ClutterCairoTexture

ClutterCairoTexture — Texture with Cairo integration

Functions

Properties

gboolean auto-resize Read / Write
guint surface-height Read / Write
guint surface-width Read / Write

Signals

CairoSurface* create-surface No Recursion
gboolean draw No Recursion

Types and Values

Object Hierarchy

    GObject
    ╰── GInitiallyUnowned
        ╰── ClutterActor
            ╰── ClutterTexture
                ╰── ClutterCairoTexture

Implemented Interfaces

ClutterCairoTexture implements ClutterContainer, ClutterScriptable, ClutterAnimatable and AtkImplementorIface.

Description

ClutterCairoTexture is a ClutterTexture that displays the contents of a Cairo context. The ClutterCairoTexture actor will create a Cairo image surface which will then be uploaded to a GL texture when needed.

Since ClutterCairoTexture uses a Cairo image surface internally all the drawing operations will be performed in software and not using hardware acceleration. This can lead to performance degradation if the contents of the texture change frequently.

In order to use a ClutterCairoTexture you should connect to the “draw” signal; the signal is emitted each time the ClutterCairoTexture has been told to invalidate its contents, by using clutter_cairo_texture_invalidate_rectangle() or its sister function, clutter_cairo_texture_invalidate().

Each callback to the “draw” signal will receive a cairo_t context which can be used for drawing; the Cairo context is owned by the ClutterCairoTexture and should not be destroyed explicitly.

Example 4. A simple ClutterCairoTexture canvas

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#include <stdlib.h>
#include <math.h>
#include <cairo.h>
#include <clutter/clutter.h>

static gboolean
draw_clock (ClutterCairoTexture *canvas,
            cairo_t             *cr)
{
  guint width, height;
  GDateTime *now;
  float hours, minutes, seconds;

  /* 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;

  /* clear the contents of the canvas, to avoid painting
   * over the previous frame
   */
  clutter_cairo_texture_clear (canvas);

  /* scale the modelview to the size of the surface */
  clutter_cairo_texture_get_surface_size (canvas, &width, &height);
  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 */
  clutter_cairo_set_source_color (cr, CLUTTER_COLOR_White);
  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 */
  clutter_cairo_set_source_color (cr, CLUTTER_COLOR_DarkChameleon);
  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_cairo_texture_invalidate (data_);

  /* keep the timeout source */
  return TRUE;
}

G_MODULE_EXPORT int
test_cairo_clock_main (int argc, char *argv[])
{
  ClutterActor *stage, *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_cairo_texture_new (300, 300);
  clutter_container_add_actor (CLUTTER_CONTAINER (stage), canvas);

  /* bind the size of the canvas to that of the stage */
  clutter_actor_add_constraint (canvas, clutter_bind_constraint_new (stage, CLUTTER_BIND_SIZE, 0));

  /* make sure to match allocation to canvas size */
  clutter_cairo_texture_set_auto_resize (CLUTTER_CAIRO_TEXTURE (canvas), TRUE);

  /* 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_cairo_texture_invalidate (CLUTTER_CAIRO_TEXTURE (canvas));

  /* set up a timer that invalidates the canvas every second */
  clutter_threads_add_timeout (1000, invalidate_clock, canvas);

  clutter_main ();

  return EXIT_SUCCESS;
}

G_MODULE_EXPORT const char *
test_cairo_clock_describe (void)
{
  return "Simple 2D canvas using a Cairo texture actor";
}

ClutterCairoTexture is available since Clutter 1.0.

Functions

CLUTTER_CAIRO_FORMAT_ARGB32

#define CLUTTER_CAIRO_FORMAT_ARGB32     (COGL_PIXEL_FORMAT_BGRA_8888_PRE)

The CoglPixelFormat to be used when uploading image data from and to a Cairo image surface using CAIRO_FORMAT_ARGB32 and CAIRO_FORMAT_RGB24 as cairo_format_t.

Since 1.8


clutter_cairo_texture_new ()

ClutterActor *
clutter_cairo_texture_new (guint width,
                           guint height);

Creates a new ClutterCairoTexture actor, with a surface of width by height pixels.

Parameters

width

the width of the surface

 

height

the height of the surface

 

Returns

the newly created ClutterCairoTexture actor

Since 1.0


clutter_cairo_texture_set_surface_size ()

void
clutter_cairo_texture_set_surface_size
                               (ClutterCairoTexture *self,
                                guint width,
                                guint height);

Resizes the Cairo surface used by self to width and height .

This function will not invalidate the contents of the Cairo texture: you will have to explicitly call either clutter_cairo_texture_invalidate_rectangle() or clutter_cairo_texture_invalidate().

Parameters

self

a ClutterCairoTexture

 

width

the new width of the surface

 

height

the new height of the surface

 

Since 1.0


clutter_cairo_texture_get_surface_size ()

void
clutter_cairo_texture_get_surface_size
                               (ClutterCairoTexture *self,
                                guint *width,
                                guint *height);

Retrieves the surface width and height for self .

Parameters

self

a ClutterCairoTexture

 

width

return location for the surface width, or NULL.

[out]

height

return location for the surface height, or NULL.

[out]

Since 1.0


clutter_cairo_texture_set_auto_resize ()

void
clutter_cairo_texture_set_auto_resize (ClutterCairoTexture *self,
                                       gboolean value);

Sets whether the ClutterCairoTexture should ensure that the backing Cairo surface used matches the allocation assigned to the actor. If the allocation changes, the contents of the ClutterCairoTexture will also be invalidated automatically.

Parameters

self

a ClutterCairoTexture

 

value

TRUE if the ClutterCairoTexture should bind the surface size to the allocation

 

Since 1.8


clutter_cairo_texture_get_auto_resize ()

gboolean
clutter_cairo_texture_get_auto_resize (ClutterCairoTexture *self);

Retrieves the value set using clutter_cairo_texture_set_auto_resize().

Parameters

Returns

TRUE if the ClutterCairoTexture should track the allocation, and FALSE otherwise

Since 1.8


clutter_cairo_texture_create ()

cairo_t *
clutter_cairo_texture_create (ClutterCairoTexture *self);

clutter_cairo_texture_create has been deprecated since version 1.8 and should not be used in newly-written code.

Use the “draw” signal and the clutter_cairo_texture_invalidate() function to obtain a Cairo context for 2D drawing.

Creates a new Cairo context for the cairo texture. It is similar to using clutter_cairo_texture_create_region() with x_offset and y_offset of 0, width equal to the cairo texture surface width and height equal to the cairo texture surface height.

Do not call this function within the paint virtual function or from a callback to the “paint” signal.

Parameters

Returns

a newly created Cairo context. Use cairo_destroy() to upload the contents of the context when done drawing

Since 1.0


clutter_cairo_texture_create_region ()

cairo_t *
clutter_cairo_texture_create_region (ClutterCairoTexture *self,
                                     gint x_offset,
                                     gint y_offset,
                                     gint width,
                                     gint height);

clutter_cairo_texture_create_region has been deprecated since version 1.8 and should not be used in newly-written code.

Use the “draw” signal and clutter_cairo_texture_invalidate_rectangle() to obtain a clipped Cairo context for 2D drawing.

Creates a new Cairo context that will updat the region defined by x_offset , y_offset , width and height .

Do not call this function within the paint virtual function or from a callback to the “paint” signal.

Parameters

self

a ClutterCairoTexture

 

x_offset

offset of the region on the X axis

 

y_offset

offset of the region on the Y axis

 

width

width of the region, or -1 for the full surface width

 

height

height of the region, or -1 for the full surface height

 

Returns

a newly created Cairo context. Use cairo_destroy() to upload the contents of the context when done drawing

Since 1.0


clutter_cairo_texture_invalidate_rectangle ()

void
clutter_cairo_texture_invalidate_rectangle
                               (ClutterCairoTexture *self,
                                cairo_rectangle_int_t *rect);

Invalidates a rectangular region of a ClutterCairoTexture.

The invalidation will cause the “draw” signal to be emitted.

See also: clutter_cairo_texture_invalidate()

Parameters

self

a ClutterCairoTexture

 

rect

a rectangle with the area to invalida, or NULL to perform an unbounded invalidation.

[allow-none]

Since 1.8


clutter_cairo_texture_invalidate ()

void
clutter_cairo_texture_invalidate (ClutterCairoTexture *self);

Invalidates the whole surface of a ClutterCairoTexture.

This function will cause the “draw” signal to be emitted.

See also: clutter_cairo_texture_invalidate_rectangle()

Parameters

Since 1.8


clutter_cairo_texture_clear ()

void
clutter_cairo_texture_clear (ClutterCairoTexture *self);

Clears self 's internal drawing surface, so that the next upload will replace the previous contents of the ClutterCairoTexture rather than adding to it.

Calling this function from within a “draw” signal handler will clear the invalidated area.

Parameters

Since 1.0


clutter_cairo_set_source_color ()

void
clutter_cairo_set_source_color (cairo_t *cr,
                                const ClutterColor *color);

Utility function for setting the source color of cr using a ClutterColor. This function is the equivalent of:

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cairo_set_source_rgba (cr,
                       color->red / 255.0,
                       color->green / 255.0,
                       color->blue / 255.0,
                       color->alpha / 255.0);

Parameters

cr

a Cairo context

 

color

a ClutterColor

 

Since 1.0

Types and Values

struct ClutterCairoTexture

struct ClutterCairoTexture;

The ClutterCairoTexture struct contains only private data.

Since 1.0


struct ClutterCairoTextureClass

struct ClutterCairoTextureClass {
  cairo_surface_t *(* create_surface) (ClutterCairoTexture *texture,
                                       guint                width,
                                       guint                height);

  gboolean         (* draw)           (ClutterCairoTexture *texture,
                                       cairo_t             *cr);
};

The ClutterCairoTextureClass struct contains only private data.

Members

create_surface ()

class handler for the “create-surface” signal

 

draw ()

class handler for the “draw” signal

 

Since 1.0

Property Details

The “auto-resize” property

  “auto-resize”              gboolean

Controls whether the ClutterCairoTexture should automatically resize the Cairo surface whenever the actor's allocation changes. If :auto-resize is set to TRUE the surface contents will also be invalidated automatically.

Flags: Read / Write

Default value: FALSE

Since 1.8


The “surface-height” property

  “surface-height”           guint

The height of the Cairo surface used by the ClutterCairoTexture actor, in pixels.

Flags: Read / Write

Default value: 0

Since 1.0


The “surface-width” property

  “surface-width”            guint

The width of the Cairo surface used by the ClutterCairoTexture actor, in pixels.

Flags: Read / Write

Default value: 0

Since 1.0

Signal Details

The “create-surface” signal

CairoSurface*
user_function (ClutterCairoTexture *texture,
               guint                width,
               guint                height,
               gpointer             user_data)

The ::create-surface signal is emitted when a ClutterCairoTexture news its surface (re)created, which happens either when the Cairo context is created with clutter_cairo_texture_create() or clutter_cairo_texture_create_region(), or when the surface is resized through clutter_cairo_texture_set_surface_size().

The first signal handler that returns a non-NULL, valid surface will stop any further signal emission, and the returned surface will be the one used.

Parameters

texture

the ClutterCairoTexture that emitted the signal

 

width

the width of the surface to create

 

height

the height of the surface to create

 

user_data

user data set when the signal handler was connected.

 

Returns

the newly created cairo_surface_t for the texture

Flags: No Recursion

Since 1.6


The “draw” signal

gboolean
user_function (ClutterCairoTexture *texture,
               CairoContext        *cr,
               gpointer             user_data)

The ::draw signal is emitted each time a ClutterCairoTexture has been invalidated.

The passed Cairo context passed will be clipped to the invalidated area.

It is safe to connect multiple callbacks to this signals; the state of the Cairo context passed to each callback is automatically saved and restored, so it's not necessary to call cairo_save() and cairo_restore().

Parameters

texture

the ClutterCairoTexture that emitted the signal

 

cr

the Cairo context to use to draw

 

user_data

user data set when the signal handler was connected.

 

Returns

TRUE if the signal emission should stop, and FALSE to continue

Flags: No Recursion

Since 1.8