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struct ClutterCanvas; struct ClutterCanvasClass; ClutterContent * clutter_canvas_new (void); gboolean clutter_canvas_set_size (ClutterCanvas *canvas,int width,int height);
The ClutterCanvas class is a ClutterContent implementation that allows drawing using the Cairo API on a 2D surface.
In order to draw on a ClutterCanvas, you should connect a handler to the
"draw" signal; the signal will receive a cairo_t context
that can be used to draw. ClutterCanvas will emit the "draw"
signal when invalidated using clutter_content_invalidate().
#include <stdlib.h>
#include <math.h>
#include <cairo.h>
#include <clutter/clutter.h>
static gboolean
draw_clock (ClutterCanvas *canvas,
cairo_t *cr,
int width,
int height)
{
GDateTime *now;
float hours, minutes, seconds;
ClutterColor color;
/* get the current time and compute the angles */
now = g_date_time_new_now_local ();
seconds = g_date_time_get_second (now) * G_PI / 30;
minutes = g_date_time_get_minute (now) * G_PI / 30;
hours = g_date_time_get_hour (now) * G_PI / 6;
cairo_save (cr);
/* clear the contents of the canvas, to avoid painting
* over the previous frame
*/
cairo_set_operator (cr, CAIRO_OPERATOR_CLEAR);
cairo_paint (cr);
cairo_restore (cr);
cairo_set_operator (cr, CAIRO_OPERATOR_OVER);
/* scale the modelview to the size of the surface */
cairo_scale (cr, width, height);
cairo_set_line_cap (cr, CAIRO_LINE_CAP_ROUND);
cairo_set_line_width (cr, 0.1);
/* the black rail that holds the seconds indicator */
clutter_cairo_set_source_color (cr, CLUTTER_COLOR_Black);
cairo_translate (cr, 0.5, 0.5);
cairo_arc (cr, 0, 0, 0.4, 0, G_PI * 2);
cairo_stroke (cr);
/* the seconds indicator */
color = *CLUTTER_COLOR_White;
color.alpha = 128;
clutter_cairo_set_source_color (cr, &color);
cairo_move_to (cr, 0, 0);
cairo_arc (cr, sinf (seconds) * 0.4, - cosf (seconds) * 0.4, 0.05, 0, G_PI * 2);
cairo_fill (cr);
/* the minutes hand */
color = *CLUTTER_COLOR_DarkChameleon;
color.alpha = 196;
clutter_cairo_set_source_color (cr, &color);
cairo_move_to (cr, 0, 0);
cairo_line_to (cr, sinf (minutes) * 0.4, -cosf (minutes) * 0.4);
cairo_stroke (cr);
/* the hours hand */
cairo_move_to (cr, 0, 0);
cairo_line_to (cr, sinf (hours) * 0.2, -cosf (hours) * 0.2);
cairo_stroke (cr);
g_date_time_unref (now);
/* we're done drawing */
return TRUE;
}
static gboolean
invalidate_clock (gpointer data_)
{
/* invalidate the contents of the canvas */
clutter_content_invalidate (data_);
/* keep the timeout source */
return G_SOURCE_CONTINUE;
}
static guint idle_resize_id;
static gboolean
idle_resize (gpointer data)
{
ClutterActor *actor = data;
float width, height;
/* match the canvas size to the actor's */
clutter_actor_get_size (actor, &width, &height);
clutter_canvas_set_size (CLUTTER_CANVAS (clutter_actor_get_content (actor)),
ceilf (width),
ceilf (height));
/* unset the guard */
idle_resize_id = 0;
/* remove the timeout */
return G_SOURCE_REMOVE;
}
static void
on_actor_resize (ClutterActor *actor,
const ClutterActorBox *allocation,
ClutterAllocationFlags flags,
gpointer user_data)
{
/* throttle multiple actor allocations to one canvas resize; we use a guard
* variable to avoid queueing multiple resize operations
*/
if (idle_resize_id == 0)
idle_resize_id = clutter_threads_add_timeout (1000, idle_resize, actor);
}
int
main (int argc, char *argv[])
{
ClutterActor *stage, *actor;
ClutterContent *canvas;
/* initialize Clutter */
if (clutter_init (&argc, &argv) != CLUTTER_INIT_SUCCESS)
return EXIT_FAILURE;
/* create a resizable stage */
stage = clutter_stage_new ();
clutter_stage_set_title (CLUTTER_STAGE (stage), "2D Clock");
clutter_stage_set_user_resizable (CLUTTER_STAGE (stage), TRUE);
clutter_actor_set_background_color (stage, CLUTTER_COLOR_LightSkyBlue);
clutter_actor_set_size (stage, 300, 300);
clutter_actor_show (stage);
/* our 2D canvas, courtesy of Cairo */
canvas = clutter_canvas_new ();
clutter_canvas_set_size (CLUTTER_CANVAS (canvas), 300, 300);
actor = clutter_actor_new ();
clutter_actor_set_content (actor, canvas);
clutter_actor_set_content_scaling_filters (actor,
CLUTTER_SCALING_FILTER_TRILINEAR,
CLUTTER_SCALING_FILTER_LINEAR);
clutter_actor_add_child (stage, actor);
/* the actor now owns the canvas */
g_object_unref (canvas);
/* bind the size of the actor to that of the stage */
clutter_actor_add_constraint (actor, clutter_bind_constraint_new (stage, CLUTTER_BIND_SIZE, 0));
/* resize the canvas whenever the actor changes size */
g_signal_connect (actor, "allocation-changed", G_CALLBACK (on_actor_resize), NULL);
/* quit on destroy */
g_signal_connect (stage, "destroy", G_CALLBACK (clutter_main_quit), NULL);
/* connect our drawing code */
g_signal_connect (canvas, "draw", G_CALLBACK (draw_clock), NULL);
/* invalidate the canvas, so that we can draw before the main loop starts */
clutter_content_invalidate (canvas);
/* set up a timer that invalidates the canvas every second */
clutter_threads_add_timeout (1000, invalidate_clock, canvas);
clutter_main ();
return EXIT_SUCCESS;
}
ClutterCanvas is available since Clutter 1.10.
struct ClutterCanvas;
The ClutterCanvas structure contains private data and should only be accessed using the provided API.
Since 1.10
struct ClutterCanvasClass {
gboolean (* draw) (ClutterCanvas *canvas,
cairo_t *cr,
int width,
int height);
};
The ClutterCanvasClass structure contains private data.
| class handler for the "draw" signal |
Since 1.10
ClutterContent * clutter_canvas_new (void);
Creates a new instance of ClutterCanvas.
You should call clutter_canvas_set_size() to set the size of the canvas.
You should call clutter_content_invalidate() every time you wish to
draw the contents of the canvas.
Returns : |
The newly allocated instance of
ClutterCanvas. Use g_object_unref() when done. [transfer full]
|
Since 1.10
gboolean clutter_canvas_set_size (ClutterCanvas *canvas,int width,int height);
Sets the size of the canvas, and invalidates the content.
This function will cause the canvas to be invalidated only
if the size of the canvas surface has changed.
If you want to invalidate the contents of the canvas when setting
the size, you can use the return value of the function to conditionally
call clutter_content_invalidate():
1 2 |
if (!clutter_canvas_set_size (canvas, width, height)) clutter_content_invalidate (CLUTTER_CONTENT (canvas)); |
|
a ClutterCanvas |
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the width of the canvas, in pixels |
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the height of the canvas, in pixels |
Returns : |
this function returns TRUE if the size change
caused a content invalidation, and FALSE otherwise |
Since 1.10
"height" property "height" gint : Read / Write
The height of the canvas.
Allowed values: >= -1
Default value: -1
Since 1.10
"draw" signalgboolean user_function (ClutterCanvas *canvas,
CairoContext *cr,
gint width,
gint height,
gpointer user_data) : No Recursion
The "draw" signal is emitted each time a canvas is invalidated.
It is safe to connect multiple handlers to this signal: each
handler invocation will be automatically protected by cairo_save()
and cairo_restore() pairs.
|
the ClutterCanvas that emitted the signal |
|
the Cairo context used to draw |
|
the width of the canvas
|
|
the height of the canvas
|
|
user data set when the signal handler was connected. |
Returns : |
TRUE if the signal emission should stop, and
FALSE otherwise |
Since 1.10