/* Copyright 2006, 2007, 2008, Soren Sandmann <sandmann@daimi.au.dk>
 *
 * 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 St, Fifth Floor,
 * Boston, MA 02110-1301, USA.
 */

#include <gdk/gdkprivate.h> /* For GDK_PARENT_RELATIVE_BG */
#include "scrollarea.h"
#include "foo-marshal.h"

G_DEFINE_TYPE (FooScrollArea, foo_scroll_area, GTK_TYPE_CONTAINER);

static GtkWidgetClass *parent_class;

typedef struct BackingStore BackingStore;

typedef void (* ExposeFunc) (cairo_t *cr, GdkRegion *region, gpointer data);

typedef struct InputPath InputPath;
typedef struct InputRegion InputRegion;
typedef struct AutoScrollInfo AutoScrollInfo;

struct InputPath
{
    gboolean                is_stroke;
    cairo_fill_rule_t       fill_rule;
    double                  line_width;
    cairo_path_t           *path;       /* In canvas coordinates */

    FooScrollAreaEventFunc  func;
    gpointer                data;

    InputPath              *next;
};

/* InputRegions are mutually disjoint */
struct InputRegion
{
    GdkRegion *region;      /* the boundary of this area in canvas coordinates */
    InputPath *paths;
};

struct AutoScrollInfo
{
    int             dx;
    int             dy;
    int             timeout_id;
    int             begin_x;
    int             begin_y;
    double          res_x;
    double          res_y;
    GTimer         *timer;
};

struct FooScrollAreaPrivate
{
    GdkWindow              *input_window;

    int                     width;
    int                     height;

    GtkAdjustment          *hadj;
    GtkAdjustment          *vadj;
    int                     x_offset;
    int                     y_offset;

    int                     min_width;
    int                     min_height;

    GPtrArray              *input_regions;

    AutoScrollInfo         *auto_scroll_info;

    /* During expose, this region is set to the region
     * being exposed. At other times, it is NULL
     *
     * It is used for clipping of input areas
     */
    GdkRegion              *expose_region;
    InputRegion            *current_input;

    gboolean                grabbed;
    FooScrollAreaEventFunc  grab_func;
    gpointer                grab_data;

    GdkPixmap              *pixmap;
    GdkRegion              *update_region;      /* In canvas coordinates */
};

enum
{
    VIEWPORT_CHANGED,
    PAINT,
    INPUT,
    LAST_SIGNAL,
};

static guint signals [LAST_SIGNAL] = { 0 };

static void foo_scroll_area_size_request (GtkWidget      *widget,
                                          GtkRequisition *requisition);

static gboolean foo_scroll_area_expose (GtkWidget      *widget,
                                        GdkEventExpose *expose);

static void foo_scroll_area_size_allocate (GtkWidget     *widget,
                                           GtkAllocation *allocation);

static void foo_scroll_area_set_scroll_adjustments (FooScrollArea *scroll_area,
                                                    GtkAdjustment *hadjustment,
                                                    GtkAdjustment *vadjustment);

static void foo_scroll_area_realize (GtkWidget *widget);
static void foo_scroll_area_unrealize (GtkWidget *widget);
static void foo_scroll_area_map (GtkWidget *widget);
static void foo_scroll_area_unmap (GtkWidget *widget);
static gboolean foo_scroll_area_button_press (GtkWidget      *widget,
                                              GdkEventButton *event);
static gboolean foo_scroll_area_button_release (GtkWidget      *widget,
                                                GdkEventButton *event);
static gboolean foo_scroll_area_motion (GtkWidget      *widget,
                                        GdkEventMotion *event);

static void
foo_scroll_area_map (GtkWidget *widget)
{
    FooScrollArea *area = FOO_SCROLL_AREA (widget);

    GTK_WIDGET_CLASS (parent_class)->map (widget);

    if (area->priv->input_window)
        gdk_window_show (area->priv->input_window);
}

static void
foo_scroll_area_unmap (GtkWidget *widget)
{
    FooScrollArea *area = FOO_SCROLL_AREA (widget);

    if (area->priv->input_window)
        gdk_window_hide (area->priv->input_window);

    GTK_WIDGET_CLASS (parent_class)->unmap (widget);
}

static void
foo_scroll_area_finalize (GObject *object)
{
    FooScrollArea *scroll_area = FOO_SCROLL_AREA (object);

    g_object_unref (scroll_area->priv->hadj);
    g_object_unref (scroll_area->priv->vadj);

    g_ptr_array_free (scroll_area->priv->input_regions, TRUE);

    g_free (scroll_area->priv);

    G_OBJECT_CLASS (foo_scroll_area_parent_class)->finalize (object);
}

static void
foo_scroll_area_class_init (FooScrollAreaClass *class)
{
    GObjectClass *object_class = G_OBJECT_CLASS (class);
    GtkWidgetClass *widget_class = GTK_WIDGET_CLASS (class);

    object_class->finalize = foo_scroll_area_finalize;

    widget_class->size_request = foo_scroll_area_size_request;
    widget_class->expose_event = foo_scroll_area_expose;

    widget_class->size_allocate = foo_scroll_area_size_allocate;
    widget_class->realize = foo_scroll_area_realize;
    widget_class->unrealize = foo_scroll_area_unrealize;
    widget_class->button_press_event = foo_scroll_area_button_press;
    widget_class->button_release_event = foo_scroll_area_button_release;
    widget_class->motion_notify_event = foo_scroll_area_motion;
    widget_class->map = foo_scroll_area_map;
    widget_class->unmap = foo_scroll_area_unmap;

    class->set_scroll_adjustments = foo_scroll_area_set_scroll_adjustments;

    parent_class = g_type_class_peek_parent (class);

    signals[VIEWPORT_CHANGED] =
    g_signal_new ("viewport_changed",
                  G_OBJECT_CLASS_TYPE (object_class),
                  G_SIGNAL_RUN_LAST | G_SIGNAL_ACTION,
                  G_STRUCT_OFFSET (FooScrollAreaClass,
                                   viewport_changed),
                  NULL, NULL,
                  foo_marshal_VOID__BOXED_BOXED,
                  G_TYPE_NONE, 2,
                  GDK_TYPE_RECTANGLE,
                  GDK_TYPE_RECTANGLE);

    signals[PAINT] =
    g_signal_new ("paint",
                  G_OBJECT_CLASS_TYPE (object_class),
                  G_SIGNAL_RUN_LAST | G_SIGNAL_ACTION,
                  G_STRUCT_OFFSET (FooScrollAreaClass,
                                   paint),
                  NULL, NULL,
                  foo_marshal_VOID__POINTER_BOXED_POINTER,
                  G_TYPE_NONE, 3,
                  G_TYPE_POINTER,
                  GDK_TYPE_RECTANGLE,
                  G_TYPE_POINTER);

    widget_class->set_scroll_adjustments_signal =
    g_signal_new ("set_scroll_adjustments",
                  G_OBJECT_CLASS_TYPE (object_class),
                  G_SIGNAL_RUN_LAST | G_SIGNAL_ACTION,
                  G_STRUCT_OFFSET (FooScrollAreaClass,
                                   set_scroll_adjustments),
                  NULL, NULL,
                  foo_marshal_VOID__OBJECT_OBJECT,
                  G_TYPE_NONE, 2,
                  GTK_TYPE_ADJUSTMENT,
                  GTK_TYPE_ADJUSTMENT);
}

static GtkAdjustment *
new_adjustment (void)
{
    return GTK_ADJUSTMENT (gtk_adjustment_new (0.0, 0.0, 0.0, 0.0, 0.0, 0.0));
}

static void
foo_scroll_area_init (FooScrollArea *scroll_area)
{
    GtkWidget *widget;

    widget = GTK_WIDGET (scroll_area);

    gtk_widget_set_has_window (widget, FALSE);
    gtk_widget_set_redraw_on_allocate (widget, FALSE);

    scroll_area->priv = g_new0 (FooScrollAreaPrivate, 1);
    scroll_area->priv->width = 0;
    scroll_area->priv->height = 0;
    scroll_area->priv->hadj = g_object_ref_sink (new_adjustment());
    scroll_area->priv->vadj = g_object_ref_sink (new_adjustment());
    scroll_area->priv->x_offset = 0.0;
    scroll_area->priv->y_offset = 0.0;
    scroll_area->priv->min_width = -1;
    scroll_area->priv->min_height = -1;
    scroll_area->priv->auto_scroll_info = NULL;
    scroll_area->priv->input_regions = g_ptr_array_new ();
    scroll_area->priv->pixmap = NULL;
    scroll_area->priv->update_region = gdk_region_new ();

    gtk_widget_set_double_buffered (widget, FALSE);
}

static void
translate_cairo_device (cairo_t       *cr,
                        int            x_offset,
                        int            y_offset)
{
    cairo_surface_t *surface = cairo_get_target (cr);
    double dev_x;
    double dev_y;

    cairo_surface_get_device_offset (surface, &dev_x, &dev_y);
    dev_x += x_offset;
    dev_y += y_offset;
    cairo_surface_set_device_offset (surface, dev_x, dev_y);
}

typedef void (* PathForeachFunc) (double  *x,
                                  double  *y,
                                  gpointer data);

static void
path_foreach_point (cairo_path_t     *path,
                    PathForeachFunc   func,
                    gpointer          user_data)
{
    int i;

    for (i = 0; i < path->num_data; i += path->data[i].header.length)
    {
        cairo_path_data_t *data = &(path->data[i]);

        switch (data->header.type)
        {
            case CAIRO_PATH_MOVE_TO:
            case CAIRO_PATH_LINE_TO:
                func (&(data[1].point.x), &(data[1].point.y), user_data);
                break;

            case CAIRO_PATH_CURVE_TO:
                func (&(data[1].point.x), &(data[1].point.y), user_data);
                func (&(data[2].point.x), &(data[2].point.y), user_data);
                func (&(data[3].point.x), &(data[3].point.y), user_data);
                break;

            case CAIRO_PATH_CLOSE_PATH:
                break;
        }
    }
}

typedef struct
{
    double x1, y1, x2, y2;
} Box;

static void
input_path_free_list (InputPath *paths)
{
    if (!paths)
        return;

    input_path_free_list (paths->next);
    cairo_path_destroy (paths->path);
    g_free (paths);
}

static void
input_region_free (InputRegion *region)
{
    input_path_free_list (region->paths);
    gdk_region_destroy (region->region);

    g_free (region);
}

static void
get_viewport (FooScrollArea *scroll_area,
              GdkRectangle  *viewport)
{
    GtkAllocation allocation;
    GtkWidget *widget = GTK_WIDGET (scroll_area);

    gtk_widget_get_allocation (widget, &allocation);

    viewport->x = scroll_area->priv->x_offset;
    viewport->y = scroll_area->priv->y_offset;
    viewport->width = allocation.width;
    viewport->height = allocation.height;
}

static void
allocation_to_canvas (FooScrollArea *area,
                      int           *x,
                      int           *y)
{
    *x += area->priv->x_offset;
    *y += area->priv->y_offset;
}

static void
clear_exposed_input_region (FooScrollArea *area,
                            GdkRegion *exposed) /* in canvas coordinates */
{
    guint i;
    GdkRegion *viewport;
    GdkRectangle allocation;

    gtk_widget_get_allocation (GTK_WIDGET (area), &allocation);
    allocation.x = 0;
    allocation.y = 0;
    allocation_to_canvas (area, &allocation.x, &allocation.y);
    viewport = gdk_region_rectangle (&allocation);
    gdk_region_subtract (viewport, exposed);

    for (i = 0; i < area->priv->input_regions->len; ++i)
    {
        InputRegion *region = area->priv->input_regions->pdata[i];

        gdk_region_intersect (region->region, viewport);

        if (gdk_region_empty (region->region))
        {
            input_region_free (region);
            g_ptr_array_remove_index_fast (area->priv->input_regions, i--);
        }
    }

    gdk_region_destroy (viewport);
}

static void
setup_background_cr (GdkWindow *window,
                     cairo_t   *cr,
                     int        x_offset,
                     int        y_offset)
{
    GdkWindowObject *private = (GdkWindowObject *)window;

    if (private->bg_pixmap == GDK_PARENT_RELATIVE_BG && private->parent)
    {
        x_offset += private->x;
        y_offset += private->y;

        setup_background_cr (GDK_WINDOW (private->parent), cr, x_offset, y_offset);
    }
    else if (private->bg_pixmap &&
         private->bg_pixmap != GDK_PARENT_RELATIVE_BG &&
         private->bg_pixmap != GDK_NO_BG)
    {
        gdk_cairo_set_source_pixmap (cr, private->bg_pixmap, -x_offset, -y_offset);
    }
    else
    {
        gdk_cairo_set_source_color (cr, &private->bg_color);
    }
}

static void
initialize_background (GtkWidget *widget,
                       cairo_t   *cr)
{
    setup_background_cr (gtk_widget_get_window (widget), cr, 0, 0);

    cairo_paint (cr);
}

static void
clip_to_region (cairo_t *cr, GdkRegion *region)
{
    int n_rects;
    GdkRectangle *rects;

    gdk_region_get_rectangles (region, &rects, &n_rects);

    cairo_new_path (cr);
    while (n_rects--)
    {
        GdkRectangle *rect = &(rects[n_rects]);

        cairo_rectangle (cr, rect->x, rect->y, rect->width, rect->height);
    }
    cairo_clip (cr);

    g_free (rects);
}

static void
simple_draw_drawable (GdkDrawable *dst,
                      GdkDrawable *src,
                      int          src_x,
                      int          src_y,
                      int          dst_x,
                      int          dst_y,
                      int          width,
                      int          height)
{
    GdkGC *gc = gdk_gc_new (dst);

    gdk_draw_drawable (dst, gc, src, src_x, src_y, dst_x, dst_y, width, height);

    g_object_unref (gc);
}

static gboolean
foo_scroll_area_expose (GtkWidget *widget,
                        GdkEventExpose *expose)
{
    FooScrollArea *scroll_area = FOO_SCROLL_AREA (widget);
    cairo_t *cr;
    GdkGC *gc;
    GdkRectangle extents;
    GdkWindow *window = gtk_widget_get_window (widget);
    GdkRegion *region;
    int x_offset, y_offset;
    GtkAllocation widget_allocation;

    /* I don't think expose can ever recurse for the same area */
    g_assert (!scroll_area->priv->expose_region);

    /* Note that this function can be called at a time
     * where the adj->value is different from x_offset.
     * Ie., the GtkScrolledWindow changed the adj->value
     * without emitting the value_changed signal.
     *
     * Hence we must always use the value we got
     * the last time the signal was emitted, ie.,
     * priv->{x,y}_offset.
     */

    x_offset = scroll_area->priv->x_offset;
    y_offset = scroll_area->priv->y_offset;

    scroll_area->priv->expose_region = expose->region;

    /* Setup input areas */
    clear_exposed_input_region (scroll_area, scroll_area->priv->update_region);

    scroll_area->priv->current_input = g_new0 (InputRegion, 1);
    scroll_area->priv->current_input->region = gdk_region_copy (scroll_area->priv->update_region);
    scroll_area->priv->current_input->paths = NULL;
    g_ptr_array_add (scroll_area->priv->input_regions,
                     scroll_area->priv->current_input);

    region = scroll_area->priv->update_region;
    scroll_area->priv->update_region = gdk_region_new ();

    /* Create cairo context */
    cr = gdk_cairo_create (scroll_area->priv->pixmap);
    translate_cairo_device (cr, -x_offset, -y_offset);
    clip_to_region (cr, region);
    initialize_background (widget, cr);

    /* Create regions */
    gdk_region_get_clipbox (region, &extents);

    g_signal_emit (widget, signals[PAINT], 0, cr, &extents, region);

    /* Destroy stuff */
    cairo_destroy (cr);

    scroll_area->priv->expose_region = NULL;
    scroll_area->priv->current_input = NULL;

    /* Finally draw the backing pixmap */
    gc = gdk_gc_new (window);

    gdk_gc_set_clip_region (gc, expose->region);

    gtk_widget_get_allocation (widget, &widget_allocation);
    gdk_draw_drawable (window, gc, scroll_area->priv->pixmap,
                       0, 0, widget_allocation.x, widget_allocation.y,
                       widget_allocation.width, widget_allocation.height);

    g_object_unref (gc);
    gdk_region_destroy (region);

    return TRUE;
}

void
foo_scroll_area_get_viewport (FooScrollArea *scroll_area,
                              GdkRectangle  *viewport)
{
    g_return_if_fail (FOO_IS_SCROLL_AREA (scroll_area));

    if (!viewport)
        return;

    get_viewport (scroll_area, viewport);
}

static void
process_event (FooScrollArea           *scroll_area,
               FooScrollAreaEventType   input_type,
               int                      x,
               int                      y);

static void
emit_viewport_changed (FooScrollArea *scroll_area,
                       GdkRectangle  *new_viewport,
                       GdkRectangle  *old_viewport)
{
    int px, py;
    g_signal_emit (scroll_area, signals[VIEWPORT_CHANGED], 0,
                   new_viewport, old_viewport);

    gdk_window_get_pointer (scroll_area->priv->input_window, &px, &py, NULL);

    process_event (scroll_area, FOO_MOTION, px, py);
}

static void
clamp_adjustment (GtkAdjustment *adj)
{
    if (gtk_adjustment_get_upper (adj) >= gtk_adjustment_get_page_size (adj))
        gtk_adjustment_set_value (adj, CLAMP (gtk_adjustment_get_value (adj), 0.0,
                                              gtk_adjustment_get_upper (adj)
                                               - gtk_adjustment_get_page_size (adj)));
    else
        gtk_adjustment_set_value (adj, 0.0);

    gtk_adjustment_changed (adj);
}

static gboolean
set_adjustment_values (FooScrollArea *scroll_area)
{
    GtkAllocation allocation;

    GtkAdjustment *hadj = scroll_area->priv->hadj;
    GtkAdjustment *vadj = scroll_area->priv->vadj;

    /* Horizontal */
    gtk_widget_get_allocation (GTK_WIDGET (scroll_area), &allocation);
    g_object_freeze_notify (G_OBJECT (hadj));
    gtk_adjustment_set_page_size (hadj, allocation.width);
    gtk_adjustment_set_step_increment (hadj, 0.1 * allocation.width);
    gtk_adjustment_set_page_increment (hadj, 0.9 * allocation.width);
    gtk_adjustment_set_lower (hadj, 0.0);
    gtk_adjustment_set_upper (hadj, scroll_area->priv->width);
    g_object_thaw_notify (G_OBJECT (hadj));

    /* Vertical */
    g_object_freeze_notify (G_OBJECT (vadj));
    gtk_adjustment_set_page_size (vadj, allocation.height);
    gtk_adjustment_set_step_increment (vadj, 0.1 * allocation.height);
    gtk_adjustment_set_page_increment (vadj, 0.9 * allocation.height);
    gtk_adjustment_set_lower (vadj, 0.0);
    gtk_adjustment_set_upper (vadj, scroll_area->priv->height);
    g_object_thaw_notify (G_OBJECT (vadj));

    clamp_adjustment (hadj);
    clamp_adjustment (vadj);

    return TRUE;
}

static void
foo_scroll_area_realize (GtkWidget *widget)
{
    FooScrollArea *area = FOO_SCROLL_AREA (widget);
    GdkWindowAttr attributes;
    GtkAllocation widget_allocation;
    GdkWindow *window;
    gint attributes_mask;

    gtk_widget_get_allocation (widget, &widget_allocation);
    gtk_widget_set_realized (widget, TRUE);

    attributes.window_type = GDK_WINDOW_CHILD;
    attributes.x = widget_allocation.x;
    attributes.y = widget_allocation.y;
    attributes.width = widget_allocation.width;
    attributes.height = widget_allocation.height;
    attributes.wclass = GDK_INPUT_ONLY;
    attributes.event_mask = gtk_widget_get_events (widget);
    attributes.event_mask |= (GDK_BUTTON_PRESS_MASK |
                              GDK_BUTTON_RELEASE_MASK |
                              GDK_BUTTON1_MOTION_MASK |
                              GDK_BUTTON2_MOTION_MASK |
                              GDK_BUTTON3_MOTION_MASK |
                              GDK_POINTER_MOTION_MASK |
                              GDK_ENTER_NOTIFY_MASK |
                              GDK_LEAVE_NOTIFY_MASK);

    attributes_mask = GDK_WA_X | GDK_WA_Y;

    window = gtk_widget_get_parent_window (widget);
    gtk_widget_set_window (widget, window);
    g_object_ref (window);

    area->priv->input_window = gdk_window_new (window,
                                               &attributes, attributes_mask);

    area->priv->pixmap = gdk_pixmap_new (window,
                                         widget_allocation.width,
                                         widget_allocation.height,
                                         -1);

    gdk_window_set_user_data (area->priv->input_window, area);

    gtk_widget_style_attach (widget);
}

static void
foo_scroll_area_unrealize (GtkWidget *widget)
{
    FooScrollArea *area = FOO_SCROLL_AREA (widget);

    if (area->priv->input_window)
    {
        gdk_window_set_user_data (area->priv->input_window, NULL);
        gdk_window_destroy (area->priv->input_window);
        area->priv->input_window = NULL;
    }

    GTK_WIDGET_CLASS (parent_class)->unrealize (widget);
}

static GdkPixmap *
create_new_pixmap (GtkWidget *widget,
                   GdkPixmap *old)
{
    GtkAllocation widget_allocation;
    GdkPixmap *new;

    gtk_widget_get_allocation (widget, &widget_allocation);

    new = gdk_pixmap_new (gtk_widget_get_window (widget),
                          widget_allocation.width,
                          widget_allocation.height,
                          -1);

    /* Unfortunately we don't know in which direction we were resized,
     * so we just assume we were dragged from the south-east corner.
     *
     * Although, maybe we could get the root coordinates of the input-window?
     * That might just work, actually. We need to make sure marco uses
     * static gravity for the window before this will be useful.
     */
    simple_draw_drawable (new, old, 0, 0, 0, 0, -1, -1);

    return new;
}

static void
allocation_to_canvas_region (FooScrollArea *area,
                 GdkRegion *region)
{
    gdk_region_offset (region, area->priv->x_offset, area->priv->y_offset);
}

static void
foo_scroll_area_size_allocate (GtkWidget     *widget,
                               GtkAllocation *allocation)
{
    FooScrollArea *scroll_area = FOO_SCROLL_AREA (widget);
    GdkRectangle new_viewport;
    GdkRectangle old_viewport;
    GdkRegion *old_allocation;
    GdkRegion *invalid;
    GtkAllocation widget_allocation;

    get_viewport (scroll_area, &old_viewport);

    gtk_widget_get_allocation (widget, &widget_allocation);
    old_allocation = gdk_region_rectangle (&widget_allocation);
    gdk_region_offset (old_allocation,
                       -widget_allocation.x, -widget_allocation.y);
    invalid = gdk_region_rectangle (allocation);
    gdk_region_offset (invalid, -allocation->x, -allocation->y);
    gdk_region_xor (invalid, old_allocation);
    allocation_to_canvas_region (scroll_area, invalid);
    foo_scroll_area_invalidate_region (scroll_area, invalid);
    gdk_region_destroy (old_allocation);
    gdk_region_destroy (invalid);

    gtk_widget_set_allocation (widget, allocation);

    if (scroll_area->priv->input_window)
    {
        GdkPixmap *new_pixmap;

        gdk_window_move_resize (scroll_area->priv->input_window,
                                allocation->x, allocation->y,
                                allocation->width, allocation->height);

        new_pixmap = create_new_pixmap (widget, scroll_area->priv->pixmap);
        g_object_unref (scroll_area->priv->pixmap);
        scroll_area->priv->pixmap = new_pixmap;
    }

    get_viewport (scroll_area, &new_viewport);

    emit_viewport_changed (scroll_area, &new_viewport, &old_viewport);
}

static void
emit_input (FooScrollArea          *scroll_area,
            FooScrollAreaEventType type,
            int                    x,
            int                    y,
            FooScrollAreaEventFunc func,
            gpointer               data)
{
    FooScrollAreaEvent event;

    if (!func)
        return;

    if (type != FOO_MOTION)
        emit_input (scroll_area, FOO_MOTION, x, y, func, data);

    event.type = type;
    event.x = x;
    event.y = y;

    func (scroll_area, &event, data);
}

static void
process_event (FooScrollArea           *scroll_area,
               FooScrollAreaEventType   input_type,
               int                      x,
               int                      y)
{
    GtkWidget *widget = GTK_WIDGET (scroll_area);
    guint i;

    allocation_to_canvas (scroll_area, &x, &y);

    if (scroll_area->priv->grabbed)
    {
        emit_input (scroll_area, input_type, x, y,
                scroll_area->priv->grab_func,
                scroll_area->priv->grab_data);
        return;
    }

    for (i = 0; i < scroll_area->priv->input_regions->len; ++i)
    {
        InputRegion *region = scroll_area->priv->input_regions->pdata[i];

        if (gdk_region_point_in (region->region, x, y))
        {
            InputPath *path;

            path = region->paths;
            while (path)
            {
                cairo_t *cr;
                gboolean inside;

                cr = gdk_cairo_create (gtk_widget_get_window (widget));
                cairo_set_fill_rule (cr, path->fill_rule);
                cairo_set_line_width (cr, path->line_width);
                cairo_append_path (cr, path->path);

                if (path->is_stroke)
                    inside = cairo_in_stroke (cr, x, y);
                else
                    inside = cairo_in_fill (cr, x, y);

                cairo_destroy (cr);

                if (inside)
                {
                    emit_input (scroll_area, input_type,
                                x, y,
                                path->func,
                                path->data);
                    return;
                }

                path = path->next;
            }

            /* Since the regions are all disjoint, no other region
             * can match. Of course we could be clever and try and
             * sort the regions, but so far I have been unable to
             * make this loop show up on a profile.
             */
            return;
        }
    }
}

static void
process_gdk_event (FooScrollArea *scroll_area,
                   int            x,
                   int            y,
                   GdkEvent      *event)
{
    FooScrollAreaEventType input_type;

    if (event->type == GDK_BUTTON_PRESS)
        input_type = FOO_BUTTON_PRESS;
    else if (event->type == GDK_BUTTON_RELEASE)
        input_type = FOO_BUTTON_RELEASE;
    else if (event->type == GDK_MOTION_NOTIFY)
        input_type = FOO_MOTION;
    else
        return;

    process_event (scroll_area, input_type, x, y);
}

static gboolean
foo_scroll_area_button_press (GtkWidget *widget,
                              GdkEventButton *event)
{
    FooScrollArea *area = FOO_SCROLL_AREA (widget);

    process_gdk_event (area, event->x, event->y, (GdkEvent *)event);

    return TRUE;
}

static gboolean
foo_scroll_area_button_release (GtkWidget      *widget,
                                GdkEventButton *event)
{
    FooScrollArea *area = FOO_SCROLL_AREA (widget);

    process_gdk_event (area, event->x, event->y, (GdkEvent *)event);

    return FALSE;
}

static gboolean
foo_scroll_area_motion (GtkWidget      *widget,
                        GdkEventMotion *event)
{
    FooScrollArea *area = FOO_SCROLL_AREA (widget);

    process_gdk_event (area, event->x, event->y, (GdkEvent *)event);
    return TRUE;
}

void
foo_scroll_area_set_size_fixed_y (FooScrollArea    *scroll_area,
                                  int               width,
                                  int               height,
                                  int               old_y,
                                  int               new_y)
{
    scroll_area->priv->width = width;
    scroll_area->priv->height = height;

    g_object_thaw_notify (G_OBJECT (scroll_area->priv->vadj));
    gtk_adjustment_set_value (scroll_area->priv->vadj, new_y);

    set_adjustment_values (scroll_area);
    g_object_thaw_notify (G_OBJECT (scroll_area->priv->vadj));
}

void
foo_scroll_area_set_size (FooScrollArea    *scroll_area,
                          int               width,
                          int               height)
{
    g_return_if_fail (FOO_IS_SCROLL_AREA (scroll_area));

    /* FIXME: Default scroll algorithm should probably be to
     * keep the same *area* outside the screen as before.
     *
     * For wrapper widgets that will do something roughly
     * right. For widgets that don't change size, it
     * will do the right thing. Except for idle-layouting
     * widgets.
     *
     * Maybe there should be some generic support for those
     * widgets. Can that even be done?
     *
     * Should we have a version of this function using
     * fixed points?
     */

    scroll_area->priv->width = width;
    scroll_area->priv->height = height;

    set_adjustment_values (scroll_area);
}

static void
foo_scroll_area_size_request (GtkWidget      *widget,
                              GtkRequisition *requisition)
{
    FooScrollArea *scroll_area = FOO_SCROLL_AREA (widget);

    requisition->width = scroll_area->priv->min_width;
    requisition->height = scroll_area->priv->min_height;
}

static void
foo_scroll_area_scroll (FooScrollArea *area,
                        gint dx,
                        gint dy)
{
    GdkRectangle allocation;
    GdkRectangle src_area;
    GdkRectangle move_area;
    GdkRegion *invalid_region;

    gtk_widget_get_allocation (GTK_WIDGET (area), &allocation);
    allocation.x = 0;
    allocation.y = 0;

    src_area = allocation;
    src_area.x -= dx;
    src_area.y -= dy;

    invalid_region = gdk_region_rectangle (&allocation);

    if (gdk_rectangle_intersect (&allocation, &src_area, &move_area))
    {
        GdkRegion *move_region;

        simple_draw_drawable (area->priv->pixmap, area->priv->pixmap,
                              move_area.x, move_area.y,
                              move_area.x + dx, move_area.y + dy,
                              move_area.width, move_area.height);

        gtk_widget_queue_draw (GTK_WIDGET (area));

        move_region = gdk_region_rectangle (&move_area);
        gdk_region_offset (move_region, dx, dy);
        gdk_region_subtract (invalid_region, move_region);
        gdk_region_destroy (move_region);
    }

    allocation_to_canvas_region (area, invalid_region);

    foo_scroll_area_invalidate_region (area, invalid_region);

    gdk_region_destroy (invalid_region);
}

static void
foo_scrollbar_adjustment_changed (GtkAdjustment *adj,
                                  FooScrollArea *scroll_area)
{
    GtkWidget *widget = GTK_WIDGET (scroll_area);
    gint dx = 0;
    gint dy = 0;
    GdkRectangle old_viewport, new_viewport;

    get_viewport (scroll_area, &old_viewport);

    if (adj == scroll_area->priv->hadj)
    {
        /* FIXME: do we treat the offset as int or double, and,
         * if int, how do we round?
         */
        dx = (int)gtk_adjustment_get_value (adj) - scroll_area->priv->x_offset;
        scroll_area->priv->x_offset = gtk_adjustment_get_value (adj);
    }
    else if (adj == scroll_area->priv->vadj)
    {
        dy = (int)gtk_adjustment_get_value (adj) - scroll_area->priv->y_offset;
        scroll_area->priv->y_offset = gtk_adjustment_get_value (adj);
    }
    else
    {
        g_assert_not_reached ();
    }

    if (gtk_widget_get_realized (widget))
    {
        foo_scroll_area_scroll (scroll_area, -dx, -dy);
    }

    get_viewport (scroll_area, &new_viewport);

    emit_viewport_changed (scroll_area, &new_viewport, &old_viewport);
}

static void
set_one_adjustment (FooScrollArea *scroll_area,
                    GtkAdjustment *adjustment,
                    GtkAdjustment **location)
{
    g_return_if_fail (location != NULL);

    if (adjustment == *location)
        return;

    if (!adjustment)
        adjustment = new_adjustment ();

    g_return_if_fail (GTK_IS_ADJUSTMENT (adjustment));

    if (*location)
    {
        g_signal_handlers_disconnect_by_func (
            *location, foo_scrollbar_adjustment_changed, scroll_area);

        g_object_unref (*location);
    }

    *location = adjustment;

    g_object_ref_sink (*location);

    g_signal_connect (*location, "value_changed",
                      G_CALLBACK (foo_scrollbar_adjustment_changed),
                      scroll_area);
}

static void
foo_scroll_area_set_scroll_adjustments (FooScrollArea *scroll_area,
                                        GtkAdjustment *hadjustment,
                                        GtkAdjustment *vadjustment)
{
    set_one_adjustment (scroll_area, hadjustment, &scroll_area->priv->hadj);
    set_one_adjustment (scroll_area, vadjustment, &scroll_area->priv->vadj);

    set_adjustment_values (scroll_area);
}

FooScrollArea *
foo_scroll_area_new (void)
{
    return g_object_new (FOO_TYPE_SCROLL_AREA, NULL);
}

void
foo_scroll_area_set_min_size (FooScrollArea *scroll_area,
                              int            min_width,
                              int            min_height)
{
    scroll_area->priv->min_width = min_width;
    scroll_area->priv->min_height = min_height;

    /* FIXME: think through invalidation.
     *
     * Goals: - no repainting everything on size_allocate(),
     *        - make sure input boxes are invalidated when
     *          needed
     */
    gtk_widget_queue_resize (GTK_WIDGET (scroll_area));
}

static void
user_to_device (double *x, double *y,
                gpointer data)
{
    cairo_t *cr = data;

    cairo_user_to_device (cr, x, y);
}

static InputPath *
make_path (FooScrollArea         *area,
           cairo_t               *cr,
           gboolean               is_stroke,
           FooScrollAreaEventFunc func,
           gpointer               data)
{
    InputPath *path = g_new0 (InputPath, 1);

    path->is_stroke = is_stroke;
    path->fill_rule = cairo_get_fill_rule (cr);
    path->line_width = cairo_get_line_width (cr);
    path->path = cairo_copy_path (cr);
    path_foreach_point (path->path, user_to_device, cr);
    path->func = func;
    path->data = data;
    path->next = area->priv->current_input->paths;
    area->priv->current_input->paths = path;
    return path;
}

/* FIXME: we probably really want a
 *
 *  foo_scroll_area_add_input_from_fill (area, cr, ...);
 * and
 *      foo_scroll_area_add_input_from_stroke (area, cr, ...);
 * as well.
 */
void
foo_scroll_area_add_input_from_fill (FooScrollArea           *scroll_area,
                                     cairo_t                 *cr,
                                     FooScrollAreaEventFunc   func,
                                     gpointer                 data)
{
    g_return_if_fail (FOO_IS_SCROLL_AREA (scroll_area));
    g_return_if_fail (cr != NULL);
    g_return_if_fail (scroll_area->priv->current_input);

    make_path (scroll_area, cr, FALSE, func, data);
}

void
foo_scroll_area_add_input_from_stroke (FooScrollArea           *scroll_area,
                                       cairo_t                  *cr,
                                       FooScrollAreaEventFunc   func,
                                       gpointer                 data)
{
    g_return_if_fail (FOO_IS_SCROLL_AREA (scroll_area));
    g_return_if_fail (cr != NULL);
    g_return_if_fail (scroll_area->priv->current_input);

    make_path (scroll_area, cr, TRUE, func, data);
}

void
foo_scroll_area_invalidate (FooScrollArea *scroll_area)
{
    GtkAllocation allocation;
    GtkWidget *widget = GTK_WIDGET (scroll_area);

    gtk_widget_get_allocation (widget, &allocation);
    foo_scroll_area_invalidate_rect (scroll_area,
                     scroll_area->priv->x_offset, scroll_area->priv->y_offset,
                     allocation.width,
                     allocation.height);
}

static void
canvas_to_window (FooScrollArea *area,
                  GdkRegion     *region)
{
    GtkAllocation allocation;
    GtkWidget *widget = GTK_WIDGET (area);

    gtk_widget_get_allocation (widget, &allocation);
    gdk_region_offset (region,
               -area->priv->x_offset + allocation.x,
               -area->priv->y_offset + allocation.y);
}

static void
window_to_canvas (FooScrollArea *area,
                  GdkRegion *region)
{
    GtkAllocation allocation;
    GtkWidget *widget = GTK_WIDGET (area);

    gtk_widget_get_allocation (widget, &allocation);
    gdk_region_offset (region,
               area->priv->x_offset - allocation.x,
               area->priv->y_offset - allocation.y);
}

void
foo_scroll_area_invalidate_region (FooScrollArea *area,
                                   GdkRegion     *region)
{
    GtkWidget *widget;

    g_return_if_fail (FOO_IS_SCROLL_AREA (area));

    widget = GTK_WIDGET (area);

    gdk_region_union (area->priv->update_region, region);

    if (gtk_widget_get_realized (widget))
    {
        canvas_to_window (area, region);

        gdk_window_invalidate_region (gtk_widget_get_window (widget),
                                      region, TRUE);

        window_to_canvas (area, region);
    }
}

void
foo_scroll_area_invalidate_rect (FooScrollArea *scroll_area,
                                 int            x,
                                 int            y,
                                 int            width,
                                 int            height)
{
    GdkRectangle rect = { x, y, width, height };
    GdkRegion *region;

    g_return_if_fail (FOO_IS_SCROLL_AREA (scroll_area));

    region = gdk_region_rectangle (&rect);

    foo_scroll_area_invalidate_region (scroll_area, region);

    gdk_region_destroy (region);
}

void
foo_scroll_area_begin_grab (FooScrollArea *scroll_area,
                            FooScrollAreaEventFunc func,
                            gpointer       input_data)
{
    g_return_if_fail (FOO_IS_SCROLL_AREA (scroll_area));
    g_return_if_fail (!scroll_area->priv->grabbed);

    scroll_area->priv->grabbed = TRUE;
    scroll_area->priv->grab_func = func;
    scroll_area->priv->grab_data = input_data;

    /* FIXME: we should probably take a server grab */
    /* Also, maybe there should be support for setting the grab cursor */
}

void
foo_scroll_area_end_grab (FooScrollArea *scroll_area)
{
    g_return_if_fail (FOO_IS_SCROLL_AREA (scroll_area));

    scroll_area->priv->grabbed = FALSE;
    scroll_area->priv->grab_func = NULL;
    scroll_area->priv->grab_data = NULL;
}

gboolean
foo_scroll_area_is_grabbed (FooScrollArea *scroll_area)
{
    return scroll_area->priv->grabbed;
}

void
foo_scroll_area_set_viewport_pos (FooScrollArea  *scroll_area,
                                  int             x,
                                  int             y)
{
    g_object_freeze_notify (G_OBJECT (scroll_area->priv->hadj));
    g_object_freeze_notify (G_OBJECT (scroll_area->priv->vadj));
    gtk_adjustment_set_value (scroll_area->priv->hadj, x);
    gtk_adjustment_set_value (scroll_area->priv->vadj, y);

    set_adjustment_values (scroll_area);
    g_object_thaw_notify (G_OBJECT (scroll_area->priv->hadj));
    g_object_thaw_notify (G_OBJECT (scroll_area->priv->vadj));
}

static gboolean
rect_contains (const GdkRectangle *rect, int x, int y)
{
    return (x >= rect->x        &&
            y >= rect->y        &&
            x  < rect->x + rect->width  &&
            y  < rect->y + rect->height);
}

static void
stop_scrolling (FooScrollArea *area)
{
    if (area->priv->auto_scroll_info)
    {
        g_source_remove (area->priv->auto_scroll_info->timeout_id);
        g_timer_destroy (area->priv->auto_scroll_info->timer);
        g_free (area->priv->auto_scroll_info);

        area->priv->auto_scroll_info = NULL;
    }
}

static gboolean
scroll_idle (gpointer data)
{
    GdkRectangle viewport, new_viewport;
    FooScrollArea *area = data;
    AutoScrollInfo *info = area->priv->auto_scroll_info;
    int new_x, new_y;
    double elapsed;

    get_viewport (area, &viewport);

    elapsed = g_timer_elapsed (info->timer, NULL);

    info->res_x = elapsed * info->dx / 0.2;
    info->res_y = elapsed * info->dy / 0.2;

    new_x = viewport.x + info->res_x;
    new_y = viewport.y + info->res_y;

    foo_scroll_area_set_viewport_pos (area, new_x, new_y);

    get_viewport (area, &new_viewport);

    if (viewport.x == new_viewport.x        &&
    viewport.y == new_viewport.y        &&
    (info->res_x > 1.0          ||
     info->res_y > 1.0          ||
     info->res_x < -1.0         ||
     info->res_y < -1.0))
    {
        stop_scrolling (area);

        /* stop scrolling if it didn't have an effect */
        return FALSE;
    }

    return TRUE;
}

static void
ensure_scrolling (FooScrollArea *area,
                  int            dx,
                  int            dy)
{
    if (!area->priv->auto_scroll_info)
    {
        area->priv->auto_scroll_info = g_new0 (AutoScrollInfo, 1);
        area->priv->auto_scroll_info->timeout_id =
            g_idle_add (scroll_idle, area);
        area->priv->auto_scroll_info->timer = g_timer_new ();
    }

    area->priv->auto_scroll_info->dx = dx;
    area->priv->auto_scroll_info->dy = dy;
}

void
foo_scroll_area_auto_scroll (FooScrollArea      *scroll_area,
                             FooScrollAreaEvent *event)
{
    GdkRectangle viewport;

    get_viewport (scroll_area, &viewport);

    if (rect_contains (&viewport, event->x, event->y))
    {
        stop_scrolling (scroll_area);
    }
    else
    {
        int dx, dy;

        dx = dy = 0;

        if (event->y < viewport.y)
        {
            dy = event->y - viewport.y;
            dy = MIN (dy + 2, 0);
        }
        else if (event->y >= viewport.y + viewport.height)
        {
            dy = event->y - (viewport.y + viewport.height - 1);
            dy = MAX (dy - 2, 0);
        }

        if (event->x < viewport.x)
        {
            dx = event->x - viewport.x;
            dx = MIN (dx + 2, 0);
        }
        else if (event->x >= viewport.x + viewport.width)
        {
            dx = event->x - (viewport.x + viewport.width - 1);
            dx = MAX (dx - 2, 0);
        }

        ensure_scrolling (scroll_area, dx, dy);
    }
}

void
foo_scroll_area_begin_auto_scroll (FooScrollArea *scroll_area)
{
    /* noop for now */
}

void
foo_scroll_area_end_auto_scroll (FooScrollArea *scroll_area)
{
    stop_scrolling (scroll_area);
}
