Xournal / Feature Requests / #184 mouse wheel zoom

I could use the same feature.

I currently use a hack for that. I do not know much about the source code, so that could break something else.
On top of that, it just zooms to the center, it only works with XInput, i only tested it on linux and there are other limitations.

--- a/xournal-0.4.8.2016/src/xo-callbacks.c
+++ b/xournal-0.4.8.2016_zoom_hack/src/xo-callbacks.c
@@ -2418,7 +2418,27 @@ on_canvas_button_press_event           (GtkWidget       *widget,
     // double-clicks may have broken axes member (free'd) due to a bug in GDK

   if (event->button > 3) { // scroll wheel events! don't paint...
-    if (ui.use_xinput && !gtk_check_version(2, 17, 0) && event->button <= 7) {
+    if (ui.use_xinput && !gtk_check_version(2, 17, 0) && event->button <= 7) 
+      {
+        guint state=(gtk_accelerator_get_default_mod_mask()&event->state); //get state of modifier keys (alt, ctrl, shift, ..)
+        if(state == GDK_SHIFT_MASK) //shift is pressed  (and no other modifier keys), => change up/down to left/right
+        { 
+          if(event->button == 4) event->button=6;  
+          if(event->button == 5) event->button=7;
+        }
+        if(state==GDK_CONTROL_MASK) //ctrl is pressed (and no other modifier keys) => zoom in and out
+        {
+          if(event->button == 4)
+          {
+            on_viewZoomIn_activate(NULL,NULL);
+            return FALSE;
+          }
+          else if(event->button == 5)
+          {
+            on_viewZoomOut_activate(NULL,NULL);
+            return FALSE;
+          }
+        }
       /* with GTK+ 2.17 and later, the entire widget hierarchy is xinput-aware,
          so the core button event gets discarded and the scroll event never 
          gets processed by the main window. This is arguably a GTK+ bug.

phbr - 2021-01-24

Thanks for your work, I use your software almost every day.

I'm digging up this old request, but this feature would be really interesting to improve the user experience. I use v. 0.4.8.2016 on Kubuntu 20.04.

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Denis Auroux - 2021-01-24

I've added to the GIT repository a quick hack for this -- essentially equivalent to what was proposed by "sadf" above, except with a less steep zoom factor (1.1 instead of the zoom factor used by the toolbar and shortcuts). It still has the same limitations -- it only works with XInput enabled (hence likely not in the Windows version), it zooms around the center of the view rather than the position of the cursor, and there's a lot of visual tearing if you zoom in too far. Sorry -- it's a useful feature even when slightly broken, and I just don't have time to implement it better at the moment.

Denis

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#184 mouse wheel zoom

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