adg: added adg_canvas_get_page_setup()

[adg.git] / src / adg / adg-gtk-area.c

/* ADG - Automatic Drawing Generation
 * Copyright (C) 2007,2008,2009,2010,2011,2012,2013  Nicola Fontana <ntd at entidi.it>
 *
 * This library 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 2 of the License, or (at your option) any later version.
 *
 * This library 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 this library; if not, write to the
 * Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
 * Boston, MA  02110-1301, USA.
 */


/**
 * SECTION:adg-gtk-area
 * @short_description: A #GtkWidget specifically designed to contain
 *                     an #AdgCanvas entity
 *
 * This is a #GtkDrawingArea derived object that provides an easy way
 * to show an ADG based canvas. The associated canvas can be set
 * directly with the adg_gtk_area_new_with_canvas() constructor
 * function or by using adg_gtk_area_set_canvas().
 *
 * The minimum size of the widget will depend on the canvas content.
 *
 * The default implementation reacts to some mouse events: if you drag
 * the mouse keeping the wheel pressed, the canvas will be translated
 * (in local space by default and in global space if %SHIFT is pressed);
 * if the mouse wheel is rotated the canvas will be scaled up or down
 * according to the wheel direction by the factor specified in the
 * #AdgGtkArea:factor property (again, in local space by default and
 * in global space if %SHIFT is pressed). The adg_gtk_area_get_zoom()
 * method could be used to retrieve the current zoom coefficient.
 *
 * A new transformation layer is present between the global space
 * and the rendering: the #AdgGtkArea:render-map matrix. This
 * transformation is applied just before the rendering and it is
 * used to align and/or apply the zoom coefficient to the canvas
 * without affecting the other layers. Local transformations,
 * instead, are directly applied to the local matrix of the canvas.
 *
 * Since: 1.0
 **/


/**
 * AdgGtkArea:
 *
 * All fields are private and should not be used directly.
 * Use its public methods instead.
 *
 * Since: 1.0
 **/

/**
 * AdgGtkAreaClass:
 * @canvas_changed:  signals that a new #AdgCanvas is bound to this widget.
 * @extents_changed: signals that the extents on the underling #AdgCanvas
 *                   has been changed.
 *
 * The default @canvas_changed resets the internal initialization flag, so at
 * the first call to the size_allocate() method the zoom factor is set to %1.
 *
 * The default @extents_changed signal does not do anything: it is intended as
 * a hook for derived class for refreshing GUI elements (such as scrollbars)
 * whenever the boundary box changes.
 *
 * Since: 1.0
 **/


#include "adg-internal.h"
#include <gtk/gtk.h>

#include "adg-container.h"
#include "adg-table.h"
#include "adg-title-block.h"
#include <adg-canvas.h>
#include "adg-gtk-utils.h"
#include "adg-matrix-fallback.h"

#include "adg-gtk-area.h"
#include "adg-gtk-area-private.h"

#define _ADG_OLD_OBJECT_CLASS   ((GObjectClass *) adg_gtk_area_parent_class)
#define _ADG_OLD_WIDGET_CLASS   ((GtkWidgetClass *) adg_gtk_area_parent_class)


G_DEFINE_TYPE(AdgGtkArea, adg_gtk_area, GTK_TYPE_DRAWING_AREA)

enum {
    PROP_0,
    PROP_CANVAS,
    PROP_FACTOR,
    PROP_AUTOZOOM,
    PROP_RENDER_MAP
};

enum {
    CANVAS_CHANGED,
    EXTENTS_CHANGED,
    LAST_SIGNAL
};


static void     _adg_dispose                (GObject         *object);
static void     _adg_get_property           (GObject         *object,
                                             guint            prop_id,
                                             GValue          *value,
                                             GParamSpec      *pspec);
static void     _adg_set_property           (GObject         *object,
                                             guint            prop_id,
                                             const GValue    *value,
                                             GParamSpec      *pspec);
static void     _adg_get_preferred_height   (GtkWidget       *widget,
                                             gint            *minimum_height,
                                             gint            *natural_height);
static void     _adg_get_preferred_height_for_width
                                            (GtkWidget       *widget,
                                             gint             width,
                                             gint            *minimum_height,
                                             gint            *natural_height);
static void     _adg_get_preferred_width    (GtkWidget       *widget,
                                             gint            *minimum_width,
                                             gint            *natural_width);
static void     _adg_get_preferred_width_for_height
                                            (GtkWidget       *widget,
                                             gint             height,
                                             gint            *minimum_width,
                                             gint            *natural_width);
static void     _adg_size_allocate          (GtkWidget       *widget,
                                             GtkAllocation   *allocation);
static gboolean _adg_draw                   (GtkWidget       *widget,
                                             cairo_t         *cr);
static gboolean _adg_scroll_event           (GtkWidget       *widget,
                                             GdkEventScroll  *event);
static gboolean _adg_button_press_event     (GtkWidget       *widget,
                                                 GdkEventButton  *event);
static gboolean _adg_motion_notify_event    (GtkWidget       *widget,
                                             GdkEventMotion  *event);
static gboolean _adg_get_map                (GtkWidget       *widget,
                                             gboolean         local_space,
                                             cairo_matrix_t  *map,
                                             cairo_matrix_t  *inverted);
static void     _adg_set_map                (GtkWidget       *widget,
                                             gboolean         local_space,
                                             const cairo_matrix_t *map);
static void     _adg_canvas_changed         (AdgGtkArea      *area,
                                             AdgCanvas       *old_canvas);
static const CpmlExtents *
                _adg_get_extents            (AdgGtkArea      *area);

static guint    _adg_signals[LAST_SIGNAL] = { 0 };


static void
adg_gtk_area_class_init(AdgGtkAreaClass *klass)
{
    GObjectClass *gobject_class;
    GtkWidgetClass *widget_class;
    GParamSpec *param;

    gobject_class = (GObjectClass *) klass;
    widget_class = (GtkWidgetClass *) klass;

    g_type_class_add_private(klass, sizeof(AdgGtkAreaPrivate));

    gobject_class->dispose = _adg_dispose;
    gobject_class->get_property = _adg_get_property;
    gobject_class->set_property = _adg_set_property;

    widget_class->get_preferred_height = _adg_get_preferred_height;
    widget_class->get_preferred_height_for_width = _adg_get_preferred_height_for_width;
    widget_class->get_preferred_width = _adg_get_preferred_width;
    widget_class->get_preferred_width_for_height = _adg_get_preferred_width_for_height;
    widget_class->size_allocate = _adg_size_allocate;
    widget_class->draw = _adg_draw;
    widget_class->scroll_event = _adg_scroll_event;
    widget_class->button_press_event = _adg_button_press_event;
    widget_class->motion_notify_event = _adg_motion_notify_event;

    klass->canvas_changed = _adg_canvas_changed;

    param = g_param_spec_object("canvas",
                                P_("Canvas"),
                                P_("The canvas to be shown"),
                                ADG_TYPE_CANVAS,
                                G_PARAM_READWRITE | G_PARAM_CONSTRUCT);
    g_object_class_install_property(gobject_class, PROP_CANVAS, param);

    param = g_param_spec_double("factor",
                                P_("Factor"),
                                P_("The factor to use while zooming in and out (usually with the mouse wheel)"),
                                1., G_MAXDOUBLE, 1.05,
                                G_PARAM_READWRITE);
    g_object_class_install_property(gobject_class, PROP_FACTOR, param);

    param = g_param_spec_boolean("autozoom",
                                 P_("Autozoom"),
                                 P_("When enabled, automatically adjust the zoom in global space at every size allocation"),
                                 FALSE,
                                 G_PARAM_READWRITE);
    g_object_class_install_property(gobject_class, PROP_AUTOZOOM, param);

    param = g_param_spec_boxed("render-map",
                               P_("Render Map"),
                               P_("The transformation to be applied on the canvas before rendering it"),
                               CAIRO_GOBJECT_TYPE_MATRIX,
                               G_PARAM_READWRITE);
    g_object_class_install_property(gobject_class, PROP_RENDER_MAP, param);

    /**
     * AdgGtkArea::canvas-changed:
     * @area: an #AdgGtkArea
     * @old_canvas: the old #AdgCanvas object
     *
     * Emitted when the #AdgGtkArea has a new canvas. If the new canvas
     * is the same as the old one, the signal is not emitted.
     *
     * Since: 1.0
     **/
    _adg_signals[CANVAS_CHANGED] =
        g_signal_new("canvas-changed", ADG_GTK_TYPE_AREA,
                     G_SIGNAL_RUN_LAST|G_SIGNAL_NO_RECURSE,
                     G_STRUCT_OFFSET(AdgGtkAreaClass, canvas_changed),
                     NULL, NULL,
                     adg_marshal_VOID__OBJECT,
                     G_TYPE_NONE, 1, ADG_TYPE_CANVAS);

    /**
     * AdgGtkArea::extents-changed:
     * @area: an #AdgGtkArea
     * @old_extents: the old #CpmlExtents struct
     *
     * Emitted when the extents of @area have been changed.
     * The old extents are always compared to the new ones,
     * so when the extents are recalculated but the result
     * is the same the signal is not emitted.
     *
     * The extents of #AdgGtkArea are subject to the render
     * map, so changing the #AdgGtkArea:render-map property
     * will emit this signal too.
     *
     * Since: 1.0
     **/
    _adg_signals[EXTENTS_CHANGED] =
        g_signal_new("extents-changed", ADG_GTK_TYPE_AREA,
                     G_SIGNAL_RUN_LAST|G_SIGNAL_NO_RECURSE,
                     G_STRUCT_OFFSET(AdgGtkAreaClass, extents_changed),
                     NULL, NULL,
                     adg_marshal_VOID__POINTER,
                     G_TYPE_NONE, 1, G_TYPE_POINTER);
}

static void
adg_gtk_area_init(AdgGtkArea *area)
{
    AdgGtkAreaPrivate *data = G_TYPE_INSTANCE_GET_PRIVATE(area,
                                                          ADG_GTK_TYPE_AREA,
                                                          AdgGtkAreaPrivate);

    data->canvas = NULL;
    data->factor = 1.05;
    data->autozoom = FALSE;
    cairo_matrix_init_identity(&data->render_map);

    data->initialized = FALSE;
    data->x_event = 0;
    data->y_event = 0;

    area->data = data;

    /* Enable GDK events to catch wheel rotation and drag */
    gtk_widget_add_events((GtkWidget *) area,
                          GDK_BUTTON_PRESS_MASK |
                          GDK_BUTTON2_MOTION_MASK |
                          GDK_SCROLL_MASK);
}

static void
_adg_dispose(GObject *object)
{
    AdgGtkAreaPrivate *data = ((AdgGtkArea *) object)->data;

    if (data->canvas) {
        g_object_unref(data->canvas);
        data->canvas = NULL;
    }

    if (_ADG_OLD_OBJECT_CLASS->dispose)
        _ADG_OLD_OBJECT_CLASS->dispose(object);
}

static void
_adg_get_property(GObject *object, guint prop_id,
                  GValue *value, GParamSpec *pspec)
{
    AdgGtkAreaPrivate *data = ((AdgGtkArea *) object)->data;

    switch (prop_id) {
    case PROP_CANVAS:
        g_value_set_object(value, data->canvas);
        break;
    case PROP_FACTOR:
        g_value_set_double(value, data->factor);
        break;
    case PROP_AUTOZOOM:
        g_value_set_boolean(value, data->autozoom);
        break;
    case PROP_RENDER_MAP:
        g_value_set_boxed(value, &data->render_map);
        break;
    default:
        G_OBJECT_WARN_INVALID_PROPERTY_ID(object, prop_id, pspec);
        break;
    }
}

static void
_adg_set_property(GObject *object, guint prop_id,
                  const GValue *value, GParamSpec *pspec)
{
    AdgGtkArea *area;
    AdgGtkAreaPrivate *data;
    AdgCanvas *new_canvas, *old_canvas;

    area = (AdgGtkArea *) object;
    data = area->data;

    switch (prop_id) {
    case PROP_CANVAS:
        new_canvas = g_value_get_object(value);
        old_canvas = data->canvas;
        if (new_canvas != old_canvas) {
            if (new_canvas != NULL)
                g_object_ref(new_canvas);
            if (old_canvas != NULL)
                g_object_unref(old_canvas);
            data->canvas = new_canvas;
            g_signal_emit(area, _adg_signals[CANVAS_CHANGED], 0, old_canvas);
        }
        break;
    case PROP_FACTOR:
        data->factor = g_value_get_double(value);
        break;
    case PROP_AUTOZOOM:
        data->autozoom = g_value_get_boolean(value);
        break;
    case PROP_RENDER_MAP:
        adg_matrix_copy(&data->render_map, g_value_get_boxed(value));
        break;
    default:
        G_OBJECT_WARN_INVALID_PROPERTY_ID(object, prop_id, pspec);
        break;
    }
}


/**
 * adg_gtk_area_new:
 *
 * Creates a new empty #AdgGtkArea. The widget is useful only after
 * an #AdgCanvas has been added either using the #AdgGtkArea:canvas
 * property or with adg_gtk_area_set_canvas().
 *
 * Returns: the newly created widget
 *
 * Since: 1.0
 **/
GtkWidget *
adg_gtk_area_new(void)
{
    return g_object_new(ADG_GTK_TYPE_AREA, NULL);
}

/**
 * adg_gtk_area_new_with_canvas:
 * @canvas: the #AdgCanvas shown by this widget
 *
 * Creates a new #AdgGtkArea and sets the #AdgGtkArea:canvas property
 * to @canvas.
 *
 * Returns: the newly created widget
 *
 * Since: 1.0
 **/
GtkWidget *
adg_gtk_area_new_with_canvas(AdgCanvas *canvas)
{
    g_return_val_if_fail(ADG_IS_CANVAS(canvas), NULL);

    return g_object_new(ADG_GTK_TYPE_AREA, "canvas", canvas, NULL);
}

/**
 * adg_gtk_area_set_canvas:
 * @area: an #AdgGtkArea
 * @canvas: the new #AdgCanvas
 *
 * Sets a new canvas on @area. The old canvas, if presents, is
 * unreferenced.
 *
 * Since: 1.0
 **/
void
adg_gtk_area_set_canvas(AdgGtkArea *area, AdgCanvas *canvas)
{
    g_return_if_fail(ADG_GTK_IS_AREA(area));
    g_object_set(area, "canvas", canvas, NULL);
}

/**
 * adg_gtk_area_get_canvas:
 * @area: an #AdgGtkArea
 *
 * Gets the canvas associated to @area. The returned canvas
 * is owned by @area and should not be modified or freed.
 *
 * Returns: (transfer none): the requested #AdgCanvas object or
 *          %NULL on errors
 *
 * Since: 1.0
 **/
AdgCanvas *
adg_gtk_area_get_canvas(AdgGtkArea *area)
{
    AdgGtkAreaPrivate *data;

    g_return_val_if_fail(ADG_GTK_IS_AREA(area), NULL);

    data = area->data;

    return data->canvas;
}

/**
 * adg_gtk_area_set_render_map:
 * @area: an #AdgGtkArea object
 * @map: the new map
 *
 * Sets the new render transformation of @area to @map:
 * the old map is discarded. If @map is %NULL, the render
 * map is left unchanged.
 *
 * <note><para>
 * The render map is an implementation detail and this function
 * is expected to be used only by #AdgGtkArea derived objects.
 * </para></note>
 *
 * Since: 1.0
 **/
void
adg_gtk_area_set_render_map(AdgGtkArea *area, const cairo_matrix_t *map)
{
    g_return_if_fail(ADG_GTK_IS_AREA(area));
    g_object_set(area, "render-map", map, NULL);
}

/**
 * adg_gtk_area_transform_render_map:
 * @area: an #AdgGtkArea object
 * @transformation: the transformation to apply
 * @mode: how @transformation should be applied
 *
 * Convenient function to change the render map of @area by
 * applying @tranformation using the @mode operator. This is
 * logically equivalent to the following:
 *
 * |[
 * cairo_matrix_t map;
 * adg_matrix_copy(&map, adg_gtk_area_get_render_map(area));
 * adg_matrix_transform(&map, transformation, mode);
 * adg_gtk_area_set_render_map(area, &map);
 * ]|
 *
 * <note><para>
 * The render map is an implementation detail and this function
 * is expected to be used only by #AdgGtkArea derived objects.
 * </para></note>
 *
 * Since: 1.0
 **/
void
adg_gtk_area_transform_render_map(AdgGtkArea *area,
                                  const cairo_matrix_t *transformation,
                                  AdgTransformMode mode)
{
    AdgGtkAreaPrivate *data;
    cairo_matrix_t map;

    g_return_if_fail(ADG_GTK_IS_AREA(area));
    g_return_if_fail(transformation != NULL);

    data = area->data;

    adg_matrix_copy(&map, &data->render_map);
    adg_matrix_transform(&map, transformation, mode);

    g_object_set(area, "render-map", &map, NULL);
}

/**
 * adg_gtk_area_get_render_map:
 * @area: an #AdgGtkArea object
 *
 * Gets the render map.
 *
 * Returns: the requested map or %NULL on errors
 *
 * Since: 1.0
 **/
const cairo_matrix_t *
adg_gtk_area_get_render_map(AdgGtkArea *area)
{
    AdgGtkAreaPrivate *data;

    g_return_val_if_fail(ADG_GTK_IS_AREA(area), NULL);

    data = area->data;

    return &data->render_map;
}

/**
 * adg_gtk_area_get_extents:
 * @area: an #AdgGtkArea
 *
 * Gets the extents of the canvas bound to @area. The returned
 * struct is owned by @area and should not modified or freed.
 *
 * The extents of an #AdgGtkArea instance are the extents of
 * its canvas (as returned by adg_entity_get_extents()) with
 * the margins added to it and the #AdgGtkArea:render-map
 * transformation applied.
 *
 * If @area does not have any canvas associated to it or the
 * canvas is invalid or empty, an undefined #CpmlExtents
 * struct will be returned.
 *
 * The canvas will be updated, meaning adg_entity_arrange()
 * is called before the extents computation.
 *
 * Returns: the extents of the @area canvas or %NULL on errors
 *
 * Since: 1.0
 **/
const CpmlExtents *
adg_gtk_area_get_extents(AdgGtkArea *area)
{
    g_return_val_if_fail(ADG_GTK_IS_AREA(area), NULL);

    return _adg_get_extents(area);
}

/**
 * adg_gtk_area_get_zoom:
 * @area: an #AdgGtkArea
 *
 * Gets the last zoom coefficient applied on the canvas of @area.
 * If the #AdgGtkArea:autozoom property is %FALSE, the value
 * returned should be always %1.
 *
 * Returns: the current zoom coefficient
 *
 * Since: 1.0
 **/
gdouble
adg_gtk_area_get_zoom(AdgGtkArea *area)
{
    AdgGtkAreaPrivate *data;

    g_return_val_if_fail(ADG_GTK_IS_AREA(area), 0.);

    data = area->data;
    return data->render_map.xx;
}

/**
 * adg_gtk_area_set_factor:
 * @area: an #AdgGtkArea
 * @factor: the new zoom factor
 *
 * Sets a new zoom factor to @area. If the factor is less than
 * 1, it will be clamped to 1.
 *
 * Since: 1.0
 **/
void
adg_gtk_area_set_factor(AdgGtkArea *area, gdouble factor)
{
    g_return_if_fail(ADG_GTK_IS_AREA(area));
    g_object_set(area, "factor", factor, NULL);
}

/**
 * adg_gtk_area_get_factor:
 * @area: an #AdgGtkArea
 *
 * Gets the zoom factor associated to @area. The zoom factor is
 * directly used to zoom in (that is, the default zoom factor of
 * 1.05 will zoom of 5% every iteration) and it is reversed while
 * zooming out (that is, the default factor will be 1/1.05).
 *
 * Returns: the requested zoom factor or 0 on error
 *
 * Since: 1.0
 **/
gdouble
adg_gtk_area_get_factor(AdgGtkArea *area)
{
    AdgGtkAreaPrivate *data;

    g_return_val_if_fail(ADG_GTK_IS_AREA(area), 0.);

    data = area->data;
    return data->factor;
}

/**
 * adg_gtk_area_switch_autozoom:
 * @area: an #AdgGtkArea
 * @state: the new autozoom state
 *
 * Sets the #AdgGtkArea:autozoom property of @area to @state. When the
 * autozoom feature is enabled, @area reacts to any size allocation
 * by adjusting its zoom coefficient in global space. This means the
 * drawing will fill the available space (keeping its aspect ratio)
 * when resizing the window.
 *
 * Since: 1.0
 **/
void
adg_gtk_area_switch_autozoom(AdgGtkArea *area, gboolean state)
{
    g_return_if_fail(ADG_GTK_IS_AREA(area));
    g_object_set(area, "autozoom", state, NULL);
}

/**
 * adg_gtk_area_has_autozoom:
 * @area: an #AdgGtkArea
 *
 * Gets the current state of the #AdgGtkArea:autozoom property on
 * the @area object.
 *
 * Returns: the current autozoom state
 *
 * Since: 1.0
 **/
gboolean
adg_gtk_area_has_autozoom(AdgGtkArea *area)
{
    AdgGtkAreaPrivate *data;

    g_return_val_if_fail(ADG_GTK_IS_AREA(area), FALSE);

    data = area->data;
    return data->autozoom;
}

/**
 * adg_gtk_area_reset:
 * @area: an #AdgGtkArea
 *
 * Forcibly resets the zoom ratio and position of the canvas bound
 * to @area. This means the canvas will be scaled and centered on
 * the current available space.
 **/
void
adg_gtk_area_reset(AdgGtkArea *area)
{
    AdgGtkAreaPrivate *data;
    GtkWidget *parent;
    const CpmlExtents *sheet;
    CpmlPair size;
    gdouble zoom;

    g_return_if_fail(ADG_GTK_IS_AREA(area));

    data = area->data;
    cairo_matrix_init_identity(&data->render_map);

    sheet = _adg_get_extents(area);
    if (!sheet->is_defined || sheet->size.x <= 0 || sheet->size.y <= 0)
        return;

    parent = gtk_widget_get_parent((GtkWidget *) area);
    size.x = gtk_widget_get_allocated_width(parent);
    size.y = gtk_widget_get_allocated_height(parent);
    zoom = MIN(size.x / sheet->size.x, size.y / sheet->size.y);

    cairo_matrix_scale(&data->render_map, zoom, zoom);
    cairo_matrix_translate(&data->render_map,
                           (size.x / zoom - sheet->size.x) / 2 - sheet->org.x,
                           (size.y / zoom - sheet->size.y) / 2 - sheet->org.y);

    /* Trigger a resize trying to hide the scrollbars on the parent */
    gtk_widget_queue_resize(parent);
}

/**
 * adg_gtk_area_canvas_changed:
 * @area: an #AdgGtkArea
 * @old_canvas: the old canvas bound to @area
 *
 * Emits the #AdgGtkArea::canvas-changed signal on @area.
 *
 * Since: 1.0
 **/
void
adg_gtk_area_canvas_changed(AdgGtkArea *area, AdgCanvas *old_canvas)
{
    g_return_if_fail(ADG_GTK_IS_AREA(area));

    g_signal_emit(area, _adg_signals[CANVAS_CHANGED], 0, old_canvas);
}

/**
 * adg_gtk_area_extents_changed:
 * @area: an #AdgGtkArea
 * @old_extents: the old extents of @area
 *
 * Emits the #AdgGtkArea::extents-changed signal on @area.
 *
 * Since: 1.0
 **/
void
adg_gtk_area_extents_changed(AdgGtkArea *area, const CpmlExtents *old_extents)
{
    g_return_if_fail(ADG_GTK_IS_AREA(area));

    g_signal_emit(area, _adg_signals[EXTENTS_CHANGED], 0, old_extents);
}


static void
_adg_get_preferred_height(GtkWidget *widget,
                          gint *minimum_height, gint *natural_height)
{
    AdgGtkArea *area;
    const CpmlExtents *extents;

    area = (AdgGtkArea *) widget;
    extents = _adg_get_extents(area);

    if (extents->is_defined) {
        *minimum_height = extents->size.y;
        *natural_height = *minimum_height;
    }
}

static void
_adg_get_preferred_height_for_width(GtkWidget *widget, gint width,
                                    gint *minimum_height, gint *natural_height)
{
    AdgGtkArea *area;
    const CpmlExtents *extents;

    area = (AdgGtkArea *) widget;
    extents = _adg_get_extents(area);

    if (extents->is_defined && extents->size.x > 0) {
        *minimum_height = extents->size.y;
        *natural_height = *minimum_height * width / extents->size.x;
    }
}

static void
_adg_get_preferred_width(GtkWidget *widget,
                         gint *minimum_width, gint *natural_width)
{
    AdgGtkArea *area;
    const CpmlExtents *extents;

    area = (AdgGtkArea *) widget;
    extents = _adg_get_extents(area);

    if (extents->is_defined) {
        *minimum_width = extents->size.x;
        *natural_width = *minimum_width;
    }
}

static void
_adg_get_preferred_width_for_height(GtkWidget *widget, gint height,
                                    gint *minimum_width, gint *natural_width)
{
    AdgGtkArea *area;
    const CpmlExtents *extents;

    area = (AdgGtkArea *) widget;
    extents = _adg_get_extents(area);

    if (extents->is_defined && extents->size.y > 0) {
        *minimum_width = extents->size.x;
        *natural_width = *minimum_width * height / extents->size.y;
    }
}

/**
 * _adg_size_allocate:
 * @widget: an #AdgGtkArea widget
 * @allocation: the new allocation struct
 *
 * Scales the drawing according to the new allocation if
 * #AdgGtkArea:autozoom is %TRUE.
 *
 * TODO: the current implementation initially centers the canvas
 * on the allocation space. Further allocations (due to a
 * window resizing, for example) use the top/left corner of the
 * canvas as reference point. Plan different policies for either
 * those situations.
 *
 * Since: 1.0
 **/
static void
_adg_size_allocate(GtkWidget *widget, GtkAllocation *allocation)
{
    AdgGtkArea *area;
    AdgGtkAreaPrivate *data;
    const CpmlExtents *sheet;
    CpmlVector size;
    gdouble factor;

    if (_ADG_OLD_WIDGET_CLASS->size_allocate)
        _ADG_OLD_WIDGET_CLASS->size_allocate(widget, allocation);

    area = (AdgGtkArea *) widget;
    data = area->data;

    sheet = _adg_get_extents(area);
    if (!sheet->is_defined || sheet->size.x <= 0 || sheet->size.y <= 0)
        return;

    size.x = allocation->width;
    size.y = allocation->height;

    if (data->autozoom)  {
        /* Adjust the zoom according to the allocation and sheet size */
        factor = MIN(size.x / sheet->size.x, size.y / sheet->size.y);
    } else if (!data->initialized) {
        /* First allocation with autozoom off: keep the current zoom */
        factor = 1;
    } else {
        /* Not the first allocation and autozoom off: keep the old map */
        return;
    }

    if (!data->initialized) {
        /* TODO: plan different attachment policies other than centering */
        cairo_matrix_init_translate(&data->render_map,
                                    (size.x - sheet->size.x) / 2 - sheet->org.x,
                                    (size.y - sheet->size.y) / 2 - sheet->org.y);
        data->initialized = TRUE;
    }

    /* TODO: plan other reference points other than left/top (x0, y0) */
    data->render_map.x0 *= factor;
    data->render_map.y0 *= factor;
    data->render_map.xx *= factor;
    data->render_map.yy *= factor;
}

static gboolean
_adg_draw(GtkWidget *widget, cairo_t *cr)
{
    AdgGtkAreaPrivate *data;
    AdgCanvas *canvas;

    data = ((AdgGtkArea *) widget)->data;
    canvas = data->canvas;

    if (canvas != NULL) {
        cairo_transform(cr, &data->render_map);
        adg_entity_render((AdgEntity *) canvas, cr);
    }

    return FALSE;
}

static gboolean
_adg_scroll_event(GtkWidget *widget, GdkEventScroll *event)
{
    gboolean zoom_in, zoom_out, local_space, global_space;
    cairo_matrix_t map, inverted;
    AdgGtkAreaPrivate *data;
    double factor, x, y;

    zoom_in = event->direction == GDK_SCROLL_UP;
    zoom_out = event->direction == GDK_SCROLL_DOWN;
    local_space = (event->state & ADG_GTK_MODIFIERS) == 0;
    global_space = (event->state & ADG_GTK_MODIFIERS) == GDK_SHIFT_MASK;

    if ((zoom_in || zoom_out) && (local_space || global_space) &&
        _adg_get_map(widget, local_space, &map, &inverted)) {
        data = ((AdgGtkArea *) widget)->data;
        factor = zoom_in ? data->factor : 1. / data->factor;
        x = event->x;
        y = event->y;

        cairo_matrix_transform_point(&inverted, &x, &y);
        cairo_matrix_scale(&map, factor, factor);
        cairo_matrix_translate(&map, x/factor - x, y/factor - y);

        _adg_set_map(widget, local_space, &map);

        gtk_widget_queue_draw(widget);

        /* Avoid to chain up the default handler:
         * this event has been grabbed by this function */
        return TRUE;
    }

    if (_ADG_OLD_WIDGET_CLASS->scroll_event == NULL)
        return FALSE;

    return _ADG_OLD_WIDGET_CLASS->scroll_event(widget, event);
}

static gboolean
_adg_button_press_event(GtkWidget *widget, GdkEventButton *event)
{
    AdgGtkAreaPrivate *data = ((AdgGtkArea *) widget)->data;

    if (event->type == GDK_BUTTON_PRESS && event->button == 2) {
        /* Remember the starting coordinates of a (probable) translation */
        data->x_event = event->x;
        data->y_event = event->y;
    }

    if (_ADG_OLD_WIDGET_CLASS->button_press_event == NULL)
        return FALSE;

    return _ADG_OLD_WIDGET_CLASS->button_press_event(widget, event);
}

static gboolean
_adg_motion_notify_event(GtkWidget *widget, GdkEventMotion *event)
{
    gboolean translating, local_space, global_space;
    cairo_matrix_t map, inverted;
    AdgGtkAreaPrivate *data;
    double x, y;

    translating = (event->state & GDK_BUTTON2_MASK) == GDK_BUTTON2_MASK;
    local_space = (event->state & ADG_GTK_MODIFIERS) == 0;
    global_space = (event->state & ADG_GTK_MODIFIERS) == GDK_SHIFT_MASK;

    if (translating && (local_space || global_space) &&
        _adg_get_map(widget, local_space, &map, &inverted)) {
        data = ((AdgGtkArea *) widget)->data;
        x = event->x - data->x_event;
        y = event->y - data->y_event;

        cairo_matrix_transform_distance(&inverted, &x, &y);
        cairo_matrix_translate(&map, x, y);
        data->x_event = event->x;
        data->y_event = event->y;

        _adg_set_map(widget, local_space, &map);

        gtk_widget_queue_draw(widget);

        /* Avoid to chain up the default handler:
         * this event has been grabbed by this function */
        return TRUE;
    }

    if (_ADG_OLD_WIDGET_CLASS->motion_notify_event == NULL)
        return FALSE;

    return _ADG_OLD_WIDGET_CLASS->motion_notify_event(widget, event);
}

static gboolean
_adg_get_map(GtkWidget *widget, gboolean local_space,
             cairo_matrix_t *map, cairo_matrix_t *inverted)
{
    AdgGtkAreaPrivate *data;
    AdgEntity *entity;

    data = ((AdgGtkArea *) widget)->data;
    entity = (AdgEntity *) data->canvas;
    if (entity == NULL)
        return FALSE;

    if (local_space) {
        adg_matrix_copy(map, adg_entity_get_local_map(entity));

        /* The inverted map is subject to the global matrix */
        adg_matrix_copy(inverted, adg_entity_get_global_matrix(entity));
        adg_matrix_transform(inverted, map, ADG_TRANSFORM_BEFORE);
    } else {
        adg_matrix_copy(map, adg_entity_get_global_map(entity));
        adg_matrix_copy(inverted, map);
    }

    return cairo_matrix_invert(inverted) == CAIRO_STATUS_SUCCESS;
}

static void
_adg_set_map(GtkWidget *widget,
             gboolean local_space,
             const cairo_matrix_t *map)
{
    AdgGtkAreaPrivate *data;
    AdgEntity *entity;

    data = ((AdgGtkArea *) widget)->data;
    entity = (AdgEntity *) data->canvas;

    if (entity == NULL)
        return;

    if (local_space) {
        /* TODO: this forcibly overwrites any local transformation */
        adg_entity_set_local_map(entity, map);
    } else {
        adg_matrix_transform(&data->render_map, map, ADG_TRANSFORM_BEFORE);
    }

    /* This will emit the extents-changed signal when applicable */
    _adg_get_extents((AdgGtkArea *) widget);
}

static void
_adg_canvas_changed(AdgGtkArea *area, AdgCanvas *old_canvas)
{
    AdgGtkAreaPrivate *data = area->data;
    data->initialized = FALSE;
}

static const CpmlExtents *
_adg_get_extents(AdgGtkArea *area)
{
    AdgGtkAreaPrivate *data;
    AdgCanvas *canvas;
    CpmlExtents old_extents;

    data = area->data;
    old_extents = data->extents;
    data->extents.is_defined = FALSE;
    canvas = data->canvas;

    if (ADG_IS_CANVAS(canvas)) {
        const CpmlExtents *extents;
        AdgEntity *entity;

        entity = (AdgEntity *) canvas;

        adg_entity_arrange(entity);
        extents = adg_entity_get_extents(entity);

        if (extents != NULL) {
            data->extents = *extents;
            adg_canvas_apply_margins(canvas, &data->extents);
            cpml_extents_transform(&data->extents, &data->render_map);
        }
    }

    if (!cpml_extents_equal(&data->extents, &old_extents))
        g_signal_emit(area, _adg_signals[EXTENTS_CHANGED], 0, &old_extents);

    return &data->extents;
}