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cookbook: Add a recipe for image loading
http://bugzilla.clutter-project.org/show_bug.cgi?id=2165 Signed-off-by: Emmanuele Bassi <ebassi@linux.intel.com>
This commit is contained in:
Elliot Smith
Emmanuele Bassi
parent
f2361a65de
commit
347f3b614d
@ -996,6 +996,214 @@ clutter_texture_get_base_size (CLUTTER_TEXTURE (texture), &width, &height);
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</section>
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<section id="textures-image-loading">
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<title>Loading image data into a texture</title>
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<section>
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<title>Problem</title>
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<para>You want to display an image inside a Clutter
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application.</para>
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</section>
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<section>
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<title>Solution</title>
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<para>Create a ClutterTexture directly from an image file:</para>
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<informalexample>
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<programlisting>
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<![CDATA[
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ClutterActor *texture;
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GError *error = NULL;
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gchar *image_path = "/path/to/image";
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texture = clutter_texture_new_from_file (image_path, &error);
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if (error != NULL)
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{
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// handle error
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}
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]]>
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</programlisting>
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</informalexample>
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<para>Or create a texture and set its source to an image
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file:</para>
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<informalexample>
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<programlisting>
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<![CDATA[
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ClutterActor *texture;
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GError *error = NULL;
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gchar *image_path = "/path/to/image";
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gboolean loaded;
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texture = clutter_texture_new ();
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/*
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* returns FALSE if file could not be loaded or texture
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* could not be set from image data in the file
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*/
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loaded = clutter_texture_set_from_file (CLUTTER_TEXTURE (texture),
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image_path,
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&error);
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if (error != NULL)
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{
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// handle error
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}
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]]>
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</programlisting>
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</informalexample>
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</section>
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<section>
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<title>Discussion</title>
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<para>Bear the following in mind when loading images into a
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texture:</para>
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<itemizedlist>
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<listitem>
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<para>An image load may fail if:
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<itemizedlist>
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<listitem>
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<para>The file does not exist.</para>
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</listitem>
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<listitem>
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<para>The image format is unsupported: most of the
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common bitmap formats (PNG, JPEG, BMP, GIF, TIFF, XPM)
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are supported, but more exotic ones may not be.</para>
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</listitem>
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</itemizedlist>
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</para>
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</listitem>
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<listitem>
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<para>Whether you're creating a texture from an image file,
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or loading an image from a file into an existing texture,
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you should specify the filesystem path to the file, rather
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than a URI.</para>
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</listitem>
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</itemizedlist>
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<section>
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<title>Synchronous vs. asynchronous image loading</title>
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<para>The code examples above show the simplest approach:
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loading an image into a texture synchronously. This means that
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the application waits for each image to be loaded before continuing;
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which is acceptable in this case, but may not be when
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loading images into multiple textures.</para>
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<para>Another approach is to load data into textures
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asynchronously. This requires some extra set up in your code:</para>
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<itemizedlist>
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<listitem>
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<para>Call g_thread_init() (from the GLib library) prior
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to calling clutter_init(), so that a local thread is used
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to load the file, rather than the main loop. (Note that
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this is not necessary if you're using GLib version >= 2.24,
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since GObject initializes threading with the type system.)</para>
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</listitem>
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<listitem>
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<para>Set the texture to load data asynchronously.</para>
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</listitem>
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<listitem>
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<para>Connect a callback to the texture's load-finished
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signal to handle any errors which occur during loading,
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and/or to do extra work if data loads successfully.</para>
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</listitem>
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</itemizedlist>
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<para>The code below shows how to put these together:</para>
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<informalexample>
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<programlisting>
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<![CDATA[
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/* callback to invoke when a texture finishes loading image data */
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static void
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_load_finished_cb (ClutterTexture *texture,
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gpointer error,
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gpointer user_data)
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{
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GError *err = (GError *)error;
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gchar *image_path = (gchar *)user_data;
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if (err != NULL)
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g_warning ("Could not load image from file %s; message: %s",
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image_path,
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err->message);
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else
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g_debug ("Image loaded from %s", image_path);
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}
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int
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main (int argc, char *argv[])
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{
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/* initialize GLib's default threading implementation */
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g_thread_init (NULL);
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clutter_init (&argc, &argv);
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/* ... get stage etc. */
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ClutterActor *texture;
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GError *error = NULL;
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texture = clutter_texture_new ();
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/* load data asynchronously */
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clutter_texture_set_load_async (CLUTTER_TEXTURE (texture), TRUE);
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/* connect a callback to the "load-finished" signal */
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g_signal_connect (texture,
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"load-finished",
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G_CALLBACK (_load_finished_cb),
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image_path);
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/* load the image from a file */
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clutter_texture_set_from_file (CLUTTER_TEXTURE (texture),
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image_path,
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&error);
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/* ... clutter_main () etc. */
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}
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]]>
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</programlisting>
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</informalexample>
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</section>
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<section>
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<title>Other ways to load image data into a texture</title>
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<para>While it's useful to load image data into a texture directly
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from a file, there are occasions where you may have image data
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in some other (non-file) format:</para>
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<itemizedlist>
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<listitem>
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<para>Various GNOME libraries provide image data in GdkPixbuf
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structures; clutter-gtk has functions for
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creating or setting a texture from a GdkPixbuf:
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gtk_clutter_texture_new_from_pixbuf()
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and gtk_clutter_texture_set_from_pixbuf() respectively.</para>
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</listitem>
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<listitem>
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<para>If you have raw RGB or YUV pixel data, ClutterTexture has
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clutter_texture_set_from_rgb_data() and
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clutter_texture_set_from_yuv_data() methods for loading it.</para>
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</listitem>
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</itemizedlist>
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</section>
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</section>
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</section>
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</chapter> <!-- textures }}} -->
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<!--
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