From 6563a5fe9ac6a34212cdcdc9767fd209fce91a6a Mon Sep 17 00:00:00 2001
From: uclaros <uclaros@gmail.com>
Date: Wed, 2 Nov 2016 15:53:09 +0200
Subject: [PATCH] Use Alt modifier to move camera center (center of rotation)
 up or down

---
 lib/Slic3r/GUI/3DScene.pm | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/lib/Slic3r/GUI/3DScene.pm b/lib/Slic3r/GUI/3DScene.pm
index 079008314c..9adf7db032 100644
--- a/lib/Slic3r/GUI/3DScene.pm
+++ b/lib/Slic3r/GUI/3DScene.pm
@@ -218,7 +218,16 @@ sub mouse_event {
         $self->_dragged(1);
         $self->Refresh;
     } elsif ($e->Dragging) {
-        if ($e->LeftIsDown) {
+        if ($e->AltDown) {
+            # Move the camera center on the Z axis based on mouse Y axis movement
+            if (defined $self->_drag_start_pos) {
+                my $orig = $self->_drag_start_pos;
+                $self->_camera_target->translate(0, 0, $pos->y - $orig->y);
+                $self->on_viewport_changed->() if $self->on_viewport_changed;
+                $self->Refresh;
+            }
+            $self->_drag_start_pos($pos);
+        } elsif ($e->LeftIsDown) {
             # if dragging over blank area with left button, rotate
             if (defined $self->_drag_start_pos) {
                 my $orig = $self->_drag_start_pos;