[PATCH 2/2] user32/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.

The calculation has also 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, so the float cast was useless. This works fine because the multiplication is done before the division (parentheses have been added to emphasize this point).

Wine-Bug: https://bugs.winehq.org/show_bug.cgi?id=22253
Signed-off-by: Gabriel Ivăncescu <gabrielopcode at gmail.com>
---
 dlls/user32/listbox.c | 19 +++++++++++++++----
 1 file changed, 15 insertions(+), 4 deletions(-)

diff --git a/dlls/user32/listbox.c b/dlls/user32/listbox.c
index 991ab87..7256095 100644
--- a/dlls/user32/listbox.c
+++ b/dlls/user32/listbox.c
@@ -2007,10 +2007,21 @@ 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(1, pulScrollLines);
+            cLineScroll = ((INT)pulScrollLines * descr->wheel_remain) / WHEEL_DELTA;
+            descr->wheel_remain -= (cLineScroll * WHEEL_DELTA) / (INT)pulScrollLines;
+            cLineScroll *= descr->page_size;
+        }
+        else
+        {
+            pulScrollLines = min((UINT) descr->page_size, pulScrollLines);
+            cLineScroll = ((INT)pulScrollLines * descr->wheel_remain) / WHEEL_DELTA;
+            descr->wheel_remain -= (cLineScroll * WHEEL_DELTA) / (INT)pulScrollLines;
+        }
         LISTBOX_SetTopItem( descr, descr->top_item - cLineScroll, TRUE );
     }
     return 0;
-- 
1.9.1