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cookbook: Add a recipe for CairoTexture
The Clutter cookbook has a chapter for textures. It would be useful to provide a recipe on simple uses of ClutterCairoTexture as part of that. Some suggested content is attached.
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Emmanuele Bassi
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5b2311aed7
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78325a34db
@ -386,8 +386,7 @@ on_paint (ClutterActor *actor)
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</chapter> <!-- actors }}} -->
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<!--
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<chapter id="textures">
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<chapter id="textures"> <!-- textures {{{ -->
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<title>Textures</title>
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<epigraph>
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@ -401,6 +400,150 @@ on_paint (ClutterActor *actor)
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<para>introduction</para>
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</section>
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<section id="textures-drawing-with-cairo">
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<title>Drawing 2D graphics onto a texture</title>
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<section>
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<title>Problem</title>
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<para>You want to draw 2D graphics inside a Clutter 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 ClutterCairoTexture, then draw onto the Cairo context
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it wraps using the Cairo API:</para>
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<informalexample>
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<programlisting>
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ClutterActor *texture;
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cairo_t *cr;
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guint width, height;
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width = 800;
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height = 600;
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texture = clutter_cairo_texture_new (width, height);
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cr = clutter_cairo_texture_create (CLUTTER_CAIRO_TEXTURE (texture));
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/*
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* write onto the Cairo context cr using the Cairo API;
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* see <ulink url="http://cairographics.org/manual/">the Cairo API reference</ulink> for details
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*/
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cairo_move_to (cr, 0, 0);
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cairo_line_to (cr, 800, 600);
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cairo_stroke (cr);
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/* does the actual drawing onto the texture */
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cairo_destroy (cr);
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</programlisting>
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</informalexample>
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<para>Here's a <ulink url="http://cairographics.org/tutorial/">useful
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Cairo tutorial</ulink> if you want to learn more about the Cairo API
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itself.</para>
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</section>
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<section>
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<title>Discussion</title>
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<para>A ClutterCairoTexture is a standard ClutterActor, so it can be
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added to ClutterContainers (e.g. a ClutterStage or ClutterGroup),
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animated, resized etc. in the usual ways.</para>
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<para>Other useful operations:</para>
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<itemizedlist>
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<listitem>
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<para><emphasis>To draw on part of the texture:</emphasis>
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use <function>clutter_cairo_texture_create_region</function> to
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retrieve a Cairo context for the region you want to draw on.</para>
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</listitem>
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<listitem>
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<para><emphasis>To clear existing content from a texture:</emphasis>
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use <function>clutter_cairo_texture_clear</function>.</para>
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<para>You may need to do this as the texture reuses the same
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Cairo context each time you call
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<function>clutter_cairo_texture_create</function> or
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<function>clutter_cairo_texture_create_region</function>.</para>
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</listitem>
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<listitem>
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<para><emphasis>To resize the Cairo context wrapped
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by a texture</emphasis>, use
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<function>clutter_cairo_texture_set_surface_size</function>.</para>
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</listitem>
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</itemizedlist>
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<section>
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<title>Drawing pages from a PDF onto a ClutterCairoContext</title>
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<para>Other libraries may provide an API for writing onto a
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Cairo context; you can make use of these APIs on the exposed
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Cairo context of a ClutterCairoTexture. For example, you
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can use the poppler-glib API to display pages
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from a PopplerDocument inside a Clutter application:</para>
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<informalexample>
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<programlisting>
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<![CDATA[
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#include <poppler/glib/poppler.h>
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/* snipped setup code (as above) */
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/*
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* cast to CLUTTER_CAIRO_TEXTURE, as the functions
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* used below require that type
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*/
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ClutterCairoTexture *cc_texture = CLUTTER_CAIRO_TEXTURE (texture);
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clutter_cairo_texture_clear (cc_texture);
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gchar *file_uri = "file:///path/to/file.pdf";
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guint page_num = 0;
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double page_width, page_height;
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PopplerDocument *doc;
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PopplerPage *page;
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GError *error = NULL;
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doc = poppler_document_new_from_file (file_uri, NULL, &error);
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page = poppler_document_get_page (doc, page_num);
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poppler_page_get_size (page, &page_width, &page_height);
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cr = clutter_cairo_texture_create (cc_texture);
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/* render the page to the context */
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poppler_page_render (page, cr);
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cairo_destroy (cr);
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]]>
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</programlisting>
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</informalexample>
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<para>Note that if the page is larger than the Cairo context,
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some of it might not be visible. Similarly, if the ClutterCairoTexture
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is larger than the stage, some of that might not be visible. So you
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may need to do some work to make the ClutterCairoTexture fit
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inside the stage properly (e.g. resize the stage), and/or some work
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to make the PDF page sit inside the Cairo context (e.g. scale the PDF
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page or put it inside a scrollable actor).</para>
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</section>
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</section>
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</section>
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<!--
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<section id="textures-aspect-ratio">
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<title>Maintaining the aspect ratio when loading a texture</title>
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@ -423,10 +566,10 @@ on_paint (ClutterActor *actor)
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</section>
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</section>
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</chapter>
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-->
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</chapter> <!-- textures }}} -->
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<!--
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<chapter id="animations">
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<title>Animations</title>
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