livetrax/libs/canvas/canvas.cc

/*
    Copyright (C) 2011 Paul Davis
    Author: Carl Hetherington <cth@carlh.net>

    This program is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
    the Free Software Foundation; either version 2 of the License, or
    (at your option) any later version.

    This program 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 General Public License for more details.

    You should have received a copy of the GNU General Public License
    along with this program; if not, write to the Free Software
    Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.

*/

/** @file  canvas/canvas.cc
 *  @brief Implementation of the main canvas classes.
 */

#include <list>
#include <cassert>
#include <gtkmm/adjustment.h>
#include <gtkmm/label.h>

#include "pbd/compose.h"
#include "pbd/stacktrace.h"

#include "canvas/canvas.h"
#include "canvas/debug.h"
#include "canvas/line.h"
#include "canvas/scroll_group.h"

using namespace std;
using namespace ArdourCanvas;

/** Construct a new Canvas */
Canvas::Canvas ()
	: _root (this)
{
	set_epoch ();
}

void
Canvas::scroll_to (Coord x, Coord y)
{
	_scroll_offset = Duple (x, y);

	/* We do things this way because we do not want to recurse through
	   the canvas for every scroll. In the presence of large MIDI
	   tracks this means traversing item lists that include
	   thousands of items (notes).

	   This design limits us to moving only those items (groups, typically)
	   that should move in certain ways as we scroll. In other terms, it
	   becomes O(1) rather than O(N).
	*/

	for (list<ScrollGroup*>::iterator i = scrollers.begin(); i != scrollers.end(); ++i) {
		(*i)->scroll_to (_scroll_offset);
	}

	pick_current_item (0); // no current mouse position 
}

void
Canvas::add_scroller (ScrollGroup& i)
{
	scrollers.push_back (&i);
}

void
Canvas::zoomed ()
{
	pick_current_item (0); // no current mouse position
}

/** Render an area of the canvas.
 *  @param area Area in canvas coordinates.
 *  @param context Cairo context to render to.
 */
void
Canvas::render (Rect const & area, Cairo::RefPtr<Cairo::Context> const & context) const
{
#ifdef CANVAS_DEBUG
	if (DEBUG_ENABLED(PBD::DEBUG::CanvasRender)) {
		cerr << this << " RENDER: " << area << endl;
		//cerr << "CANVAS @ " << this << endl;
		//dump (cerr);
		//cerr << "-------------------------\n";
	}
#endif

	render_count = 0;
	
	boost::optional<Rect> root_bbox = _root.bounding_box();
	if (!root_bbox) {
		/* the root has no bounding box, so there's nothing to render */
		return;
	}

	boost::optional<Rect> draw = root_bbox->intersection (area);
	if (draw) {
		
		/* there's a common area between the root and the requested
		   area, so render it.
		*/

		_root.render (*draw, context);

		// This outlines the rect being rendered, after it has been drawn.
		// context->rectangle (draw->x0, draw->y0, draw->x1 - draw->x0, draw->y1 - draw->y0);
		// context->set_source_rgba (1.0, 0, 0, 1.0);
		// context->stroke ();

	}

}

ostream&
operator<< (ostream& o, Canvas& c)
{
	c.dump (o);
	return o;
}

std::string
Canvas::indent() const
{ 
	string s;

	for (int n = 0; n < ArdourCanvas::dump_depth; ++n) {
		s += '\t';
	}

	return s;
}

std::string
Canvas::render_indent() const
{ 
	string s;

	for (int n = 0; n < ArdourCanvas::render_depth; ++n) {
		s += ' ';
	}

	return s;
}

void
Canvas::dump (ostream& o) const
{
	dump_depth = 0;
	_root.dump (o);
}	

/** Called when an item has been shown or hidden.
 *  @param item Item that has been shown or hidden.
 */
void
Canvas::item_shown_or_hidden (Item* item)
{
	boost::optional<Rect> bbox = item->bounding_box ();
	if (bbox) {
		queue_draw_item_area (item, bbox.get ());
	}
}

/** Called when an item has a change to its visual properties
 *  that do NOT affect its bounding box.
 *  @param item Item that has been modified.
 */
void
Canvas::item_visual_property_changed (Item* item)
{
	boost::optional<Rect> bbox = item->bounding_box ();
	if (bbox) {
		queue_draw_item_area (item, bbox.get ());
	}
}

/** Called when an item has changed, but not moved.
 *  @param item Item that has changed.
 *  @param pre_change_bounding_box The bounding box of item before the change,
 *  in the item's coordinates.
 */
void
Canvas::item_changed (Item* item, boost::optional<Rect> pre_change_bounding_box)
{
	if (pre_change_bounding_box) {
		/* request a redraw of the item's old bounding box */
		queue_draw_item_area (item, pre_change_bounding_box.get ());
	}

	boost::optional<Rect> post_change_bounding_box = item->bounding_box ();
	if (post_change_bounding_box) {
		/* request a redraw of the item's new bounding box */
		queue_draw_item_area (item, post_change_bounding_box.get ());
	}
}

Duple
Canvas::window_to_canvas (Duple const & d) const
{
	return d.translate (Duple (_scroll_offset.x, _scroll_offset.y));
}

Duple
Canvas::canvas_to_window (Duple const & d, bool rounded) const
{
	Duple wd = d.translate (Duple (-_scroll_offset.x, -_scroll_offset.y));

	/* Note that this intentionally almost always returns integer coordinates */

	if (rounded) {
		wd.x = round (wd.x);
		wd.y = round (wd.y);
	}

	return wd;
}

Rect
Canvas::window_to_canvas (Rect const & r) const
{
	return r.translate (Duple (_scroll_offset.x, _scroll_offset.y));
}

Rect
Canvas::canvas_to_window (Rect const & r, bool rounded) const
{
	Rect wr = r.translate (Duple (-_scroll_offset.x, -_scroll_offset.y));

	/* Note that this intentionally almost always returns integer coordinates */

	if (rounded) {
		wr.x0 = round (wr.x0);
		wr.x1 = round (wr.x1);
		wr.y0 = round (wr.y0);
		wr.y1 = round (wr.y1);
	}

	return wr;
}	

/** Called when an item has moved.
 *  @param item Item that has moved.
 *  @param pre_change_parent_bounding_box The bounding box of the item before
 *  the move, in its parent's coordinates.
 */
void
Canvas::item_moved (Item* item, boost::optional<Rect> pre_change_parent_bounding_box)
{
	if (pre_change_parent_bounding_box) {
		/* request a redraw of where the item used to be. The box has
		 * to be in parent coordinate space since the bounding box of
		 * an item does not change when moved. If we use
		 * item->item_to_canvas() on the old bounding box, we will be

		 * using the item's new position, and so will compute the wrong
		 * invalidation area. If we use the parent (which has not
		 * moved, then this will work.
		 */
		queue_draw_item_area (item->parent(), pre_change_parent_bounding_box.get ());
	}

	boost::optional<Rect> post_change_bounding_box = item->bounding_box ();
	if (post_change_bounding_box) {
		/* request a redraw of where the item now is */
		queue_draw_item_area (item, post_change_bounding_box.get ());
	}
}

/** Request a redraw of a particular area in an item's coordinates.
 *  @param item Item.
 *  @param area Area to redraw in the item's coordinates.
 */
void
Canvas::queue_draw_item_area (Item* item, Rect area)
{
	ArdourCanvas::Rect canvas_area = item->item_to_canvas (area);
	// cerr << "CANVAS " << this << " for " << item << ' ' << item->whatami() << ' ' << item->name << " invalidate " << area << " TRANSLATE AS " << canvas_area << " window = " << canvas_to_window (canvas_area) << std::endl;
	request_redraw (canvas_area);
}

/** Construct a GtkCanvas */
GtkCanvas::GtkCanvas ()
	: _current_item (0)
	, _new_current_item (0)
	, _grabbed_item (0)
	, _focused_item (0)
{
	/* these are the events we want to know about */
	add_events (Gdk::BUTTON_PRESS_MASK | Gdk::BUTTON_RELEASE_MASK | Gdk::POINTER_MOTION_MASK |
		    Gdk::ENTER_NOTIFY_MASK | Gdk::LEAVE_NOTIFY_MASK);
}

void
GtkCanvas::pick_current_item (int state)
{
	int x;
	int y;

	/* this version of ::pick_current_item() is called after an item is
	 * added or removed, so we have no coordinates to work from as is the
	 * case with a motion event. Find out where the mouse is and use that.
	 */
	     
	Glib::RefPtr<const Gdk::Window> pointer_window = Gdk::Display::get_default()->get_window_at_pointer (x, y);

	if (pointer_window != get_window()) {
		return;
	}

	pick_current_item (window_to_canvas (Duple (x, y)), state);
}
		
void
GtkCanvas::pick_current_item (Duple const & point, int state)
{
	/* we do not enter/leave items during a drag/grab */

	if (_grabbed_item) {
		return;
	}

	/* find the items at the given position */

	vector<Item const *> items;
	_root.add_items_at_point (point, items);

	DEBUG_TRACE (PBD::DEBUG::CanvasEnterLeave, string_compose ("%1 covers %2 items\n", point, items.size()));

#ifndef NDEBUG
	if (DEBUG_ENABLED(PBD::DEBUG::CanvasEnterLeave)) {
		for (vector<Item const*>::const_iterator it = items.begin(); it != items.end(); ++it) {
#ifdef CANVAS_DEBUG
			std::cerr << "\tItem " << (*it)->whatami() << '/' << (*it)->name << std::endl;
#else
			std::cerr << "\tItem " << (*it)->whatami() << std::endl;
#endif
		}
	}
#endif

	/* put all items at point that are event-sensitive and visible and NOT
	   groups into within_items. Note that items is sorted from bottom to
	   top, but we're going to reverse that for within_items so that its
	   first item is the upper-most item that can be chosen as _current_item.
	*/
	
	vector<Item const *>::const_iterator i;
	list<Item const *> within_items;

	for (i = items.begin(); i != items.end(); ++i) {

		Item const * new_item = *i;

		/* We ignore invisible items, groups and items that ignore events */

		if (!new_item->visible() || new_item->ignore_events() || dynamic_cast<Group const *>(new_item) != 0) {
			continue;
		}
		
		within_items.push_front (new_item);
	}

	if (within_items.empty()) {

		/* no items at point, just send leave event below */
		_new_current_item = 0;

	} else {

		if (within_items.front() == _current_item) {
			/* uppermost item at point is already _current_item */
			return;
		}
	
		_new_current_item = const_cast<Item*> (within_items.front());
	}

	if (_new_current_item != _current_item) {
		deliver_enter_leave (point, state);
	}
}

void
GtkCanvas::deliver_enter_leave (Duple const & point, int state)
{
	/* setup enter & leave event structures */

	GdkEventCrossing enter_event;
	enter_event.type = GDK_ENTER_NOTIFY;
	enter_event.window = get_window()->gobj();
	enter_event.send_event = 0;
	enter_event.subwindow = 0;
	enter_event.mode = GDK_CROSSING_NORMAL;
	enter_event.focus = FALSE;
	enter_event.state = state;
	enter_event.x = point.x;
	enter_event.y = point.y;

	GdkEventCrossing leave_event = enter_event;
	leave_event.type = GDK_LEAVE_NOTIFY;

	Item* i;
	GdkNotifyType enter_detail;
	GdkNotifyType leave_detail;
	vector<Item*> items_to_leave_virtual;
	vector<Item*> items_to_enter_virtual;

	if (_new_current_item == 0) {

		leave_detail = GDK_NOTIFY_UNKNOWN;

		if (_current_item) {

			/* no current item, so also send virtual leave events to the
			 * entire heirarchy for the current item
			 */

			for (i = _current_item->parent(); i ; i = i->parent()) {
				items_to_leave_virtual.push_back (i);
			}
		}

	} else if (_current_item == 0) {

		enter_detail = GDK_NOTIFY_UNKNOWN;

		/* no current item, so also send virtual enter events to the
		 * entire heirarchy for the new item 
		 */

		for (i = _new_current_item->parent(); i ; i = i->parent()) {
			items_to_enter_virtual.push_back (i);
		}

	} else if (_current_item->is_descendant_of (*_new_current_item)) {

		/* move from descendant to ancestor (X: "_current_item is an
		 * inferior ("child") of _new_current_item") 
		 *
		 * Deliver "virtual" leave notifications to all items in the
		 * heirarchy between current and new_current.
		 */
		

		for (i = _current_item->parent(); i && i != _new_current_item; i = i->parent()) {
			items_to_leave_virtual.push_back (i);
		}

		enter_detail = GDK_NOTIFY_INFERIOR;
		leave_detail = GDK_NOTIFY_ANCESTOR;


	} else if (_new_current_item->is_descendant_of (*_current_item)) {
		/* move from ancestor to descendant (X: "_new_current_item is
		 * an inferior ("child") of _current_item")
		 *
		 * Deliver "virtual" enter notifications to all items in the
		 * heirarchy between current and new_current.
		 */

		for (i = _new_current_item->parent(); i && i != _current_item; i = i->parent()) {
			items_to_enter_virtual.push_back (i);
		}

		enter_detail = GDK_NOTIFY_ANCESTOR;
		leave_detail = GDK_NOTIFY_INFERIOR;

	} else {

		Item const * common_ancestor = _current_item->closest_ancestor_with (*_new_current_item);

		/* deliver virtual leave events to everything between _current
		 * and common_ancestor.
		 */

		for (i = _current_item->parent(); i && i != common_ancestor; i = i->parent()) {
			items_to_leave_virtual.push_back (i);
		}

		/* deliver virtual enter events to everything between
		 * _new_current and common_ancestor.
		 */

		for (i = _new_current_item->parent(); i && i != common_ancestor; i = i->parent()) {
			items_to_enter_virtual.push_back (i);
		}

		enter_detail = GDK_NOTIFY_NONLINEAR;
		leave_detail = GDK_NOTIFY_NONLINEAR;
	}
	

	if (_current_item && !_current_item->ignore_events ()) {
		leave_event.detail = leave_detail;
		_current_item->Event ((GdkEvent*)&leave_event);
		DEBUG_TRACE (PBD::DEBUG::CanvasEnterLeave, string_compose ("LEAVE %1/%2\n", _current_item->whatami(), _current_item->name));
	}

	leave_event.detail = GDK_NOTIFY_VIRTUAL;
	enter_event.detail = GDK_NOTIFY_VIRTUAL;

	for (vector<Item*>::iterator it = items_to_leave_virtual.begin(); it != items_to_leave_virtual.end(); ++it) {
		if (!(*it)->ignore_events()) {
			DEBUG_TRACE (PBD::DEBUG::CanvasEnterLeave, string_compose ("leave %1/%2\n", (*it)->whatami(), (*it)->name));
			(*it)->Event ((GdkEvent*)&leave_event);
		}
	}

	for (vector<Item*>::iterator it = items_to_enter_virtual.begin(); it != items_to_enter_virtual.end(); ++it) {
		if (!(*it)->ignore_events()) {
			DEBUG_TRACE (PBD::DEBUG::CanvasEnterLeave, string_compose ("enter %1/%2\n", (*it)->whatami(), (*it)->name));
			(*it)->Event ((GdkEvent*)&enter_event);
			// std::cerr << "enter " << (*it)->whatami() << '/' << (*it)->name << std::endl;
		}
	}

	if (_new_current_item && !_new_current_item->ignore_events()) {
		enter_event.detail = enter_detail;
		DEBUG_TRACE (PBD::DEBUG::CanvasEnterLeave, string_compose ("ENTER %1/%2\n", _new_current_item->whatami(), _new_current_item->name));
		_new_current_item->Event ((GdkEvent*)&enter_event);
	}

	_current_item = _new_current_item;
}


/** Deliver an event to the appropriate item; either the grabbed item, or
 *  one of the items underneath the event.
 *  @param point Position that the event has occurred at, in canvas coordinates.
 *  @param event The event.
 */
bool
GtkCanvas::deliver_event (GdkEvent* event)
{
	/* Point in in canvas coordinate space */

	const Item* event_item;

	if (_grabbed_item) {
		/* we have a grabbed item, so everything gets sent there */
		DEBUG_TRACE (PBD::DEBUG::CanvasEvents, string_compose ("%1 %2 (%3) was grabbed, send event there\n",
								       _grabbed_item, _grabbed_item->whatami(), _grabbed_item->name));
		event_item = _grabbed_item;
	} else {
		event_item = _current_item;
	}

	if (!event_item) {
		return false;
	}

	/* run through the items from child to parent, until one claims the event */

	Item* item = const_cast<Item*> (event_item);
	
	while (item) {

		Item* parent = item->parent ();

		if (!item->ignore_events () && 
		    item->Event (event)) {
			/* this item has just handled the event */
			DEBUG_TRACE (
				PBD::DEBUG::CanvasEvents,
				string_compose ("canvas event handled by %1 %2\n", item->whatami(), item->name.empty() ? "[unknown]" : item->name)
				);
			
			return true;
		}
		
		DEBUG_TRACE (PBD::DEBUG::CanvasEvents, string_compose ("canvas event %3 left unhandled by %1 %2\n", item->whatami(), item->name.empty() ? "[unknown]" : item->name, event_type_string (event->type)));

		if ((item = parent) == 0) {
			break;
		}

	}

	return false;
}

/** Called when an item is being destroyed.
 *  @param item Item being destroyed.
 *  @param bounding_box Last known bounding box of the item.
 */
void
GtkCanvas::item_going_away (Item* item, boost::optional<Rect> bounding_box)
{
	if (bounding_box) {
		queue_draw_item_area (item, bounding_box.get ());
	}
	
	if (_new_current_item == item) {
		_new_current_item = 0;
	}

	if (_grabbed_item == item) {
		_grabbed_item = 0;
	}

	if (_focused_item == item) {
		_focused_item = 0;
	}

	ScrollGroup* sg = dynamic_cast<ScrollGroup*>(item);
	if (sg) {
		scrollers.remove (sg);
	}

	if (_current_item == item) {
		/* no need to send a leave event to this item, since it is going away 
		 */
		_current_item = 0;
		pick_current_item (0); // no mouse state
	}
	
}

/** Handler for GDK expose events.
 *  @param ev Event.
 *  @return true if the event was handled.
 */
bool
GtkCanvas::on_expose_event (GdkEventExpose* ev)
{
	Cairo::RefPtr<Cairo::Context> cairo_context = get_window()->create_cairo_context ();
	render (Rect (ev->area.x, ev->area.y, ev->area.x + ev->area.width, ev->area.y + ev->area.height), cairo_context);
	return true;
}

/** @return Our Cairo context, or 0 if we don't have one */
Cairo::RefPtr<Cairo::Context>
GtkCanvas::context ()
{
	Glib::RefPtr<Gdk::Window> w = get_window ();
	if (!w) {
		return Cairo::RefPtr<Cairo::Context> ();
	}

	return w->create_cairo_context ();
}

/** Handler for GDK button press events.
 *  @param ev Event.
 *  @return true if the event was handled.
 */
bool
GtkCanvas::on_button_press_event (GdkEventButton* ev)
{
	/* translate event coordinates from window to canvas */

	GdkEvent copy = *((GdkEvent*)ev);
	Duple where = window_to_canvas (Duple (ev->x, ev->y));

	copy.button.x = where.x;
	copy.button.y = where.y;
	
	/* Coordinates in the event will be canvas coordinates, correctly adjusted
	   for scroll if this GtkCanvas is in a GtkCanvasViewport.
	*/

	pick_current_item (where, ev->state);
	DEBUG_TRACE (PBD::DEBUG::CanvasEvents, string_compose ("canvas button press @ %1, %2 => %3\n", ev->x, ev->y, where));
	return deliver_event (reinterpret_cast<GdkEvent*>(&copy));
}

/** Handler for GDK button release events.
 *  @param ev Event.
 *  @return true if the event was handled.
 */
bool
GtkCanvas::on_button_release_event (GdkEventButton* ev)
{	
	/* translate event coordinates from window to canvas */

	GdkEvent copy = *((GdkEvent*)ev);
	Duple where = window_to_canvas (Duple (ev->x, ev->y));
	
	pick_current_item (where, ev->state);

	copy.button.x = where.x;
	copy.button.y = where.y;

	/* Coordinates in the event will be canvas coordinates, correctly adjusted
	   for scroll if this GtkCanvas is in a GtkCanvasViewport.
	*/

	pick_current_item (where, ev->state);
	DEBUG_TRACE (PBD::DEBUG::CanvasEvents, string_compose ("canvas button release @ %1, %2 => %3\n", ev->x, ev->y, where));
	return deliver_event (reinterpret_cast<GdkEvent*>(&copy));
}

/** Handler for GDK motion events.
 *  @param ev Event.
 *  @return true if the event was handled.
 */
bool
GtkCanvas::on_motion_notify_event (GdkEventMotion* ev)
{
	/* translate event coordinates from window to canvas */

	GdkEvent copy = *((GdkEvent*)ev);
	Duple point (ev->x, ev->y);
	Duple where = window_to_canvas (point);

	copy.motion.x = where.x;
	copy.motion.y = where.y;

	/* Coordinates in "copy" will be canvas coordinates, 
	*/

	// DEBUG_TRACE (PBD::DEBUG::CanvasEvents, string_compose ("canvas motion @ %1, %2\n", ev->x, ev->y));

	pick_current_item (where, ev->state);

	/* Now deliver the motion event.  It may seem a little inefficient
	   to recompute the items under the event, but the enter notify/leave
	   events may have deleted canvas items so it is important to
	   recompute the list in deliver_event.
	*/

	return deliver_event (reinterpret_cast<GdkEvent*> (&copy));
}

bool
GtkCanvas::on_enter_notify_event (GdkEventCrossing* ev)
{
	Duple where = window_to_canvas (Duple (ev->x, ev->y));
	pick_current_item (where, ev->state);
	return true;
}

bool
GtkCanvas::on_leave_notify_event (GdkEventCrossing* ev)
{
	_new_current_item = 0;
	Duple where = window_to_canvas (Duple (ev->x, ev->y));
	deliver_enter_leave (where, ev->state);
	return true;
}

/** Called to request a redraw of our canvas.
 *  @param area Area to redraw, in canvas coordinates.
 */
void
GtkCanvas::request_redraw (Rect const & request)
{
	boost::optional<Rect> req = request.intersection (visible_area());

	if (req) {
		Rect r = req.get();
		Rect area = canvas_to_window (r);
		queue_draw_area (area.x0, area.y0, area.width(), area.height());
	}
}

/** Called to request that we try to get a particular size for ourselves.
 *  @param size Size to request, in pixels.
 */
void
GtkCanvas::request_size (Duple size)
{
	Duple req = size;

	if (req.x > INT_MAX) {
		req.x = INT_MAX;
	}

	if (req.y > INT_MAX) {
		req.y = INT_MAX;
	}

	set_size_request (req.x, req.y);
}

/** `Grab' an item, so that all events are sent to that item until it is `ungrabbed'.
 *  This is typically used for dragging items around, so that they are grabbed during
 *  the drag.
 *  @param item Item to grab.
 */
void
GtkCanvas::grab (Item* item)
{
	/* XXX: should this be doing gdk_pointer_grab? */
	_grabbed_item = item;
}


/** `Ungrab' any item that was previously grabbed */
void
GtkCanvas::ungrab ()
{
	/* XXX: should this be doing gdk_pointer_ungrab? */
	_grabbed_item = 0;
}

/** Set keyboard focus on an item, so that all keyboard events are sent to that item until the focus
 *  moves elsewhere.
 *  @param item Item to grab.
 */
void
GtkCanvas::focus (Item* item)
{
	_focused_item = item;
}

void
GtkCanvas::unfocus (Item* item)
{
	if (item == _focused_item) {
		_focused_item = 0;
	}
}

/** @return The visible area of the canvas, in canvas coordinates */
Rect
GtkCanvas::visible_area () const
{
	Distance const xo = _scroll_offset.x;
	Distance const yo = _scroll_offset.y;
	return Rect (xo, yo, xo + get_allocation().get_width (), yo + get_allocation().get_height ());
}

/** Create a GtkCanvaSViewport.
 *  @param hadj Adjustment to use for horizontal scrolling.
 *  @param vadj Adjustment to use for vertica scrolling.
 */
GtkCanvasViewport::GtkCanvasViewport (Gtk::Adjustment& hadj, Gtk::Adjustment& vadj)
	: Alignment (0, 0, 1.0, 1.0)
	, hadjustment (hadj)
	, vadjustment (vadj)
{
	add (_canvas);

	hadj.signal_value_changed().connect (sigc::mem_fun (*this, &GtkCanvasViewport::scrolled));
	vadj.signal_value_changed().connect (sigc::mem_fun (*this, &GtkCanvasViewport::scrolled));
}

void
GtkCanvasViewport::scrolled ()
{
	_canvas.scroll_to (hadjustment.get_value(), vadjustment.get_value());
	queue_draw ();
}

/** Handler for when GTK asks us what minimum size we want.
 *  @param req Requsition to fill in.
 */
void
GtkCanvasViewport::on_size_request (Gtk::Requisition* req)
{
	/* force the canvas to size itself */
	// _canvas.root()->bounding_box(); 

	req->width = 16;
	req->height = 16;
}