ClutterCanvas

ClutterCanvas — Content for 2D painting

Functions

Properties

gint height Read / Write
gint width Read / Write

Signals

gboolean draw No Recursion

Types and Values

Object Hierarchy

    GObject
    ╰── ClutterCanvas

Implemented Interfaces

ClutterCanvas implements ClutterContent.

Description

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.

Functions

clutter_canvas_new ()

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


clutter_canvas_set_size ()

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():

  if (!clutter_canvas_set_size (canvas, width, height))
    clutter_content_invalidate (CLUTTER_CONTENT (canvas));

Parameters

canvas

a ClutterCanvas

 

width

the width of the canvas, in pixels

 

height

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

Types and Values

struct ClutterCanvas

struct ClutterCanvas;

The ClutterCanvas structure contains private data and should only be accessed using the provided API.

Since 1.10


struct ClutterCanvasClass

struct ClutterCanvasClass {
  gboolean (* draw) (ClutterCanvas *canvas,
                     cairo_t       *cr,
                     int            width,
                     int            height);
};

The ClutterCanvasClass structure contains private data.

Members

draw ()

class handler for the “draw” signal

 

Since 1.10

Property Details

The “height” property

  “height”                   gint

The height of the canvas.

Flags: Read / Write

Allowed values: >= -1

Default value: -1

Since 1.10


The “width” property

  “width”                    gint

The width of the canvas.

Flags: Read / Write

Allowed values: >= -1

Default value: -1

Since 1.10

Signal Details

The “draw” signal

gboolean
user_function (ClutterCanvas *canvas,
               CairoContext  *cr,
               gint           width,
               gint           height,
               gpointer       user_data)

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.

Parameters

canvas

the ClutterCanvas that emitted the signal

 

cr

the Cairo context used to draw

 

width

the width of the canvas

 

height

the height of the canvas

 

user_data

user data set when the signal handler was connected.

 

Returns

TRUE if the signal emission should stop, and FALSE otherwise

Flags: No Recursion

Since 1.10

See Also

ClutterContent