libgtkflow/libgtkflow3/nodeview.vala

/********************************************************************
# Copyright 2014-2022 Daniel 'grindhold' Brendle
#
# This file is part of libgtkflow.
#
# libgtkflow is free software: you can redistribute it and/or
# modify it under the terms of the GNU Lesser General Public License
# as published by the Free Software Foundation, either
# version 3 of the License, or (at your option) any later
# version.
#
# libgtkflow is distributed in the hope that it will be
# useful, but WITHOUT ANY WARRANTY; without even the implied
# warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR
# PURPOSE. See the GNU Lesser General Public License for more details.
#
# You should have received a copy of the GNU Lesser General Public
# License along with libgtkflow.
# If not, see http://www.gnu.org/licenses/.
*********************************************************************/

namespace GtkFlow {
    /**
     * A Gtk Widget that shows nodes and their connections to the user
     * It also lets the user edit said connections.
     */
    public class NodeView : Gtk.Container {
        private List<Node> nodes = new List<Node>();

        // The node that is currently being dragged around
        private const int DRAG_THRESHOLD = 3;
        private Node? drag_node = null;
        private bool drag_threshold_fulfilled = false;
        // Coordinates where the drag started
        private double drag_start_x = 0;
        private double drag_start_y = 0;
        // Difference from the chosen drag-point to the
        // upper left corner of the drag_node
        private int drag_diff_x = 0;
        private int drag_diff_y = 0;

        // Remember if a closebutton was pressed
        private bool close_button_pressed = false;
        // Remember if we are resizing a node
        private Node? resize_node = null;
        private int resize_start_x = 0;
        private int resize_start_y = 0;

        // Remember positions of rubberband
        private Gtk.Allocation? rubber_alloc = null;
        private int rubber_start_x = 0;
        private int rubber_start_y = 0;

        // Remember the last dock the mouse hovered over, so we can unhighlight it
        private GFlow.Dock? hovered_dock = null;

        // The dock that we are targeting for dragging a new connector
        private GFlow.Dock? drag_dock = null;
        // The dock that we are targeting to drop a connector on
        private GFlow.Dock? drop_dock = null;
        // The connector that is being used to draw a non-established connection
        private Gtk.Allocation? temp_connector = null;

        /**
         * Connect to this signal if you wish to set custom colors for the
         * connectors depending on what values they transport. Whenever
         * the value of a connected {@link GFlow.Source} changes, this
         * signal will be emitted. Return the color you desire as hex-string
         * similar to those used in css without the preceding hash ('#').
         * Example:  red would be "ff0000"
         */
        public virtual signal string color_calculation(GLib.Value v) {
            return this.default_connector_color;
        }

        /**
         * Determines whether docks should be rendered with type-indicators
         */
        public bool show_types {
            get {
                return this._show_types;
            }
            set {
                this._show_types = value;
                this.render_all();
            }
        }
        private bool _show_types = false;

        /**
         * Determines whether the displayed Nodes can be edited by the user
         * e.g. alter their positions by dragging and dropping or drawing
         * new collections or erasing old ones
         */
        public bool editable {get; set; default=true;}

        /**
         * If this property is set to true, the nodeview will not perform
         * any check wheter newly created connections will result in cycles
         * in the graph. It's completely up to the application programmer
         * to make sure that the logic inside the nodes he uses avoids
         * endlessly backpropagated loops
         */
        public bool allow_recursion {get; set; default=false;}

        /**
         * A string that is displayed at the center of the NodeView
         * When no nodes are displayed. You can use it to e.g display
         * a text that encourages the user to spawn nodes.
         */
        public string placeholder {get; set; default="";}
        private Pango.Layout placeholder_layout;

        /**
         * Used to store fg color at iniialization as getting this on the
         * fly has lead to endless-loop-problems.
         */
        private string default_connector_color = "000000";

        /**
         * Creates a new empty {@link NodeView}
         */
        public NodeView() {
            Object();

            this.placeholder_layout = (new Gtk.Label("")).create_pango_layout("");
            this.notify["placeholder"].connect(()=>{
                this.placeholder_layout.set_markup(this.placeholder, -1);
                this.queue_draw();
            });

            this.set_size_request(100,100);
            this.draw.connect((cr)=>{ return this.do_draw(cr); });
            this.motion_notify_event.connect((e)=>{ return this.do_motion_notify_event(e); });
            this.button_press_event.connect((e)=>{ return this.do_button_press_event(e); });
            this.button_release_event.connect((e)=>{ return this.do_button_release_event(e); });

            Gtk.StyleContext sc = this.get_style_context();
            Gdk.RGBA fg = sc.get_color(Gtk.StateFlags.NORMAL);
            this.default_connector_color = "%2x%2x%2x".printf(col_f2h(fg.red), col_f2h(fg.green), col_f2h(fg.blue));
        }

        public signal void node_added(GFlow.Node n);

        private void add_common(Node n) {
            if (this.nodes.index(n) == -1) {
                this.nodes.insert(n,0);
                n.node_view = this;
            }
            this.queue_draw();
            n.set_parent(this);
        }

        private void render_all() {
            foreach (Node n in this.nodes)
                n.render_all();
            this.queue_draw();
        }

        /**
         * This methods adds a {@link GFlow.Node} to this NodeView
         */
        public void add_node(GFlow.Node gn, Gtk.Widget? title=null) {
            Node n = new Node.with_child(gn, new Gtk.Box(Gtk.Orientation.VERTICAL,0), title);
            n.set_allocation({1,1,0,0});
            this.add_common(n);
            node_added(gn);
        }

        /**
         * This method adds a {@link GFlow.Node} to this nodeview and
         * assigns an arbitrary {@link Gtk.Widget} as its child.
         */
        public void add_with_child(GFlow.Node gn, Gtk.Widget child, Gtk.Widget? title=null) {
            Node n = new Node.with_child(gn, child, title);
            this.add_common(n);
            node_added(gn);
        }

        /**
         * This tells the NodeView to use another {@link NodeRenderer} than
         * the DefaultNodeRenderer for the given {@link GFlow.Node}
         *
         * If you want to use one of libgtkflow's internal node renderers,
         * you can just pass the parameter nrt with one of the values in
         * {@link GtkFlow.NodeRendererType}. If you want to place a custom
         * renderer, set nrt to {@link GtkFlow.NodeRendererType.CUSTOM} and
         * pass the instance of your custom node renderer to the third parameter
         * called nr.
         */
        public void set_node_renderer(GFlow.Node gn, NodeRendererType nrt, NodeRenderer? nr=null) throws GFlow.NodeError, NodeRendererError {
            Node n = this.get_node_from_gflow_node(gn);
            switch (nrt) {
                case NodeRendererType.DOCKLINE:
                    n.node_renderer = new DocklineNodeRenderer(n);
                    break;
                case NodeRendererType.DEFAULT:
                    n.node_renderer = new DefaultNodeRenderer(n);
                    break;
                case NodeRendererType.CUSTOM:
                    if (nr == null) {
                        throw new NodeRendererError.NO_CUSTOM_NODE_RENDERER("You must pass a valid node renderer, not null");
                    }
                    n.node_renderer = nr;
                    break;
                default:
                    throw new NodeRendererError.NOT_A_NODE_RENDERER("This is not a valid node renderer");
            }
            this.queue_draw();
        }

        /**
         * Use this method to register childwidgets for custom node
         * renderes to the supplied {@link GFlow.Node}
         */
        public void register_child(GFlow.Node gn, Gtk.Widget child) {
            Node n = this.get_node_from_gflow_node(gn);
            if (n != null) {
                n.add(child);
                n.show_all();
            }
        }

        /**
         * Use this method to unregister childwidgets from the supplied
         * {@link GFlow.Node}
         */
        public void unregister_child(GFlow.Node gn, Gtk.Widget child) {
            Node n = this.get_node_from_gflow_node(gn);
            if (n != null) {
                n.remove(child);
            }
        }

        internal Node? get_node_from_gflow_node(GFlow.Node gn) {
            foreach (Node n in this.nodes) {
                if (n.gnode == gn) {
                    return n;
                }
            }
            return null;
        }

        /**
         * Autolayout this graph
         */
        public void layout(Layout l) {
            var passnodes = this.nodes.copy();
            l.arrange(passnodes);
        }

        /**
         * Used by {@link GtkFlow.Minimap} to get info about nodes.
         */
        internal unowned List<Node> get_nodes(){
            return this.nodes;
        }

        /**
         * Returns nodes that reside inside the given rectangle
         */
        private List<Node> get_nodes_in_rect(Gtk.Allocation alloc) {
            var result = new List<Node>();
            Gdk.Rectangle res;
            Gtk.Allocation node_alloc;
            foreach (Node n in this.nodes) {
                n.get_allocation(out node_alloc);
                node_alloc.union(alloc, out res);
                if (alloc.equal(res)) {
                    result.append(n);
                }
            }
            return result;
        }

        /**
         * This signal is being triggered when a node is
         * being removed from this NodeView
         */
        public signal void node_removed(GFlow.Node n);

        /**
         * Remove a {@link GFlow.Node}  from this NodeView
         */
        public void remove_node(GFlow.Node n) {
            n.unlink_all();
            Node gn = this.get_node_from_gflow_node(n);
            gn.forall_internal(true, (c)=>{c.destroy();});
            if (this.nodes.index(gn) != -1) {
                this.nodes.remove(gn);
                gn.node_view = null;
                assert (gn is Gtk.Widget);
                ((Gtk.Widget)gn).destroy();
                this.node_removed(n);
                this.queue_draw();
            }
        }

        private Node? get_node_on_position(double x,double y) {
            Gtk.Allocation alloc;
            foreach (Node n in this.nodes) {
                n.get_allocation(out alloc);
                if ( x >= alloc.x && y >= alloc.y &&
                         x <= alloc.x + alloc.width && y <= alloc.y + alloc.height ) {
                    return n;
                }
            }
            return null;
        }

        private bool do_button_press_event(Gdk.EventButton e) {
            if (   e.type == Gdk.EventType.@2BUTTON_PRESS
                || e.type == Gdk.EventType.@3BUTTON_PRESS)
                return false;
            if (!this.editable)
                return false;
            Node? n = this.get_node_on_position(e.x, e.y);
            GFlow.Dock? targeted_dock = null;
            Gdk.Point pos = {(int)e.x,(int)e.y};
            if (n != null) {
                if (!n.selected) {
                    this.unselect_all();
                }
                Gtk.Allocation alloc;
                n.get_allocation(out alloc);
                bool cbp = n.gnode.deletable && n.node_renderer.is_on_closebutton(
                    pos, alloc,
                    n.border_width
                );
                if (cbp) {
                    this.close_button_pressed = true;
                    this.unselect_all();
                }
                targeted_dock = n.node_renderer.get_dock_on_position(
                    pos, n.get_dock_renderers(),
                    n.border_width, alloc, n.title
                );
                if (targeted_dock != null) {
                    this.drag_dock = targeted_dock;
                    this.drag_dock.active = true;
                    int startpos_x = 0, startpos_y = 0;
                    if (this.drag_dock is GFlow.Sink && this.drag_dock.is_linked()){
                        GFlow.Source s = ((GFlow.Sink)this.drag_dock).sources.last().nth_data(0);
                        Node srcnode = this.get_node_from_gflow_node(s.node);
                        Gtk.Allocation src_alloc;
                        srcnode.get_allocation(out src_alloc);
                        if (!srcnode.node_renderer.get_dock_position(
                                s, srcnode.get_dock_renderers(),
                                (int)srcnode.border_width, src_alloc,
                                out startpos_x, out startpos_y,
                                srcnode.title )) {
                            warning("No dock on position. Aborting drag");
                            return false;
                        }
                        Gdk.Point startpos = {startpos_x,startpos_y};
                        this.temp_connector = {startpos.x, startpos.y,
                                               (int)e.x-startpos.x, (int)e.y-startpos.y};
                    } else {
                        if (!n.node_renderer.get_dock_position(
                                this.drag_dock, n.get_dock_renderers(),
                                (int)n.border_width, alloc,
                                out startpos_x, out startpos_y,
                                n.title )) {
                            warning("No dock on position. Aborting drag");
                            return false;
                        }
                        Gdk.Point startpos = {startpos_x,startpos_y};
                        this.temp_connector = {startpos.x, startpos.y, 0, 0};
                    }
                    this.queue_draw();
                    return true;
                }
            }
            // Set a new drag node.
            if (n != null) {
                Gtk.Allocation alloc;
                n.get_allocation(out alloc);
                bool on_resize = n.gnode.resizable && n.node_renderer.is_on_resize_handle(
                    pos, alloc,
                    n.border_width
                );

                if (on_resize && this.resize_node == null) {
                    this.resize_node = n;
                    this.resize_node.get_allocation(out alloc);
                    if ((this.get_style_context().get_state() & Gtk.StateFlags.DIR_LTR) > 0) {
                        this.resize_start_x = alloc.width;
                        this.resize_start_y = alloc.height;
                    } else {
                        this.resize_start_x = 0;
                        this.resize_start_y = alloc.height;
                    }
                } else if (this.resize_node == null && this.drag_node == null) {
                    this.drag_node = n;
                    this.drag_node.get_allocation(out alloc);
                } else {
                    return false;
                }
                this.drag_start_x = e.x;
                this.drag_start_y = e.y;
                this.drag_diff_x = (int)this.drag_start_x - alloc.x;
                this.drag_diff_y = (int)this.drag_start_y - alloc.y;
            } else {
                this.unselect_all();
                this.rubber_alloc = {(int)e.x, (int)e.y, 0, 0};
                this.rubber_start_x = (int)e.x;
                this.rubber_start_y = (int)e.y;
            }
            return false;
        }

        /**
         * Every currently selected node is being unselected
         */
        public void unselect_all() {
            foreach (Node n in this.nodes) {
                n.selected = false;
            }
            this.queue_draw();
        }

        private List<Node> get_selected_nodes() {
            var result = new List<Node>();
            foreach (Node n in this.nodes) {
                if (n.selected)
                    result.append(n);
            }
            return result;
        }

        /**
         * Returns each {@link GFlow.Node} that is currently selected
         */
        public List<GFlow.Node> get_selected() {
            var result = new List<GFlow.Node>();
            foreach (Node n in this.nodes) {
                if (n.selected)
                    result.append(n.gnode);
            }
            return result;
        }

        //Empty remove implementation to avoid warning message
        /**
         * Empty default implementation. Do not use. To remove {@link GFlow.Node}s
         * from a NodeView please use {@link NodeView.remove_node}
         */
        public override void remove(Gtk.Widget w) {}

        private bool do_button_release_event(Gdk.EventButton e) {
            if (!this.editable)
                return false;
            // Determine if this was a closebutton press
            if (this.close_button_pressed) {
                Node? n = this.get_node_on_position(e.x, e.y);
                if (n != null) {
                    Gdk.Point pos = {(int)e.x,(int)e.y};
                    Gtk.Allocation alloc;
                    n.get_allocation(out alloc);
                    bool cbp = n.node_renderer.is_on_closebutton(
                        pos, alloc,
                        n.border_width
                    );
                    if (cbp) {
                        this.remove_node(n.gnode);
                        this.close_button_pressed = false;
                        return true;
                    }
                }
            }
            // Try to build a new connection
            if (this.drag_dock != null) {
                try {
                    if (this.drag_dock is GFlow.Source && this.drop_dock is GFlow.Sink) {
                        ((GFlow.Source)this.drag_dock).link(this.drop_dock as GFlow.Sink);
                    }
                    else if (this.drag_dock is GFlow.Sink && this.drop_dock is GFlow.Source) {
                        ((GFlow.Source)this.drop_dock).link(this.drag_dock as GFlow.Sink);
                    }
                    else if (this.drag_dock is GFlow.Sink && this.drop_dock is GFlow.Sink) {
                        GFlow.Source? src = ((GFlow.Sink)this.drag_dock).sources.last().nth_data(0);
                        if (src != null) {
                            src.unlink(this.drag_dock as GFlow.Sink);
                            src.link(this.drop_dock as GFlow.Sink);
                        }
                    }
                    else if (this.drag_dock is GFlow.Sink && this.drop_dock == null) {
                        GFlow.Source? src = ((GFlow.Sink)this.drag_dock).sources.last().nth_data(0);
                        if (src != null) {
                            src.unlink((GFlow.Sink)this.drag_dock);
                        }
                    }
                } catch (GLib.Error e) {
                    warning(e.message);
                }
            }
            this.stop_dragging();
            this.queue_draw();
            return false;
        }

        private void stop_dragging() {
            this.drag_start_x = 0;
            this.drag_start_y = 0;

            this.drag_diff_x = 0;
            this.drag_diff_y = 0;

            this.rubber_alloc = null;

            this.drag_node = null;
            if (this.drag_dock != null) {
                this.drag_dock.active = false;
            }
            this.drag_dock = null;
            if (this.drop_dock != null) {
                this.drop_dock.active = false;
            }
            this.drop_dock = null;
            this.temp_connector = null;
            this.drag_threshold_fulfilled = false;
            this.resize_node = null;
            this.get_window().set_cursor(null);
        }

        private Gdk.Cursor resize_cursor = null;
        private Gdk.Cursor? get_resize_cursor() {
            if (resize_cursor == null && this.get_realized()) {
                if ((this.get_style_context().get_state() & Gtk.StateFlags.DIR_LTR) > 0 ){
                    resize_cursor = new Gdk.Cursor.for_display(
                        this.get_window().get_display(),
                        Gdk.CursorType.BOTTOM_RIGHT_CORNER
                    );
                } else {
                    resize_cursor = new Gdk.Cursor.for_display(
                        this.get_window().get_display(),
                        Gdk.CursorType.BOTTOM_LEFT_CORNER
                    );
                }
            }
            return resize_cursor;
        }

        private bool do_motion_notify_event(Gdk.EventMotion e) {
            if (!this.editable)
                return false;
            // Check if we are on a node. If yes, check if we are
            // currently pointing on a dock. if this is true, we
            // Want to draw a new connector instead of dragging the node
            Node? n = this.get_node_on_position(e.x, e.y);
            GFlow.Dock? targeted_dock = null;
            if (n != null) {
                Gdk.Point pos = {(int)e.x, (int)e.y};
                Gtk.Allocation alloc;
                n.get_allocation(out alloc);
                // If the close button is pressed, deactivate it when
                // we moved the node
                if (this.close_button_pressed) {
                    bool cbp = n.node_renderer.is_on_closebutton(
                        pos, alloc,
                        n.border_width
                    );
                    if (!cbp)
                        this.close_button_pressed = false;
                }
                // Update cursor if we are on the resize area
                bool on_resize = n.gnode.resizable && n.node_renderer.is_on_resize_handle(
                    pos, alloc,
                    n.border_width
                );
                if (on_resize)
                    this.get_window().set_cursor(this.get_resize_cursor());
                else if (this.resize_node == null)
                    this.get_window().set_cursor(null);
                targeted_dock = n.node_renderer.get_dock_on_position(
                    pos, n.get_dock_renderers(),
                    n.border_width, alloc, n.title
                );
                if (this.drag_dock == null && targeted_dock != this.hovered_dock) {
                    this.set_hovered_dock(targeted_dock);
                }
                else if (this.drag_dock != null && targeted_dock != null
                      && targeted_dock != this.hovered_dock
                      && this.is_suitable_target(this.drag_dock, targeted_dock)) {
                    this.set_hovered_dock(targeted_dock);
                }
            } else {
                // If we are leaving the node we will also have to
                // un-highlight the last hovered dock
                if (this.hovered_dock != null)
                    this.hovered_dock.highlight = false;
                this.hovered_dock = null;
                this.queue_draw();
                // Update cursor to be default as we are guaranteed not on any
                // resize handle outside of any node.
                // The check for resize node is a cosmetical fix. If there is a
                // Node bing resized in haste, the cursor tends to flicker
                if (this.resize_node == null)
                    this.get_window().set_cursor(null);
            }

            // Check if the cursor has been dragged a few pixels (defined by DRAG_THRESHOLD)
            // If yes, actually start dragging
            if ( ( this.drag_node != null || this.drag_dock != null || this.resize_node != null)
                    && (Math.fabs(drag_start_x - e.x) > NodeView.DRAG_THRESHOLD
                    ||  Math.fabs(drag_start_y - e.y) > NodeView.DRAG_THRESHOLD )) {
                this.drag_threshold_fulfilled = true;
            }

            // Actually something
            if (this.drag_threshold_fulfilled ) {
                Gtk.Allocation alloc;
                if (this.drag_node != null) {
                    // Actually move the node(s)
                    var nodes_to_drag = this.get_selected_nodes();
                    Gtk.Allocation drag_node_alloc;
                    this.drag_node.get_allocation(out drag_node_alloc);
                    if (nodes_to_drag.length() == 0) {
                        nodes_to_drag.append(this.drag_node);
                    }
                    Gtk.Allocation union = {0,0,0,0};
                    bool first = true;
                    Gdk.Point upperleft = {int.MAX,int.MAX};
                    foreach (Node node in nodes_to_drag) {
                        node.get_allocation(out alloc);
                        upperleft.x = (int)Math.fmin(alloc.x, upperleft.x);
                        upperleft.y = (int)Math.fmin(alloc.y, upperleft.y);
                        alloc.x = (int)Math.fmax(0,(int)e.x - this.drag_diff_x);
                        alloc.y = (int)Math.fmax(0,(int)e.y - this.drag_diff_y);

                        if (first) {
                            union = alloc;
                        } else {
                            Gdk.Rectangle tmp;
                            union.union(alloc, out tmp);
                            union = (Gtk.Allocation)tmp;
                        }
                    }
                    foreach (Node node in nodes_to_drag) {
                        node.get_allocation(out alloc);
                        int dn_diff_x = alloc.x - drag_node_alloc.x;
                        int dn_diff_y = alloc.y - drag_node_alloc.y;
                        int ul_diff_x = alloc.x - upperleft.x;
                        int ul_diff_y = alloc.y - upperleft.y;
                        alloc.x = (int)Math.fmax(ul_diff_x,(int)e.x - this.drag_diff_x + dn_diff_x);
                        alloc.y = (int)Math.fmax(ul_diff_y,(int)e.y - this.drag_diff_y + dn_diff_y);
                        node.size_allocate(alloc);
                    }
                }
                if (this.drag_dock != null) {
                    // Manipulate the temporary connector
                    this.temp_connector.width = (int)e.x-this.temp_connector.x;
                    this.temp_connector.height = (int)e.y-this.temp_connector.y;
                    if (targeted_dock == null) {
                        this.set_drop_dock(null);
                    }
                    else if (this.is_suitable_target(this.drag_dock, targeted_dock))
                        this.set_drop_dock(targeted_dock);

                }
                if (this.resize_node != null) {
                    // resize the node
                    this.resize_node.get_allocation(out alloc);
                    if ((this.get_style_context().get_state() & Gtk.StateFlags.DIR_LTR) > 0 ){
                        alloc.width =  resize_start_x + (int)e.x - (int)this.drag_start_x;
                        alloc.height = resize_start_y + (int)e.y - (int)this.drag_start_y;
                    } else {
                        //FIXME: far from perfect. strange behaviour when resizing
                        alloc.x = (int)e.x;
                        alloc.width = alloc.width + ((int)this.drag_start_x - (int)e.x);
                        alloc.height = resize_start_y + (int)e.y - (int)this.drag_start_y;
                    }
                    this.resize_node.size_allocate(alloc);
                }
                this.allocate_minimum();
                this.queue_draw();
            }
            if (this.rubber_alloc != null) {
                if (e.x >= this.rubber_start_x) {
                    this.rubber_alloc.x = (int)this.rubber_start_x;
                    this.rubber_alloc.width = (int)e.x - this.rubber_alloc.x;
                } else {
                    this.rubber_alloc.x = (int)e.x;
                    this.rubber_alloc.width = this.rubber_start_x - (int)e.x;
                }
                if (e.y >= this.rubber_start_y) {
                    this.rubber_alloc.y = (int)this.rubber_start_y;
                    this.rubber_alloc.height = (int)e.y - this.rubber_alloc.y;
                } else {
                    this.rubber_alloc.y = (int)e.y;
                    this.rubber_alloc.height = this.rubber_start_y - (int)e.y;
                }
                var selected_nodes = this.get_nodes_in_rect(this.rubber_alloc);
                foreach (Node node in this.nodes) {
                    node.selected = selected_nodes.index(node) != -1;
                }
                this.allocate_minimum();
                this.queue_draw();
            }
            return false;

        }

        /**
         * Allocates the minimum size needed to draw the
         * contained nodes at their respective positions
         * with their respective sizes to this NodeView
         * If the minimunsize is smaller than the containing
         * parent (which ideally should be a scrolledwindow
         * scrolledwindow) the parent's size will be allocated
         * in order to prevent the nodeview from collapsing
         * to a size of 0x0 px thus being inable to receive
         * mouse-events
         */
        private void allocate_minimum() {
            int minwidth = 0, minheight = 0, _ = 0;
            this.get_preferred_width(out minwidth, out _);
            this.get_preferred_height(out minheight, out _);
            this.set_size_request(minwidth, minheight);
            Gtk.Allocation nv_alloc;
            this.get_allocation(out nv_alloc);
            nv_alloc.width = minwidth;
            nv_alloc.height = minheight;

            if (this.parent != null) {
                Gtk.Allocation palloc;
                this.parent.get_allocation(out palloc);
                nv_alloc.width = int.max(minwidth, palloc.width);
                nv_alloc.height = int.max(minheight, palloc.height);
            }

            this.size_allocate(nv_alloc);
        }

        /**
         * Calculates the NodeView's minimum and preferred widths
         */
        public new void get_preferred_width(out int minimum_width, out int natural_width) {
            double x_min = 0, x_max = 0;
            Gtk.Allocation alloc;
            foreach (Node n in this.nodes) {
                n.get_allocation(out alloc);
                x_min = Math.fmin(x_min, alloc.x);
                x_max = Math.fmax(x_max, alloc.x+alloc.width);
            }
            if (this.rubber_alloc != null) {
                x_min = Math.fmin(x_min, rubber_alloc.x);
                x_max = Math.fmax(x_max, rubber_alloc.x + rubber_alloc.width);
            }
            if (this.temp_connector != null) {
                x_min = Math.fmin(x_min, temp_connector.x);
                x_max = Math.fmax(x_max, temp_connector.x + temp_connector.width);
            }
            x_min = Math.fmax(0, x_min);
            minimum_width = natural_width = (int)x_max - (int)x_min;
        }

        /**
         * Calculates the NodeView's minimum and preferred heights
         */
        public new void get_preferred_height(out int minimum_height, out int natural_height) {
            double y_min = 0, y_max = 0;
            Gtk.Allocation alloc;
            foreach (Node n in this.nodes) {
                n.get_allocation(out alloc);
                y_min = Math.fmin(y_min, alloc.y);
                y_max = Math.fmax(y_max, alloc.y+alloc.height);
            }
            if (this.rubber_alloc != null) {
                y_min = Math.fmin(y_min, rubber_alloc.y);
                y_max = Math.fmax(y_max, rubber_alloc.y + rubber_alloc.height);
            }
            if (this.temp_connector != null) {
                y_min = Math.fmin(y_min, temp_connector.y);
                y_max = Math.fmax(y_max, temp_connector.y + temp_connector.height);
            }
            y_min = Math.fmax(0, y_min);
            minimum_height = natural_height = (int)y_max - (int)y_min;
        }

        /**
         * Determines wheter one dock can be dropped on another
         */
        private bool is_suitable_target (GFlow.Dock from, GFlow.Dock to) {
            // Check whether the docks have the same type
            if (!from.has_same_type(to))
                return false;
            // Check if the target would lead to a recursion
            // If yes, return the value of allow_recursion. If this
            // value is set to true, it's completely fine to have
            // a recursive graph
            if (to is GFlow.Source && from is GFlow.Sink) {
                if (!this.allow_recursion)
                    if (from.node.is_recursive_forward(to.node) ||
                           to.node.is_recursive_backward(from.node))
                        return false;
            }
            if (to is GFlow.Sink && from is GFlow.Source) {
                if (!this.allow_recursion)
                    if (to.node.is_recursive_forward(from.node) ||
                           from.node.is_recursive_backward(to.node))
                        return false;
            }
            if (to is GFlow.Sink && from is GFlow.Sink) {
                GFlow.Source? s = ((GFlow.Sink)from).sources.last().nth_data(0);
                if (s == null)
                    return false;
                if (!this.allow_recursion)
                    if (to.node.is_recursive_forward(s.node) ||
                           s.node.is_recursive_backward(to.node))
                        return false;
            }
            // If the from from-target is a sink, check if the
            // to target is either a source which does not belong to the own node
            // or if the to target is another sink (this is valid as we can
            // move a connection from one sink to another
            if (from is GFlow.Sink
                    && ((to is GFlow.Sink
                    && to != from)
                    || (to is GFlow.Source
                    && (!to.node.has_dock(from) || this.allow_recursion)))) {
                return true;
            }
            // Check if the from-target is a source. if yes, make sure the
            // to-target is a sink and it does not belong to the own node
            else if (from is GFlow.Source
                    && to is GFlow.Sink
                    && (!to.node.has_dock(from) || this.allow_recursion)) {
                return true;
            }
            return false;
        }

        /**
         * Sets the dock that is currently being hovered over to drop
         * a connector on
         */
        private void set_drop_dock(GFlow.Dock? d) {
            if (this.drop_dock != null)
                this.drop_dock.active = false;
            this.drop_dock = d;
            if (this.drop_dock != null)
                this.drop_dock.active = true;
            this.queue_draw();
        }

        /**
         * Sets the dock that is currently being hovered over
         */
        private void set_hovered_dock(GFlow.Dock? d) {
            if (this.hovered_dock != null)
                this.hovered_dock.highlight = false;
            this.hovered_dock = d;
            if (this.hovered_dock != null)
                this.hovered_dock.highlight = true;
            this.queue_draw();
        }

        /**
         * Manually set the position of the given {@link GFlow.Node} on this nodeview
         */
        public void set_node_position(GFlow.Node gn, int x, int y) {
            Node n = this.get_node_from_gflow_node(gn);
            n.set_position(x,y);
            this.allocate_minimum();
            this.queue_draw();
        }

        /**
         * Manually set the allocation of the given {@link GFlow.Node} on this nodeview
         */
        public void set_node_allocation(GFlow.Node gn, Gtk.Allocation alloc) {
            Node n = this.get_node_from_gflow_node(gn);
            n.set_allocation(alloc);
            this.allocate_minimum();
            this.queue_draw();
        }

        /**
         * Return the position of the given {@link GFlow.Node} on this nodeview
         */
        public unowned Gdk.Point get_node_position(GFlow.Node gn) {
            Node n = this.get_node_from_gflow_node(gn);
            return n.get_position();
        }

        /**
         * Returns the allocation of the given {@link GFlow.Node}
         */
        public unowned Gtk.Allocation get_node_allocation(GFlow.Node gn) {
            Gtk.Allocation alloc;
            Node n = this.get_node_from_gflow_node(gn);
            n.get_allocation(out alloc);
            return alloc;
        }

        private bool do_draw(Cairo.Context cr) {
            Gtk.StyleContext sc = this.get_style_context();
            Gtk.Allocation nv_alloc;
            this.get_allocation(out nv_alloc);
            sc.render_background(cr, 0, 0, nv_alloc.width, nv_alloc.height);

            // Draw nodes
            this.nodes.reverse();
            foreach (Node n in this.nodes) {
                n.current_cairo_ctx = cr;
                Gtk.Allocation alloc;
                n.get_allocation(out alloc);
                var node_properties = NodeProperties();
                node_properties.editable = this.editable;
                node_properties.deletable = n.gnode.deletable;
                node_properties.resizable = n.gnode.resizable;
                node_properties.selected = n.selected;

                n.node_renderer.draw_node(
                    this,
                    cr,
                    alloc,
                    n.get_dock_renderers(),
                    n.get_childlist(),
                    (int)n.border_width,
                    node_properties,
                    n.title
                );

                if (n.highlight_color != null) {
                    var hl = n.highlight_color;
                    Gtk.Allocation node_alloc;
                    n.get_allocation(out node_alloc);
                    cr.save();
                    cr.set_source_rgba(hl.red, hl.green, hl.blue, 0.3);
                    cr.rectangle(node_alloc.x, node_alloc.y, node_alloc.width, node_alloc.height);
                    cr.fill();
                    cr.restore();
                    cr.save();
                    cr.set_source_rgba(hl.red, hl.green, hl.blue, 0.9);
                    cr.rectangle(node_alloc.x, node_alloc.y, node_alloc.width, node_alloc.height);
                    cr.stroke();
                    cr.restore();
                }
                n.current_cairo_ctx = null;
            }
            this.nodes.reverse();
            // Draw connectors
            foreach (Node n in this.nodes) {
                foreach(GFlow.Source source in n.gnode.get_sources()) {
                    Gtk.Allocation alloc;
                    n.get_allocation(out alloc);
                    int source_pos_x = 0, source_pos_y = 0;
                    if (!n.node_renderer.get_dock_position(
                            source,
                            n.get_dock_renderers(),
                            (int)n.border_width,
                            alloc, out source_pos_x, out source_pos_y,
                            n.title)) {
                        warning("No dock on position. Ommiting connector");
                        continue;
                    }
                    Gdk.Point source_pos = {source_pos_x,source_pos_y};
                    foreach(GFlow.Sink sink in source.sinks) {
                        // Don't draw the connection to a sink if we are dragging it
                        if (sink == this.drag_dock && source == sink.sources.last().nth_data(0))
                            continue;
                        Node? sink_node = this.get_node_from_gflow_node(sink.node);
                        sink_node.get_allocation(out alloc);
                        int sink_pos_x = 0, sink_pos_y = 0;
                        if (!sink_node.node_renderer.get_dock_position(
                                sink,
                                sink_node.get_dock_renderers(),
                                (int)sink_node.border_width,
                                alloc, out sink_pos_x, out sink_pos_y,
                                sink_node.title )) {
                            warning("No dock on position. Ommiting connector");
                            continue;
                        }
                        Gdk.Point sink_pos = {sink_pos_x,sink_pos_y};
                        int w = sink_pos.x - source_pos.x;
                        int h = sink_pos.y - source_pos.y;
                        cr.save();

                        double r=0, g=0, b=0;
                        if (source != null && source.get_last_value() != null) {
                            string hexcol = color_calculation(source.get_last_value());
                            this.hex2col(hexcol ,out r, out g, out b);
                            cr.set_source_rgba(r,g,b,1.0);
                        } else {
                            this.hex2col(default_connector_color ,out r, out g, out b);
                        }
                        cr.set_source_rgba(r,g,b,1.0);

                        cr.move_to(source_pos.x, source_pos.y);
                        if (w > 0) {
                            cr.rel_curve_to(w/3,0,2*w/3,h,w,h);
                        } else {
                            cr.rel_curve_to(-w/3,0,1.3*w,h,w,h);
                        }
                        cr.stroke();
                        cr.restore();
                    }
                }
            }
            // Draw temporary connector if any
            if (this.temp_connector != null) {
                int w = this.temp_connector.width;
                int h = this.temp_connector.height;
                cr.move_to(this.temp_connector.x, this.temp_connector.y);
                if (w > 0) {
                    cr.rel_curve_to(w/3,0,2*w/3,h,w,h);
                } else {
                    cr.rel_curve_to(-w/3,0,1.3*w,h,w,h);
                }
                cr.stroke();
            }
            // Draw rubberband
            if (this.rubber_alloc != null) {
                draw_rubberband(this, cr,
                                this.rubber_alloc.x, this.rubber_alloc.y,
                                Gtk.StateFlags.NORMAL,
                                &this.rubber_alloc.width, &this.rubber_alloc.height);
            }
            // Draw placeholder if there are no nodes
            if (this.nodes.length() == 0) {
                sc.save();
                cr.save();
                sc.add_class(Gtk.STYLE_CLASS_BUTTON);
                Gdk.RGBA col = sc.get_color(Gtk.StateFlags.NORMAL);
                cr.set_source_rgba(col.red,col.green,col.blue,col.alpha);

                int placeholder_width, placeholder_height;
                this.placeholder_layout.get_pixel_size(out placeholder_width, out placeholder_height);

                cr.move_to(nv_alloc.width / 2 - placeholder_width / 2,
                           nv_alloc.height / 2 - placeholder_height / 2);
                Pango.cairo_show_layout(cr, this.placeholder_layout);
                cr.restore();
                sc.restore();
            }
            return false;
        }

        private void hex2col(string hex, out double r, out double g, out double b) {
            string hexdigits ="0123456789abcdef";
            r = col_h2f(hexdigits.index_of_char(hex[0]) * 16 + hexdigits.index_of_char(hex[1]));
            g = col_h2f(hexdigits.index_of_char(hex[2]) * 16 + hexdigits.index_of_char(hex[3]));
            b = col_h2f(hexdigits.index_of_char(hex[4]) * 16 + hexdigits.index_of_char(hex[5]));
        }

        private double col_h2f(uint col) {
            return col/255.0f;
        }

        private uint col_f2h(double col) {
            return (uint)int.parse( (col*255.0d).to_string() ).abs();
        }

        /**
         * Internal method to initialize this NodeView as a {@link Gtk.Widget}
         */
        public override void realize() {
            Gtk.Allocation alloc;
            this.get_allocation(out alloc);
            var attr = Gdk.WindowAttr();
            attr.window_type = Gdk.WindowType.CHILD;
            attr.x = alloc.x;
            attr.y = alloc.y;
            attr.width = alloc.width;
            attr.height = alloc.height;
            attr.visual = this.get_visual();
            attr.event_mask = this.get_events()
                 | Gdk.EventMask.POINTER_MOTION_MASK
                 | Gdk.EventMask.BUTTON_PRESS_MASK
                 | Gdk.EventMask.BUTTON_RELEASE_MASK
                 | Gdk.EventMask.LEAVE_NOTIFY_MASK;
            Gdk.WindowAttributesType mask = Gdk.WindowAttributesType.X
                 | Gdk.WindowAttributesType.X
                 | Gdk.WindowAttributesType.VISUAL;
            var window = new Gdk.Window(this.get_parent_window(), attr, mask);
            this.set_window(window);
            this.register_window(window);
            this.set_realized(true);
        }

        /**
         * Internal method so that GtkInspector can see child widgets
         */
        public override void forall_internal(bool include_internal, Gtk.Callback cb) {
            nodes.foreach(n => cb(n));
        }

        /**
         * Highlight a node in a user-specified color
         *
         * When set to a non-null value, the node will be displayed in the tint
         * of the given color. You can use this to convey status information
         * or to indicate that something with this node is not allright.
         */
        public void set_node_highlight(GFlow.Node gn, Gdk.RGBA? c) {
            Node? n = this.get_node_from_gflow_node(gn);
            if (n == null) {
                warning("Tried to set highlight color to node that does not belong to nodeview.");
                return;
            }
            n.highlight_color = c;
            this.queue_draw();
        }
    }

    /**
     * Draw radiobutton.
     * Implemented in drawinghelper.c
     */
    private extern void draw_radio(Gtk.Widget widget,
                                   Cairo.Context cr,
                                   int x,
                                   int y,
                                   Gtk.StateFlags state,
                                   int* width,
                                   int* height);
    /**
     * Draw rubberband selection.
     * Implemented in drawinghelper.c
     */
    private extern void draw_rubberband(Gtk.Widget widget,
                                   Cairo.Context cr,
                                   int x,
                                   int y,
                                   Gtk.StateFlags state,
                                   int* width,
                                   int* height);
}