logdiag/liblogdiag/ld-canvas.c

/*
 * ld-canvas.c
 *
 * This file is a part of logdiag.
 * Copyright Přemysl Janouch 2010 - 2011. All rights reserved.
 *
 * See the file LICENSE for licensing information.
 *
 */

#include <math.h>
#include <string.h>
#include <gdk/gdkkeysyms.h>

#include "liblogdiag.h"
#include "config.h"


/**
 * SECTION:ld-canvas
 * @short_description: A canvas
 * @see_also: #LdDiagram
 *
 * #LdCanvas displays and enables the user to manipulate with an #LdDiagram.
 */

/* Milimetres per inch. */
#define MM_PER_INCH 25.4
/* The default screen resolution in DPI units. */
#define DEFAULT_SCREEN_RESOLUTION 96

/* The maximal, minimal and default values of zoom. */
#define ZOOM_MIN 0.01
#define ZOOM_MAX 100
#define ZOOM_DEFAULT 1
/* Multiplication factor for zooming. */
#define ZOOM_STEP 1.4

/* When drawing is requested, extend all sides of
 * the rectangle to be drawn by this number of pixels.
 */
#define QUEUE_DRAW_EXTEND 3
/* Cursor tolerance for object borders. */
#define OBJECT_BORDER_TOLERANCE 3
/* Tolerance on all sides of symbols for strokes. */
#define SYMBOL_CLIP_TOLERANCE 5

/* Size of a highlighted terminal. */
#define TERMINAL_RADIUS 5
/* Tolerance around terminal points. */
#define TERMINAL_HOVER_TOLERANCE 8

/*
 * OperationEnd:
 *
 * Called upon ending an operation.
 */
typedef void (*OperationEnd) (LdCanvas *self);

enum
{
	OPER_0,
	OPER_ADD_OBJECT,
	OPER_CONNECT,
	OPER_SELECT,
	OPER_MOVE_SELECTION
};

typedef struct _AddObjectData AddObjectData;
typedef struct _ConnectData ConnectData;
typedef struct _SelectData SelectData;
typedef struct _MoveSelectionData MoveSelectionData;

struct _AddObjectData
{
	LdDiagramObject *object;
	gboolean visible;
};

struct _ConnectData
{
	LdDiagramConnection *connection;
	LdPoint origin;
};

struct _SelectData
{
	LdPoint drag_last_pos;
};

struct _MoveSelectionData
{
	LdPoint move_origin;
};

enum
{
	COLOR_BASE,
	COLOR_GRID,
	COLOR_OBJECT,
	COLOR_SELECTION,
	COLOR_TERMINAL,
	COLOR_COUNT
};

typedef struct _LdCanvasColor LdCanvasColor;

struct _LdCanvasColor
{
	gdouble r;
	gdouble g;
	gdouble b;
	gdouble a;
};

/*
 * LdCanvasPrivate:
 * @diagram: a diagram object assigned to this canvas as a model.
 * @library: a library object assigned to this canvas as a model.
 * @adjustment_h: an adjustment object for the horizontal axis, if any.
 * @adjustment_v: an adjustment object for the vertical axis, if any.
 * @x: the X coordinate of the center of view.
 * @y: the Y coordinate of the center of view.
 * @zoom: the current zoom of the canvas.
 * @terminal: position of the highlighted terminal.
 * @terminal_hovered: whether a terminal is hovered.
 * @drag_start_pos: position of the mouse pointer when dragging started.
 * @drag_operation: the operation to start when dragging starts.
 * @operation: the current operation.
 * @operation_data: data related to the current operation.
 * @operation_end: a callback to end the operation.
 * @palette: colors used by the widget.
 */
struct _LdCanvasPrivate
{
	LdDiagram *diagram;
	LdLibrary *library;

	GtkAdjustment *adjustment_h;
	GtkAdjustment *adjustment_v;

	gdouble x;
	gdouble y;
	gdouble zoom;

	LdPoint terminal;
	gboolean terminal_hovered;

	LdPoint drag_start_pos;
	gint drag_operation;

	gint operation;
	union
	{
		AddObjectData add_object;
		ConnectData connect;
		SelectData select;
		MoveSelectionData move_selection;
	}
	operation_data;
	OperationEnd operation_end;

	LdCanvasColor palette[COLOR_COUNT];
};

#define OPER_DATA(self, member) ((self)->priv->operation_data.member)
#define COLOR_GET(self, name) (&(self)->priv->palette[name])

/*
 * DrawData:
 * @self: our #LdCanvas.
 * @cr: a cairo context to draw on.
 * @exposed_rect: the area that is to be redrawn.
 * @scale: computed size of one diagram unit in pixels.
 */
typedef struct _DrawData DrawData;

struct _DrawData
{
	LdCanvas *self;
	cairo_t *cr;
	LdRectangle exposed_rect;
	gdouble scale;
};

enum
{
	PROP_0,
	PROP_DIAGRAM,
	PROP_LIBRARY,
	PROP_ZOOM
};

static void ld_canvas_get_property (GObject *object, guint property_id,
	GValue *value, GParamSpec *pspec);
static void ld_canvas_set_property (GObject *object, guint property_id,
	const GValue *value, GParamSpec *pspec);
static void ld_canvas_finalize (GObject *gobject);

static void ld_canvas_real_set_scroll_adjustments
	(LdCanvas *self, GtkAdjustment *horizontal, GtkAdjustment *vertical);
static void on_adjustment_value_changed
	(GtkAdjustment *adjustment, LdCanvas *self);
static void on_size_allocate (GtkWidget *widget, GtkAllocation *allocation,
	gpointer user_data);
static void update_adjustments (LdCanvas *self);
static void ld_canvas_real_move (LdCanvas *self, gdouble dx, gdouble dy);

static void diagram_connect_signals (LdCanvas *self);
static void diagram_disconnect_signals (LdCanvas *self);

static gdouble ld_canvas_get_base_unit_in_px (GtkWidget *self);
static gdouble ld_canvas_get_scale_in_px (LdCanvas *self);

/* Helper functions. */
static void ld_canvas_color_set (LdCanvasColor *color,
	gdouble r, gdouble g, gdouble b, gdouble a);
static void ld_canvas_color_apply (LdCanvasColor *color, cairo_t *cr);
static guint32 ld_canvas_color_to_cairo_argb (LdCanvasColor *color);

static gdouble point_to_line_segment_distance
	(const LdPoint *point, const LdPoint *p1, const LdPoint *p2);

/* Generic functions. */
static gboolean object_hit_test (LdCanvas *self,
	LdDiagramObject *object, const LdPoint *point);
static gboolean get_object_clip_area (LdCanvas *self,
	LdDiagramObject *object, LdRectangle *rect);

static void move_object_to_point (LdCanvas *self, LdDiagramObject *object,
	const LdPoint *point);
static LdDiagramObject *get_object_at_point (LdCanvas *self,
	const LdPoint *point);

static void move_selection (LdCanvas *self, gdouble dx, gdouble dy);
static gboolean is_object_selected (LdCanvas *self, LdDiagramObject *object);

static void queue_draw (LdCanvas *self, LdRectangle *rect);
static void queue_object_draw (LdCanvas *self, LdDiagramObject *object);

/* Symbol terminals. */
static void check_terminals (LdCanvas *self, const LdPoint *point);
static void hide_terminals (LdCanvas *self);
static void queue_terminal_draw (LdCanvas *self, LdPoint *terminal);

/* Diagram symbol. */
static gboolean symbol_hit_test (LdCanvas *self,
	LdDiagramSymbol *symbol, const LdPoint *point);
static gboolean get_symbol_clip_area (LdCanvas *self,
	LdDiagramSymbol *symbol, LdRectangle *rect);

static gboolean get_symbol_area (LdCanvas *self,
	LdDiagramSymbol *symbol, LdRectangle *rect);
static LdSymbol *resolve_symbol (LdCanvas *self,
	LdDiagramSymbol *diagram_symbol);

/* Diagram connection. */
static gboolean connection_hit_test (LdCanvas *self,
	LdDiagramConnection *connection, const LdPoint *point);
static gboolean get_connection_clip_area (LdCanvas *self,
	LdDiagramConnection *connection, LdRectangle *rect);

static gboolean get_connection_area (LdCanvas *self,
	LdDiagramConnection *connection, LdRectangle *rect);

/* Operations. */
static void ld_canvas_real_cancel_operation (LdCanvas *self);
static void oper_add_object_end (LdCanvas *self);

static void oper_connect_begin (LdCanvas *self, const LdPoint *point);
static void oper_connect_end (LdCanvas *self);
static void oper_connect_motion (LdCanvas *self, const LdPoint *point);

static void oper_select_begin (LdCanvas *self, const LdPoint *point);
static void oper_select_end (LdCanvas *self);
static void oper_select_get_rectangle (LdCanvas *self, LdRectangle *rect);
static void oper_select_queue_draw (LdCanvas *self);
static void oper_select_draw (GtkWidget *widget, DrawData *data);
static void oper_select_motion (LdCanvas *self, const LdPoint *point);

static void oper_move_selection_begin (LdCanvas *self, const LdPoint *point);
static void oper_move_selection_end (LdCanvas *self);
static void oper_move_selection_motion (LdCanvas *self, const LdPoint *point);

/* Events, rendering. */
static void simulate_motion (LdCanvas *self);
static gboolean on_motion_notify (GtkWidget *widget, GdkEventMotion *event,
	gpointer user_data);
static gboolean on_leave_notify (GtkWidget *widget, GdkEventCrossing *event,
	gpointer user_data);
static gboolean on_button_press (GtkWidget *widget, GdkEventButton *event,
	gpointer user_data);
static gboolean on_button_release (GtkWidget *widget, GdkEventButton *event,
	gpointer user_data);
static gboolean on_scroll (GtkWidget *widget, GdkEventScroll *event,
	gpointer user_data);

static gboolean on_expose_event (GtkWidget *widget, GdkEventExpose *event,
	gpointer user_data);
static void draw_grid (GtkWidget *widget, DrawData *data);
static void draw_diagram (GtkWidget *widget, DrawData *data);
static void draw_terminal (GtkWidget *widget, DrawData *data);
static void draw_object (LdDiagramObject *diagram_object, DrawData *data);
static void draw_symbol (LdDiagramSymbol *diagram_symbol, DrawData *data);
static void draw_connection (LdDiagramConnection *connection, DrawData *data);


G_DEFINE_TYPE (LdCanvas, ld_canvas, GTK_TYPE_DRAWING_AREA);

static void
ld_canvas_class_init (LdCanvasClass *klass)
{
	GObjectClass *object_class;
	GtkWidgetClass *widget_class;
	GtkBindingSet *binding_set;
	GParamSpec *pspec;

	widget_class = GTK_WIDGET_CLASS (klass);

	object_class = G_OBJECT_CLASS (klass);
	object_class->get_property = ld_canvas_get_property;
	object_class->set_property = ld_canvas_set_property;
	object_class->finalize = ld_canvas_finalize;

	klass->set_scroll_adjustments = ld_canvas_real_set_scroll_adjustments;
	klass->cancel_operation = ld_canvas_real_cancel_operation;
	klass->move = ld_canvas_real_move;

	binding_set = gtk_binding_set_by_class (klass);
	gtk_binding_entry_add_signal (binding_set, GDK_Escape, 0,
		"cancel-operation", 0);
	gtk_binding_entry_add_signal (binding_set, GDK_Left, 0,
		"move", 2, G_TYPE_DOUBLE, (gdouble) -1, G_TYPE_DOUBLE, (gdouble) 0);
	gtk_binding_entry_add_signal (binding_set, GDK_Right, 0,
		"move", 2, G_TYPE_DOUBLE, (gdouble) 1, G_TYPE_DOUBLE, (gdouble) 0);
	gtk_binding_entry_add_signal (binding_set, GDK_Up, 0,
		"move", 2, G_TYPE_DOUBLE, (gdouble) 0, G_TYPE_DOUBLE, (gdouble) -1);
	gtk_binding_entry_add_signal (binding_set, GDK_Down, 0,
		"move", 2, G_TYPE_DOUBLE, (gdouble) 0, G_TYPE_DOUBLE, (gdouble) 1);

/**
 * LdCanvas:diagram:
 *
 * The underlying #LdDiagram object of this canvas.
 */
	pspec = g_param_spec_object ("diagram", "Diagram",
		"The underlying diagram object of this canvas.",
		LD_TYPE_DIAGRAM, G_PARAM_READWRITE);
	g_object_class_install_property (object_class, PROP_DIAGRAM, pspec);

/**
 * LdCanvas:library:
 *
 * The #LdLibrary that this canvas retrieves symbols from.
 */
	pspec = g_param_spec_object ("library", "Library",
		"The library that this canvas retrieves symbols from.",
		LD_TYPE_LIBRARY, G_PARAM_READWRITE);
	g_object_class_install_property (object_class, PROP_LIBRARY, pspec);

/**
 * LdCanvas:zoom:
 *
 * The zoom of this canvas.
 */
	pspec = g_param_spec_double ("zoom", "Zoom",
		"The zoom of this canvas.",
		ZOOM_MIN, ZOOM_MAX, ZOOM_DEFAULT, G_PARAM_READWRITE);
	g_object_class_install_property (object_class, PROP_ZOOM, pspec);

/**
 * LdCanvas::set-scroll-adjustments:
 * @self: an #LdCanvas object.
 * @horizontal: the horizontal #GtkAdjustment.
 * @vertical: the vertical #GtkAdjustment.
 *
 * Set scroll adjustments for the canvas.
 */
	widget_class->set_scroll_adjustments_signal = g_signal_new
		("set-scroll-adjustments", G_TYPE_FROM_CLASS (widget_class),
		G_SIGNAL_RUN_LAST | G_SIGNAL_ACTION,
		G_STRUCT_OFFSET (LdCanvasClass, set_scroll_adjustments),
		NULL, NULL,
		ld_marshal_VOID__OBJECT_OBJECT,
		G_TYPE_NONE, 2, GTK_TYPE_ADJUSTMENT, GTK_TYPE_ADJUSTMENT);

/**
 * LdCanvas::cancel-operation:
 * @self: an #LdCanvas object.
 *
 * Cancel any current operation.
 */
	klass->cancel_operation_signal = g_signal_new
		("cancel-operation", G_TYPE_FROM_CLASS (klass),
		G_SIGNAL_RUN_LAST | G_SIGNAL_ACTION,
		G_STRUCT_OFFSET (LdCanvasClass, cancel_operation), NULL, NULL,
		g_cclosure_marshal_VOID__VOID,
		G_TYPE_NONE, 0);

/**
 * LdCanvas::move:
 * @self: an #LdCanvas object.
 * @dx: The difference by which to move on the horizontal axis.
 * @dy: The difference by which to move on the vertical axis.
 *
 * Move the selection, if any, or the document.
 */
	klass->move_signal = g_signal_new
		("move", G_TYPE_FROM_CLASS (klass),
		G_SIGNAL_RUN_LAST | G_SIGNAL_ACTION,
		G_STRUCT_OFFSET (LdCanvasClass, move), NULL, NULL,
		ld_marshal_VOID__DOUBLE_DOUBLE,
		G_TYPE_NONE, 2, G_TYPE_DOUBLE, G_TYPE_DOUBLE);

	g_type_class_add_private (klass, sizeof (LdCanvasPrivate));
}

static void
ld_canvas_init (LdCanvas *self)
{
	self->priv = G_TYPE_INSTANCE_GET_PRIVATE
		(self, LD_TYPE_CANVAS, LdCanvasPrivate);

	self->priv->x = 0;
	self->priv->y = 0;
	self->priv->zoom = ZOOM_DEFAULT;

	ld_canvas_color_set (COLOR_GET (self, COLOR_BASE), 1, 1, 1, 1);
	ld_canvas_color_set (COLOR_GET (self, COLOR_GRID), 0.5, 0.5, 0.5, 1);
	ld_canvas_color_set (COLOR_GET (self, COLOR_OBJECT), 0, 0, 0, 1);
	ld_canvas_color_set (COLOR_GET (self, COLOR_SELECTION), 0, 0, 1, 1);
	ld_canvas_color_set (COLOR_GET (self, COLOR_TERMINAL), 1, 0.5, 0.5, 1);

	g_signal_connect (self, "size-allocate",
		G_CALLBACK (on_size_allocate), NULL);
	g_signal_connect (self, "expose-event",
		G_CALLBACK (on_expose_event), NULL);

	g_signal_connect (self, "motion-notify-event",
		G_CALLBACK (on_motion_notify), NULL);
	g_signal_connect (self, "leave-notify-event",
		G_CALLBACK (on_leave_notify), NULL);
	g_signal_connect (self, "button-press-event",
		G_CALLBACK (on_button_press), NULL);
	g_signal_connect (self, "button-release-event",
		G_CALLBACK (on_button_release), NULL);
	g_signal_connect (self, "scroll-event",
		G_CALLBACK (on_scroll), NULL);

	g_object_set (self, "can-focus", TRUE, NULL);

	gtk_widget_add_events (GTK_WIDGET (self),
		GDK_POINTER_MOTION_MASK | GDK_POINTER_MOTION_HINT_MASK
		| GDK_BUTTON_PRESS_MASK | GDK_BUTTON_RELEASE_MASK
		| GDK_LEAVE_NOTIFY_MASK);
}

static void
ld_canvas_finalize (GObject *gobject)
{
	LdCanvas *self;

	self = LD_CANVAS (gobject);

	ld_canvas_real_set_scroll_adjustments (self, NULL, NULL);

	if (self->priv->diagram)
	{
		diagram_disconnect_signals (self);
		g_object_unref (self->priv->diagram);
	}
	if (self->priv->library)
		g_object_unref (self->priv->library);

	/* Chain up to the parent class. */
	G_OBJECT_CLASS (ld_canvas_parent_class)->finalize (gobject);
}

static void
ld_canvas_get_property (GObject *object, guint property_id,
	GValue *value, GParamSpec *pspec)
{
	LdCanvas *self;

	self = LD_CANVAS (object);
	switch (property_id)
	{
	case PROP_DIAGRAM:
		g_value_set_object (value, ld_canvas_get_diagram (self));
		break;
	case PROP_LIBRARY:
		g_value_set_object (value, ld_canvas_get_library (self));
		break;
	case PROP_ZOOM:
		g_value_set_double (value, ld_canvas_get_zoom (self));
		break;
	default:
		G_OBJECT_WARN_INVALID_PROPERTY_ID (object, property_id, pspec);
	}
}

static void
ld_canvas_set_property (GObject *object, guint property_id,
	const GValue *value, GParamSpec *pspec)
{
	LdCanvas *self;

	self = LD_CANVAS (object);
	switch (property_id)
	{
	case PROP_DIAGRAM:
		ld_canvas_set_diagram (self, LD_DIAGRAM (g_value_get_object (value)));
		break;
	case PROP_LIBRARY:
		ld_canvas_set_library (self, LD_LIBRARY (g_value_get_object (value)));
		break;
	case PROP_ZOOM:
		ld_canvas_set_zoom (self, g_value_get_double (value));
		break;
	default:
		G_OBJECT_WARN_INVALID_PROPERTY_ID (object, property_id, pspec);
	}
}

static void
ld_canvas_real_set_scroll_adjustments (LdCanvas *self,
	GtkAdjustment *horizontal, GtkAdjustment *vertical)
{
	/* TODO: Infinite canvas. */
	GtkWidget *widget;
	gdouble scale;

	widget = GTK_WIDGET (self);
	scale = ld_canvas_get_scale_in_px (self);

	if (horizontal != self->priv->adjustment_h)
	{
		if (self->priv->adjustment_h)
		{
			g_signal_handlers_disconnect_by_func (self->priv->adjustment_h,
				on_adjustment_value_changed, self);
			g_object_unref (self->priv->adjustment_h);

			self->priv->adjustment_h = NULL;
		}
		if (horizontal)
		{
			g_object_ref (horizontal);
			g_signal_connect (horizontal, "value-changed",
				G_CALLBACK (on_adjustment_value_changed), self);

			horizontal->upper = 100;
			horizontal->lower = -100;
			horizontal->step_increment = 0.5;
			horizontal->page_increment = 5;
			horizontal->page_size = widget->allocation.width / scale;
			horizontal->value = -horizontal->page_size / 2;

			self->priv->adjustment_h = horizontal;
		}
	}

	if (vertical != self->priv->adjustment_v)
	{
		if (self->priv->adjustment_v)
		{
			g_signal_handlers_disconnect_by_func (self->priv->adjustment_v,
				on_adjustment_value_changed, self);
			g_object_unref (self->priv->adjustment_v);

			self->priv->adjustment_v = NULL;
		}
		if (vertical)
		{
			g_object_ref (vertical);
			g_signal_connect (vertical, "value-changed",
				G_CALLBACK (on_adjustment_value_changed), self);

			vertical->upper = 100;
			vertical->lower = -100;
			vertical->step_increment = 0.5;
			vertical->page_increment = 5;
			vertical->page_size = widget->allocation.height / scale;
			vertical->value = -vertical->page_size / 2;

			self->priv->adjustment_v = vertical;
		}
	}
}

static void
on_adjustment_value_changed (GtkAdjustment *adjustment, LdCanvas *self)
{
	GtkWidget *widget;
	gdouble scale;

	widget = GTK_WIDGET (self);
	scale = ld_canvas_get_scale_in_px (self);

	if (adjustment == self->priv->adjustment_h)
	{
		self->priv->x = adjustment->value
			+ widget->allocation.width / scale / 2;
		gtk_widget_queue_draw (widget);
	}
	else if (adjustment == self->priv->adjustment_v)
	{
		self->priv->y = adjustment->value
			+ widget->allocation.height / scale / 2;
		gtk_widget_queue_draw (widget);
	}
}

static void
on_size_allocate (GtkWidget *widget, GtkAllocation *allocation,
	gpointer user_data)
{
	LdCanvas *self;

	self = LD_CANVAS (widget);

	/* FIXME: If the new allocation is bigger, we may see more than
	 *        what we're supposed to be able to see -> adjust X and Y.
	 *
	 *        If the visible area is so large that we simply must see more,
	 *        let's disable the scrollbars in question.
	 */
	update_adjustments (self);
}

static void
update_adjustments (LdCanvas *self)
{
	gdouble scale;

	scale = ld_canvas_get_scale_in_px (self);

	if (self->priv->adjustment_h)
	{
		self->priv->adjustment_h->page_size
			= GTK_WIDGET (self)->allocation.width  / scale;
		self->priv->adjustment_h->value
			= self->priv->x - self->priv->adjustment_h->page_size / 2;
		gtk_adjustment_changed (self->priv->adjustment_h);
	}
	if (self->priv->adjustment_v)
	{
		self->priv->adjustment_v->page_size
			= GTK_WIDGET (self)->allocation.height / scale;
		self->priv->adjustment_v->value
			= self->priv->y - self->priv->adjustment_v->page_size / 2;
		gtk_adjustment_changed (self->priv->adjustment_v);
	}
}

static void
ld_canvas_real_move (LdCanvas *self, gdouble dx, gdouble dy)
{
	LdDiagram *diagram;

	diagram = self->priv->diagram;
	if (!diagram)
		return;

	/* TODO: Check/move boundaries, also implement normal
	 *       getters and setters for priv->x and priv->y.
	 */
	if (ld_diagram_get_selection (diagram))
		move_selection (self, dx, dy);
	else
	{
		self->priv->x += dx;
		self->priv->y += dy;

		simulate_motion (self);
		update_adjustments (self);
	}
	gtk_widget_queue_draw (GTK_WIDGET (self));
}


/* ===== Generic interface etc. ============================================ */

/**
 * ld_canvas_new:
 *
 * Create an instance.
 */
GtkWidget *
ld_canvas_new (void)
{
	return g_object_new (LD_TYPE_CANVAS, NULL);
}

/**
 * ld_canvas_set_diagram:
 * @self: an #LdCanvas object.
 * @diagram: the #LdDiagram to be assigned to the canvas.
 *
 * Assign an #LdDiagram object to the canvas.
 */
void
ld_canvas_set_diagram (LdCanvas *self, LdDiagram *diagram)
{
	g_return_if_fail (LD_IS_CANVAS (self));
	g_return_if_fail (LD_IS_DIAGRAM (diagram));

	if (self->priv->diagram)
	{
		diagram_disconnect_signals (self);
		g_object_unref (self->priv->diagram);
	}

	self->priv->diagram = diagram;
	diagram_connect_signals (self);
	g_object_ref (diagram);

	g_object_notify (G_OBJECT (self), "diagram");
}

/**
 * ld_canvas_get_diagram:
 * @self: an #LdCanvas object.
 *
 * Get the #LdDiagram object assigned to this canvas.
 * The reference count on the diagram is not incremented.
 */
LdDiagram *
ld_canvas_get_diagram (LdCanvas *self)
{
	g_return_val_if_fail (LD_IS_CANVAS (self), NULL);
	return self->priv->diagram;
}

static void
diagram_connect_signals (LdCanvas *self)
{
	g_return_if_fail (LD_IS_DIAGRAM (self->priv->diagram));

	g_signal_connect_swapped (self->priv->diagram, "changed",
		G_CALLBACK (gtk_widget_queue_draw), self);
	g_signal_connect_swapped (self->priv->diagram, "selection-changed",
		G_CALLBACK (gtk_widget_queue_draw), self);
}

static void
diagram_disconnect_signals (LdCanvas *self)
{
	g_return_if_fail (LD_IS_DIAGRAM (self->priv->diagram));

	g_signal_handlers_disconnect_matched (self->priv->diagram,
		G_SIGNAL_MATCH_FUNC | G_SIGNAL_MATCH_DATA, 0, 0, NULL,
		gtk_widget_queue_draw, self);
}

/**
 * ld_canvas_set_library:
 * @self: an #LdCanvas object.
 * @library: the #LdLibrary to be assigned to the canvas.
 *
 * Assign an #LdLibrary object to the canvas.
 */
void
ld_canvas_set_library (LdCanvas *self, LdLibrary *library)
{
	g_return_if_fail (LD_IS_CANVAS (self));
	g_return_if_fail (LD_IS_LIBRARY (library));

	if (self->priv->library)
		g_object_unref (self->priv->library);

	self->priv->library = library;
	g_object_ref (library);

	g_object_notify (G_OBJECT (self), "library");
}

/**
 * ld_canvas_get_library:
 * @self: an #LdCanvas object.
 *
 * Get the #LdLibrary object assigned to this canvas.
 * The reference count on the library is not incremented.
 */
LdLibrary *
ld_canvas_get_library (LdCanvas *self)
{
	g_return_val_if_fail (LD_IS_CANVAS (self), NULL);
	return self->priv->library;
}

/*
 * ld_canvas_get_base_unit_in_px:
 * @self: a #GtkWidget object to retrieve DPI from (indirectly).
 *
 * Return value: length of the base unit in pixels.
 */
static gdouble
ld_canvas_get_base_unit_in_px (GtkWidget *self)
{
	gdouble resolution;

	g_return_val_if_fail (GTK_IS_WIDGET (self), 1);

	resolution = gdk_screen_get_resolution (gtk_widget_get_screen (self));
	if (resolution == -1)
		resolution = DEFAULT_SCREEN_RESOLUTION;

	/* XXX: It might look better if the unit was rounded to a whole number. */
	return resolution / MM_PER_INCH * LD_CANVAS_BASE_UNIT_LENGTH;
}

/*
 * ld_canvas_get_scale_in_px:
 * @self: an #LdCanvas object.
 *
 * Return value: displayed length of the base unit in pixels.
 */
static gdouble
ld_canvas_get_scale_in_px (LdCanvas *self)
{
	g_return_val_if_fail (LD_IS_CANVAS (self), 1);

	return ld_canvas_get_base_unit_in_px (GTK_WIDGET (self))
		* self->priv->zoom;
}

/**
 * ld_canvas_widget_to_diagram_coords:
 * @self: an #LdCanvas object.
 * @wx: the X coordinate to be translated.
 * @wy: the Y coordinate to be translated.
 * @dx: (out): the translated X coordinate.
 * @dy: (out): the translated Y coordinate.
 *
 * Translate coordinates located inside the canvas window
 * into diagram coordinates.
 */
void
ld_canvas_widget_to_diagram_coords (LdCanvas *self,
	gdouble wx, gdouble wy, gdouble *dx, gdouble *dy)
{
	GtkWidget *widget;
	gdouble scale;

	g_return_if_fail (LD_IS_CANVAS (self));
	g_return_if_fail (dx != NULL);
	g_return_if_fail (dy != NULL);

	widget = GTK_WIDGET (self);
	scale = ld_canvas_get_scale_in_px (self);

	/* We know diagram coordinates of the center of the canvas, so we may
	 * translate the given X and Y coordinates to this center and then scale
	 * them by dividing them by the current scale.
	 */
	*dx = self->priv->x + (wx - (widget->allocation.width  * 0.5)) / scale;
	*dy = self->priv->y + (wy - (widget->allocation.height * 0.5)) / scale;
}

/**
 * ld_canvas_diagram_to_widget_coords:
 * @self: an #LdCanvas object.
 * @dx: the X coordinate to be translated.
 * @dy: the Y coordinate to be translated.
 * @wx: (out): the translated X coordinate.
 * @wy: (out): the translated Y coordinate.
 *
 * Translate diagram coordinates into canvas coordinates.
 */
void
ld_canvas_diagram_to_widget_coords (LdCanvas *self,
	gdouble dx, gdouble dy, gdouble *wx, gdouble *wy)
{
	GtkWidget *widget;
	gdouble scale;

	g_return_if_fail (LD_IS_CANVAS (self));
	g_return_if_fail (wx != NULL);
	g_return_if_fail (wy != NULL);

	widget = GTK_WIDGET (self);
	scale = ld_canvas_get_scale_in_px (self);

	/* Just the reversal of ld_canvas_widget_to_diagram_coords(). */
	*wx = scale * (dx - self->priv->x) + 0.5 * widget->allocation.width;
	*wy = scale * (dy - self->priv->y) + 0.5 * widget->allocation.height;
}

/**
 * ld_canvas_get_zoom:
 * @self: an #LdCanvas object.
 *
 * Return value: zoom of the canvas.
 */
gdouble
ld_canvas_get_zoom (LdCanvas *self)
{
	g_return_val_if_fail (LD_IS_CANVAS (self), -1);
	return self->priv->zoom;
}

/**
 * ld_canvas_set_zoom:
 * @self: an #LdCanvas object.
 * @zoom: the zoom.
 *
 * Set zoom of the canvas.
 */
void
ld_canvas_set_zoom (LdCanvas *self, gdouble zoom)
{
	gdouble clamped_zoom;

	g_return_if_fail (LD_IS_CANVAS (self));

	clamped_zoom = CLAMP (zoom, ZOOM_MIN, ZOOM_MAX);
	if (self->priv->zoom == clamped_zoom)
		return;

	self->priv->zoom = clamped_zoom;

	simulate_motion (self);
	update_adjustments (self);
	gtk_widget_queue_draw (GTK_WIDGET (self));

	g_object_notify (G_OBJECT (self), "zoom");
}

/**
 * ld_canvas_can_zoom_in:
 * @self: an #LdCanvas object.
 *
 * Return value: %TRUE if the view can be zoomed in.
 */
gboolean
ld_canvas_can_zoom_in (LdCanvas *self)
{
	g_return_val_if_fail (LD_IS_CANVAS (self), FALSE);
	return self->priv->zoom < ZOOM_MAX;
}

/**
 * ld_canvas_can_zoom_out:
 * @self: an #LdCanvas object.
 *
 * Return value: %TRUE if the view can be zoomed out.
 */
gboolean
ld_canvas_can_zoom_out (LdCanvas *self)
{
	g_return_val_if_fail (LD_IS_CANVAS (self), FALSE);
	return self->priv->zoom > ZOOM_MIN;
}

/**
 * ld_canvas_zoom_in:
 * @self: an #LdCanvas object.
 *
 * Zoom the view in.
 */
void
ld_canvas_zoom_in (LdCanvas *self)
{
	g_return_if_fail (LD_IS_CANVAS (self));
	ld_canvas_set_zoom (self, self->priv->zoom * ZOOM_STEP);
}

/**
 * ld_canvas_zoom_out:
 * @self: an #LdCanvas object.
 *
 * Zoom the view out.
 */
void
ld_canvas_zoom_out (LdCanvas *self)
{
	g_return_if_fail (LD_IS_CANVAS (self));
	ld_canvas_set_zoom (self, self->priv->zoom / ZOOM_STEP);
}


/* ===== Helper functions ================================================== */

static void
ld_canvas_color_set (LdCanvasColor *color,
	gdouble r, gdouble g, gdouble b, gdouble a)
{
	color->r = r;
	color->g = g;
	color->b = b;
	color->a = a;
}

static void
ld_canvas_color_apply (LdCanvasColor *color, cairo_t *cr)
{
	cairo_set_source_rgba (cr, color->r, color->g, color->b, color->a);
}

static guint32
ld_canvas_color_to_cairo_argb (LdCanvasColor *color)
{
	return (guint) (color->a            * 255) << 24
	     | (guint) (color->r * color->a * 255) << 16
	     | (guint) (color->g * color->a * 255) << 8
	     | (guint) (color->b * color->a * 255);
}

static gdouble
point_to_line_segment_distance
	(const LdPoint *point, const LdPoint *p1, const LdPoint *p2)
{
	gdouble dx, dy, u;

	dx = p2->x - p1->x;
	dy = p2->y - p1->y;

	if (dx == 0. && dy == 0.)
		return ld_point_distance (point, p1->x, p1->y);

	/* Find projection of the point onto the line. */
	u = ((point->x - p1->x) * dx + (point->y - p1->y) * dy)
		/ (dx * dx + dy * dy);

	/* The projection is beyond the line segment. */
	if (u < 0.)
		return ld_point_distance (point, p1->x, p1->y);
	else if (u > 1.)
		return ld_point_distance (point, p2->x, p2->y);

	/* The projection is on the line segment. */
	return ld_point_distance (point, p1->x + u * dx, p1->y + u * dy);
}


/* ===== Generic functions ================================================= */

static gboolean
object_hit_test (LdCanvas *self, LdDiagramObject *object, const LdPoint *point)
{
	if (LD_IS_DIAGRAM_SYMBOL (object))
		return symbol_hit_test (self,
			LD_DIAGRAM_SYMBOL (object), point);
	if (LD_IS_DIAGRAM_CONNECTION (object))
		return connection_hit_test (self,
			LD_DIAGRAM_CONNECTION (object), point);
	return FALSE;
}

static gboolean
get_object_clip_area (LdCanvas *self,
	LdDiagramObject *object, LdRectangle *rect)
{
	if (LD_IS_DIAGRAM_SYMBOL (object))
		return get_symbol_clip_area (self,
			LD_DIAGRAM_SYMBOL (object), rect);
	if (LD_IS_DIAGRAM_CONNECTION (object))
		return get_connection_clip_area (self,
			LD_DIAGRAM_CONNECTION (object), rect);
	return FALSE;
}

static void
move_object_to_point (LdCanvas *self, LdDiagramObject *object,
	const LdPoint *point)
{
	gdouble diagram_x, diagram_y;

	ld_canvas_widget_to_diagram_coords (self,
		point->x, point->y, &diagram_x, &diagram_y);
	g_object_set (object,
		"x", floor (diagram_x + 0.5),
		"y", floor (diagram_y + 0.5),
		NULL);
}

static LdDiagramObject *
get_object_at_point (LdCanvas *self, const LdPoint *point)
{
	GList *objects, *iter;

	/* Iterate from the top object downwards. */
	objects = (GList *) ld_diagram_get_objects (self->priv->diagram);
	for (iter = g_list_last (objects); iter; iter = g_list_previous (iter))
	{
		LdDiagramObject *object;

		object = LD_DIAGRAM_OBJECT (iter->data);
		if (object_hit_test (self, object, point))
			return object;
	}
	return NULL;
}

static void
move_selection (LdCanvas *self, gdouble dx, gdouble dy)
{
	LdDiagram *diagram;
	GList *selection, *iter;

	diagram = self->priv->diagram;
	if (!diagram)
		return;

	selection = ld_diagram_get_selection (diagram);
	if (!selection)
		return;

	ld_diagram_begin_user_action (diagram);
	for (iter = selection; iter; iter = g_list_next (iter))
	{
		gdouble x, y;

		g_object_get (iter->data, "x", &x, "y", &y, NULL);
		x += dx;
		y += dy;
		g_object_set (iter->data, "x", x, "y", y, NULL);
	}
	ld_diagram_end_user_action (diagram);
}

static gboolean
is_object_selected (LdCanvas *self, LdDiagramObject *object)
{
	return g_list_find (ld_diagram_get_selection (self->priv->diagram),
		object) != NULL;
}

static void
queue_draw (LdCanvas *self, LdRectangle *rect)
{
	LdRectangle area;

	area = *rect;
	ld_rectangle_extend (&area, QUEUE_DRAW_EXTEND);
	gtk_widget_queue_draw_area (GTK_WIDGET (self),
		area.x, area.y, area.width, area.height);
}

static void
queue_object_draw (LdCanvas *self, LdDiagramObject *object)
{
	LdRectangle rect;

	if (!get_object_clip_area (self, object, &rect))
		return;
	queue_draw (self, &rect);
}


/* ===== Symbol terminals ================================================== */

static void
check_terminals (LdCanvas *self, const LdPoint *point)
{
	GList *objects, *iter;
	LdDiagramSymbol *closest_symbol = NULL;
	gdouble closest_distance = TERMINAL_HOVER_TOLERANCE;
	LdPoint closest_terminal;

	objects = (GList *) ld_diagram_get_objects (self->priv->diagram);
	for (iter = objects; iter; iter = g_list_next (iter))
	{
		LdDiagramObject *diagram_object;
		gdouble object_x, object_y;
		LdDiagramSymbol *diagram_symbol;
		LdSymbol *symbol;
		const LdPointArray *terminals;
		guint i;

		if (!LD_IS_DIAGRAM_SYMBOL (iter->data))
			continue;

		diagram_symbol = LD_DIAGRAM_SYMBOL (iter->data);
		symbol = resolve_symbol (self, diagram_symbol);
		if (!symbol)
			continue;

		diagram_object = LD_DIAGRAM_OBJECT (iter->data);
		g_object_get (diagram_object, "x", &object_x, "y", &object_y, NULL);

		terminals = ld_symbol_get_terminals (symbol);

		for (i = 0; i < terminals->length; i++)
		{
			LdPoint cur_term, widget_coords;
			gdouble distance;

			cur_term = terminals->points[i];
			cur_term.x += object_x;
			cur_term.y += object_y;

			ld_canvas_diagram_to_widget_coords (self,
				cur_term.x, cur_term.y, &widget_coords.x, &widget_coords.y);
			distance = ld_point_distance (&widget_coords, point->x, point->y);
			if (distance <= closest_distance)
			{
				closest_symbol = diagram_symbol;
				closest_distance = distance;
				closest_terminal = cur_term;
			}
		}
	}

	hide_terminals (self);

	if (closest_symbol)
	{
		self->priv->terminal_hovered = TRUE;
		self->priv->terminal = closest_terminal;
		queue_terminal_draw (self, &closest_terminal);
	}
}

static void
hide_terminals (LdCanvas *self)
{
	if (self->priv->terminal_hovered)
	{
		self->priv->terminal_hovered = FALSE;
		queue_terminal_draw (self, &self->priv->terminal);
	}
}

static void
queue_terminal_draw (LdCanvas *self, LdPoint *terminal)
{
	LdRectangle rect;
	LdPoint widget_coords;

	ld_canvas_diagram_to_widget_coords (self,
		terminal->x, terminal->y, &widget_coords.x, &widget_coords.y);

	rect.x = widget_coords.x - TERMINAL_RADIUS;
	rect.y = widget_coords.y - TERMINAL_RADIUS;
	rect.width  = 2 * TERMINAL_RADIUS;
	rect.height = 2 * TERMINAL_RADIUS;

	queue_draw (self, &rect);
}


/* ===== Diagram symbol ==================================================== */

static gboolean
symbol_hit_test (LdCanvas *self, LdDiagramSymbol *symbol, const LdPoint *point)
{
	LdRectangle rect;

	if (!get_symbol_area (self, symbol, &rect))
		return FALSE;
	ld_rectangle_extend (&rect, OBJECT_BORDER_TOLERANCE);
	return ld_rectangle_contains_point (&rect, point);
}

static gboolean
get_symbol_clip_area (LdCanvas *self,
	LdDiagramSymbol *symbol, LdRectangle *rect)
{
	LdRectangle object_rect;

	if (!get_symbol_area (self, symbol, &object_rect))
		return FALSE;

	*rect = object_rect;
	ld_rectangle_extend (rect, SYMBOL_CLIP_TOLERANCE);
	return TRUE;
}

static gboolean
get_symbol_area (LdCanvas *self, LdDiagramSymbol *symbol, LdRectangle *rect)
{
	gdouble object_x, object_y;
	LdSymbol *library_symbol;
	LdRectangle area;
	gdouble x1, x2;
	gdouble y1, y2;

	g_object_get (symbol, "x", &object_x, "y", &object_y, NULL);

	library_symbol = resolve_symbol (self, symbol);
	if (library_symbol)
		ld_symbol_get_area (library_symbol, &area);
	else
		return FALSE;

	/* TODO: Rotate the rectangle for other orientations. */
	ld_canvas_diagram_to_widget_coords (self,
		object_x + area.x,
		object_y + area.y,
		&x1, &y1);
	ld_canvas_diagram_to_widget_coords (self,
		object_x + area.x + area.width,
		object_y + area.y + area.height,
		&x2, &y2);

	x1 = floor (x1);
	y1 = floor (y1);
	x2 = ceil (x2);
	y2 = ceil (y2);

	rect->x = x1;
	rect->y = y1;
	rect->width  = x2 - x1;
	rect->height = y2 - y1;
	return TRUE;
}

static LdSymbol *
resolve_symbol (LdCanvas *self, LdDiagramSymbol *diagram_symbol)
{
	LdSymbol *symbol;
	gchar *klass;

	if (!self->priv->library)
		return NULL;

	klass = ld_diagram_symbol_get_class (diagram_symbol);
	symbol = ld_library_find_symbol (self->priv->library, klass);
	g_free (klass);
	return symbol;
}


/* ===== Diagram connection ================================================ */

static gboolean
connection_hit_test (LdCanvas *self, LdDiagramConnection *connection,
	const LdPoint *point)
{
	gdouble object_x, object_y, length;
	LdPointArray *points;
	guint i;

	g_object_get (connection, "x", &object_x, "y", &object_y, NULL);

	points = ld_diagram_connection_get_points (connection);
	if (points->length < 2)
	{
		ld_point_array_free (points);
		return FALSE;
	}

	for (i = 0; i < points->length; i++)
	{
		ld_canvas_diagram_to_widget_coords (self,
			points->points[i].x + object_x,
			points->points[i].y + object_y,
			&points->points[i].x,
			&points->points[i].y);

		if (!i)
			continue;

		length = point_to_line_segment_distance
			(point, &points->points[i - 1], &points->points[i]);
		if (length <= OBJECT_BORDER_TOLERANCE)
		{
			ld_point_array_free (points);
			return TRUE;
		}
	}
	ld_point_array_free (points);
	return FALSE;
}

static gboolean
get_connection_clip_area (LdCanvas *self,
	LdDiagramConnection *connection, LdRectangle *rect)
{
	return get_connection_area (self, connection, rect);
}

static gboolean
get_connection_area (LdCanvas *self,
	LdDiagramConnection *connection, LdRectangle *rect)
{
	gdouble x_origin, y_origin;
	gdouble x, y, x_min, x_max, y_min, y_max;
	LdPointArray *points;
	guint i;

	points = ld_diagram_connection_get_points (connection);
	if (!points->length)
	{
		ld_point_array_free (points);
		return FALSE;
	}

	g_object_get (connection, "x", &x_origin, "y", &y_origin, NULL);

	ld_canvas_diagram_to_widget_coords (self,
		x_origin + points->points[0].x,
		y_origin + points->points[0].y,
		&x, &y);

	x_max = x_min = x;
	y_max = y_min = y;

	for (i = 1; i < points->length; i++)
	{
		ld_canvas_diagram_to_widget_coords (self,
			x_origin + points->points[i].x,
			y_origin + points->points[i].y,
			&x, &y);

		if (x < x_min)
			x_min = x;
		else if (x > x_max)
			x_max = x;

		if (y < y_min)
			y_min = y;
		else if (y > y_max)
			y_max = y;
	}

	rect->x = x_min;
	rect->y = y_min;
	rect->width  = x_max - x_min;
	rect->height = y_max - y_min;

	ld_point_array_free (points);
	return TRUE;
}


/* ===== Operations ======================================================== */

static void
ld_canvas_real_cancel_operation (LdCanvas *self)
{
	g_return_if_fail (LD_IS_CANVAS (self));

	if (self->priv->operation)
	{
		if (self->priv->operation_end)
			self->priv->operation_end (self);
		self->priv->operation = OPER_0;
		self->priv->operation_end = NULL;
	}
}

/**
 * ld_canvas_add_object_begin:
 * @self: an #LdCanvas object.
 * @object: (transfer full): the object to be added to the diagram.
 *
 * Begin an operation for adding an object into the diagram.
 */
void
ld_canvas_add_object_begin (LdCanvas *self, LdDiagramObject *object)
{
	AddObjectData *data;

	g_return_if_fail (LD_IS_CANVAS (self));
	g_return_if_fail (LD_IS_DIAGRAM_OBJECT (object));

	ld_canvas_real_cancel_operation (self);

	self->priv->operation = OPER_ADD_OBJECT;
	self->priv->operation_end = oper_add_object_end;

	data = &OPER_DATA (self, add_object);
	data->object = object;
}

static void
oper_add_object_end (LdCanvas *self)
{
	AddObjectData *data;

	data = &OPER_DATA (self, add_object);
	if (data->object)
	{
		queue_object_draw (self, data->object);
		g_object_unref (data->object);
		data->object = NULL;
	}
}

static void
oper_connect_begin (LdCanvas *self, const LdPoint *point)
{
	ConnectData *data;

	ld_canvas_real_cancel_operation (self);

	self->priv->operation = OPER_CONNECT;
	self->priv->operation_end = oper_connect_end;

	data = &OPER_DATA (self, connect);
	data->connection = ld_diagram_connection_new (NULL);

	data->origin = self->priv->terminal;
	g_object_set (data->connection,
		"x", data->origin.x,
		"y", data->origin.y,
		NULL);

	self->priv->terminal_hovered = FALSE;

	oper_connect_motion (self, point);
}

static void
oper_connect_end (LdCanvas *self)
{
	ConnectData *data;

	data = &OPER_DATA (self, connect);
	queue_object_draw (self, LD_DIAGRAM_OBJECT (data->connection));

	ld_diagram_insert_object (self->priv->diagram,
		LD_DIAGRAM_OBJECT (data->connection), -1);

	g_object_unref (data->connection);
}

static void
oper_connect_motion (LdCanvas *self, const LdPoint *point)
{
	ConnectData *data;
	LdPointArray *points;
	gdouble diagram_x, diagram_y;

	data = &OPER_DATA (self, connect);

	/* Find an orthogonal path between the points. */
	/* TODO: This alghorithm is pretty lame, needs to be improved. */
	points = ld_point_array_sized_new (4);
	points->length = 4;

	points->points[0].x = 0;
	points->points[0].y = 0;

	ld_canvas_widget_to_diagram_coords (self,
		point->x, point->y, &diagram_x, &diagram_y);
	points->points[3].x = floor (diagram_x - data->origin.x + 0.5);
	points->points[3].y = floor (diagram_y - data->origin.y + 0.5);

	if (ABS (points->points[3].x) > ABS (points->points[3].y))
	{
		points->points[1].x = points->points[3].x / 2;
		points->points[1].y = 0;
		points->points[2].x = points->points[3].x / 2;
		points->points[2].y = points->points[3].y;
	}
	else
	{
		points->points[1].x = 0;
		points->points[1].y = points->points[3].y / 2;
		points->points[2].x = points->points[3].x;
		points->points[2].y = points->points[3].y / 2;
	}

	queue_object_draw (self, LD_DIAGRAM_OBJECT (data->connection));
	ld_diagram_connection_set_points (data->connection, points);
	queue_object_draw (self, LD_DIAGRAM_OBJECT (data->connection));
	ld_point_array_free (points);

	check_terminals (self, point);

	if (self->priv->terminal.x == data->origin.x
		&& self->priv->terminal.y == data->origin.y)
		self->priv->terminal_hovered = FALSE;
}

static void
oper_select_begin (LdCanvas *self, const LdPoint *point)
{
	SelectData *data;

	ld_canvas_real_cancel_operation (self);

	self->priv->operation = OPER_SELECT;
	self->priv->operation_end = oper_select_end;

	data = &OPER_DATA (self, select);
	data->drag_last_pos.x = self->priv->drag_start_pos.x;
	data->drag_last_pos.y = self->priv->drag_start_pos.y;

	oper_select_motion (self, point);
}

static void
oper_select_end (LdCanvas *self)
{
	oper_select_queue_draw (self);
}

static void
oper_select_get_rectangle (LdCanvas *self, LdRectangle *rect)
{
	SelectData *data;

	data = &OPER_DATA (self, select);
	rect->x = MIN (self->priv->drag_start_pos.x, data->drag_last_pos.x);
	rect->y = MIN (self->priv->drag_start_pos.y, data->drag_last_pos.y);
	rect->width  = ABS (self->priv->drag_start_pos.x - data->drag_last_pos.x);
	rect->height = ABS (self->priv->drag_start_pos.y - data->drag_last_pos.y);
}

static void
oper_select_queue_draw (LdCanvas *self)
{
	LdRectangle rect;
	SelectData *data;

	data = &OPER_DATA (self, select);
	oper_select_get_rectangle (self, &rect);
	queue_draw (self, &rect);
}

static void
oper_select_draw (GtkWidget *widget, DrawData *data)
{
	static const double dashes[] = {3, 5};
	SelectData *select_data;

	g_return_if_fail (data->self->priv->operation == OPER_SELECT);

	ld_canvas_color_apply (COLOR_GET (data->self, COLOR_GRID), data->cr);
	cairo_set_line_width (data->cr, 1);
	cairo_set_line_cap (data->cr, CAIRO_LINE_CAP_SQUARE);
	cairo_set_dash (data->cr, dashes, G_N_ELEMENTS (dashes), 0);

	select_data = &OPER_DATA (data->self, select);

	cairo_rectangle (data->cr,
		data->self->priv->drag_start_pos.x - 0.5,
		data->self->priv->drag_start_pos.y - 0.5,
		select_data->drag_last_pos.x - data->self->priv->drag_start_pos.x + 1,
		select_data->drag_last_pos.y - data->self->priv->drag_start_pos.y + 1);
	cairo_stroke (data->cr);
}

static void
oper_select_motion (LdCanvas *self, const LdPoint *point)
{
	SelectData *data;
	GList *objects, *iter;
	LdRectangle selection_rect, rect;

	data = &OPER_DATA (self, select);

	oper_select_queue_draw (self);
	data->drag_last_pos = *point;
	oper_select_queue_draw (self);

	oper_select_get_rectangle (self, &selection_rect);
	objects = (GList *) ld_diagram_get_objects (self->priv->diagram);

	for (iter = objects; iter; iter = g_list_next (iter))
	{
		LdDiagramObject *object;

		object = LD_DIAGRAM_OBJECT (iter->data);
		if (LD_IS_DIAGRAM_SYMBOL (object))
		{
			if (!get_symbol_area (self,
				LD_DIAGRAM_SYMBOL (object), &rect))
				continue;
		}
		else if (LD_IS_DIAGRAM_CONNECTION (object))
		{
			if (!get_connection_area (self,
				LD_DIAGRAM_CONNECTION (object), &rect))
				continue;
		}

		ld_rectangle_extend (&rect, OBJECT_BORDER_TOLERANCE);
		if (ld_rectangle_contains (&selection_rect, &rect))
			ld_diagram_select (self->priv->diagram, object);
		else
			ld_diagram_unselect (self->priv->diagram, object);
	}
}

static void
oper_move_selection_begin (LdCanvas *self, const LdPoint *point)
{
	MoveSelectionData *data;

	ld_canvas_real_cancel_operation (self);

	self->priv->operation = OPER_MOVE_SELECTION;
	self->priv->operation_end = oper_move_selection_end;

	ld_diagram_begin_user_action (self->priv->diagram);

	data = &OPER_DATA (self, move_selection);
	data->move_origin = self->priv->drag_start_pos;

	oper_move_selection_motion (self, point);
}

static void
oper_move_selection_end (LdCanvas *self)
{
	ld_diagram_end_user_action (self->priv->diagram);
}

static void
oper_move_selection_motion (LdCanvas *self, const LdPoint *point)
{
	MoveSelectionData *data;
	gdouble scale, dx, dy, move_x, move_y;
	gdouble move = FALSE;

	scale = ld_canvas_get_scale_in_px (self);
	data = &OPER_DATA (self, move_selection);

	dx = point->x - data->move_origin.x;
	dy = point->y - data->move_origin.y;

	move_x = dx < 0 ? ceil (dx / scale) : floor (dx / scale);
	move_y = dy < 0 ? ceil (dy / scale) : floor (dy / scale);

	if (ABS (move_x) >= 1)
	{
		data->move_origin.x += move_x * scale;
		move = TRUE;
	}
	if (ABS (move_y) >= 1)
	{
		data->move_origin.y += move_y * scale;
		move = TRUE;
	}

	if (move)
		move_selection (self, move_x, move_y);
}


/* ===== Events, rendering ================================================= */

static void
simulate_motion (LdCanvas *self)
{
	GdkEventMotion event;
	GtkWidget *widget;
	gint x, y;
	GdkModifierType state;

	widget = GTK_WIDGET (self);

	if (gdk_window_get_pointer (widget->window, &x, &y, &state)
		!= widget->window)
		return;

	memset (&event, 0, sizeof (event));
	event.type = GDK_MOTION_NOTIFY;
	event.window = widget->window;
	event.x = x;
	event.y = y;
	event.state = state;

	on_motion_notify (widget, &event, NULL);
}

static gboolean
on_motion_notify (GtkWidget *widget, GdkEventMotion *event, gpointer user_data)
{
	LdPoint point;
	LdCanvas *self;
	AddObjectData *add_data;

	point.x = event->x;
	point.y = event->y;

	self = LD_CANVAS (widget);
	switch (self->priv->operation)
	{
	case OPER_ADD_OBJECT:
		add_data = &OPER_DATA (self, add_object);
		add_data->visible = TRUE;

		queue_object_draw (self, add_data->object);
		move_object_to_point (self, add_data->object, &point);
		queue_object_draw (self, add_data->object);
		break;
	case OPER_CONNECT:
		oper_connect_motion (self, &point);
		break;
	case OPER_SELECT:
		oper_select_motion (self, &point);
		break;
	case OPER_MOVE_SELECTION:
		oper_move_selection_motion (self, &point);
		break;
	case OPER_0:
		if (event->state & GDK_BUTTON1_MASK
			&& (event->x != self->priv->drag_start_pos.x
			|| event->y != self->priv->drag_start_pos.y))
		{
			switch (self->priv->drag_operation)
			{
			case OPER_CONNECT:
				oper_connect_begin (self, &point);
				break;
			case OPER_SELECT:
				oper_select_begin (self, &point);
				break;
			case OPER_MOVE_SELECTION:
				oper_move_selection_begin (self, &point);
				break;
			}
		}
		check_terminals (self, &point);
		break;
	}
	return FALSE;
}

static gboolean
on_leave_notify (GtkWidget *widget, GdkEventCrossing *event, gpointer user_data)
{
	LdCanvas *self;

	self = LD_CANVAS (widget);
	switch (self->priv->operation)
	{
		AddObjectData *data;

	case OPER_ADD_OBJECT:
		data = &OPER_DATA (self, add_object);
		data->visible = FALSE;

		queue_object_draw (self, data->object);
		break;
	}
	return FALSE;
}

static gboolean
on_button_press (GtkWidget *widget, GdkEventButton *event, gpointer user_data)
{
	LdPoint point;
	LdCanvas *self;
	AddObjectData *data;
	LdDiagramObject *object;

	if (event->button != 1)
		return FALSE;
	if (!gtk_widget_has_focus (widget))
		gtk_widget_grab_focus (widget);

	point.x = event->x;
	point.y = event->y;

	self = LD_CANVAS (widget);
	if (!self->priv->diagram)
		return FALSE;

	self->priv->drag_operation = OPER_0;
	switch (self->priv->operation)
	{
	case OPER_ADD_OBJECT:
		data = &OPER_DATA (self, add_object);

		queue_object_draw (self, data->object);
		move_object_to_point (self, data->object, &point);
		ld_diagram_insert_object (self->priv->diagram, data->object, -1);

		/* XXX: "cancel" causes confusion. */
		ld_canvas_real_cancel_operation (self);
		break;
	case OPER_0:
		self->priv->drag_start_pos = point;

		if (self->priv->terminal_hovered)
		{
			self->priv->drag_operation = OPER_CONNECT;
			break;
		}

		object = get_object_at_point (self, &point);
		if (!object)
		{
			ld_diagram_unselect_all (self->priv->diagram);
			self->priv->drag_operation = OPER_SELECT;
		}
		else if (!is_object_selected (self, object))
		{
			if (event->state != GDK_SHIFT_MASK)
				ld_diagram_unselect_all (self->priv->diagram);
			ld_diagram_select (self->priv->diagram, object);
			self->priv->drag_operation = OPER_MOVE_SELECTION;
		}
		else
			self->priv->drag_operation = OPER_MOVE_SELECTION;
		break;
	}
	return FALSE;
}

static gboolean
on_button_release (GtkWidget *widget, GdkEventButton *event, gpointer user_data)
{
	LdPoint point;
	LdCanvas *self;
	LdDiagramObject *object;

	if (event->button != 1)
		return FALSE;

	point.x = event->x;
	point.y = event->y;

	self = LD_CANVAS (widget);
	if (!self->priv->diagram)
		return FALSE;

	switch (self->priv->operation)
	{
	case OPER_SELECT:
	case OPER_MOVE_SELECTION:
	case OPER_CONNECT:
		ld_canvas_real_cancel_operation (self);
		break;
	case OPER_0:
		object = get_object_at_point (self, &point);
		if (object && is_object_selected (self, object))
		{
			if (!(event->state & GDK_SHIFT_MASK))
				ld_diagram_unselect_all (self->priv->diagram);
			ld_diagram_select (self->priv->diagram, object);
		}
		break;
	}
	return FALSE;
}

static gboolean
on_scroll (GtkWidget *widget, GdkEventScroll *event, gpointer user_data)
{
	gdouble prev_x, prev_y;
	gdouble new_x, new_y;
	LdPoint point;
	LdCanvas *self;

	point.x = event->x;
	point.y = event->y;
	self = LD_CANVAS (widget);

	ld_canvas_widget_to_diagram_coords (self,
		event->x, event->y, &prev_x, &prev_y);

	switch (event->direction)
	{
	case GDK_SCROLL_UP:
		ld_canvas_zoom_in (self);
		break;
	case GDK_SCROLL_DOWN:
		ld_canvas_zoom_out (self);
		break;
	default:
		return FALSE;
	}

	ld_canvas_widget_to_diagram_coords (self,
		event->x, event->y, &new_x, &new_y);

	/* Focus on the point under the cursor. */
	self->priv->x += prev_x - new_x;
	self->priv->y += prev_y - new_y;

	check_terminals (self, &point);
	return TRUE;
}

static gboolean
on_expose_event (GtkWidget *widget, GdkEventExpose *event, gpointer user_data)
{
	DrawData data;

	data.cr = gdk_cairo_create (widget->window);
	data.self = LD_CANVAS (widget);
	data.scale = ld_canvas_get_scale_in_px (data.self);
	data.exposed_rect.x = event->area.x;
	data.exposed_rect.y = event->area.y;
	data.exposed_rect.width = event->area.width;
	data.exposed_rect.height = event->area.height;

	gdk_cairo_rectangle (data.cr, &event->area);
	cairo_clip (data.cr);

	ld_canvas_color_apply (COLOR_GET (data.self, COLOR_BASE), data.cr);
	cairo_paint (data.cr);

	draw_grid (widget, &data);
	draw_diagram (widget, &data);
	draw_terminal (widget, &data);

	if (data.self->priv->operation == OPER_SELECT)
		oper_select_draw (widget, &data);

	cairo_destroy (data.cr);
	return FALSE;
}

static void
draw_grid (GtkWidget *widget, DrawData *data)
{
	gdouble grid_step;
	gint grid_factor;
	gdouble x_init, y_init;
	gdouble x, y;
	cairo_surface_t *grid_surface;
	gint stride;
	unsigned char *pixels;
	guint32 color;

	grid_step = data->scale;
	grid_factor = 1;
	while (grid_step < 5)
	{
		grid_step *= 5;
		grid_factor *= 5;
	}

	/* Paint manually on our own raster surface for speed. */
	stride = cairo_format_stride_for_width
		(CAIRO_FORMAT_ARGB32, data->exposed_rect.width);
	pixels = g_malloc0 (stride * data->exposed_rect.height);
	grid_surface = cairo_image_surface_create_for_data
		(pixels, CAIRO_FORMAT_ARGB32,
		data->exposed_rect.width, data->exposed_rect.height, stride);

	/* Get coordinates of the top-left point. */
	ld_canvas_widget_to_diagram_coords (data->self,
		data->exposed_rect.x, data->exposed_rect.y, &x_init, &y_init);

	x_init = ceil (x_init);
	x_init = x_init - (gint) x_init % grid_factor;
	y_init = ceil (y_init);
	y_init = y_init - (gint) y_init % grid_factor;

	ld_canvas_diagram_to_widget_coords (data->self,
		x_init, y_init, &x_init, &y_init);

	x_init -= data->exposed_rect.x;
	y_init -= data->exposed_rect.y;

	while (x_init < 0)
		x_init += grid_step;
	while (y_init < 0)
		y_init += grid_step;

	color = ld_canvas_color_to_cairo_argb (COLOR_GET (data->self, COLOR_GRID));

	for     (x = x_init; x < data->exposed_rect.width;  x += grid_step)
		for (y = y_init; y < data->exposed_rect.height; y += grid_step)
			*((guint32 *) (pixels + stride * (gint) y) + (gint) x) = color;

	cairo_set_source_surface (data->cr, grid_surface,
		data->exposed_rect.x, data->exposed_rect.y);
	cairo_paint (data->cr);

	cairo_surface_destroy (grid_surface);
	g_free (pixels);
}

static void
draw_terminal (GtkWidget *widget, DrawData *data)
{
	LdCanvasPrivate *priv;
	LdPoint widget_coords;

	priv = data->self->priv;
	if (!priv->terminal_hovered)
		return;

	ld_canvas_color_apply (COLOR_GET (data->self, COLOR_TERMINAL), data->cr);
	cairo_set_line_width (data->cr, 1);

	cairo_new_path (data->cr);
	ld_canvas_diagram_to_widget_coords (data->self,
		priv->terminal.x, priv->terminal.y,
		&widget_coords.x, &widget_coords.y);
	cairo_arc (data->cr, widget_coords.x, widget_coords.y,
		TERMINAL_RADIUS, 0, 2 * G_PI);
	cairo_stroke (data->cr);
}

static void
draw_diagram (GtkWidget *widget, DrawData *data)
{
	GList *objects, *iter;

	if (!data->self->priv->diagram)
		return;

	cairo_save (data->cr);
	cairo_set_line_width (data->cr, 1 / data->scale);

	/* Draw objects from the diagram, from bottom to top. */
	objects = (GList *) ld_diagram_get_objects (data->self->priv->diagram);
	for (iter = objects; iter; iter = g_list_next (iter))
		draw_object (LD_DIAGRAM_OBJECT (iter->data), data);

	switch (data->self->priv->operation)
	{
		AddObjectData *add_data;
		ConnectData *connect_data;

	case OPER_ADD_OBJECT:
		add_data = &OPER_DATA (data->self, add_object);
		if (add_data->visible)
			draw_object (add_data->object, data);
		break;
	case OPER_CONNECT:
		connect_data = &OPER_DATA (data->self, connect);
		draw_object (LD_DIAGRAM_OBJECT (connect_data->connection), data);
		break;
	}

	cairo_restore (data->cr);
}

static void
draw_object (LdDiagramObject *diagram_object, DrawData *data)
{
	g_return_if_fail (LD_IS_DIAGRAM_OBJECT (diagram_object));
	g_return_if_fail (data != NULL);

	if (is_object_selected (data->self, diagram_object))
		ld_canvas_color_apply (COLOR_GET (data->self,
			COLOR_SELECTION), data->cr);
	else
		ld_canvas_color_apply (COLOR_GET (data->self,
			COLOR_OBJECT), data->cr);

	if (LD_IS_DIAGRAM_SYMBOL (diagram_object))
		draw_symbol (LD_DIAGRAM_SYMBOL (diagram_object), data);
	else if (LD_IS_DIAGRAM_CONNECTION (diagram_object))
		draw_connection (LD_DIAGRAM_CONNECTION (diagram_object), data);
}

static void
draw_symbol (LdDiagramSymbol *diagram_symbol, DrawData *data)
{
	LdSymbol *symbol;
	LdRectangle clip_rect;
	gdouble x, y;

	symbol = resolve_symbol (data->self, diagram_symbol);

	/* TODO: Resolve this better; draw a cross or whatever. */
	if (!symbol)
	{
		gchar *klass;

		klass = ld_diagram_symbol_get_class (diagram_symbol);
		g_warning ("cannot find symbol `%s' in the library", klass);
		g_free (klass);
		return;
	}

	if (!get_symbol_clip_area (data->self, diagram_symbol, &clip_rect)
		|| !ld_rectangle_intersects (&clip_rect, &data->exposed_rect))
		return;

	cairo_save (data->cr);

	cairo_rectangle (data->cr, clip_rect.x, clip_rect.y,
		clip_rect.width, clip_rect.height);
	cairo_clip (data->cr);

	/* TODO: Rotate the space for other orientations. */
	g_object_get (diagram_symbol, "x", &x, "y", &y, NULL);
	ld_canvas_diagram_to_widget_coords (data->self, x, y, &x, &y);
	cairo_translate (data->cr, x, y);
	cairo_scale (data->cr, data->scale, data->scale);

	ld_symbol_draw (symbol, data->cr);
	cairo_restore (data->cr);
}

static void
draw_connection (LdDiagramConnection *connection, DrawData *data)
{
	LdRectangle clip_rect;
	LdPointArray *points;
	gdouble x, y;
	guint i;

	if (!get_connection_clip_area (data->self, connection, &clip_rect)
		|| !ld_rectangle_intersects (&clip_rect, &data->exposed_rect))
		return;

	points = ld_diagram_connection_get_points (connection);
	if (points->length < 2)
		goto draw_connection_end;

	cairo_save (data->cr);

	g_object_get (connection, "x", &x, "y", &y, NULL);
	ld_canvas_diagram_to_widget_coords (data->self, x, y, &x, &y);
	cairo_translate (data->cr, x, y);
	cairo_scale (data->cr, data->scale, data->scale);

	for (i = 1; i < points->length; i++)
	{
		cairo_move_to (data->cr,
			points->points[i - 1].x,
			points->points[i - 1].y);
		cairo_line_to (data->cr,
			points->points[i].x,
			points->points[i].y);
		cairo_stroke (data->cr);
	}
	cairo_restore (data->cr);

draw_connection_end:
	ld_point_array_free (points);
	return;
}