Wrote up the hscroll code. Not sure why it doesn't work yet. Not yet applied to headers or drawing.

wintable/new/header.h

@@ -68,8 +68,8 @@ static void updateTableWidth(struct table *t)
 			panic("error getting Table column width for updateTableWidth()");
 		t->width += item.cxy;
 	}
-	// TODO replace this with a call to hscrollby(t, 0)
-	recomputeHScroll(t);
+	// do a dummy scroll to update the horizontal scrollbar to use the new width
+	hscrollby(t, 0);
 }
 
 HANDLER(headerNotifyHandler)

wintable/new/hscroll.h

@@ -1,33 +1,106 @@
 // 9 december 2014
 
+// forward declaration needed here
+static void repositionHeader(struct table *);
+
 static void hscrollto(struct table *t, intptr_t pos)
 {
-	// TODO
+	RECT scrollArea;
+	SCROLLINFO si;
+
+	if (pos < 0)
+		pos = 0;
+	if (pos > t->width - t->hpagesize)
+		pos = t->width - t->hpagesize;
+
+	// we don't want to scroll the header
+	if (GetClientRect(t->hwnd, &scrollArea) == 0)
+		panic("error getting Table client rect for hscrollto()");
+	scrollArea.top += t->headerHeight;
+
+	// negative because ScrollWindowEx() is "backwards"
+	if (ScrollWindowEx(t->hwnd, -(pos - t->hscrollpos), 0,
+		&scrollArea, &scrollArea, NULL, NULL,
+		SW_ERASE | SW_INVALIDATE) == ERROR)
+		panic("error horizontally scrolling Table");
+	// TODO call UpdateWindow()?
+
+	t->hscrollpos = pos;
+
+	// now commit our new scrollbar setup...
+	ZeroMemory(&si, sizeof (SCROLLINFO));
+	si.cbSize = sizeof (SCROLLINFO);
+	si.fMask = SIF_PAGE | SIF_POS | SIF_RANGE;
+	// the width of scrollArea is unchanged here; use it
+	t->hpagesize = scrollArea.right - scrollArea.left;
+	si.nPage = t->hpagesize;
+	si.nMin = 0;
+	si.nMax = t->width - 1;		// endpoint inclusive
+	si.nPos = t->hscrollpos;
+	SetScrollInfo(t->hwnd, SB_HORZ, &si, TRUE);
+
+	// and finally move the header
+	repositionHeader(t);
 }
 
 static void hscrollby(struct table *t, intptr_t delta)
 {
-	// TODO
+	hscrollto(t, t->hscrollpos + delta);
 }
 
 static void hscroll(struct table *t, WPARAM wParam, LPARAM lParam)
 {
-	// TODO
-}
-
-static void recomputeHScroll(struct table *t)
-{
+	intptr_t pos;
 	SCROLLINFO si;
-	RECT r;
 
-	if (GetClientRect(t->hwnd, &r) == 0)
-		panic("error getting Table client rect for recomputeHScroll()");
-	ZeroMemory(&si, sizeof (SCROLLINFO));
-	si.cbSize = sizeof (SCROLLINFO);
-	si.fMask = SIF_PAGE | SIF_RANGE;
-	si.nPage = r.right - r.left;
-	si.nMin = 0;
-	si.nMax = t->width - 1;		// endpoint inclusive
-	SetScrollInfo(t->hwnd, SB_HORZ, &si, TRUE);
-	// TODO what happens if the above call renders the current scroll position moot?
+	pos = t->hscrollpos;
+	switch (LOWORD(wParam)) {
+	case SB_LEFT:
+		pos = 0;
+		break;
+	case SB_RIGHT:
+		pos = t->width - t->hpagesize;
+		break;
+	case SB_LINELEFT:
+		pos--;
+		break;
+	case SB_LINERIGHT:
+		pos++;
+		break;
+	case SB_PAGELEFT:
+		pos -= t->hpagesize;
+		break;
+	case SB_PAGERIGHT:
+		pos += t->hpagesize;
+		break;
+	case SB_THUMBPOSITION:
+		ZeroMemory(&si, sizeof (SCROLLINFO));
+		si.cbSize = sizeof (SCROLLINFO);
+		si.fMask = SIF_POS;
+		if (GetScrollInfo(t->hwnd, SB_HORZ, &si) == 0)
+			panic("error getting thumb position for WM_HSCROLL in Table");
+		pos = si.nPos;
+		break;
+	case SB_THUMBTRACK:
+		ZeroMemory(&si, sizeof (SCROLLINFO));
+		si.cbSize = sizeof (SCROLLINFO);
+		si.fMask = SIF_TRACKPOS;
+		if (GetScrollInfo(t->hwnd, SB_HORZ, &si) == 0)
+			panic("error getting thumb track position for WM_HSCROLL in Table");
+		pos = si.nTrackPos;
+		break;
+	}
+	hscrollto(t, pos);
 }
+
+// TODO find out if we can indicriminately check for WM_WHEELHSCROLL
+HANDLER(hscrollHandler)
+{
+	if (uMsg != WM_HSCROLL)
+		return FALSE;
+	hscroll(t, wParam, lParam);
+	*lResult = 0;
+	return TRUE;
+}
+
+// TODO when we write vscroll.h, see just /what/ is common so we can isolate it

wintable/new/main.c

@@ -54,6 +54,8 @@ struct table {
 	int *columnTypes;
 	intptr_t width;
 	intptr_t headerHeight;
+	intptr_t hscrollpos;
+	intptr_t hpagesize;
 };
 
 #include "util.h"
@@ -72,6 +74,7 @@ static const handlerfunc handlers[] = {
 	resizeHandler,
 	drawHandlers,
 	apiHandlers,
+	hscrollHandler,
 	NULL,
 };