gtk/gdk/gdkpixbuf-drawable.c

/* GdkPixbuf library - convert X drawable information to RGB
 *
 * Copyright (C) 1999 Michael Zucchi
 *
 * Authors: Michael Zucchi <zucchi@zedzone.mmc.com.au>
 *          Cody Russell <bratsche@dfw.net>
 * 	    Federico Mena-Quintero <federico@gimp.org>
 *
 * 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, see <http://www.gnu.org/licenses/>.
 */

#include "config.h"

#include "gdkpixbuf.h"

#include "gdkwindow.h"
#include "gdkinternals.h"

#include <gdk-pixbuf/gdk-pixbuf.h>

/**
 * SECTION:pixbufs
 * @Short_description: Functions for obtaining pixbufs
 * @Title: Pixbufs
 *
 * Pixbufs are client-side images. For details on how to create
 * and manipulate pixbufs, see the #GdkPixbuf API documentation.
 *
 * The functions described here allow to obtain pixbufs from
 * #GdkWindows and cairo surfaces.
 */


/**
 * gdk_pixbuf_get_from_window:
 * @window: Source window
 * @src_x: Source X coordinate within @window
 * @src_y: Source Y coordinate within @window
 * @width: Width in pixels of region to get
 * @height: Height in pixels of region to get
 *
 * Transfers image data from a #GdkWindow and converts it to an RGB(A)
 * representation inside a #GdkPixbuf.
 *
 * In other words, copies image data from a server-side drawable to a
 * client-side RGB(A) buffer. This allows you to efficiently read
 * individual pixels on the client side.
 *
 * This function will create an RGB pixbuf with 8 bits per channel with
 * the size specified by the @width and @height arguments scaled by the
 * scale factor of @window. The pixbuf will contain an alpha channel if
 * the @window contains one.
 *
 * If the window is off the screen, then there is no image data in the
 * obscured/offscreen regions to be placed in the pixbuf. The contents of
 * portions of the pixbuf corresponding to the offscreen region are
 * undefined.
 *
 * If the window you’re obtaining data from is partially obscured by
 * other windows, then the contents of the pixbuf areas corresponding
 * to the obscured regions are undefined.
 *
 * If the window is not mapped (typically because it’s iconified/minimized
 * or not on the current workspace), then %NULL will be returned.
 *
 * If memory can’t be allocated for the return value, %NULL will be returned
 * instead.
 *
 * In short, there are several ways this function can fail, and if it fails
 * it returns %NULL; so check the return value.
 *
 * You should rarely, if ever, need to call this function.
 *
 * Returns: (nullable) (transfer full): A newly-created pixbuf with a
 *   reference count of 1, or %NULL on error
 */
GdkPixbuf *
gdk_pixbuf_get_from_window (GdkWindow *src,
                            gint       src_x,
                            gint       src_y,
                            gint       width,
                            gint       height)
{
  cairo_surface_t *surface;
  cairo_surface_t *copy;
  cairo_t *cr;
  GdkPixbuf *dest;
  int scale;

  g_return_val_if_fail (GDK_IS_WINDOW (src), NULL);
  g_return_val_if_fail (gdk_window_is_viewable (src), NULL);

  surface = _gdk_window_ref_cairo_surface (src);
  scale = gdk_window_get_scale_factor (src);

  /* We do not know what happened to this surface outside of GDK.
   * Especially for foreign windows, they will have been modified
   * by external applications.
   *
   * So be on the safe side and:
   * - flush the Cairo state
   * - mark the surface as dirty, in case the GdkWindow was
   *   created from a foreign X11 surface
   *
   * THE ORDER IS IMPORTANT. DO NOT CHANGE IT.
   *
   * For reference, see:
   * - https://bugzilla.gnome.org/show_bug.cgi?id=754952
   * - https://gitlab.gnome.org/GNOME/gtk/-/issues/4456
   * - https://gitlab.gnome.org/GNOME/gtk/-/issues/5691
   */
  cairo_surface_flush (surface);
  cairo_surface_mark_dirty (surface);

  if (cairo_surface_get_content (surface) & CAIRO_CONTENT_ALPHA)
    copy = cairo_image_surface_create (CAIRO_FORMAT_ARGB32, width * scale, height * scale);
  else
    copy = cairo_image_surface_create (CAIRO_FORMAT_RGB24, width * scale, height * scale);

  cairo_surface_set_device_scale (copy, scale, scale);

  cr = cairo_create (copy);
  cairo_set_operator (cr, CAIRO_OPERATOR_SOURCE);
  cairo_set_source_surface (cr, surface, -src_x, -src_y);
  cairo_paint (cr);
  cairo_destroy (cr);

  dest = gdk_pixbuf_get_from_surface (copy, 0, 0, width * scale, height * scale);

  cairo_surface_destroy (copy);
  cairo_surface_destroy (surface);

  return dest;
}

static cairo_format_t
gdk_cairo_format_for_content (cairo_content_t content)
{
  switch (content)
    {
    case CAIRO_CONTENT_COLOR:
      return CAIRO_FORMAT_RGB24;
    case CAIRO_CONTENT_ALPHA:
      return CAIRO_FORMAT_A8;
    case CAIRO_CONTENT_COLOR_ALPHA:
    default:
      return CAIRO_FORMAT_ARGB32;
    }
}

static cairo_surface_t *
gdk_cairo_surface_coerce_to_image (cairo_surface_t *surface,
                                   cairo_content_t  content,
                                   int              src_x,
                                   int              src_y,
                                   int              width,
                                   int              height)
{
  cairo_surface_t *copy;
  cairo_t *cr;

  copy = cairo_image_surface_create (gdk_cairo_format_for_content (content),
                                     width,
                                     height);

  cr = cairo_create (copy);
  cairo_set_operator (cr, CAIRO_OPERATOR_SOURCE);
  cairo_set_source_surface (cr, surface, -src_x, -src_y);
  cairo_paint (cr);
  cairo_destroy (cr);

  return copy;
}

static void
convert_alpha (guchar *dest_data,
               int     dest_stride,
               guchar *src_data,
               int     src_stride,
               int     src_x,
               int     src_y,
               int     width,
               int     height)
{
  int x, y;

  src_data += src_stride * src_y + src_x * 4;

  for (y = 0; y < height; y++) {
    guint32 *src = (guint32 *) src_data;

    for (x = 0; x < width; x++) {
      guint alpha = src[x] >> 24;

      if (alpha == 0)
        {
          dest_data[x * 4 + 0] = 0;
          dest_data[x * 4 + 1] = 0;
          dest_data[x * 4 + 2] = 0;
        }
      else
        {
          dest_data[x * 4 + 0] = (((src[x] & 0xff0000) >> 16) * 255 + alpha / 2) / alpha;
          dest_data[x * 4 + 1] = (((src[x] & 0x00ff00) >>  8) * 255 + alpha / 2) / alpha;
          dest_data[x * 4 + 2] = (((src[x] & 0x0000ff) >>  0) * 255 + alpha / 2) / alpha;
        }
      dest_data[x * 4 + 3] = alpha;
    }

    src_data += src_stride;
    dest_data += dest_stride;
  }
}

static void
convert_no_alpha (guchar *dest_data,
                  int     dest_stride,
                  guchar *src_data,
                  int     src_stride,
                  int     src_x,
                  int     src_y,
                  int     width,
                  int     height)
{
  int x, y;

  src_data += src_stride * src_y + src_x * 4;

  for (y = 0; y < height; y++) {
    guint32 *src = (guint32 *) src_data;

    for (x = 0; x < width; x++) {
      dest_data[x * 3 + 0] = src[x] >> 16;
      dest_data[x * 3 + 1] = src[x] >>  8;
      dest_data[x * 3 + 2] = src[x];
    }

    src_data += src_stride;
    dest_data += dest_stride;
  }
}

/**
 * gdk_pixbuf_get_from_surface:
 * @surface: surface to copy from
 * @src_x: Source X coordinate within @surface
 * @src_y: Source Y coordinate within @surface
 * @width: Width in pixels of region to get
 * @height: Height in pixels of region to get
 *
 * Transfers image data from a #cairo_surface_t and converts it to an RGB(A)
 * representation inside a #GdkPixbuf. This allows you to efficiently read
 * individual pixels from cairo surfaces. For #GdkWindows, use
 * gdk_pixbuf_get_from_window() instead.
 *
 * This function will create an RGB pixbuf with 8 bits per channel.
 * The pixbuf will contain an alpha channel if the @surface contains one.
 *
 * Returns: (nullable) (transfer full): A newly-created pixbuf with a
 *     reference count of 1, or %NULL on error
 */
GdkPixbuf *
gdk_pixbuf_get_from_surface  (cairo_surface_t *surface,
                              gint             src_x,
                              gint             src_y,
                              gint             width,
                              gint             height)
{
  cairo_content_t content;
  GdkPixbuf *dest;

  /* General sanity checks */
  g_return_val_if_fail (surface != NULL, NULL);
  g_return_val_if_fail (width > 0 && height > 0, NULL);

  content = cairo_surface_get_content (surface) | CAIRO_CONTENT_COLOR;
  dest = gdk_pixbuf_new (GDK_COLORSPACE_RGB,
                         !!(content & CAIRO_CONTENT_ALPHA),
                         8,
                         width, height);

  if (cairo_surface_get_type (surface) == CAIRO_SURFACE_TYPE_IMAGE &&
      cairo_image_surface_get_format (surface) == gdk_cairo_format_for_content (content))
    surface = cairo_surface_reference (surface);
  else
    {
      surface = gdk_cairo_surface_coerce_to_image (surface, content,
						   src_x, src_y,
						   width, height);
      src_x = 0;
      src_y = 0;
    }
  cairo_surface_flush (surface);
  if (cairo_surface_status (surface) || dest == NULL)
    {
      cairo_surface_destroy (surface);
      g_clear_object (&dest);
      return NULL;
    }

  if (gdk_pixbuf_get_has_alpha (dest))
    convert_alpha (gdk_pixbuf_get_pixels (dest),
                   gdk_pixbuf_get_rowstride (dest),
                   cairo_image_surface_get_data (surface),
                   cairo_image_surface_get_stride (surface),
                   src_x, src_y,
                   width, height);
  else
    convert_no_alpha (gdk_pixbuf_get_pixels (dest),
                      gdk_pixbuf_get_rowstride (dest),
                      cairo_image_surface_get_data (surface),
                      cairo_image_surface_get_stride (surface),
                      src_x, src_y,
                      width, height);

  cairo_surface_destroy (surface);
  return dest;
}