[PATCH resend 1/6] comctl32/listbox: Handle Mouse Wheel scrolling for multi-column listboxes properly

[Gabriel Ivăncescu]

Multi-column listboxes scroll horizontally, so each wheel tick must go an
entire page at a time instead of an item at a time. But we have to limit
the amount of scrolling in this case to avoid "jumping over" columns,
if the window is too small. This matches Windows behavior.

Wine-Bug: https://bugs.winehq.org/show_bug.cgi?id=22253
Signed-off-by: Gabriel Ivăncescu <gabrielopcode at gmail.com>
---

These notes apply to all the patches in the series.

The calculation has been simplified to just integer arithmetic in all
cases, since the division (the only operation with a fractional result)
was immediately truncated to integer anyway.

Note that the float doesn't help with overflow either. As you can see, it
gets assigned to cLineScroll (which is integer) and then gets multiplied
back by WHEEL_DELTA, so if the float were to help with overflow, it would
overflow on the next line anyway... Anyway, overflow is extremely unlikely
(and probably impossible in practice) since WHEEL_DELTA is just 120, and
it was already vulnerable to overflow currently.

 dlls/comctl32/listbox.c | 25 +++++++++++++++++++------
 1 file changed, 19 insertions(+), 6 deletions(-)

diff --git a/dlls/comctl32/listbox.c b/dlls/comctl32/listbox.c
index cb645b4..9f56a2f 100644
--- a/dlls/comctl32/listbox.c
+++ b/dlls/comctl32/listbox.c
@@ -2012,9 +2012,11 @@ static LRESULT LISTBOX_HandleHScroll( LB_DESCR *descr, WORD scrollReq, WORD pos
 
 static LRESULT LISTBOX_HandleMouseWheel(LB_DESCR *descr, SHORT delta )
 {
-    UINT pulScrollLines = 3;
+    INT pulScrollLines;
+    UINT tmp = 3;
 
-    SystemParametersInfoW(SPI_GETWHEELSCROLLLINES,0, &pulScrollLines, 0);
+    SystemParametersInfoW(SPI_GETWHEELSCROLLLINES,0, &tmp, 0);
+    pulScrollLines = tmp;
 
     /* if scrolling changes direction, ignore left overs */
     if ((delta < 0 && descr->wheel_remain < 0) ||
@@ -2025,10 +2027,21 @@ static LRESULT LISTBOX_HandleMouseWheel(LB_DESCR *descr, SHORT delta )
 
     if (descr->wheel_remain && pulScrollLines)
     {
-        int cLineScroll;
-        pulScrollLines = min((UINT) descr->page_size, pulScrollLines);
-        cLineScroll = pulScrollLines * (float)descr->wheel_remain / WHEEL_DELTA;
-        descr->wheel_remain -= WHEEL_DELTA * cLineScroll / (int)pulScrollLines;
+        INT cLineScroll;
+        if (descr->style & LBS_MULTICOLUMN)
+        {
+            pulScrollLines = min((UINT)descr->width / descr->column_width, pulScrollLines);
+            pulScrollLines = max(1U, pulScrollLines);
+            cLineScroll = (pulScrollLines * descr->wheel_remain) / WHEEL_DELTA;
+            descr->wheel_remain -= (cLineScroll * WHEEL_DELTA) / pulScrollLines;
+            cLineScroll *= descr->page_size;
+        }
+        else
+        {
+            pulScrollLines = min((UINT)descr->page_size, pulScrollLines);
+            cLineScroll = (pulScrollLines * descr->wheel_remain) / WHEEL_DELTA;
+            descr->wheel_remain -= (cLineScroll * WHEEL_DELTA) / pulScrollLines;
+        }
         LISTBOX_SetTopItem( descr, descr->top_item - cLineScroll, TRUE );
     }
     return 0;
-- 
2.19.1