Big change: with the current event model, it's safe to call Area.RepaintAll() (and the future Area.Repaint()) from within AreaHandler.Key() and AreaHandler.Mouse(); get rid of the bool returns from each. The future Area.Repaint() is important; the bool returns repainted the whole Area, which may not be optimal.

redo/area.go

@@ -68,16 +68,14 @@ type AreaHandler interface {
 	// Mouse is called when the Area receives a mouse event.
 	// You are allowed to do nothing in this handler (to ignore mouse events).
 	// See MouseEvent for details.
-	// If repaint is true, the Area is marked as needing to be redrawn.
 	// After handling the mouse event, package ui will decide whether to perform platform-dependent event chain continuation based on that platform's designated action (so it is not possible to override global mouse events this way).
-	Mouse(e MouseEvent) (repaint bool)
+	Mouse(e MouseEvent)
 
 	// Key is called when the Area receives a keyboard event.
 	// You are allowed to do nothing in this handler (to ignore keyboard events).
 	// See KeyEvent for details.
-	// If repaint is true, the Area is marked as needing to be redrawn.
 	// After handling the key event, package ui will decide whether to perform platform-dependent event chain continuation based on that platform's designated action (so it is not possible to override global key events, such as Alt-Tab, this way).
-	Key(e KeyEvent) (repaint bool)
+	Key(e KeyEvent)
 }
 
 // MouseEvent contains all the information for a mous event sent by Area.Mouse.

redo/area_darwin.go

@@ -126,10 +126,7 @@ func areaMouseEvent(self C.id, e C.id, click bool, up bool, data unsafe.Pointer)
 		}
 		held >>= 1
 	}
-	repaint := a.handler.Mouse(me)
-	if repaint {
-		C.display(self)
-	}
+	a.handler.Mouse(me)
 }
 
 //export areaView_mouseMoved_mouseDragged
@@ -152,10 +149,7 @@ func areaView_mouseUp(self C.id, e C.id, data unsafe.Pointer) {
 
 func sendKeyEvent(self C.id, ke KeyEvent, data unsafe.Pointer) {
 	a := (*area)(data)
-	repaint := a.handler.Key(ke)
-	if repaint {
-		C.display(self)
-	}
+	a.handler.Key(ke)
 }
 
 func areaKeyEvent(self C.id, e C.id, up bool, data unsafe.Pointer) {

redo/area_unix.go

@@ -190,10 +190,7 @@ func finishMouseEvent(widget *C.GtkWidget, data C.gpointer, me MouseEvent, mb ui
 	if me.Up >= 8 {
 		me.Up -= 4
 	}
-	repaint := a.handler.Mouse(me)
-	if repaint {
-		C.gtk_widget_queue_draw(widget)
-	}
+	a.handler.Mouse(me)
 }
 
 // convenience name to make our intent clear
@@ -298,10 +295,7 @@ func doKeyEvent(widget *C.GtkWidget, event *C.GdkEvent, data C.gpointer, up bool
 		return
 	}
 	ke.Up = up
-	repaint := a.handler.Key(ke)
-	if repaint {
-		C.gtk_widget_queue_draw(widget)
-	}
+	a.handler.Key(ke)
 }
 
 //export our_area_key_press_event_callback

redo/area_windows.go

@@ -150,10 +150,7 @@ func finishAreaMouseEvent(data unsafe.Pointer, cbutton C.DWORD, up C.BOOL, wPara
 	if button != 5 && (wParam & C.MK_XBUTTON2) != 0 {
 		me.Held = append(me.Held, 5)
 	}
-	repaint := a.handler.Mouse(me)
-	if repaint {
-		a.RepaintAll()
-	}
+	a.handler.Mouse(me)
 }
 
 //export areaKeyEvent
@@ -188,11 +185,7 @@ func areaKeyEvent(data unsafe.Pointer, up C.BOOL, wParam C.WPARAM, lParam C.LPAR
 		return
 	}
 	ke.Up = up != C.FALSE
-	// TODO repaint may no longer be needed
-	repaint := a.handler.Key(ke)
-	if repaint {
-		a.RepaintAll()
-	}
+	a.handler.Key(ke)
 }
 
 // all mappings come from GLFW - https://github.com/glfw/glfw/blob/master/src/win32_window.c#L152

redo/future

@@ -17,6 +17,8 @@ Tab
 		// It panics if index is out of range.
 		// After Delete(), the effect of accessing the Control of the deleted tab or any of its children is undefned. [TODO reword?]
 	investigate close buttons (especially for LikeTab)
+Area
+	Repaint(rect image.Rectangle)
 
 so I don't forget, some TODOs:
 windows

redo/zz_test.go

@@ -50,8 +50,8 @@ func (a *areaHandler) Paint(r image.Rectangle) *image.RGBA {
 	draw.Draw(i, r, &image.Uniform{color.RGBA{128,0,128,255}}, image.ZP, draw.Src)
 	return i
 }
-func (a *areaHandler) Mouse(me MouseEvent) bool { fmt.Printf("%#v\n", me); return false }
-func (a *areaHandler) Key(ke KeyEvent) bool { fmt.Printf("%#v\n", ke); return false }
+func (a *areaHandler) Mouse(me MouseEvent) { fmt.Printf("%#v\n", me) }
+func (a *areaHandler) Key(ke KeyEvent) { fmt.Printf("%#v\n", ke) }
 
 func (tw *testwin) make(done chan struct{}) {
 	tw.t = NewTab()