Support smooth scrolling (part 2)

Fix scrolling when smooth scrolling is enabled /
allow to scroll smoothly for:
- canvas palette
- node selection in path tool
- selection cycling in select tool while holding Alt key
- spraying in spray tool with mouse wheel
- adjusting color by scrolling in lower left stroke/fill fields

1 files changed, 12 insertions, 1 deletions

diff --git a/src/ui/previewholder.cpp b/src/ui/previewholder.cpp
index ae6907cc7..a39eb7ca6 100644
--- a/src/ui/previewholder.cpp
+++ b/src/ui/previewholder.cpp
@@ -76,7 +76,18 @@ bool PreviewHolder::on_scroll_event(GdkEventScroll *event)
         return FALSE;
     }
 
-    int move = (event->direction == GDK_SCROLL_DOWN) ? adj->get_page_size() : -adj->get_page_size();
+    int move;
+    switch (event->direction) {
+        case GDK_SCROLL_UP:
+            move = -adj->get_page_size();
+            break;
+        case GDK_SCROLL_DOWN:
+            move =  adj->get_page_size();
+            break;
+        case GDK_SCROLL_SMOOTH:
+            move = event->delta_y > 0 ? adj->get_page_size() : -adj->get_page_size();
+            break;
+    }
 
     double value = std::min(adj->get_upper() - move, adj->get_value() + move );