Implemented Area.Repaint() on Windows.

redo/area_windows.c

@@ -289,10 +289,10 @@ static void adjustAreaScrollbars(HWND hwnd, void *data)
 	SetScrollInfo(hwnd, SB_VERT, &si, TRUE);
 }
 
-void repaintArea(HWND hwnd)
+void repaintArea(HWND hwnd, RECT *r)
 {
 	// NULL - the whole area; TRUE - have windows erase if possible
-	if (InvalidateRect(hwnd, NULL, TRUE) == 0)
+	if (InvalidateRect(hwnd, r, TRUE) == 0)
 		xpanic("error flagging Area as needing repainting after event", GetLastError());
 	if (UpdateWindow(hwnd) == 0)
 		xpanic("error repainting Area after event", GetLastError());
@@ -386,10 +386,16 @@ static LRESULT CALLBACK areaWndProc(HWND hwnd, UINT uMsg, WPARAM wParam, LPARAM
 		return (LRESULT) areaKeyEvent(data, TRUE, wParam, lParam);
 	case msgAreaSizeChanged:
 		adjustAreaScrollbars(hwnd, data);
-		repaintArea(hwnd);		// this calls for an update
+		repaintArea(hwnd, NULL);		// this calls for an update
+		return 0;
+	case msgAreaGetScroll:
+		getScrollPos(hwnd, (int *) wParam, (int *) lParam);
+		return 0;
+	case msgAreaRepaint:
+		repaintArea(hwnd, (RECT *) lParam);
 		return 0;
 	case msgAreaRepaintAll:
-		repaintArea(hwnd);
+		repaintArea(hwnd, NULL);
 		return 0;
 	default:
 		return DefWindowProcW(hwnd, uMsg, wParam, lParam);

redo/area_windows.go

@@ -46,6 +46,23 @@ func (a *area) SetSize(width, height int) {
 	C.SendMessageW(a._hwnd, C.msgAreaSizeChanged, 0, 0)
 }
 
+func (a *area) Repaint(r image.Rectangle) {
+	var hscroll, vscroll C.int
+	var rect C.RECT
+
+	C.SendMessageW(a._hwnd, C.msgAreaGetScroll, C.WPARAM(uintptr(unsafe.Pointer(&hscroll))), C.LPARAM(uintptr(unsafe.Pointer(&vscroll))))
+	r = r.Add(image.Pt(int(hscroll), int(vscroll))) // adjust by scroll position
+	r = image.Rect(0, 0, a.width, a.height).Intersect(r)
+	if r.Empty() {
+		return
+	}
+	rect.left = C.LONG(r.Min.X)
+	rect.top = C.LONG(r.Min.Y)
+	rect.right = C.LONG(r.Max.X)
+	rect.bottom = C.LONG(r.Max.Y)
+	C.SendMessageW(a._hwnd, C.msgAreaRepaint, 0, C.LPARAM(uintptr(unsafe.Pointer(&rect))))
+}
+
 func (a *area) RepaintAll() {
 	C.SendMessageW(a._hwnd, C.msgAreaRepaintAll, 0, 0)
 }

redo/winapi_windows.h

@@ -30,6 +30,8 @@ enum {
 	msgCOMMAND,				// WM_COMMAND proxy; see forwardCommand() in controls_windows.go
 	msgNOTIFY,					// WM_NOTIFY proxy
 	msgAreaSizeChanged,
+	msgAreaGetScroll,
+	msgAreaRepaint,
 	msgAreaRepaintAll,
 	msgTabCurrentTabHasChildren,
 	msgBeginModal,
@@ -122,7 +124,7 @@ extern void calculateBaseUnits(HWND, int *, int *, LONG *);
 
 // area_window.c
 #define areaWindowClass L"gouiarea"
-extern void repaintArea(HWND);
+extern void repaintArea(HWND, RECT *);
 extern DWORD makeAreaWindowClass(char **);
 extern HWND newArea(void *);