mirror of
https://github.com/brl/mutter.git
synced 2024-11-10 07:56:14 -05:00
cookbook: Added walk through of code example for mouse scroll
Modified the mouse scroll example to fit better with the tutorial walkthrough. Added a stepped walkthrough of the scrollable actor code example.
This commit is contained in:
parent
57ba89c8de
commit
f568a68ee1
@ -435,15 +435,225 @@ _scroll_event_cb (ClutterActor *actor,
|
||||
events may also be emitted.</para>
|
||||
|
||||
<section>
|
||||
<title>Creating a full scrollable actor</title>
|
||||
<title>Creating a scrolling viewport for an actor</title>
|
||||
|
||||
<para>While the simple outline above explains the basics
|
||||
of how to connect to scroll events, it doesn't do much to
|
||||
help with really implementing a scrollable actor. That's what
|
||||
we'll do in this section. The full code for the example we'll
|
||||
walk through here is available
|
||||
<link linkend="events-mouse-scroll-example">in this later
|
||||
section</link>.</para>
|
||||
help with <emphasis>really</emphasis> implementing scrolling
|
||||
over an actor. That's what we'll do in this section.</para>
|
||||
|
||||
<note>
|
||||
<para>The full code for the example we'll walk through here is
|
||||
available in <link linkend="events-mouse-scroll-example">this later
|
||||
section</link>.</para>
|
||||
</note>
|
||||
|
||||
<para>Scrolling over an actor actually requires coordination
|
||||
between two components:</para>
|
||||
|
||||
<orderedlist>
|
||||
<listitem>
|
||||
<formalpara>
|
||||
<title>Scrollable actor</title>
|
||||
<para>An actor which is too large to fit on the stage
|
||||
or inside the area of the UI assigned to it (otherwise
|
||||
there's no need to scroll over it...).</para>
|
||||
</formalpara>
|
||||
</listitem>
|
||||
<listitem>
|
||||
<formalpara>
|
||||
<title>Viewport</title>
|
||||
<para>This displays a cropped view of part of the scrollable
|
||||
actor, revealing different parts of it as scroll events
|
||||
occur.</para>
|
||||
</formalpara>
|
||||
</listitem>
|
||||
</orderedlist>
|
||||
|
||||
<para>Here are the steps required to set up the two actors:</para>
|
||||
|
||||
<orderedlist>
|
||||
<listitem>
|
||||
<para>Create the scrollable actor; it should be larger
|
||||
than the scrollview. This example uses a <type>ClutterTexture</type>,
|
||||
but any <type>ClutterActor</type> will work:</para>
|
||||
<informalexample>
|
||||
<programlisting>
|
||||
/* get image file path, set up stage etc. */
|
||||
|
||||
ClutterActor *texture;
|
||||
texture = clutter_texture_new ();
|
||||
clutter_texture_set_keep_aspect_ratio (CLUTTER_TEXTURE (texture),
|
||||
TRUE);
|
||||
|
||||
/*
|
||||
* set the texture's height so it's as tall as the stage
|
||||
* (STAGE_HEIGHT is define'd at the top of the file);
|
||||
* see <link linkend="textures-aspect-ratio">this recipe</link>
|
||||
* for more about loading images into textures
|
||||
*/
|
||||
clutter_actor_set_request_mode (texture, CLUTTER_REQUEST_WIDTH_FOR_HEIGHT);
|
||||
clutter_actor_set_height (texture, STAGE_HEIGHT);
|
||||
|
||||
/* load the image file */
|
||||
clutter_texture_set_from_file (CLUTTER_TEXTURE (texture),
|
||||
image_file_path,
|
||||
NULL);
|
||||
</programlisting>
|
||||
</informalexample>
|
||||
</listitem>
|
||||
|
||||
<listitem>
|
||||
|
||||
<para>Create the viewport. The simplest way to do
|
||||
this is with a <type>ClutterGroup</type>:</para>
|
||||
|
||||
<informalexample>
|
||||
<programlisting>
|
||||
<![CDATA[
|
||||
ClutterActor *viewport;
|
||||
viewport = clutter_group_new ();
|
||||
|
||||
/* viewport is _shorter_ than the stage (and the texture) */
|
||||
clutter_actor_set_size (viewport, STAGE_WIDTH, STAGE_HEIGHT * 0.5);
|
||||
|
||||
/* align the viewport to the center of the stage's y axis */
|
||||
clutter_actor_add_constraint (viewport,
|
||||
clutter_align_constraint_new (stage, CLUTTER_BIND_Y, 0.5));
|
||||
|
||||
/* viewport needs to respond to scroll events */
|
||||
clutter_actor_set_reactive (viewport, TRUE);
|
||||
|
||||
/* clip all actors inside the viewport to that group's allocation */
|
||||
clutter_actor_set_clip_to_allocation (viewport, TRUE);
|
||||
]]>
|
||||
</programlisting>
|
||||
</informalexample>
|
||||
|
||||
<para>The key here is calling
|
||||
<code>clutter_actor_set_clip_to_allocation (viewport, TRUE)</code>.
|
||||
This configures the <varname>viewport</varname> group so
|
||||
that any of its children are clipped: i.e. only the area of
|
||||
the children which fits inside the group is visible. This
|
||||
in turn requires setting an explicit size on the group,
|
||||
rather than allowing it to size itself to fit its
|
||||
children (the default).</para>
|
||||
|
||||
</listitem>
|
||||
|
||||
<listitem>
|
||||
<para>Put the scrollable actor into the scroll view and
|
||||
the scroll view into its container (in this case,
|
||||
the default stage):</para>
|
||||
|
||||
<informalexample>
|
||||
<programlisting>
|
||||
clutter_container_add_actor (CLUTTER_CONTAINER (viewport), texture);
|
||||
|
||||
clutter_container_add_actor (CLUTTER_CONTAINER (stage), viewport);
|
||||
</programlisting>
|
||||
</informalexample>
|
||||
|
||||
</listitem>
|
||||
|
||||
<listitem>
|
||||
<para>Create a callback handler for scroll event signals
|
||||
emitted by the viewport:</para>
|
||||
|
||||
<informalexample>
|
||||
<programlisting>
|
||||
<![CDATA[
|
||||
static gboolean
|
||||
_scroll_event_cb (ClutterActor *viewport,
|
||||
ClutterEvent *event,
|
||||
gpointer user_data)
|
||||
{
|
||||
ClutterActor *scrollable = CLUTTER_ACTOR (user_data);
|
||||
|
||||
gfloat viewport_height = clutter_actor_get_height (viewport);
|
||||
gfloat scrollable_height = clutter_actor_get_height (scrollable);
|
||||
|
||||
/* no need to scroll if the scrollable is shorter than the viewport */
|
||||
if (scrollable_height < viewport_height)
|
||||
return TRUE;
|
||||
|
||||
gfloat y = clutter_actor_get_y (scrollable);
|
||||
|
||||
ClutterScrollDirection direction;
|
||||
direction = clutter_event_get_scroll_direction (event);
|
||||
|
||||
switch (direction)
|
||||
{
|
||||
case CLUTTER_SCROLL_UP:
|
||||
y -= SCROLL_AMOUNT;
|
||||
break;
|
||||
case CLUTTER_SCROLL_DOWN:
|
||||
y += SCROLL_AMOUNT;
|
||||
break;
|
||||
|
||||
/* we're only interested in up and down */
|
||||
case CLUTTER_SCROLL_LEFT:
|
||||
case CLUTTER_SCROLL_RIGHT:
|
||||
break;
|
||||
}
|
||||
|
||||
/*
|
||||
* the CLAMP macro returns a value for the first argument
|
||||
* that falls within the range specified by the second and
|
||||
* third arguments
|
||||
*
|
||||
* we allow the scrollable's y position to be decremented to the point
|
||||
* where its base is aligned with the base of the viewport
|
||||
*/
|
||||
y = CLAMP (y,
|
||||
viewport_height - scrollable_height,
|
||||
0.0);
|
||||
|
||||
clutter_actor_animate (scrollable,
|
||||
CLUTTER_EASE_OUT_CUBIC,
|
||||
300,
|
||||
"y", y,
|
||||
NULL);
|
||||
|
||||
return TRUE;
|
||||
}
|
||||
]]>
|
||||
</programlisting>
|
||||
</informalexample>
|
||||
|
||||
<para>The approach taken here is to move the scrollable
|
||||
actor up, relative to the viewport. Initially, the
|
||||
scrollable will have a <code>y</code> coordinate value
|
||||
of <code>0.0</code> (it is aligned to the top of the viewport).
|
||||
Scrolling up subtracts from the
|
||||
<code>y</code> coordinate (down to a minumum of
|
||||
<code>viewport_height - scrollable_height</code>). This moves
|
||||
the top of the scrollable "outside" the clip area of the
|
||||
viewport; simultaneously, more of the bottom part of the
|
||||
scrollable moves into the clip area, becoming visible.</para>
|
||||
|
||||
<para>Scrolling down adds to the <code>y</code> coordinate
|
||||
(but only up to a maximum value of <code>0.0</code>).</para>
|
||||
</listitem>
|
||||
|
||||
<listitem>
|
||||
<para>Connect the callback handler to the signal; note
|
||||
that we pass the scrollable (the texture) to the callback,
|
||||
as we're moving the texture inside the viewport to
|
||||
create the scrolling effect:</para>
|
||||
|
||||
<informalexample>
|
||||
<programlisting>
|
||||
g_signal_connect (viewport,
|
||||
"scroll-event",
|
||||
G_CALLBACK (_scroll_event_cb),
|
||||
texture);
|
||||
</programlisting>
|
||||
</informalexample>
|
||||
</listitem>
|
||||
|
||||
</orderedlist>
|
||||
|
||||
</section>
|
||||
</section>
|
||||
|
||||
@ -451,7 +661,7 @@ _scroll_event_cb (ClutterActor *actor,
|
||||
<title>Full example</title>
|
||||
|
||||
<example id="events-mouse-scroll-example">
|
||||
<title>Mouse scrolling over <type>ClutterActor</type></title>
|
||||
<title>Mouse scrolling over a <type>ClutterActor</type></title>
|
||||
<programlisting>
|
||||
<xi:include href="examples/events-mouse-scroll.c" parse="text">
|
||||
<xi:fallback>a code sample should be here... but isn't</xi:fallback>
|
||||
|
@ -4,8 +4,6 @@
|
||||
#define STAGE_WIDTH STAGE_HEIGHT
|
||||
#define SCROLL_AMOUNT STAGE_HEIGHT * 0.125
|
||||
|
||||
static const ClutterColor stage_color = { 0x33, 0x33, 0x55, 0xff };
|
||||
|
||||
static gboolean
|
||||
_scroll_event_cb (ClutterActor *viewport,
|
||||
ClutterEvent *event,
|
||||
@ -13,6 +11,13 @@ _scroll_event_cb (ClutterActor *viewport,
|
||||
{
|
||||
ClutterActor *scrollable = CLUTTER_ACTOR (user_data);
|
||||
|
||||
gfloat viewport_height = clutter_actor_get_height (viewport);
|
||||
gfloat scrollable_height = clutter_actor_get_height (scrollable);
|
||||
|
||||
/* no need to scroll if the scrollable is shorter than the viewport */
|
||||
if (scrollable_height < viewport_height)
|
||||
return TRUE;
|
||||
|
||||
gfloat y = clutter_actor_get_y (scrollable);
|
||||
|
||||
ClutterScrollDirection direction;
|
||||
@ -26,14 +31,23 @@ _scroll_event_cb (ClutterActor *viewport,
|
||||
case CLUTTER_SCROLL_DOWN:
|
||||
y += SCROLL_AMOUNT;
|
||||
break;
|
||||
|
||||
/* we're only interested in up and down */
|
||||
case CLUTTER_SCROLL_LEFT:
|
||||
case CLUTTER_SCROLL_RIGHT:
|
||||
break;
|
||||
}
|
||||
|
||||
/*
|
||||
* the CLAMP macro returns a value for the first argument
|
||||
* that falls within the range specified by the second and
|
||||
* third arguments
|
||||
*
|
||||
* we allow the scrollable's y position to be decremented to the point
|
||||
* where its base is aligned with the base of the viewport
|
||||
*/
|
||||
y = CLAMP (y,
|
||||
clutter_actor_get_height (viewport)
|
||||
- clutter_actor_get_height (scrollable),
|
||||
viewport_height - scrollable_height,
|
||||
0.0);
|
||||
|
||||
clutter_actor_animate (scrollable,
|
||||
@ -48,6 +62,13 @@ _scroll_event_cb (ClutterActor *viewport,
|
||||
int
|
||||
main (int argc, char *argv[])
|
||||
{
|
||||
gchar *image_file_path = TESTS_DATA_DIR "/redhand.png";
|
||||
|
||||
if (argc > 1)
|
||||
{
|
||||
image_file_path = argv[1];
|
||||
}
|
||||
|
||||
ClutterActor *stage;
|
||||
ClutterActor *viewport;
|
||||
ClutterActor *texture;
|
||||
@ -56,8 +77,6 @@ main (int argc, char *argv[])
|
||||
|
||||
stage = clutter_stage_get_default ();
|
||||
clutter_actor_set_size (stage, STAGE_WIDTH, STAGE_HEIGHT);
|
||||
clutter_stage_set_color (CLUTTER_STAGE (stage), &stage_color);
|
||||
g_signal_connect (stage, "destroy", G_CALLBACK (clutter_main_quit), NULL);
|
||||
|
||||
/* the scrollable actor */
|
||||
texture = clutter_texture_new ();
|
||||
@ -69,7 +88,7 @@ main (int argc, char *argv[])
|
||||
clutter_actor_set_height (texture, STAGE_HEIGHT);
|
||||
|
||||
clutter_texture_set_from_file (CLUTTER_TEXTURE (texture),
|
||||
TESTS_DATA_DIR "/redhand.png",
|
||||
image_file_path,
|
||||
NULL);
|
||||
|
||||
/* the viewport which the box is scrolled within */
|
||||
|
Loading…
Reference in New Issue
Block a user