[gimp] app: in GimpCurveView, snap to curve when holding Ctrl

[Ell <ell src gnome org>]

commit 8357c9ad645b6ecff6882b39b828440ccfe004e6
Author: Ell <ell_se yahoo com>
Date:   Wed Apr 17 17:48:49 2019 -0400

    app: in GimpCurveView, snap to curve when holding Ctrl
    
    In GimpCurveView, when holding down Ctrl while adding/dragging a
    point, snap the y-coordinate to the original curve (at the start of
    the drag).  This is particularly useful for adding points along the
    curve, without changing their y-coordinate.
    
    Likewise, have the coordinate indicator show the snapped
    coordinate.

 app/widgets/gimpcurveview.c | 15 +++++++++++++++
 app/widgets/gimpcurveview.h |  1 +
 2 files changed, 16 insertions(+)
---
diff --git a/app/widgets/gimpcurveview.c b/app/widgets/gimpcurveview.c
index dae61ef934..ec42ebee21 100644
--- a/app/widgets/gimpcurveview.c
+++ b/app/widgets/gimpcurveview.c
@@ -243,6 +243,8 @@ gimp_curve_view_finalize (GObject *object)
 {
   GimpCurveView *view = GIMP_CURVE_VIEW (object);
 
+  g_clear_object (&view->orig_curve);
+
   g_clear_object (&view->layout);
   g_clear_object (&view->cursor_layout);
 
@@ -811,6 +813,8 @@ gimp_curve_view_button_press (GtkWidget      *widget,
 
   view->grabbed = TRUE;
 
+  view->orig_curve = GIMP_CURVE (gimp_data_duplicate (GIMP_DATA (curve)));
+
   set_cursor (view, GDK_TCROSS);
 
   switch (gimp_curve_get_curve_type (curve))
@@ -852,6 +856,9 @@ gimp_curve_view_button_press (GtkWidget      *widget,
         }
       else
         {
+          if (bevent->state & gimp_get_constrain_behavior_mask ())
+            y = 1.0 - gimp_curve_map_value (view->orig_curve, x);
+
           gimp_curve_set_point (curve, view->selected, x, 1.0 - y);
         }
       break;
@@ -879,6 +886,8 @@ gimp_curve_view_button_release (GtkWidget      *widget,
   if (bevent->button != 1)
     return TRUE;
 
+  g_clear_object (&view->orig_curve);
+
   view->offset_x = 0.0;
   view->offset_y = 0.0;
 
@@ -942,12 +951,18 @@ gimp_curve_view_motion_notify (GtkWidget      *widget,
           else
             {
               new_cursor = GDK_TCROSS;
+
+              if (mevent->state & gimp_get_constrain_behavior_mask ())
+                y = 1.0 - gimp_curve_map_value (view->curve, x);
             }
         }
       else /*  Else, drag the grabbed point  */
         {
           new_cursor = GDK_TCROSS;
 
+          if (mevent->state & gimp_get_constrain_behavior_mask ())
+            y = 1.0 - gimp_curve_map_value (view->orig_curve, x);
+
           gimp_data_freeze (GIMP_DATA (curve));
 
           gimp_curve_set_point (curve, view->selected, -1.0, -1.0);
diff --git a/app/widgets/gimpcurveview.h b/app/widgets/gimpcurveview.h
index 49b43ebba6..b41358441e 100644
--- a/app/widgets/gimpcurveview.h
+++ b/app/widgets/gimpcurveview.h
@@ -55,6 +55,7 @@ struct _GimpCurveView
   gdouble            leftmost;
   gdouble            rightmost;
   gboolean           grabbed;
+  GimpCurve         *orig_curve;
 
   GdkCursorType      cursor_type;