From 13370c22d314f6e8b7d87e692e392f3606388703 Mon Sep 17 00:00:00 2001
From: Pietro Gagliardi <pietro10@mac.com>
Date: Tue, 25 Mar 2014 08:23:31 -0400
Subject: [PATCH] Added the actual scrolling to Windows Areas. Now to just
 adjust the cliprect properly...

---
 area_windows.go     | 25 ++++++++++++++++++++++++-
 controls_windows.go |  9 +++++++++
 2 files changed, 33 insertions(+), 1 deletion(-)

diff --git a/area_windows.go b/area_windows.go
index 33692fb..4b4eedc 100644
--- a/area_windows.go
+++ b/area_windows.go
@@ -208,7 +208,30 @@ func scrollArea(hwnd _HWND, wparam _WPARAM, which uintptr) {
 		return
 	}
 
-	// TODO scroll
+	delta := -(newpos - si.nPos)	// negative because ScrollWindowEx() scrolls in the opposite direction
+	dx := delta
+	dy := int32(0)
+	if which == uintptr(_SB_VERT) {
+		dx = int32(0)
+		dy = delta
+	}
+	r1, _, err = _scrollWindowEx.Call(
+		uintptr(hwnd),
+		uintptr(dx),
+		uintptr(dy),
+		uintptr(0),			// these four change what is scrolled and record info about the scroll; we're scrolling the whole client area and don't care about the returned information here
+		uintptr(0),
+		uintptr(0),
+		uintptr(0),
+		// TODO also SW_ERASE? or will the GetUpdateRect() call handle it?
+		uintptr(_SW_INVALIDATE))					// mark the remaining rect as needing redraw...
+	if r1 == _ERROR {		// failure
+		panic(fmt.Errorf("error scrolling Area: %v", err))
+	}
+	r1, _, err = _updateWindow.Call(uintptr(hwnd))		// ...and redraw it
+	if r1 == 0 {		// failure
+		panic(fmt.Errorf("error updating Area after scrolling: %v", err))
+	}
 
 	// we actually have to commit the change back to the scrollbar; otherwise the scroll position will merely reset itself
 	si.cbSize = uint32(unsafe.Sizeof(si))
diff --git a/controls_windows.go b/controls_windows.go
index 24adcfa..ab227ee 100644
--- a/controls_windows.go
+++ b/controls_windows.go
@@ -490,6 +490,15 @@ const (
 	_SIF_ALL = (_SIF_RANGE | _SIF_PAGE | _SIF_POS | _SIF_TRACKPOS)
 )
 
+// ScrollWindowEx return values.
+const (
+	// from wingdi.h
+	_ERROR = 0
+	_NULLREGION = 1
+	_SIMPLEREGION = 2
+	_COMPLEXREGION = 3
+)
+
 var (
 	_getScrollInfo = user32.NewProc("GetScrollInfo")
 	_getScrollPos = user32.NewProc("GetScrollPos")