gtk/gdk/gdkcairo.c

/* GDK - The GIMP Drawing Kit
 * Copyright (C) 2005 Red Hat, Inc. 
 *
 * 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., 59 Temple Place - Suite 330,
 * Boston, MA 02111-1307, USA.
 */

#include "gdkcairo.h"

#include <math.h>

#include "gdkdrawable.h"
#include "gdkinternals.h"


/**
 * SECTION:cairo_interaction
 * @Short_description: Functions to support using Cairo
 * @Title: Cairo Interaction
 *
 * <link href="http://cairographics.org">Cairo</link> is a graphics
 * library that supports vector graphics and image compositing that
 * can be used with GDK. Since 2.8, GTK+ does most of its drawing
 * using Cairo.
 *
 * GDK does not wrap the Cairo API, instead it allows to create Cairo
 * contexts which can be used to draw on #GdkDrawables. Additional
 * functions allow to convert GDK's rectangles and regions into
 * Cairo paths and to use pixbufs as sources for drawing operations.
 */


/**
 * gdk_cairo_create:
 * @drawable: a #GdkDrawable
 * 
 * Creates a Cairo context for drawing to @drawable.
 *
 * <note><para>
 * Note that due to double-buffering, Cairo contexts created 
 * in a GTK+ expose event handler cannot be cached and reused 
 * between different expose events. 
 * </para></note>
 *
 * Return value: A newly created Cairo context. Free with
 *  cairo_destroy() when you are done drawing.
 * 
 * Since: 2.8
 **/
cairo_t *
gdk_cairo_create (GdkDrawable *drawable)
{
  cairo_surface_t *surface;
  cairo_t *cr;
    
  g_return_val_if_fail (GDK_IS_DRAWABLE (drawable), NULL);

  surface = _gdk_drawable_ref_cairo_surface (drawable);
  cr = cairo_create (surface);

  if (GDK_DRAWABLE_GET_CLASS (drawable)->set_cairo_clip)
    GDK_DRAWABLE_GET_CLASS (drawable)->set_cairo_clip (drawable, cr);
    
  cairo_surface_destroy (surface);

  return cr;
}

/**
 * gdk_cairo_reset_clip:
 * @cr: a #cairo_t
 * @drawable: a #GdkDrawable
 *
 * Resets the clip region for a Cairo context created by gdk_cairo_create().
 *
 * This resets the clip region to the "empty" state for the given drawable.
 * This is required for non-native windows since a direct call to
 * cairo_reset_clip() would unset the clip region inherited from the
 * drawable (i.e. the window clip region), and thus let you e.g.
 * draw outside your window.
 *
 * This is rarely needed though, since most code just create a new cairo_t
 * using gdk_cairo_create() each time they want to draw something.
 *
 * Since: 2.18
 **/
void
gdk_cairo_reset_clip (cairo_t            *cr,
		      GdkDrawable        *drawable)
{
  cairo_reset_clip (cr);

  if (GDK_DRAWABLE_GET_CLASS (drawable)->set_cairo_clip)
    GDK_DRAWABLE_GET_CLASS (drawable)->set_cairo_clip (drawable, cr);
}

/**
 * gdk_cairo_get_clip_rectangle:
 * @cr: a cairo context
 * @rect: (out) (allow-none): return location for the clip, or %NULL
 *
 * This is a convenience function around cairo_clip_extents(). It rounds
 * the clip extents to integer coordinates and returns a boolean
 * indicating if a clip area exists.
 *
 * Returns: %TRUE if a clip rectangle exists, %FALSE if all of @cr is
 * clipped and all drawing can be skipped.
 **/
gboolean
gdk_cairo_get_clip_rectangle (cairo_t      *cr,
                              GdkRectangle *rect)
{
  double x1, y1, x2, y2;
  gboolean clip_exists;

  cairo_clip_extents (cr, &x1, &y1, &x2, &y2);

  clip_exists = x1 < x2 && y1 < y2;

  if (rect)
    {
      x1 = floor (x1);
      y1 = floor (y1);
      x2 = ceil (x2);
      y2 = ceil (y2);

      rect->x      = CLAMP (x1,      G_MININT, G_MAXINT);
      rect->y      = CLAMP (y1,      G_MININT, G_MAXINT);
      rect->width  = CLAMP (x2 - x1, G_MININT, G_MAXINT);
      rect->height = CLAMP (y2 - y1, G_MININT, G_MAXINT);
    }

  return clip_exists;
}

/**
 * gdk_cairo_set_source_color:
 * @cr: a #cairo_t
 * @color: a #GdkColor
 * 
 * Sets the specified #GdkColor as the source color of @cr.
 *
 * Since: 2.8
 **/
void
gdk_cairo_set_source_color (cairo_t        *cr,
			    const GdkColor *color)
{
  g_return_if_fail (cr != NULL);
  g_return_if_fail (color != NULL);
    
  cairo_set_source_rgb (cr,
			color->red / 65535.,
			color->green / 65535.,
			color->blue / 65535.);
}

/**
 * gdk_cairo_rectangle:
 * @cr: a #cairo_t
 * @rectangle: a #GdkRectangle
 * 
 * Adds the given rectangle to the current path of @cr.
 *
 * Since: 2.8
 **/
void
gdk_cairo_rectangle (cairo_t            *cr,
		     const GdkRectangle *rectangle)
{
  g_return_if_fail (cr != NULL);
  g_return_if_fail (rectangle != NULL);

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

/**
 * gdk_cairo_region:
 * @cr: a #cairo_t
 * @region: a #cairo_region_t
 * 
 * Adds the given region to the current path of @cr.
 *
 * Since: 2.8
 **/
void
gdk_cairo_region (cairo_t         *cr,
		  const cairo_region_t *region)
{
  cairo_rectangle_int_t box;
  gint n_boxes, i;

  g_return_if_fail (cr != NULL);
  g_return_if_fail (region != NULL);

  n_boxes = cairo_region_num_rectangles (region);

  for (i = 0; i < n_boxes; i++)
    {
      cairo_region_get_rectangle (region, i, &box);
      cairo_rectangle (cr, box.x, box.y, box.width, box.height);
    }
}

/**
 * gdk_cairo_set_source_pixbuf:
 * @cr: a #Cairo context
 * @pixbuf: a #GdkPixbuf
 * @pixbuf_x: X coordinate of location to place upper left corner of @pixbuf
 * @pixbuf_y: Y coordinate of location to place upper left corner of @pixbuf
 * 
 * Sets the given pixbuf as the source pattern for the Cairo context.
 * The pattern has an extend mode of %CAIRO_EXTEND_NONE and is aligned
 * so that the origin of @pixbuf is @pixbuf_x, @pixbuf_y
 *
 * Since: 2.8
 **/
void
gdk_cairo_set_source_pixbuf (cairo_t         *cr,
			     const GdkPixbuf *pixbuf,
			     double           pixbuf_x,
			     double           pixbuf_y)
{
  gint width = gdk_pixbuf_get_width (pixbuf);
  gint height = gdk_pixbuf_get_height (pixbuf);
  guchar *gdk_pixels = gdk_pixbuf_get_pixels (pixbuf);
  int gdk_rowstride = gdk_pixbuf_get_rowstride (pixbuf);
  int n_channels = gdk_pixbuf_get_n_channels (pixbuf);
  int cairo_stride;
  guchar *cairo_pixels;
  cairo_format_t format;
  cairo_surface_t *surface;
  static const cairo_user_data_key_t key;
  int j;

  if (n_channels == 3)
    format = CAIRO_FORMAT_RGB24;
  else
    format = CAIRO_FORMAT_ARGB32;

  cairo_stride = cairo_format_stride_for_width (format, width);
  cairo_pixels = g_malloc (height * cairo_stride);
  surface = cairo_image_surface_create_for_data ((unsigned char *)cairo_pixels,
                                                 format,
                                                 width, height, cairo_stride);

  cairo_surface_set_user_data (surface, &key,
			       cairo_pixels, (cairo_destroy_func_t)g_free);

  for (j = height; j; j--)
    {
      guchar *p = gdk_pixels;
      guchar *q = cairo_pixels;

      if (n_channels == 3)
	{
	  guchar *end = p + 3 * width;
	  
	  while (p < end)
	    {
#if G_BYTE_ORDER == G_LITTLE_ENDIAN
	      q[0] = p[2];
	      q[1] = p[1];
	      q[2] = p[0];
#else	  
	      q[1] = p[0];
	      q[2] = p[1];
	      q[3] = p[2];
#endif
	      p += 3;
	      q += 4;
	    }
	}
      else
	{
	  guchar *end = p + 4 * width;
	  guint t1,t2,t3;
	    
#define MULT(d,c,a,t) G_STMT_START { t = c * a + 0x7f; d = ((t >> 8) + t) >> 8; } G_STMT_END

	  while (p < end)
	    {
#if G_BYTE_ORDER == G_LITTLE_ENDIAN
	      MULT(q[0], p[2], p[3], t1);
	      MULT(q[1], p[1], p[3], t2);
	      MULT(q[2], p[0], p[3], t3);
	      q[3] = p[3];
#else	  
	      q[0] = p[3];
	      MULT(q[1], p[0], p[3], t1);
	      MULT(q[2], p[1], p[3], t2);
	      MULT(q[3], p[2], p[3], t3);
#endif
	      
	      p += 4;
	      q += 4;
	    }
	  
#undef MULT
	}

      gdk_pixels += gdk_rowstride;
      cairo_pixels += cairo_stride;
    }

  cairo_set_source_surface (cr, surface, pixbuf_x, pixbuf_y);
  cairo_surface_destroy (surface);
}

/**
 * gdk_cairo_set_source_window:
 * @cr: a #Cairo context
 * @window: a #GdkWindow
 * @x: X coordinate of location to place upper left corner of @window
 * @y: Y coordinate of location to place upper left corner of @window
 *
 * Sets the given window as the source pattern for the Cairo context.
 * The pattern has an extend mode of %CAIRO_EXTEND_NONE and is aligned
 * so that the origin of @window is @x, @y. The window contains all its
 * subwindows when rendering.
 *
 * Note that the contents of @window are undefined outside of the
 * visible part of @window, so use this function with care.
 *
 * Since: 2.24
 */
void
gdk_cairo_set_source_window (cairo_t   *cr,
                             GdkWindow *window,
                             double     x,
                             double     y)
{
  cairo_surface_t *surface;
  
  g_return_if_fail (cr != NULL);
  g_return_if_fail (GDK_IS_WINDOW (window));

  surface = _gdk_drawable_ref_cairo_surface (GDK_DRAWABLE (window));
  cairo_set_source_surface (cr, surface, x, y);
  cairo_surface_destroy (surface);
}

/**
 * _gdk_cairo_surface_extents:
 * @surface: surface to measure
 * @extents: (out): rectangle to put the extents
 *
 * Measures the area covered by @surface and puts it into @extents.
 * Note that this function respects device offsets set on @surface.
 * if @surface is unbounded, the resulting extents will be empty and
 * not be a maximal sized rectangle. This is to avoid careless coding.
 * You must explicitly check the return value of you want to handle
 * that case.
 *
 * Returns: %TRUE if the extents fit in a #GdkRectangle, %FALSE if not.
 **/
gboolean
_gdk_cairo_surface_extents (cairo_surface_t *surface,
                            GdkRectangle *extents)
{
  double x1, x2, y1, y2;
  cairo_t *cr;

  g_return_val_if_fail (surface != NULL, FALSE);
  g_return_val_if_fail (extents != NULL, FALSE);

  cr = cairo_create (surface);
  cairo_clip_extents (cr, &x1, &y1, &x2, &y2);

  x1 = floor (x1);
  y1 = floor (y1);
  x2 = ceil (x2);
  y2 = ceil (y2);
  x2 -= x1;
  y2 -= y1;
  
  if (x1 < G_MININT || x1 > G_MAXINT ||
      y1 < G_MININT || y1 > G_MAXINT ||
      x2 > G_MAXINT || y2 > G_MAXINT)
    {
      extents->x = extents->y = extents->width = extents->height = 0;
      return FALSE;
    }

  extents->x = x1;
  extents->y = y1;
  extents->width = x2;
  extents->height = y2;

  return TRUE;
}

/* This function originally from Jean-Edouard Lachand-Robert, and
 * available at www.codeguru.com. Simplified for our needs, not sure
 * how much of the original code left any longer. Now handles just
 * one-bit deep bitmaps (in Window parlance, ie those that GDK calls
 * bitmaps (and not pixmaps), with zero pixels being transparent.
 */
/**
 * gdk_cairo_region_create_from_surface:
 * @surface: A surface
 *
 * Creates region that describes covers the area where the given @surface
 * is more than 50% opaque. This function takes into account device
 * offsets that might be set with cairo_surface_set_device_offset().
 *
 * Returns: A new region
 **/
cairo_region_t *
gdk_cairo_region_create_from_surface (cairo_surface_t *surface)
{
  cairo_region_t *region;
  GdkRectangle extents, rect;
  cairo_surface_t *image;
  cairo_t *cr;
  gint x, y, stride;
  guchar *data;

  _gdk_cairo_surface_extents (surface, &extents);

  if (cairo_surface_get_content (surface) == CAIRO_CONTENT_COLOR)
    return cairo_region_create_rectangle (&extents);

  if (cairo_surface_get_type (surface) != CAIRO_SURFACE_TYPE_IMAGE ||
      cairo_image_surface_get_format (surface) != CAIRO_FORMAT_A1)
    {
      /* coerce to an A1 image */
      image = cairo_image_surface_create (CAIRO_FORMAT_A1,
                                          extents.width, extents.height);
      cr = cairo_create (image);
      cairo_set_source_surface (cr, surface, -extents.x, -extents.y);
      cairo_paint (cr);
      cairo_destroy (cr);
    }
  else
    image = cairo_surface_reference (surface);

  data = cairo_image_surface_get_data (image);
  stride = cairo_image_surface_get_stride (image);

  region = cairo_region_create ();

  for (y = 0; y < extents.height; y++)
    {
      for (x = 0; x < extents.width; x++)
	{
	  /* Search for a continuous range of "non transparent pixels"*/
	  gint x0 = x;
	  while (x < extents.width)
	    {
	      if (((data[x / 8] >> (x%8)) & 1) == 0)
		/* This pixel is "transparent"*/
		break;
	      x++;
	    }
	  
	  if (x > x0)
	    {
	      /* Add the pixels (x0, y) to (x, y+1) as a new rectangle
	       * in the region
	       */
              rect.x = x0;
              rect.width = x - x0;
              rect.y = y;
              rect.height = 1;

              cairo_region_union_rectangle (region, &rect);
	    }
	}
      data += stride;
    }

  cairo_surface_destroy (image);
  
  cairo_region_translate (region, extents.x, extents.y);

  return region;
}