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cookbook: Added basic mouse scroll recipe
Added a recipe explaining the basics of mouse scroll events.
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Elliot Smith
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@ -345,4 +345,119 @@ clutter_stage_set_key_focus (stage, actor);
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</section>
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</section>
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<section id="events-mouse-scroll">
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<title>Detecting mouse wheel scrolling on an actor</title>
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<section>
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<title>Problem</title>
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<para>You want to detect when the mouse wheel is scrolled on an
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actor.</para>
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</section>
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<section>
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<title>Solution</title>
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<para>Connect a callback handler to the scroll-event signal
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for an actor.</para>
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<para>First, ensure that the actor is reactive (i.e. will
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respond to events):</para>
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<informalexample>
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<programlisting>
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<![CDATA[
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clutter_actor_set_reactive (actor, TRUE);
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]]>
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</programlisting>
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</informalexample>
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<para>Next, connect a callback handler to the
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<code>scroll-event</code> signal of the actor:</para>
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<informalexample>
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<programlisting>
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<![CDATA[
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g_signal_connect (actor,
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"scroll-event",
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G_CALLBACK (_scroll_event_cb),
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NULL);
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]]>
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</programlisting>
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</informalexample>
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<para>Finally, create a callback handler to examine the scroll
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event and respond to it:</para>
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<informalexample>
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<programlisting>
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<![CDATA[
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static gboolean
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_scroll_event_cb (ClutterActor *actor,
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ClutterEvent *event,
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gpointer user_data)
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{
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/* determine the direction the mouse wheel was scrolled */
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ClutterScrollDirection direction;
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direction = clutter_event_get_scroll_direction (event);
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/* replace these stubs with real code to move the actor etc. */
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switch (direction)
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{
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case CLUTTER_SCROLL_UP:
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g_debug ("Scrolled up");
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break;
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case CLUTTER_SCROLL_DOWN:
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g_debug ("Scrolled down");
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break;
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case CLUTTER_SCROLL_RIGHT:
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g_debug ("Scrolled right");
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break;
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case CLUTTER_SCROLL_LEFT:
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g_debug ("Scrolled left");
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break;
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}
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return TRUE; /* event has been handled */
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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>A standard mouse wheel will only return up and
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down movements; but in cases where the mouse has left and
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right scrolling (e.g. a trackball mouse), left and right scroll
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events may also be emitted.</para>
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<section>
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<title>Creating a full scrollable actor</title>
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<para>While the simple outline above explains the basics
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of how to connect to scroll events, it doesn't do much to
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help with really implementing a scrollable actor. That's what
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we'll do in this section. The full code for the example we'll
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walk through here is available <link linkend="">in this
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later section</link>.</para>
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</section>
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</section>
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<section>
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<title>Full example</title>
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<example id="events-mouse-scroll-example">
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<title>Mouse scrolling over <type>ClutterActor</type></title>
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<programlisting>
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<xi:include href="examples/events-mouse-scroll.c" parse="text">
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<xi:fallback>a code sample should be here... but isn't</xi:fallback>
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</xi:include>
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</programlisting>
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</example>
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</section>
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</section>
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</chapter>
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108
doc/cookbook/examples/events-mouse-scroll.c
Normal file
108
doc/cookbook/examples/events-mouse-scroll.c
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@ -0,0 +1,108 @@
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/*
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* Scroll in the y axis by moving an enclosed box (with layout)
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* up and down inside a "letterbox" in the center of the stage
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*
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* gcc -g -O0 -DTESTS_DATA_DIR="\"/home/ell/dev/clutter_src/tests/data\"" -o events-mouse-scroll events-mouse-scroll.c `pkg-config --libs --cflags clutter-1.0 glib-2.0` -lm
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*/
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#include <clutter/clutter.h>
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#define STAGE_HEIGHT 400
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#define STAGE_WIDTH STAGE_HEIGHT * 2
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#define SCROLL_AMOUNT STAGE_HEIGHT * 0.2
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static const ClutterColor stage_color = { 0x33, 0x33, 0x55, 0xff };
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static const ClutterColor box_color = { 0xaa, 0xaa, 0x55, 0xff };
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static gboolean
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_scroll_event_cb (ClutterActor *scroll,
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ClutterEvent *event,
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gpointer user_data)
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{
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ClutterActor *viewport = CLUTTER_ACTOR (user_data);
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gfloat y = clutter_actor_get_y (viewport);
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ClutterScrollDirection direction;
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direction = clutter_event_get_scroll_direction (event);
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switch (direction)
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{
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case CLUTTER_SCROLL_UP:
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y -= SCROLL_AMOUNT;
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break;
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case CLUTTER_SCROLL_DOWN:
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y += SCROLL_AMOUNT;
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break;
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}
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y = CLAMP (y,
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clutter_actor_get_height (scroll)
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+ clutter_actor_get_y (scroll)
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- clutter_actor_get_height (viewport),
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0.0);
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clutter_actor_animate (viewport,
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CLUTTER_EASE_OUT_CUBIC,
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300,
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"y", y,
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NULL);
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return TRUE;
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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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ClutterActor *stage;
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ClutterActor *scroll;
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ClutterActor *viewport;
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ClutterActor *texture;
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clutter_init (&argc, &argv);
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stage = clutter_stage_get_default ();
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clutter_actor_set_size (stage, STAGE_WIDTH, STAGE_HEIGHT);
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clutter_stage_set_color (CLUTTER_STAGE (stage), &stage_color);
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g_signal_connect (stage, "destroy", G_CALLBACK (clutter_main_quit), NULL);
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/* the "letterbox" which the viewport is scrolled within */
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scroll = clutter_group_new ();
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clutter_actor_set_size (scroll, STAGE_WIDTH, STAGE_HEIGHT * 0.75);
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clutter_actor_add_constraint (scroll, clutter_align_constraint_new (stage, CLUTTER_BIND_Y, 0.5));
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clutter_actor_set_reactive (scroll, TRUE);
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/* this clips all actors inside the scroll group to that group's allocation */
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clutter_actor_set_clip_to_allocation (scroll, TRUE);
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viewport = clutter_box_new (clutter_bin_layout_new (CLUTTER_BIN_ALIGNMENT_CENTER,
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CLUTTER_BIN_ALIGNMENT_CENTER));
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clutter_box_set_color (CLUTTER_BOX (viewport), &box_color);
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/* the actor to scroll */
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texture = clutter_texture_new ();
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clutter_actor_set_request_mode (texture, CLUTTER_REQUEST_HEIGHT_FOR_WIDTH);
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clutter_texture_set_keep_aspect_ratio (CLUTTER_TEXTURE (texture),
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TRUE);
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/* the box resizes itself to fit this texture */
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clutter_actor_set_width (texture, STAGE_WIDTH);
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clutter_texture_set_from_file (CLUTTER_TEXTURE (texture),
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TESTS_DATA_DIR "/redhand.png",
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NULL);
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g_signal_connect (scroll,
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"scroll-event",
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G_CALLBACK (_scroll_event_cb),
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viewport);
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clutter_container_add_actor (CLUTTER_CONTAINER (viewport), texture);
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clutter_container_add_actor (CLUTTER_CONTAINER (scroll), viewport);
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clutter_container_add_actor (CLUTTER_CONTAINER (stage), scroll);
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clutter_actor_show (stage);
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clutter_main ();
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return 0;
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}
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