#define __SP_RULER_C__

/*
 * Customized ruler class for inkscape
 *
 * Authors:
 *   Lauris Kaplinski <lauris@kaplinski.com>
 *   Frank Felfe <innerspace@iname.com>
 *   bulia byak <buliabyak@users.sf.net>
 *   Diederik van Lierop <mail@diedenrezi.nl>
 *
 * Copyright (C) 1999-2008 authors
 *
 * Released under GNU GPL, read the file 'COPYING' for more information
 */

#include <cstring>
#include <cmath>
#include <cstdio>

#include "widget-sizes.h"
#include "desktop-widget.h"
#include "ruler.h"
#include "unit-constants.h"
#include "round.h"

#define MINIMUM_INCR          5
#define MAXIMUM_SUBDIVIDE     5
#define MAXIMUM_SCALES        10
#define UNUSED_PIXELS         2     // There appear to be two pixels that are not being used at each end of the ruler

static void sp_hruler_class_init    (SPHRulerClass *klass);
static void sp_hruler_init          (SPHRuler      *hruler);
static gint sp_hruler_motion_notify (GtkWidget      *widget, GdkEventMotion *event);
static void sp_hruler_draw_ticks    (GtkRuler       *ruler);
static void sp_hruler_draw_pos      (GtkRuler       *ruler);
static void sp_hruler_size_allocate (GtkWidget *widget, GtkAllocation *allocation);

static GtkWidgetClass *hruler_parent_class;

GtkType
sp_hruler_get_type (void)
{
  static GtkType hruler_type = 0;

  if (!hruler_type)
    {
      static const GtkTypeInfo hruler_info =
      {
        "SPHRuler",
        sizeof (SPHRuler),
        sizeof (SPHRulerClass),
        (GtkClassInitFunc) sp_hruler_class_init,
        (GtkObjectInitFunc) sp_hruler_init,
        /* reserved_1 */ NULL,
        /* reserved_2 */ NULL,
        (GtkClassInitFunc) NULL,
      };
  
      hruler_type = gtk_type_unique (gtk_ruler_get_type (), &hruler_info);
    }

  return hruler_type;
}

static void
sp_hruler_class_init (SPHRulerClass *klass)
{
  GtkWidgetClass *widget_class;
  GtkRulerClass *ruler_class;

  hruler_parent_class = (GtkWidgetClass *) gtk_type_class (GTK_TYPE_RULER);

  widget_class = (GtkWidgetClass*) klass;
  ruler_class = (GtkRulerClass*) klass;

  widget_class->motion_notify_event = sp_hruler_motion_notify;
  widget_class->size_allocate = sp_hruler_size_allocate;

  ruler_class->draw_ticks = sp_hruler_draw_ticks;
  ruler_class->draw_pos = sp_hruler_draw_pos;
}

static void
sp_hruler_init (SPHRuler *hruler)
{
  GtkWidget *widget;

  widget = GTK_WIDGET (hruler);
  widget->requisition.width = widget->style->xthickness * 2 + 1;
  widget->requisition.height = widget->style->ythickness * 2 + RULER_HEIGHT;
}


GtkWidget*
sp_hruler_new (void)
{
  return GTK_WIDGET (gtk_type_new (sp_hruler_get_type ()));
}

static gint
sp_hruler_motion_notify (GtkWidget      *widget,
			  GdkEventMotion *event)
{
  GtkRuler *ruler;
  
  g_return_val_if_fail (widget != NULL, FALSE);
  g_return_val_if_fail (SP_IS_HRULER (widget), FALSE);
  g_return_val_if_fail (event != NULL, FALSE);

  ruler = GTK_RULER (widget);
  double x = event->x; //Although event->x is double according to the docs, it only appears to return integers
  ruler->position = ruler->lower + (ruler->upper - ruler->lower) * (x + UNUSED_PIXELS) / (widget->allocation.width + 2*UNUSED_PIXELS);
  
  /*  Make sure the ruler has been allocated already  */
  if (ruler->backing_store != NULL)
    gtk_ruler_draw_pos (ruler);

  return FALSE;
}

static void
sp_hruler_draw_ticks (GtkRuler *ruler)
{
  GtkWidget *widget;
  GdkGC *gc, *bg_gc;
  PangoFontDescription *pango_desc;
  PangoContext *pango_context;
  PangoLayout *pango_layout;
  gint i, tick_index;
  gint width, height;
  gint xthickness;
  gint ythickness;
  gint length, ideal_length;
  double lower, upper;		/* Upper and lower limits, in ruler units */
  double increment;		/* Number of pixels per unit */
  gint scale;			/* Number of units per major unit */
  double subd_incr;
  double start, end, cur;
  gchar unit_str[32];
  gint digit_height;
  gint text_width;
  gint pos;

  g_return_if_fail (ruler != NULL);
  g_return_if_fail (SP_IS_HRULER (ruler));

  if (!GTK_WIDGET_DRAWABLE (ruler)) 
    return;

  widget = GTK_WIDGET (ruler);

  gc = widget->style->fg_gc[GTK_STATE_NORMAL];
  bg_gc = widget->style->bg_gc[GTK_STATE_NORMAL];
  
  pango_desc = widget->style->font_desc;
  
  // Create the pango layout
  pango_context = gtk_widget_get_pango_context (widget);

  pango_layout = pango_layout_new (pango_context);

  PangoFontDescription *fs = pango_font_description_new ();
  pango_font_description_set_size (fs, RULER_FONT_SIZE);
  pango_layout_set_font_description (pango_layout, fs);
  pango_font_description_free (fs);

  digit_height = (int) floor (RULER_FONT_SIZE * RULER_FONT_VERTICAL_SPACING / PANGO_SCALE + 0.5);

  xthickness = widget->style->xthickness;
  ythickness = widget->style->ythickness;

  width = widget->allocation.width; // in pixels; is apparently 2 pixels shorter than the canvas at each end
  height = widget->allocation.height;// - ythickness * 2;
    
  gtk_paint_box (widget->style, ruler->backing_store,
		 GTK_STATE_NORMAL, GTK_SHADOW_NONE, 
		 NULL, widget, "hruler",
		 0, 0, 
		 widget->allocation.width, widget->allocation.height);

  upper = ruler->upper / ruler->metric->pixels_per_unit; // upper and lower are expressed in ruler units
  lower = ruler->lower / ruler->metric->pixels_per_unit;
  /* "pixels_per_unit" should be "points_per_unit". This is the size of the unit
   * in 1/72nd's of an inch and has nothing to do with screen pixels */
  
  if ((upper - lower) == 0) 
    return;
  increment = (double) (width + 2*UNUSED_PIXELS) / (upper - lower); // screen pixels per ruler unit
  
   /* determine the scale
   *  We calculate the text size as for the vruler instead of using
   *  text_width = gdk_string_width(font, unit_str), so that the result
   *  for the scale looks consistent with an accompanying vruler
   */
  scale = (int)(ceil (ruler->max_size / ruler->metric->pixels_per_unit));
  sprintf (unit_str, "%d", scale);
  text_width = strlen (unit_str) * digit_height + 1;

  for (scale = 0; scale < MAXIMUM_SCALES; scale++)
    if (ruler->metric->ruler_scale[scale] * fabs(increment) > 2 * text_width)
      break;

  if (scale == MAXIMUM_SCALES)
    scale = MAXIMUM_SCALES - 1;

  /* drawing starts here */
  length = 0;
  for (i = MAXIMUM_SUBDIVIDE - 1; i >= 0; i--)
    {
      subd_incr = ruler->metric->ruler_scale[scale] / 
	          ruler->metric->subdivide[i];
      if (subd_incr * fabs(increment) <= MINIMUM_INCR) 
    continue;

      /* Calculate the length of the tickmarks. Make sure that
       * this length increases for each set of ticks
       */
      ideal_length = height / (i + 1) - 1;
      if (ideal_length > ++length)
	length = ideal_length;

      if (lower < upper)
	{
	  start = floor (lower / subd_incr) * subd_incr;
	  end   = ceil  (upper / subd_incr) * subd_incr;
	}
      else
	{
	  start = floor (upper / subd_incr) * subd_incr;
	  end   = ceil  (lower / subd_incr) * subd_incr;
	}

    tick_index = 0;
    cur = start; // location (in ruler units) of the first invisible tick at the left side of the canvas 

	while (cur <= end)
	{
	  // due to the typical values for cur, lower and increment, pos will often end up to
      // be e.g. 641.50000000000; rounding behaviour is not defined in such a case (see round.h)
      // and jitter will be apparent (upon redrawing some of the lines on the ruler might jump a
      // by a pixel, and jump back on the next redraw). This is suppressed by adding 1e-9 (that's only one nanopixel ;-))
      pos = int(Inkscape::round((cur - lower) * increment + 1e-12)) - UNUSED_PIXELS; 
      gdk_draw_line (ruler->backing_store, gc,
			 pos, height + ythickness, 
			 pos, height - length + ythickness);

	  /* draw label */
        double label_spacing_px = (increment*(double)ruler->metric->ruler_scale[scale])/ruler->metric->subdivide[i];
	  if (i == 0 && 
				(label_spacing_px > 6*digit_height || tick_index%2 == 0 || cur == 0) && 
				(label_spacing_px > 3*digit_height || tick_index%4 == 0 ||  cur == 0))
	    {
				if (fabs((int)cur) >= 2000 && (((int) cur)/1000)*1000 == ((int) cur))
					sprintf (unit_str, "%dk", ((int) cur)/1000);
				else
					sprintf (unit_str, "%d", (int) cur);
	
				pango_layout_set_text (pango_layout, unit_str, -1);
	      
				gdk_draw_layout (ruler->backing_store, gc,
	                       pos + 2, 0, pango_layout);
	    }

      /* Calculate cur from start rather than incrementing by subd_incr
       * in each iteration. This is to avoid propagation of floating point 
       * errors in subd_incr.
       */
      ++tick_index;
      cur = start + tick_index * subd_incr;
	}
    }
}

static void
sp_hruler_draw_pos (GtkRuler *ruler)
{
  GtkWidget *widget;
  GdkGC *gc;
  int i;
  gint x, y;
  gint width, height;
  gint bs_width, bs_height;
  gint xthickness;
  gint ythickness;
  gfloat increment;

  g_return_if_fail (ruler != NULL);
  g_return_if_fail (SP_IS_HRULER (ruler));

  if (GTK_WIDGET_DRAWABLE (ruler))
    {
      widget = GTK_WIDGET (ruler);

      gc = widget->style->fg_gc[GTK_STATE_NORMAL];
      xthickness = widget->style->xthickness;
      ythickness = widget->style->ythickness;
      width = widget->allocation.width; // in pixels; is apparently 2 pixels shorter than the canvas at each end
      height = widget->allocation.height - ythickness * 2;

      bs_width = height / 2;
      bs_width |= 1;  /* make sure it's odd */
      bs_height = bs_width / 2 + 1;

      if ((bs_width > 0) && (bs_height > 0))
	{
	  /*  If a backing store exists, restore the ruler  */
	  if (ruler->backing_store && ruler->non_gr_exp_gc)
	    gdk_draw_pixmap (ruler->widget.window,
			     ruler->non_gr_exp_gc,
			     ruler->backing_store,
			     ruler->xsrc, ruler->ysrc,
			     ruler->xsrc, ruler->ysrc,
			     bs_width, bs_height);

	  increment = (gfloat) (width + 2*UNUSED_PIXELS) / (ruler->upper - ruler->lower);

	  // Calculate the coordinates (x, y, in pixels) of the tip of the triangle
      x = int(Inkscape::round((ruler->position - ruler->lower) * increment + double(xthickness - bs_width) / 2.0) - UNUSED_PIXELS);
	  y = (height + bs_height) / 2 + ythickness;

	  for (i = 0; i < bs_height; i++)
	    gdk_draw_line (widget->window, gc,
			   x + i, y + i,
			   x + bs_width - 1 - i, y + i);


	  ruler->xsrc = x;
	  ruler->ysrc = y;
	}
    }
}

/**
 * The hruler widget's size_allocate callback.
 */
static void
sp_hruler_size_allocate (GtkWidget *widget, GtkAllocation *allocation)
{
    g_assert (widget != NULL);
    g_assert (SP_IS_HRULER (widget));    
    
    // First call the default gtk_widget_size_allocate() method (which is being overridden here)
    if (GTK_WIDGET_CLASS (hruler_parent_class)->size_allocate)
        (* GTK_WIDGET_CLASS (hruler_parent_class)->size_allocate) (widget, allocation);
 
    // Now the size of the ruler has changed, the ruler bounds (upper & lower) need to be updated
    // For this we first need to obtain a pointer to the desktop, by walking up the tree of ancestors    
    GtkWidget *parent = gtk_widget_get_parent(widget);    
    do {
        if (SP_IS_DESKTOP_WIDGET(parent)) {
            // Now we've found the desktop widget we can have the ruler boundaries updated 
            sp_desktop_widget_update_hruler(SP_DESKTOP_WIDGET(parent));
            // If the size of the ruler has increased, then a blank part is uncovered; therefore
            // it must be redrawn  
            sp_hruler_draw_ticks(GTK_RULER(widget));
            break;   
        }
        parent = gtk_widget_get_parent(parent);
    } while (parent != NULL);
}




// vruler

static void sp_vruler_class_init    (SPVRulerClass *klass);
static void sp_vruler_init          (SPVRuler      *vruler);
static gint sp_vruler_motion_notify (GtkWidget      *widget,
				      GdkEventMotion *event);
static void sp_vruler_draw_ticks    (GtkRuler       *ruler);
static void sp_vruler_draw_pos      (GtkRuler       *ruler);
static void sp_vruler_size_allocate (GtkWidget *widget, GtkAllocation *allocation);

static GtkWidgetClass *vruler_parent_class;

GtkType
sp_vruler_get_type (void)
{
  static GtkType vruler_type = 0;

  if (!vruler_type)
    {
      static const GtkTypeInfo vruler_info =
      {
	"SPVRuler",
	sizeof (SPVRuler),
	sizeof (SPVRulerClass),
	(GtkClassInitFunc) sp_vruler_class_init,
	(GtkObjectInitFunc) sp_vruler_init,
	/* reserved_1 */ NULL,
        /* reserved_2 */ NULL,
        (GtkClassInitFunc) NULL,
      };

      vruler_type = gtk_type_unique (gtk_ruler_get_type (), &vruler_info);
    }

  return vruler_type;
}

static void
sp_vruler_class_init (SPVRulerClass *klass)
{
  GtkWidgetClass *widget_class;
  GtkRulerClass *ruler_class;

  vruler_parent_class = (GtkWidgetClass *) gtk_type_class (GTK_TYPE_RULER);

  widget_class = (GtkWidgetClass*) klass;
  ruler_class = (GtkRulerClass*) klass;

  widget_class->motion_notify_event = sp_vruler_motion_notify;
  widget_class->size_allocate = sp_vruler_size_allocate;

  ruler_class->draw_ticks = sp_vruler_draw_ticks;
  ruler_class->draw_pos = sp_vruler_draw_pos;
}

static void
sp_vruler_init (SPVRuler *vruler)
{
  GtkWidget *widget;

  widget = GTK_WIDGET (vruler);
  widget->requisition.width = widget->style->xthickness * 2 + RULER_WIDTH;
  widget->requisition.height = widget->style->ythickness * 2 + 1;
}

GtkWidget*
sp_vruler_new (void)
{
  return GTK_WIDGET (gtk_type_new (sp_vruler_get_type ()));
}


static gint
sp_vruler_motion_notify (GtkWidget      *widget,
			  GdkEventMotion *event)
{
  GtkRuler *ruler;
  
  g_return_val_if_fail (widget != NULL, FALSE);
  g_return_val_if_fail (SP_IS_VRULER (widget), FALSE);
  g_return_val_if_fail (event != NULL, FALSE);

  ruler = GTK_RULER (widget);
  double y = event->y; //Although event->y is double according to the docs, it only appears to return integers
  ruler->position = ruler->lower + (ruler->upper - ruler->lower) * (y + UNUSED_PIXELS) / (widget->allocation.height + 2*UNUSED_PIXELS);

  /*  Make sure the ruler has been allocated already  */
  if (ruler->backing_store != NULL)
    gtk_ruler_draw_pos (ruler);

  return FALSE;
}

static void
sp_vruler_draw_ticks (GtkRuler *ruler)
{
  GtkWidget *widget;
  GdkGC *gc, *bg_gc;
  PangoFontDescription *pango_desc;
  PangoContext *pango_context;
  PangoLayout *pango_layout;
  gint i, j, tick_index;
  gint width, height;
  gint xthickness;
  gint ythickness;
  gint length, ideal_length;
  double lower, upper;		/* Upper and lower limits, in ruler units */
  double increment;		/* Number of pixels per unit */
  gint scale;			/* Number of units per major unit */
  double subd_incr;
  double start, end, cur;
  gchar unit_str[32];
  gchar digit_str[2] = { '\0', '\0' };
  gint digit_height;
  gint text_height;
  gint pos;

  g_return_if_fail (ruler != NULL);
  g_return_if_fail (SP_IS_VRULER (ruler));

  if (!GTK_WIDGET_DRAWABLE (ruler)) 
    return;

  widget = GTK_WIDGET (ruler);

  gc = widget->style->fg_gc[GTK_STATE_NORMAL];
  bg_gc = widget->style->bg_gc[GTK_STATE_NORMAL];
  
  pango_desc = widget->style->font_desc;
  
  // Create the pango layout
  pango_context = gtk_widget_get_pango_context (widget);

  pango_layout = pango_layout_new (pango_context);

  PangoFontDescription *fs = pango_font_description_new ();
  pango_font_description_set_size (fs, RULER_FONT_SIZE);
  pango_layout_set_font_description (pango_layout, fs);
  pango_font_description_free (fs);

  digit_height = (int) floor (RULER_FONT_SIZE * RULER_FONT_VERTICAL_SPACING / PANGO_SCALE + 0.5);
  
  xthickness = widget->style->xthickness;
  ythickness = widget->style->ythickness;

  width = widget->allocation.height; //in pixels; is apparently 2 pixels shorter than the canvas at each end
  height = widget->allocation.width;// - ythickness * 2;

  gtk_paint_box (widget->style, ruler->backing_store,
		 GTK_STATE_NORMAL, GTK_SHADOW_NONE, 
		 NULL, widget, "vruler",
		 0, 0, 
		 widget->allocation.width, widget->allocation.height);
  
  upper = ruler->upper / ruler->metric->pixels_per_unit; // upper and lower are expressed in ruler units
  lower = ruler->lower / ruler->metric->pixels_per_unit;
  /* "pixels_per_unit" should be "points_per_unit". This is the size of the unit
   * in 1/72nd's of an inch and has nothing to do with screen pixels */
  
  if ((upper - lower) == 0)
    return;
  increment = (double) (width + 2*UNUSED_PIXELS) / (upper - lower); // screen pixels per ruler unit

  /* determine the scale
   *   use the maximum extents of the ruler to determine the largest
   *   possible number to be displayed.  Calculate the height in pixels
   *   of this displayed text. Use this height to find a scale which
   *   leaves sufficient room for drawing the ruler.  
   */
  scale = (int)ceil (ruler->max_size / ruler->metric->pixels_per_unit);
  sprintf (unit_str, "%d", scale);
  text_height = strlen (unit_str) * digit_height + 1;

  for (scale = 0; scale < MAXIMUM_SCALES; scale++)
    if (ruler->metric->ruler_scale[scale] * fabs(increment) > 2 * text_height)
      break;

  if (scale == MAXIMUM_SCALES)
    scale = MAXIMUM_SCALES - 1;

  /* drawing starts here */
  length = 0;
  for (i = MAXIMUM_SUBDIVIDE - 1; i >= 0; i--) {
		subd_incr = (double) ruler->metric->ruler_scale[scale] / 
			(double) ruler->metric->subdivide[i];
		if (subd_incr * fabs(increment) <= MINIMUM_INCR) 
			continue;

		/* Calculate the length of the tickmarks. Make sure that
		 * this length increases for each set of ticks
		 */
		ideal_length = height / (i + 1) - 1;
		if (ideal_length > ++length)
			length = ideal_length;

		if (lower < upper)
			{
				start = floor (lower / subd_incr) * subd_incr;
				end   = ceil  (upper / subd_incr) * subd_incr;
			}
		else
			{
				start = floor (upper / subd_incr) * subd_incr;
				end   = ceil  (lower / subd_incr) * subd_incr;
			}

    tick_index = 0;
    cur = start; // location (in ruler units) of the first invisible tick at the top side of the canvas       

    while (cur < end) {
          // due to the typical values for cur, lower and increment, pos will often end up to
          // be e.g. 641.50000000000; rounding behaviour is not defined in such a case (see round.h)
          // and jitter will be apparent (upon redrawing some of the lines on the ruler might jump a
          // by a pixel, and jump back on the next redraw). This is suppressed by adding 1e-9 (that's only one nanopixel ;-))
            pos = int(Inkscape::round((cur - lower) * increment + 1e-12)) - UNUSED_PIXELS;

			gdk_draw_line (ruler->backing_store, gc,
										 height + xthickness - length, pos,
										 height + xthickness, pos);

			/* draw label */
			double label_spacing_px = fabs((increment*(double)ruler->metric->ruler_scale[scale])/ruler->metric->subdivide[i]);
			if (i == 0 && 
					(label_spacing_px > 6*digit_height || tick_index%2 == 0 || cur == 0) && 
					(label_spacing_px > 3*digit_height || tick_index%4 == 0 || cur == 0))
				{
					if (fabs((int)cur) >= 2000 && (((int) cur)/1000)*1000 == ((int) cur))
						sprintf (unit_str, "%dk", ((int) cur)/1000);
					else
						sprintf (unit_str, "%d", (int) cur);
					for (j = 0; j < (int) strlen (unit_str); j++)
						{
							digit_str[0] = unit_str[j];
                  
							pango_layout_set_text (pango_layout, digit_str, 1);
      
							gdk_draw_layout (ruler->backing_store, gc,
															 xthickness + 1, 
															 pos + digit_height * (j) + 1,
															 pango_layout); 
						}
				}

			/* Calculate cur from start rather than incrementing by subd_incr
			 * in each iteration. This is to avoid propagation of floating point 
			 * errors in subd_incr.
			 */
			++tick_index;
			cur = start + tick_index * subd_incr;
		}
	}
}

static void
sp_vruler_draw_pos (GtkRuler *ruler)
{
  GtkWidget *widget;
  GdkGC *gc;
  int i;
  gint x, y;
  gint width, height;
  gint bs_width, bs_height;
  gint xthickness;
  gint ythickness;
  gfloat increment;

  g_return_if_fail (ruler != NULL);
  g_return_if_fail (SP_IS_VRULER (ruler));

  if (GTK_WIDGET_DRAWABLE (ruler))
    {
      widget = GTK_WIDGET (ruler);

      gc = widget->style->fg_gc[GTK_STATE_NORMAL];
      xthickness = widget->style->xthickness;
      ythickness = widget->style->ythickness;
      width = widget->allocation.width - xthickness * 2;
      height = widget->allocation.height; // in pixels; is apparently 2 pixels shorter than the canvas at each end

      bs_height = width / 2;
      bs_height |= 1;  /* make sure it's odd */
      bs_width = bs_height / 2 + 1;

      if ((bs_width > 0) && (bs_height > 0))
	{
	  /*  If a backing store exists, restore the ruler  */
	  if (ruler->backing_store && ruler->non_gr_exp_gc)
	    gdk_draw_pixmap (ruler->widget.window,
			     ruler->non_gr_exp_gc,
			     ruler->backing_store,
			     ruler->xsrc, ruler->ysrc,
			     ruler->xsrc, ruler->ysrc,
			     bs_width, bs_height);

	  increment = (gfloat) (height + 2*UNUSED_PIXELS) / (ruler->upper - ruler->lower);

	  // Calculate the coordinates (x, y, in pixels) of the tip of the triangle
      x = (width + bs_width) / 2 + xthickness;
	  y = int(Inkscape::round((ruler->position - ruler->lower) * increment + double(ythickness - bs_height) / 2.0) - UNUSED_PIXELS);

	  for (i = 0; i < bs_width; i++)
	    gdk_draw_line (widget->window, gc,
			   x + i, y + i,
			   x + i, y + bs_height - 1 - i);

	  ruler->xsrc = x;
	  ruler->ysrc = y;
	}
    }
}

/**
 * The vruler widget's size_allocate callback.
 */
static void
sp_vruler_size_allocate (GtkWidget *widget, GtkAllocation *allocation)
{
    g_assert (widget != NULL);
    g_assert (SP_IS_VRULER (widget));    
    
    // First call the default gtk_widget_size_allocate() method (which is being overridden here)
    if (GTK_WIDGET_CLASS (vruler_parent_class)->size_allocate)
        (* GTK_WIDGET_CLASS (vruler_parent_class)->size_allocate) (widget, allocation);
 
    // Now the size of the ruler has changed, the ruler bounds (upper & lower) need to be updated
    // For this we first need to obtain a pointer to the desktop, by walking up the tree of ancestors    
    GtkWidget *parent = gtk_widget_get_parent(widget);    
    do {
        if (SP_IS_DESKTOP_WIDGET(parent)) {
            // Now we've found the desktop widget we can have the ruler boundaries updated 
            sp_desktop_widget_update_vruler(SP_DESKTOP_WIDGET(parent));
            // If the size of the ruler has increased, then a blank part is uncovered; therefore
            // it must be redrawn  
            sp_vruler_draw_ticks(GTK_RULER(widget));
            break;   
        }
        parent = gtk_widget_get_parent(parent);
    } while (parent != NULL);
}


/// Ruler metrics.
static GtkRulerMetric const sp_ruler_metrics[] = {
  // NOTE: the order of records in this struct must correspond to the SPMetric enum.
  {"NONE",  "", 1, { 1, 2, 5, 10, 25, 50, 100, 250, 500, 1000 }, { 1, 5, 10, 50, 100 }},
  {"millimeters",  "mm", PX_PER_MM, { 1, 2, 5, 10, 25, 50, 100, 250, 500, 1000 }, { 1, 5, 10, 50, 100 }},
  {"centimeters", "cm", PX_PER_CM, { 1, 2, 5, 10, 25, 50, 100, 250, 500, 1000 }, { 1, 5, 10, 50, 100 }},
  {"inches",      "in", PX_PER_IN, { 1, 2, 4, 8, 16, 32, 64, 128, 256, 512 }, { 1, 2, 4, 8, 16 }},
  {"feet",        "ft", PX_PER_FT, { 1, 2, 5, 10, 25, 50, 100, 250, 500, 1000 }, { 1, 5, 10, 50, 100 }},
  {"points",      "pt", PX_PER_PT, { 1, 2, 5, 10, 25, 50, 100, 250, 500, 1000 }, { 1, 5, 10, 50, 100 }},
  {"picas",       "pc", PX_PER_PC, { 1, 2, 5, 10, 25, 50, 100, 250, 500, 1000 }, { 1, 5, 10, 50, 100 }},
  {"pixels",      "px", PX_PER_PX, { 1, 2, 5, 10, 25, 50, 100, 250, 500, 1000 }, { 1, 5, 10, 50, 100 }},
  {"meters",      "m",  PX_PER_M,  { 1, 2, 5, 10, 25, 50, 100, 250, 500, 1000 }, { 1, 5, 10, 50, 100 }},
};

void
sp_ruler_set_metric (GtkRuler *ruler,
		     SPMetric  metric)
{
  g_return_if_fail (ruler != NULL);
  g_return_if_fail (GTK_IS_RULER (ruler));
  g_return_if_fail((unsigned) metric < G_N_ELEMENTS(sp_ruler_metrics));

  if (metric == 0) 
	return;

  ruler->metric = const_cast<GtkRulerMetric *>(&sp_ruler_metrics[metric]);

  if (GTK_WIDGET_DRAWABLE (ruler))
    gtk_widget_queue_draw (GTK_WIDGET (ruler));
}