Added portable code for Area's MouseEvent.

area.go

@@ -17,6 +17,10 @@ type Area struct {
 	// See the documentation of PaintRequest for details.
 	Paint		chan PaintRequest
 
+	// Mouse is signaled when the Area receives a mouse event.
+	// See MouseEvent for details.
+	Mouse	chan MouseEvent
+
 	lock		sync.Mutex
 	created	bool
 	sysData	*sysData
@@ -44,11 +48,59 @@ type PaintRequest struct {
 	Out		chan<- *image.NRGBA
 }
 
+// MouseEvent contains all the information for a mous event sent by Area.Mouse.
+// Mouse button IDs start at 1, with 1 being the left mouse button, 2 being the middle mouse button, and 3 being the right mouse button.
+// (TODO "If additional buttons are supported, they will be returned with 4 being the first additional button (XBUTTON1 on Windows), 5 being the second (XBUTTON2 on Windows), and so on."?) (TODO get the user-facing name for XBUTTON1/2; find out if there's a way to query available button count)
+type MouseEvent struct {
+	// Pos is the position of the mouse in the Area at the time of the event.
+	Pos			image.Point
+
+	// If the event was generated by a mouse button being pressed, Down contains the ID of that button.
+	// Otherwise, Down contains 0.
+	Down		uint
+
+	// If the event was generated by a mouse button being released, Up contains the ID of that button.
+	// Otherwise, Up contains 0.
+	Up			uint
+
+	// If Down is nonzero, Count indicates the number of clicks: 1 for single-click, 2 for double-click.
+	// If Count == 2, AT LEAST one event with Count == 1 will have been sent prior.
+	// (This is a platform-specific issue: some platforms send one, some send two.)
+	Count		uint
+
+	// Modifiers is a bit mask indicating the modifier keys being held during the event.
+	Modifiers		Modifiers
+
+	// Held is a slice of button IDs that indicate which mouse buttons are being held during the event.
+	// (TODO "There is no guarantee that Held is sorted."?)
+	// (TODO will this include or exclude Down and Up?)
+	Held			[]uint
+}
+
+// HeldBits returns Held as a bit mask.
+// Bit 0 maps to button 1, bit 1 maps to button 2, etc.
+func (e MouseEvent) HeldBits() (h uintptr) {
+	for _, x := range e.Held {
+		h |= uintptr(1) << (x - 1)
+	}
+	return h
+}
+
+// Modifiers indicates modifier keys being held during a mouse event.
+// There is no way to differentiate between left and right modifier keys.
+type Modifiers uintptr
+const (
+	Ctrl Modifiers = 1 << iota		// the canonical Ctrl keys ([TODO] on Mac OS X, Control on others)
+	Alt						// the canonical Alt keys ([TODO] on Mac OS X, Meta on Unix systems, Alt on others)
+	Shift						// the Shift keys
+)
+
 // NewArea creates a new Area.
 func NewArea() *Area {
 	return &Area{
 		sysData:	mksysdata(c_area),
 		Paint:	make(chan PaintRequest),
+		Mouse:	make(chan MouseEvent),
 	}
 }
 
@@ -57,6 +109,7 @@ func (a *Area) make(window *sysData) error {
 	defer a.lock.Unlock()
 
 	a.sysData.paint = a.Paint
+	a.sysData.mouse = a.Mouse
 	err := a.sysData.make("", window)
 	if err != nil {
 		return err

sysdata.go

@@ -22,6 +22,7 @@ type cSysData struct {
 
 	// for Area
 	paint		chan PaintRequest
+	mouse	chan MouseEvent
 }
 func (c *cSysData) make(initText string, window *sysData) error {
 	panic(runtime.GOOS + " sysData does not define make()")