# cairooverlay

cairooverlay renders an overlay using a application provided render function.

The full example can be found in tests/examples/cairo/cairo_overlay.c

## Example code

     #include &lt;gst/gst.h&gt;
     #include &lt;gst/video/video.h&gt;

     ...

     typedef struct {
       gboolean valid;
       int width;
       int height;
     } CairoOverlayState;

     ...

     static void
     prepare_overlay (GstElement * overlay, GstCaps * caps, gpointer user_data)
     {
       CairoOverlayState *state = (CairoOverlayState *)user_data;

       gst_video_format_parse_caps (caps, NULL, &amp;state-&gt;width, &amp;state-&gt;height);
       state-&gt;valid = TRUE;
     }

     static void
     draw_overlay (GstElement * overlay, cairo_t * cr, guint64 timestamp,
       guint64 duration, gpointer user_data)
     {
       CairoOverlayState *s = (CairoOverlayState *)user_data;
       double scale;

       if (!s-&gt;valid)
         return;

       scale = 2*(((timestamp/(int)1e7) % 70)+30)/100.0;
       cairo_translate(cr, s-&gt;width/2, (s-&gt;height/2)-30);
       cairo_scale (cr, scale, scale);

       cairo_move_to (cr, 0, 0);
       cairo_curve_to (cr, 0,-30, -50,-30, -50,0);
       cairo_curve_to (cr, -50,30, 0,35, 0,60 );
       cairo_curve_to (cr, 0,35, 50,30, 50,0 ); *
       cairo_curve_to (cr, 50,-30, 0,-30, 0,0 );
       cairo_set_source_rgba (cr, 0.9, 0.0, 0.1, 0.7);
       cairo_fill (cr);
     }

     ...

     cairo_overlay = gst_element_factory_make (&quot;cairooverlay&quot;, &quot;overlay&quot;);

     g_signal_connect (cairo_overlay, &quot;draw&quot;, G_CALLBACK (draw_overlay),
       overlay_state);
     g_signal_connect (cairo_overlay, &quot;caps-changed&quot;,
       G_CALLBACK (prepare_overlay), overlay_state);
     ...

## Hierarchy

    GObject
        ╰──GInitiallyUnowned
            ╰──GstObject
                ╰──GstElement
                    ╰──GstBaseTransform
                        ╰──cairooverlay

## Factory details

Authors: – Jon Nordby

Classification: – `Filter/Editor/Video`

Rank – none

Plugin – cairo

Package – GStreamer Good Plug-ins

## Pad Templates

### `sink`

    video/x-raw:
             format: { BGRx, BGRA, RGB16 }
              width: [ 1, 2147483647 ]
             height: [ 1, 2147483647 ]
          framerate: [ 0/1, 2147483647/1 ]

Presence – always

Direction – sink

Object type – GstPad

### `src`

    video/x-raw:
             format: { BGRx, BGRA, RGB16 }
              width: [ 1, 2147483647 ]
             height: [ 1, 2147483647 ]
          framerate: [ 0/1, 2147483647/1 ]

Presence – always

Direction – src

Object type – GstPad

## Signals

### caps-changed

    caps_changed_callback (GstElement * overlay,
                           GstCaps * caps,
                           gpointer udata)

    def caps_changed_callback (overlay, caps, udata):
        #python callback for the 'caps-changed' signal

    function caps_changed_callback(overlay: GstElement * overlay, caps: GstCaps * caps, udata: gpointer udata): {
        // javascript callback for the 'caps-changed' signal
    }

This signal is emitted when the caps of the element has changed.

Parameters:

`overlay` –

Overlay element emitting the signal.

`caps` –

The GstCaps of the element.

`udata` –
No description available

Flags:

### draw

    draw_callback (GstElement * overlay,
                   CairoContext * cr,
                   guint64 timestamp,
                   guint64 duration,
                   gpointer udata)

    def draw_callback (overlay, cr, timestamp, duration, udata):
        #python callback for the 'draw' signal

    function draw_callback(overlay: GstElement * overlay, cr: CairoContext * cr, timestamp: guint64 timestamp, duration: guint64 duration, udata: gpointer udata): {
        // javascript callback for the 'draw' signal
    }

This signal is emitted when the overlay should be drawn.

Parameters:

`overlay` –

Overlay element emitting the signal.

`cr` –

Cairo context to draw to.

`timestamp` –

Timestamp (see GstClockTime) of the current buffer.

`duration` –

Duration (see GstClockTime) of the current buffer.

`udata` –
No description available

Flags:

## Properties

### draw-on-transparent-surface

    “draw-on-transparent-surface” gboolean

Let the draw signal work on a transparent surface and blend the results with the video at a later time

Flags : Read / Write

Default value : false

The results of the search are