app: support horizontal scrolling on Windows and Linux

Fixes #181.

Signed-off-by: pierre <pierre.curto@gmail.com>

app/internal/window/os_windows.go

@@ -271,7 +271,9 @@ func windowProc(hwnd syscall.Handle, msg uint32, wParam, lParam uintptr) uintptr
 			Time:     windows.GetMessageTime(),
 		})
 	case windows.WM_MOUSEWHEEL:
-		w.scrollEvent(wParam, lParam)
+		w.scrollEvent(wParam, lParam, false)
+	case windows.WM_MOUSEHWHEEL:
+		w.scrollEvent(wParam, lParam, true)
 	case windows.WM_DESTROY:
 		windows.PostQuitMessage(0)
 	case windows.WM_PAINT:
@@ -352,7 +354,7 @@ func coordsFromlParam(lParam uintptr) (int, int) {
 	return x, y
 }
 
-func (w *window) scrollEvent(wParam, lParam uintptr) {
+func (w *window) scrollEvent(wParam, lParam uintptr, horizontal bool) {
 	x, y := coordsFromlParam(lParam)
 	// The WM_MOUSEWHEEL coordinates are in screen coordinates, in contrast
 	// to other mouse events.
@@ -360,12 +362,16 @@ func (w *window) scrollEvent(wParam, lParam uintptr) {
 	windows.ScreenToClient(w.hwnd, &np)
 	p := f32.Point{X: float32(np.X), Y: float32(np.Y)}
 	dist := float32(int16(wParam >> 16))
+	sp := f32.Point{Y: -dist}
+	if horizontal {
+		sp.X, sp.Y = sp.Y, sp.X
+	}
 	w.w.Event(pointer.Event{
 		Type:     pointer.Scroll,
 		Source:   pointer.Mouse,
 		Position: p,
 		Buttons:  w.pointerBtns,
-		Scroll:   f32.Point{Y: -dist},
+		Scroll:   sp,
 		Time:     windows.GetMessageTime(),
 	})
 }

app/internal/window/os_x11.go

@@ -346,6 +346,15 @@ func (h *x11EventHandler) handleEvents() bool {
 				// scroll down
 				ev.Type = pointer.Scroll
 				ev.Scroll.Y = +scrollScale
+			case 6:
+				// http://xahlee.info/linux/linux_x11_mouse_button_number.html
+				// scroll left
+				ev.Type = pointer.Scroll
+				ev.Scroll.X = -scrollScale * 2
+			case 7:
+				// scroll right
+				ev.Type = pointer.Scroll
+				ev.Scroll.X = +scrollScale * 2
 			default:
 				continue
 			}

app/internal/windows/windows.go

@@ -142,6 +142,7 @@ const (
 	WM_MBUTTONUP     = 0x0208
 	WM_MOUSEMOVE     = 0x0200
 	WM_MOUSEWHEEL    = 0x020A
+	WM_MOUSEHWHEEL   = 0x020E
 	WM_PAINT         = 0x000F
 	WM_CLOSE         = 0x0010
 	WM_QUIT          = 0x0012