 		// winheight is used here because (0,0) is the bottom-left corner, not the top-left corner
-		resizeList := sysData.resize(int(r.x), int(r.y), int(r.width), int(r.height))
-		for _, s := range resizeList {
+		s.resizes = s.resizes[0:0]		// set len to 0 without changing cap
+		s.resize(0, 0, width, height, &s.resizes)
+		for _, s := range s.resizes {
 			err := s.sysData.setRect(s.x, s.y, s.width, s.height, int(r.height))
 			if err != nil {
 				panic("child resize failed: " + err.Error())

grid.go

@@ -120,7 +120,7 @@ func (g *Grid) make(window *sysData) error {
 	return nil
 }
 
-func (g *Grid) setRect(x int, y int, width int, height int) (rr []resizerequest) {
+func (g *Grid) setRect(x int, y int, width int, height int, rr *[]resizerequest) {
 	max := func(a int, b int) int {
 		if a > b {
 			return a
@@ -171,13 +171,13 @@ func (g *Grid) setRect(x int, y int, width int, height int) (rr []resizerequest)
 				w = g.colwidths[col]
 				h = g.rowheights[row]
 			}
-			rr = append(rr, c.setRect(x, y, w, h)...)
+			c.setRect(x, y, w, h, rr)
 			x += g.colwidths[col]
 		}
 		x = startx
 		y += g.rowheights[row]
 	}
-	return rr
+	return
 }
 
 // filling and stretchy are ignored for preferred size calculation

label.go

@@ -55,14 +55,14 @@ func (l *Label) make(window *sysData) error {
 	return nil
 }
 
-func (l *Label) setRect(x int, y int, width int, height int) []resizerequest {
-	return []resizerequest{resizerequest{
+func (l *Label) setRect(x int, y int, width int, height int, rr *[]resizerequest) {
+	*rr = append(*rr, resizerequest{
 		sysData:	l.sysData,
 		x:		x,
 		y:		y,
 		width:	width,
 		height:	height,
-	}}
+	})
 }
 
 func (l *Label) preferredSize() (width int, height int) {

lineedit.go

@@ -67,14 +67,14 @@ func (l *LineEdit) make(window *sysData) error {
 	return nil
 }
 
-func (l *LineEdit) setRect(x int, y int, width int, height int) []resizerequest {
-	return []resizerequest{resizerequest{
+func (l *LineEdit) setRect(x int, y int, width int, height int, rr *[]resizerequest) {
+	*rr = append(*rr, resizerequest{
 		sysData:	l.sysData,
 		x:		x,
 		y:		y,
 		width:	width,
 		height:	height,
-	}}
+	})
 }
 
 func (l *LineEdit) preferredSize() (width int, height int) {

listbox.go

@@ -144,14 +144,14 @@ func (l *Listbox) make(window *sysData) (err error) {
 	return nil
 }
 
-func (l *Listbox) setRect(x int, y int, width int, height int) []resizerequest {
-	return []resizerequest{resizerequest{
+func (l *Listbox) setRect(x int, y int, width int, height int, rr *[]resizerequest) {
+	*rr = append(*rr, resizerequest{
 		sysData:	l.sysData,
 		x:		x,
 		y:		y,
 		width:	width,
 		height:	height,
-	}}
+	})
 }
 
 func (l *Listbox) preferredSize() (width int, height int) {

progressbar.go

@@ -55,14 +55,14 @@ func (p *ProgressBar) make(window *sysData) error {
 	return nil
 }
 
-func (p *ProgressBar) setRect(x int, y int, width int, height int) []resizerequest {
-	return []resizerequest{resizerequest{
+func (p *ProgressBar) setRect(x int, y int, width int, height int, rr *[]resizerequest) {
+	*rr = append(*rr, resizerequest{
 		sysData:	p.sysData,
 		x:		x,
 		y:		y,
 		width:	width,
 		height:	height,
-	}}
+	})
 }
 
 func (p *ProgressBar) preferredSize() (width int, height int) {

stack.go

@@ -77,11 +77,11 @@ func (s *Stack) make(window *sysData) error {
 	return nil
 }
 
-func (s *Stack) setRect(x int, y int, width int, height int) (rr []resizerequest) {
+func (s *Stack) setRect(x int, y int, width int, height int, rr *[]resizerequest) {
 	var stretchywid, stretchyht int
 
 	if len(s.controls) == 0 {		// do nothing if there's nothing to do
-		return nil
+		return
 	}
 	// 1) get height and width of non-stretchy controls; figure out how much space is alloted to stretchy controls
 	stretchywid = width
@@ -120,14 +120,14 @@ func (s *Stack) setRect(x int, y int, width int, height int) (rr []resizerequest
 	}
 	// 3) now actually place controls
 	for i, c := range s.controls {
-		rr = append(rr, c.setRect(x, y, s.width[i], s.height[i])...)
+		c.setRect(x, y, s.width[i], s.height[i], rr)
 		if s.orientation == horizontal {
 			x += s.width[i]
 		} else {
 			y += s.height[i]
 		}
 	}
-	return rr
+	return
 }
 
 // The preferred size of a Stack is the sum of the preferred sizes of non-stretchy controls + (the number of stretchy controls * the largest preferred size among all stretchy controls).

stdwndclass_windows.go

@@ -53,8 +53,9 @@ func stdWndProc(s *sysData) func(hwnd _HWND, uMsg uint32, wParam _WPARAM, lParam
 					panic("GetClientRect failed: " + err.Error())
 				}
 				// top-left corner is (0,0) so no need for winheight
-				resizeList := s.resize(int(r.Left), int(r.Top), int(r.Right), int(r.Bottom))
-				for _, s := range resizeList {
+				s.resizes = s.resizes[0:0]		// set len to 0 without changing cap
+				s.resize(0, 0, width, height, &s.resizes)
+				for _, s := range s.resizes {
 					err = s.sysData.setRect(s.x, s.y, s.width, s.height, 0)
 					if err != nil {
 						panic("child resize failed: " + err.Error())

sysdata.go

@@ -17,7 +17,8 @@ func newEvent() chan struct{} {
 type cSysData struct {
 	ctype	int
 	event	chan struct{}
-	resize	func(x int, y int, width int, height int) []resizerequest
+	resize	func(x int, y int, width int, height int, rr *[]resizerequest)
+	resizes	[]resizerequest
 	alternate	bool			// editable for Combobox, multi-select for listbox, password for lineedit
 	handler	AreaHandler	// for Areas
 }
@@ -103,11 +104,15 @@ const (
 )
 
 func mksysdata(ctype int) *sysData {
-	return &sysData{
+	s := &sysData{
 		cSysData:		cSysData{
 			ctype:	ctype,
 		},
 	}
+	if ctype == c_window {		// make resizes non-nil so it can be passed in
+		s.resizes = make([]resizerequest, 0, 0)
+	}
+	return s
 }
 
 type resizerequest struct {