[dia] Zooming per area works more consistently

[Hans Breuer <hans src gnome org>]

commit 9a5a4f7b78122ddf31809752a0fded247d7ed745
Author: Hans Breuer <hans breuer org>
Date:   Wed Oct 20 21:00:37 2010 +0200

    Zooming per area works more consistently
    
    the whole zoom rectangle should be visible, not just it's square equivalent

 app/magnify.c |    5 ++++-
 1 files changed, 4 insertions(+), 1 deletions(-)
---
diff --git a/app/magnify.c b/app/magnify.c
index 26f1f40..8827829 100644
--- a/app/magnify.c
+++ b/app/magnify.c
@@ -63,7 +63,10 @@ magnify_button_release(MagnifyTool *tool, GdkEventButton *event,
       ddisplay_add_update_all(ddisp);
       ddisplay_flush(ddisp);
     } else if (!(event->state & GDK_CONTROL_MASK)) {
-      factor = (visible->right - visible->left) / diff;
+      /* the whole zoom rect should be visible, not just it's square equivalent */
+      real fh = fabs(p2.y - p1.y) / (visible->bottom - visible->top);
+      real fw = fabs(p2.x - p1.x) / (visible->right - visible->left);
+      factor = 1.0 / MAX(fh, fw);
       tl.x += (visible->right - visible->left)/(2.0*factor);
       tl.y += (visible->bottom - visible->top)/(2.0*factor);
       ddisplay_zoom(ddisp, &tl, factor);