gnome-shell/src/shell-screenshot.c

/* -*- mode: C; c-file-style: "gnu"; indent-tabs-mode: nil; -*- */

#include <clutter/clutter.h>
#include <cogl/cogl.h>
#include <meta/display.h>
#include <meta/util.h>
#include <meta/meta-plugin.h>
#include <meta/meta-shaped-texture.h>
#include <meta/meta-cursor-tracker.h>
#include <st/st.h>

#include "shell-global.h"
#include "shell-screenshot.h"
#include "shell-util.h"

typedef struct _ShellScreenshotPrivate  ShellScreenshotPrivate;

struct _ShellScreenshot
{
  GObject parent_instance;

  ShellScreenshotPrivate *priv;
};

struct _ShellScreenshotPrivate
{
  ShellGlobal *global;

  char *filename;
  char *filename_used;

  GDateTime *datetime;

  cairo_surface_t *image;
  cairo_rectangle_int_t screenshot_area;

  gboolean include_cursor;
  gboolean include_frame;
};

typedef enum
{
  SHELL_SCREENSHOT_SCREEN,
  SHELL_SCREENSHOT_WINDOW,
  SHELL_SCREENSHOT_AREA,
} ShellScreenshotMode;

G_DEFINE_TYPE_WITH_PRIVATE (ShellScreenshot, shell_screenshot, G_TYPE_OBJECT);

static void
shell_screenshot_class_init (ShellScreenshotClass *screenshot_class)
{
  (void) screenshot_class;
}

static void
shell_screenshot_init (ShellScreenshot *screenshot)
{
  screenshot->priv = shell_screenshot_get_instance_private (screenshot);
  screenshot->priv->global = shell_global_get ();
}

static void
on_screenshot_written (GObject      *source,
                       GAsyncResult *task,
                       gpointer      user_data)
{
  ShellScreenshot *screenshot = SHELL_SCREENSHOT (source);
  ShellScreenshotPrivate *priv = screenshot->priv;
  GTask *result = user_data;

  g_task_return_boolean (result, g_task_propagate_boolean (G_TASK (task), NULL));
  g_object_unref (result);

  g_clear_pointer (&priv->image, cairo_surface_destroy);
  g_clear_pointer (&priv->filename, g_free);
  g_clear_pointer (&priv->filename_used, g_free);
  g_clear_pointer (&priv->datetime, g_date_time_unref);

  meta_enable_unredirect_for_display (shell_global_get_display (priv->global));
}

/* called in an I/O thread */
static GOutputStream *
get_stream_for_unique_path (const gchar *path,
                            const gchar *filename,
                            gchar **filename_used)
{
  GOutputStream *stream;
  GFile *file;
  gchar *real_path, *real_filename, *name, *ptr;
  gint idx;

  ptr = g_strrstr (filename, ".png");

  if (ptr != NULL)
    real_filename = g_strndup (filename, ptr - filename);
  else
    real_filename = g_strdup (filename);

  idx = 0;
  real_path = NULL;

  do
    {
      if (idx == 0)
        name = g_strdup_printf ("%s.png", real_filename);
      else
        name = g_strdup_printf ("%s - %d.png", real_filename, idx);

      real_path = g_build_filename (path, name, NULL);
      g_free (name);

      file = g_file_new_for_path (real_path);
      stream = G_OUTPUT_STREAM (g_file_create (file, G_FILE_CREATE_NONE, NULL, NULL));
      g_object_unref (file);

      if (stream != NULL)
        *filename_used = real_path;
      else
        g_free (real_path);

      idx++;
    }
  while (stream == NULL);

  g_free (real_filename);

  return stream;
}

/* called in an I/O thread */
static GOutputStream *
get_stream_for_filename (const gchar *filename,
                         gchar **filename_used)
{
  const gchar *path;

  path = g_get_user_special_dir (G_USER_DIRECTORY_PICTURES);
  if (!g_file_test (path, G_FILE_TEST_EXISTS))
    {
      path = g_get_home_dir ();
      if (!g_file_test (path, G_FILE_TEST_EXISTS))
        return NULL;
    }

  return get_stream_for_unique_path (path, filename, filename_used);
}

static GOutputStream *
prepare_write_stream (const gchar *filename,
                      gchar **filename_used)
{
  GOutputStream *stream;
  GFile *file;

  if (g_path_is_absolute (filename))
    {
      file = g_file_new_for_path (filename);
      *filename_used = g_strdup (filename);
      stream = G_OUTPUT_STREAM (g_file_replace (file, NULL, FALSE, G_FILE_CREATE_NONE, NULL, NULL));
      g_object_unref (file);
    }
  else
    {
      stream = get_stream_for_filename (filename, filename_used);
    }

  return stream;
}

static void
write_screenshot_thread (GTask        *result,
                         gpointer      object,
                         gpointer      task_data,
                         GCancellable *cancellable)
{
  cairo_status_t status;
  GOutputStream *stream;
  ShellScreenshot *screenshot = SHELL_SCREENSHOT (object);
  ShellScreenshotPrivate *priv;
  char *creation_time;

  g_assert (screenshot != NULL);

  priv = screenshot->priv;

  stream = prepare_write_stream (priv->filename,
                                 &priv->filename_used);

  if (stream == NULL)
    status = CAIRO_STATUS_FILE_NOT_FOUND;
  else
    {
      GdkPixbuf *pixbuf;

      pixbuf = gdk_pixbuf_get_from_surface (priv->image,
                                            0, 0,
                                            cairo_image_surface_get_width (priv->image),
                                            cairo_image_surface_get_height (priv->image));
      creation_time = g_date_time_format (priv->datetime, "%c");

      if (!creation_time)
        creation_time = g_date_time_format (priv->datetime, "%FT%T%z");

      if (gdk_pixbuf_save_to_stream (pixbuf, stream, "png", NULL, NULL,
                                     "tEXt::Software", "gnome-screenshot",
                                     "tEXt::Creation Time", creation_time,
                                     NULL))
        status = CAIRO_STATUS_SUCCESS;
      else
        status = CAIRO_STATUS_WRITE_ERROR;

      g_object_unref (pixbuf);
      g_free (creation_time);
    }


  g_task_return_boolean (result, status == CAIRO_STATUS_SUCCESS);

  g_clear_object (&stream);
}

static void
do_grab_screenshot (ShellScreenshot *screenshot,
                    ClutterStage    *stage,
                    int               x,
                    int               y,
                    int               width,
                    int               height)
{
  ShellScreenshotPrivate *priv = screenshot->priv;
  cairo_rectangle_int_t screenshot_rect = { x, y, width, height };
  ClutterCapture *captures;
  int n_captures;
  int i;

  if (!clutter_stage_capture (stage, FALSE,
                              &screenshot_rect,
                              &captures,
                              &n_captures))
    return;

  if (n_captures == 1)
    priv->image = cairo_surface_reference (captures[0].image);
  else
    {
      float target_scale;

      clutter_stage_get_capture_final_size (stage, &screenshot_rect,
                                            &width, &height, &target_scale);
      priv->image = shell_util_composite_capture_images (captures,
                                                         n_captures,
                                                         x, y,
                                                         width, height,
                                                         target_scale);
    }

  priv->datetime = g_date_time_new_now_local ();

  for (i = 0; i < n_captures; i++)
    cairo_surface_destroy (captures[i].image);

  g_free (captures);
}

static gboolean
should_draw_cursor_image (ShellScreenshotMode mode)
{
  if (mode == SHELL_SCREENSHOT_WINDOW || !meta_is_wayland_compositor ())
    {
      StSettings *settings = st_settings_get ();
      gboolean magnifier_active = FALSE;

      g_object_get (settings, "magnifier-active", &magnifier_active, NULL);

      if (!magnifier_active)
        return TRUE;
    }

  return FALSE;
}

static void
draw_cursor_image (cairo_surface_t       *surface,
                   cairo_rectangle_int_t  area)
{
  CoglTexture *texture;
  int width, height;
  int stride;
  guint8 *data;
  MetaDisplay *display;
  MetaCursorTracker *tracker;
  cairo_surface_t *cursor_surface;
  cairo_region_t *screenshot_region;
  cairo_t *cr;
  int x, y;
  int xhot, yhot;
  double xscale, yscale;

  display = shell_global_get_display (shell_global_get ());
  tracker = meta_cursor_tracker_get_for_display (display);
  texture = meta_cursor_tracker_get_sprite (tracker);

  if (!texture)
    return;

  screenshot_region = cairo_region_create_rectangle (&area);
  meta_cursor_tracker_get_pointer (tracker, &x, &y, NULL);

  if (!cairo_region_contains_point (screenshot_region, x, y))
    {
      cairo_region_destroy (screenshot_region);
      return;
    }

  meta_cursor_tracker_get_hot (tracker, &xhot, &yhot);
  width = cogl_texture_get_width (texture);
  height = cogl_texture_get_height (texture);
  stride = 4 * width;
  data = g_new (guint8, stride * height);
  cogl_texture_get_data (texture, CLUTTER_CAIRO_FORMAT_ARGB32, stride, data);

  /* FIXME: cairo-gl? */
  cursor_surface = cairo_image_surface_create_for_data (data,
                                                        CAIRO_FORMAT_ARGB32,
                                                        width, height,
                                                        stride);

  cairo_surface_get_device_scale (surface, &xscale, &yscale);

  if (xscale != 1.0 || yscale != 1.0)
    {
      int monitor;
      float monitor_scale;
      MetaRectangle cursor_rect = {
        .x = x, .y = y, .width = width, .height = height
      };

      monitor = meta_display_get_monitor_index_for_rect (display, &cursor_rect);
      monitor_scale = meta_display_get_monitor_scale (display, monitor);

      cairo_surface_set_device_scale (cursor_surface, monitor_scale, monitor_scale);
    }

  cr = cairo_create (surface);
  cairo_set_source_surface (cr,
                            cursor_surface,
                            x - xhot - area.x,
                            y - yhot - area.y);
  cairo_paint (cr);

  cairo_destroy (cr);
  cairo_surface_destroy (cursor_surface);
  cairo_region_destroy (screenshot_region);
  g_free (data);
}

static void
grab_screenshot (ClutterActor *stage,
                 GTask        *result)
{
  MetaDisplay *display;
  int width, height;
  ShellScreenshot *screenshot = g_task_get_source_object (result);
  ShellScreenshotPrivate *priv = screenshot->priv;
  GTask *task;

  display = shell_global_get_display (priv->global);
  meta_display_get_size (display, &width, &height);

  do_grab_screenshot (screenshot, CLUTTER_STAGE (stage), 0, 0, width, height);

  if (meta_display_get_n_monitors (display) > 1)
    {
      cairo_region_t *screen_region = cairo_region_create ();
      cairo_region_t *stage_region;
      MetaRectangle monitor_rect;
      cairo_rectangle_int_t stage_rect;
      int i;
      cairo_t *cr;

      for (i = meta_display_get_n_monitors (display) - 1; i >= 0; i--)
        {
          meta_display_get_monitor_geometry (display, i, &monitor_rect);
          cairo_region_union_rectangle (screen_region,
                                        (const cairo_rectangle_int_t *) &monitor_rect);
        }

      stage_rect.x = 0;
      stage_rect.y = 0;
      stage_rect.width = width;
      stage_rect.height = height;

      stage_region = cairo_region_create_rectangle ((const cairo_rectangle_int_t *) &stage_rect);
      cairo_region_xor (stage_region, screen_region);
      cairo_region_destroy (screen_region);

      cr = cairo_create (priv->image);

      for (i = 0; i < cairo_region_num_rectangles (stage_region); i++)
        {
          cairo_rectangle_int_t rect;
          cairo_region_get_rectangle (stage_region, i, &rect);
          cairo_rectangle (cr, (double) rect.x, (double) rect.y, (double) rect.width, (double) rect.height);
          cairo_fill (cr);
        }

      cairo_destroy (cr);
      cairo_region_destroy (stage_region);
    }

  priv->screenshot_area.x = 0;
  priv->screenshot_area.y = 0;
  priv->screenshot_area.width = width;
  priv->screenshot_area.height = height;

  if (priv->include_cursor)
    draw_cursor_image (priv->image, priv->screenshot_area);

  g_signal_handlers_disconnect_by_func (stage, grab_screenshot, result);

  task = g_task_new (screenshot, NULL, on_screenshot_written, result);
  g_task_run_in_thread (task, write_screenshot_thread);
  g_object_unref (task);
}

static void
grab_area_screenshot (ClutterActor *stage,
                      GTask        *result)
{
  ShellScreenshot *screenshot = g_task_get_source_object (result);
  ShellScreenshotPrivate *priv = screenshot->priv;
  GTask *task;

  do_grab_screenshot (screenshot,
                      CLUTTER_STAGE (stage),
                      priv->screenshot_area.x,
                      priv->screenshot_area.y,
                      priv->screenshot_area.width,
                      priv->screenshot_area.height);

  g_signal_handlers_disconnect_by_func (stage, grab_area_screenshot, result);
  task = g_task_new (screenshot, NULL, on_screenshot_written, result);
  g_task_run_in_thread (task, write_screenshot_thread);
  g_object_unref (task);
}

static void
grab_window_screenshot (ClutterActor *stage,
                        GTask        *result)
{
  ShellScreenshot *screenshot = g_task_get_source_object (result);
  ShellScreenshotPrivate *priv = screenshot->priv;
  GTask *task;
  MetaDisplay *display = shell_global_get_display (priv->global);
  MetaWindow *window = meta_display_get_focus_window (display);
  ClutterActor *window_actor;
  gfloat actor_x, actor_y;
  MetaShapedTexture *stex;
  MetaRectangle rect;
  cairo_rectangle_int_t clip;

  window_actor = CLUTTER_ACTOR (meta_window_get_compositor_private (window));
  clutter_actor_get_position (window_actor, &actor_x, &actor_y);

  meta_window_get_frame_rect (window, &rect);

  if (!priv->include_frame)
    meta_window_frame_rect_to_client_rect (window, &rect, &rect);

  priv->screenshot_area.x = rect.x;
  priv->screenshot_area.y = rect.y;
  clip.x = rect.x - (gint) actor_x;
  clip.y = rect.y - (gint) actor_y;

  clip.width = priv->screenshot_area.width = rect.width;
  clip.height = priv->screenshot_area.height = rect.height;

  stex = META_SHAPED_TEXTURE (meta_window_actor_get_texture (META_WINDOW_ACTOR (window_actor)));
  priv->image = meta_shaped_texture_get_image (stex, &clip);
  priv->datetime = g_date_time_new_now_local ();

  if (priv->include_cursor)
    {
      if (meta_window_get_client_type (window) == META_WINDOW_CLIENT_TYPE_WAYLAND)
        {
          float resource_scale;
          if (!clutter_actor_get_resource_scale (window_actor, &resource_scale))
            resource_scale = 1.0f;

          cairo_surface_set_device_scale (priv->image, resource_scale, resource_scale);
        }

      draw_cursor_image (priv->image, priv->screenshot_area);
    }

  g_signal_handlers_disconnect_by_func (stage, grab_window_screenshot, result);
  task = g_task_new (screenshot, NULL, on_screenshot_written, result);
  g_task_run_in_thread (task, write_screenshot_thread);
  g_object_unref (task);
}

static void
grab_pixel (ClutterActor *stage,
            GTask        *result)
{
  ShellScreenshot *screenshot = g_task_get_source_object (result);
  ShellScreenshotPrivate *priv = screenshot->priv;

  do_grab_screenshot (screenshot,
                      CLUTTER_STAGE (stage),
                      priv->screenshot_area.x,
                      priv->screenshot_area.y,
                      1,
                      1);

  meta_enable_unredirect_for_display (shell_global_get_display (priv->global));

  g_signal_handlers_disconnect_by_func (stage, grab_pixel, result);
  g_task_return_boolean (result, TRUE);
  g_object_unref (result);
}

static gboolean
finish_screenshot (ShellScreenshot        *screenshot,
                   GAsyncResult           *result,
                   cairo_rectangle_int_t **area,
                   const char            **filename_used,
                   GError                **error)
{
  ShellScreenshotPrivate *priv = screenshot->priv;

  if (!g_task_propagate_boolean (G_TASK (result), error))
    return FALSE;

  if (area)
    *area = &priv->screenshot_area;

  if (filename_used)
    *filename_used = priv->filename_used;

  return TRUE;
}

/**
 * shell_screenshot_screenshot:
 * @screenshot: the #ShellScreenshot
 * @include_cursor: Whether to include the cursor or not
 * @filename: The filename for the screenshot
 * @callback: (scope async): function to call returning success or failure
 * of the async grabbing
 * @user_data: the data to pass to callback function
 *
 * Takes a screenshot of the whole screen
 * in @filename as png image.
 *
 */
void
shell_screenshot_screenshot (ShellScreenshot     *screenshot,
                             gboolean             include_cursor,
                             const char          *filename,
                             GAsyncReadyCallback  callback,
                             gpointer             user_data)
{
  ClutterActor *stage;
  ShellScreenshotPrivate *priv = screenshot->priv;
  const char *paint_signal;
  GTask *result;

  if (priv->filename != NULL) {
    if (callback)
      g_task_report_new_error (screenshot,
                               callback,
                               user_data,
                               shell_screenshot_screenshot,
                               G_IO_ERROR,
                               G_IO_ERROR_PENDING,
                               "Only one screenshot operation at a time "
                               "is permitted");
    return;
  }

  result = g_task_new (screenshot, NULL, callback, user_data);
  g_task_set_source_tag (result, shell_screenshot_screenshot);

  priv->filename = g_strdup (filename);
  priv->include_cursor = FALSE;

  stage = CLUTTER_ACTOR (shell_global_get_stage (priv->global));
  paint_signal = "actors-painted";

  meta_disable_unredirect_for_display (shell_global_get_display (priv->global));

  if (include_cursor)
    {
      if (should_draw_cursor_image (SHELL_SCREENSHOT_SCREEN))
        priv->include_cursor = TRUE;
      else
        paint_signal = "paint";
    }

  g_signal_connect_after (stage, paint_signal, G_CALLBACK (grab_screenshot), result);

  clutter_actor_queue_redraw (stage);
}

/**
 * shell_screenshot_screenshot_finish:
 * @screenshot: the #ShellScreenshot
 * @result: the #GAsyncResult that was provided to the callback
 * @area: (out) (transfer none): the area that was grabbed in screen coordinates
 * @filename_used: (out) (transfer none): the name of the file the screenshot
 * was written to
 * @error: #GError for error reporting
 *
 * Finish the asynchronous operation started by shell_screenshot_screenshot()
 * and obtain its result.
 *
 * Returns: whether the operation was successful
 *
 */
gboolean
shell_screenshot_screenshot_finish (ShellScreenshot        *screenshot,
                                    GAsyncResult           *result,
                                    cairo_rectangle_int_t **area,
                                    const char            **filename_used,
                                    GError                **error)
{
  g_return_val_if_fail (g_async_result_is_tagged (result,
                                                  shell_screenshot_screenshot),
                        FALSE);
  return finish_screenshot (screenshot, result, area, filename_used, error);
}

/**
 * shell_screenshot_screenshot_area:
 * @screenshot: the #ShellScreenshot
 * @x: The X coordinate of the area
 * @y: The Y coordinate of the area
 * @width: The width of the area
 * @height: The height of the area
 * @filename: The filename for the screenshot
 * @callback: (scope async): function to call returning success or failure
 * of the async grabbing
 * @user_data: the data to pass to callback function
 *
 * Takes a screenshot of the passed in area and saves it
 * in @filename as png image.
 *
 */
void
shell_screenshot_screenshot_area (ShellScreenshot     *screenshot,
                                  int                  x,
                                  int                  y,
                                  int                  width,
                                  int                  height,
                                  const char          *filename,
                                  GAsyncReadyCallback  callback,
                                  gpointer             user_data)
{
  ClutterActor *stage;
  ShellScreenshotPrivate *priv = screenshot->priv;
  GTask *result;

  if (priv->filename != NULL) {
    if (callback)
      g_task_report_new_error (screenshot,
                               callback,
                               NULL,
                               shell_screenshot_screenshot_area,
                               G_IO_ERROR,
                               G_IO_ERROR_PENDING,
                               "Only one screenshot operation at a time "
                               "is permitted");
    return;
  }

  result = g_task_new (screenshot, NULL, callback, user_data);
  g_task_set_source_tag (result, shell_screenshot_screenshot_area);

  priv->filename = g_strdup (filename);
  priv->screenshot_area.x = x;
  priv->screenshot_area.y = y;
  priv->screenshot_area.width = width;
  priv->screenshot_area.height = height;

  stage = CLUTTER_ACTOR (shell_global_get_stage (priv->global));

  meta_disable_unredirect_for_display (shell_global_get_display (shell_global_get ()));

  g_signal_connect_after (stage, "actors-painted", G_CALLBACK (grab_area_screenshot), result);

  clutter_actor_queue_redraw (stage);
}

/**
 * shell_screenshot_screenshot_area_finish:
 * @screenshot: the #ShellScreenshot
 * @result: the #GAsyncResult that was provided to the callback
 * @area: (out) (transfer none): the area that was grabbed in screen coordinates
 * @filename_used: (out) (transfer none): the name of the file the screenshot
 * was written to
 * @error: #GError for error reporting
 *
 * Finish the asynchronous operation started by shell_screenshot_screenshot_area()
 * and obtain its result.
 *
 * Returns: whether the operation was successful
 *
 */
gboolean
shell_screenshot_screenshot_area_finish (ShellScreenshot        *screenshot,
                                         GAsyncResult           *result,
                                         cairo_rectangle_int_t **area,
                                         const char            **filename_used,
                                         GError                **error)
{
  g_return_val_if_fail (g_async_result_is_tagged (result,
                                                  shell_screenshot_screenshot_area),
                        FALSE);
  return finish_screenshot (screenshot, result, area, filename_used, error);
}

/**
 * shell_screenshot_screenshot_window:
 * @screenshot: the #ShellScreenshot
 * @include_frame: Whether to include the frame or not
 * @include_cursor: Whether to include the cursor or not
 * @filename: The filename for the screenshot
 * @callback: (scope async): function to call returning success or failure
 * of the async grabbing
 * @user_data: the data to pass to callback function
 *
 * Takes a screenshot of the focused window (optionally omitting the frame)
 * in @filename as png image.
 *
 */
void
shell_screenshot_screenshot_window (ShellScreenshot     *screenshot,
                                    gboolean             include_frame,
                                    gboolean             include_cursor,
                                    const char          *filename,
                                    GAsyncReadyCallback  callback,
                                    gpointer             user_data)
{
  ShellScreenshotPrivate *priv = screenshot->priv;
  MetaDisplay *display = shell_global_get_display (priv->global);
  ClutterActor *stage;
  MetaWindow *window = meta_display_get_focus_window (display);
  GTask *result;

  if (priv->filename != NULL || !window) {
    if (callback)
      g_task_report_new_error (screenshot,
                               callback,
                               NULL,
                               shell_screenshot_screenshot_window,
                               G_IO_ERROR,
                               G_IO_ERROR_PENDING,
                               "Only one screenshot operation at a time "
                               "is permitted");
    return;
  }

  result = g_task_new (screenshot, NULL, callback, user_data);
  g_task_set_source_tag (result, shell_screenshot_screenshot_window);

  priv->filename = g_strdup (filename);
  priv->include_frame = include_frame;
  priv->include_cursor = include_cursor &&
                         should_draw_cursor_image (SHELL_SCREENSHOT_WINDOW);

  stage = CLUTTER_ACTOR (shell_global_get_stage (priv->global));

  meta_disable_unredirect_for_display (shell_global_get_display (shell_global_get ()));

  g_signal_connect_after (stage, "actors-painted", G_CALLBACK (grab_window_screenshot), result);

  clutter_actor_queue_redraw (stage);
}

/**
 * shell_screenshot_screenshot_window_finish:
 * @screenshot: the #ShellScreenshot
 * @result: the #GAsyncResult that was provided to the callback
 * @area: (out) (transfer none): the area that was grabbed in screen coordinates
 * @filename_used: (out) (transfer none): the name of the file the screenshot
 * was written to
 * @error: #GError for error reporting
 *
 * Finish the asynchronous operation started by shell_screenshot_screenshot_window()
 * and obtain its result.
 *
 * Returns: whether the operation was successful
 *
 */
gboolean
shell_screenshot_screenshot_window_finish (ShellScreenshot        *screenshot,
                                           GAsyncResult           *result,
                                           cairo_rectangle_int_t **area,
                                           const char            **filename_used,
                                           GError                **error)
{
  g_return_val_if_fail (g_async_result_is_tagged (result,
                                                  shell_screenshot_screenshot_window),
                        FALSE);
  return finish_screenshot (screenshot, result, area, filename_used, error);
}

/**
 * shell_screenshot_pick_color:
 * @screenshot: the #ShellScreenshot
 * @x: The X coordinate to pick
 * @y: The Y coordinate to pick
 * @callback: (scope async): function to call returning success or failure
 * of the async grabbing
 *
 * Picks the pixel at @x, @y and returns its color as #ClutterColor.
 *
 */
void
shell_screenshot_pick_color (ShellScreenshot     *screenshot,
                             int                  x,
                             int                  y,
                             GAsyncReadyCallback  callback,
                             gpointer             user_data)
{
  ShellScreenshotPrivate *priv = screenshot->priv;
  MetaDisplay *display = shell_global_get_display (priv->global);
  ClutterActor *stage;
  GTask *result;

  result = g_task_new (screenshot, NULL, callback, user_data);
  g_task_set_source_tag (result, shell_screenshot_pick_color);

  priv->screenshot_area.x = x;
  priv->screenshot_area.y = y;
  priv->screenshot_area.width = 1;
  priv->screenshot_area.height = 1;

  stage = CLUTTER_ACTOR (shell_global_get_stage (priv->global));

  meta_disable_unredirect_for_display (display);

  g_signal_connect_after (stage, "actors-painted", G_CALLBACK (grab_pixel), result);

  clutter_actor_queue_redraw (stage);
}

#if G_BYTE_ORDER == G_LITTLE_ENDIAN
#define INDEX_A 3
#define INDEX_R 2
#define INDEX_G 1
#define INDEX_B 0
#else
#define INDEX_A 0
#define INDEX_R 1
#define INDEX_G 2
#define INDEX_B 3
#endif

/**
 * shell_screenshot_pick_color_finish:
 * @screenshot: the #ShellScreenshot
 * @result: the #GAsyncResult that was provided to the callback
 * @color: (out caller-allocates): the picked color
 * @error: #GError for error reporting
 *
 * Finish the asynchronous operation started by shell_screenshot_pick_color()
 * and obtain its result.
 *
 * Returns: whether the operation was successful
 *
 */
gboolean
shell_screenshot_pick_color_finish (ShellScreenshot  *screenshot,
                                    GAsyncResult     *result,
                                    ClutterColor     *color,
                                    GError          **error)
{
  ShellScreenshotPrivate *priv = screenshot->priv;

  g_return_val_if_fail (g_async_result_is_tagged (result,
                                                  shell_screenshot_pick_color),
                        FALSE);

  if (!g_task_propagate_boolean (G_TASK (result), error))
    return FALSE;

  /* protect against mutter changing the format used for stage captures */
  g_assert (cairo_image_surface_get_format (priv->image) == CAIRO_FORMAT_ARGB32);

  if (color)
    {
      uint8_t *data = cairo_image_surface_get_data (priv->image);

      color->alpha = data[INDEX_A];
      color->red   = data[INDEX_R];
      color->green = data[INDEX_G];
      color->blue  = data[INDEX_B];
    }

  return TRUE;
}

#undef INDEX_A
#undef INDEX_R
#undef INDEX_G
#undef INDEX_B

ShellScreenshot *
shell_screenshot_new (void)
{
  return g_object_new (SHELL_TYPE_SCREENSHOT, NULL);
}