From d40f0be188b927edf4431769073a86fb2ce16b84 Mon Sep 17 00:00:00 2001
From: Antonio Ospite <ao2@ao2.it>
Date: Sat, 16 Jul 2016 15:45:10 +0200
Subject: [PATCH] Show a control point for the center of an ellipse

Ellipses in Inkscape are defined by the center and the radius, but the
user cannot easily control the position of the center.

Show a control point for the center so it's easier to move the shape
around and snap it by its center.

https://bugs.launchpad.net/inkscape/+bug/481506
---
 src/ui/object-edit.cpp | 36 ++++++++++++++++++++++++++++++++++++
 1 file changed, 36 insertions(+)

diff --git a/src/ui/object-edit.cpp b/src/ui/object-edit.cpp
index b11a61710..b76e97c15 100644
--- a/src/ui/object-edit.cpp
+++ b/src/ui/object-edit.cpp
@@ -782,6 +782,12 @@ public:
     virtual void knot_click(unsigned int state);
 };
 
+class ArcKnotHolderEntityCenter : public KnotHolderEntity {
+public:
+    virtual Geom::Point knot_get() const;
+    virtual void knot_set(Geom::Point const &p, Geom::Point const &origin, unsigned int state);
+};
+
 /*
  * return values:
  *   1  : inside
@@ -983,6 +989,30 @@ ArcKnotHolderEntityRY::knot_click(unsigned int state)
     }
 }
 
+void
+ArcKnotHolderEntityCenter::knot_set(Geom::Point const &p, Geom::Point const &/*origin*/, unsigned int state)
+{
+    SPGenericEllipse *ge = dynamic_cast<SPGenericEllipse *>(item);
+    g_assert(ge != NULL);
+
+    Geom::Point const s = snap_knot_position(p, state);
+
+    ge->cx = s[Geom::X];
+    ge->cy = s[Geom::Y];
+
+    item->requestDisplayUpdate(SP_OBJECT_MODIFIED_FLAG);
+}
+
+Geom::Point
+ArcKnotHolderEntityCenter::knot_get() const
+{
+    SPGenericEllipse const *ge = dynamic_cast<SPGenericEllipse *>(item);
+    g_assert(ge != NULL);
+
+    return Geom::Point(ge->cx.computed, ge->cy.computed);
+}
+
+
 ArcKnotHolder::ArcKnotHolder(SPDesktop *desktop, SPItem *item, SPKnotHolderReleasedFunc relhandler) :
     KnotHolder(desktop, item, relhandler)
 {
@@ -990,6 +1020,7 @@ ArcKnotHolder::ArcKnotHolder(SPDesktop *desktop, SPItem *item, SPKnotHolderRelea
     ArcKnotHolderEntityRY *entity_ry = new ArcKnotHolderEntityRY();
     ArcKnotHolderEntityStart *entity_start = new ArcKnotHolderEntityStart();
     ArcKnotHolderEntityEnd *entity_end = new ArcKnotHolderEntityEnd();
+    ArcKnotHolderEntityCenter *entity_center = new ArcKnotHolderEntityCenter();
 
     entity_rx->create(desktop, item, this, Inkscape::CTRL_TYPE_SIZER,
                       _("Adjust ellipse <b>width</b>, with <b>Ctrl</b> to make circle"),
@@ -1011,10 +1042,15 @@ ArcKnotHolder::ArcKnotHolder(SPDesktop *desktop, SPItem *item, SPKnotHolderRelea
                          "ellipse for arc, <b>outside</b> for segment"),
                        SP_KNOT_SHAPE_CIRCLE, SP_KNOT_MODE_XOR);
 
+    entity_center->create(desktop, item, this, Inkscape::CTRL_TYPE_POINT,
+                          _("Move the ellipse"),
+                          SP_KNOT_SHAPE_CROSS);
+
     entity.push_back(entity_rx);
     entity.push_back(entity_ry);
     entity.push_back(entity_start);
     entity.push_back(entity_end);
+    entity.push_back(entity_center);
 
     add_pattern_knotholder();
 }
-- 
2.11.0