Fix/mouse exit windows (#202)

* fixes #198

* fixe weird edge case

Author: pchampio

application.go

@@ -237,6 +237,11 @@ func (a *Application) Run() error {
 	a.window.SetRefreshCallback(m.glfwRefreshCallback)
 	a.window.SetPosCallback(m.glfwPosCallback)
 
+	// flutter's PlatformMessage handler is registered through the dart:ui.Window
+	// interface. ui.Window must have at least paint one frame, before any
+	// platfrom message can be corectly handled by ui.Window.onPlatformMessage.
+	glfw.WaitEvents()
+
 	a.window.SetKeyCallback(
 		func(window *glfw.Window, key glfw.Key, scancode int, action glfw.Action, mods glfw.ModifierKey) {
 			defaultTextinputPlugin.glfwKeyCallback(window, key, scancode, action, mods)

glfw.go

@@ -105,9 +105,17 @@ func (m *windowManager) glfwCursorEnterCallback(window *glfw.Window, entered boo
 	x, y := window.GetCursorPos()
 	if entered {
 		m.sendPointerEvent(window, embedder.PointerPhaseAdd, x, y)
-		m.pointerPhase = embedder.PointerPhaseHover
+		// the mouse can enter the windows while having button pressed.
+		// if so, don't overwrite the phase.
+		if m.pointerButton == 0 {
+			m.pointerPhase = embedder.PointerPhaseHover
+		}
 	} else {
-		m.sendPointerEvent(window, embedder.PointerPhaseRemove, x, y)
+		// if the mouse is still in 'phaseMove' outside the window (click-drag
+		// outside). Don't remove the cursor.
+		if m.pointerButton == 0 {
+			m.sendPointerEvent(window, embedder.PointerPhaseRemove, x, y)
+		}
 	}
 }