gstreamer/ext/cairo/gsttextoverlay.c

/* GStreamer
 * Copyright (C) <1999> Erik Walthinsen <omega@cse.ogi.edu>
 * Copyright (C) <2003> David Schleef <ds@schleef.org>
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Library General Public
 * License as published by the Free Software Foundation; either
 * version 2 of the License, or (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Library General Public License for more details.
 *
 * You should have received a copy of the GNU Library General Public
 * License along with this library; if not, write to the
 * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
 * Boston, MA 02111-1307, USA.
 */

#ifdef HAVE_CONFIG_H
#include <config.h>
#endif
#include <string.h>
#include <strings.h>
#include <gst/gst.h>
#include "gsttextoverlay.h"

static GstElementDetails textoverlay_details = {
  "Text Overlay",
  "Filter/Editor/Video",
  "Adds text strings on top of a video buffer",
  "David Schleef <ds@schleef.org>"
};

enum
{
  ARG_0,
  ARG_TEXT,
  ARG_VALIGN,
  ARG_HALIGN,
  ARG_X0,
  ARG_Y0,
  ARG_FONT_DESC
};


static GstStaticPadTemplate textoverlay_src_template_factory =
GST_STATIC_PAD_TEMPLATE ("src",
    GST_PAD_SRC,
    GST_PAD_ALWAYS,
    GST_STATIC_CAPS ("video/x-raw-yuv, "
        "format = (fourcc) I420, "
        "width = (int) [ 1, MAX ], " "height = (int) [ 1, MAX ]")
    );

static GstStaticPadTemplate video_sink_template_factory =
GST_STATIC_PAD_TEMPLATE ("video_sink",
    GST_PAD_SINK,
    GST_PAD_ALWAYS,
    GST_STATIC_CAPS ("video/x-raw-yuv, "
        "format = (fourcc) I420, "
        "width = (int) [ 1, MAX ], " "height = (int) [ 1, MAX ]")
    );

static GstStaticPadTemplate text_sink_template_factory =
GST_STATIC_PAD_TEMPLATE ("text_sink",
    GST_PAD_SINK,
    GST_PAD_ALWAYS,
    GST_STATIC_CAPS ("text/plain")
    );

static void gst_textoverlay_base_init (gpointer g_class);
static void gst_textoverlay_class_init (GstTextOverlayClass * klass);
static void gst_textoverlay_init (GstTextOverlay * overlay);
static void gst_textoverlay_set_property (GObject * object,
    guint prop_id, const GValue * value, GParamSpec * pspec);
static void gst_textoverlay_get_property (GObject * object,
    guint prop_id, GValue * value, GParamSpec * pspec);
static GstStateChangeReturn gst_textoverlay_change_state (GstElement * element);
static void gst_textoverlay_finalize (GObject * object);


static GstElementClass *parent_class = NULL;

/*static guint gst_textoverlay_signals[LAST_SIGNAL] = { 0 }; */


GType
gst_textoverlay_get_type (void)
{
  static GType textoverlay_type = 0;

  if (!textoverlay_type) {
    static const GTypeInfo textoverlay_info = {
      sizeof (GstTextOverlayClass),
      gst_textoverlay_base_init,
      NULL,
      (GClassInitFunc) gst_textoverlay_class_init,
      NULL,
      NULL,
      sizeof (GstTextOverlay),
      0,
      (GInstanceInitFunc) gst_textoverlay_init,
    };

    textoverlay_type =
        g_type_register_static (GST_TYPE_ELEMENT, "GstTextOverlay",
        &textoverlay_info, 0);
  }
  return textoverlay_type;
}

static void
gst_textoverlay_base_init (gpointer g_class)
{
  GstElementClass *element_class = GST_ELEMENT_CLASS (g_class);

  gst_element_class_add_pad_template (element_class,
      gst_static_pad_template_get (&textoverlay_src_template_factory));
  gst_element_class_add_pad_template (element_class,
      gst_static_pad_template_get (&video_sink_template_factory));
  gst_element_class_add_pad_template (element_class,
      gst_static_pad_template_get (&text_sink_template_factory));

  gst_element_class_set_details (element_class, &textoverlay_details);
}

static void
gst_textoverlay_class_init (GstTextOverlayClass * klass)
{
  GObjectClass *gobject_class;
  GstElementClass *gstelement_class;

  gobject_class = (GObjectClass *) klass;
  gstelement_class = (GstElementClass *) klass;

  parent_class = g_type_class_peek_parent (klass);

  gobject_class->finalize = gst_textoverlay_finalize;
  gobject_class->set_property = gst_textoverlay_set_property;
  gobject_class->get_property = gst_textoverlay_get_property;

  gstelement_class->change_state = gst_textoverlay_change_state;
  g_object_class_install_property (G_OBJECT_CLASS (klass), ARG_TEXT,
      g_param_spec_string ("text", "text",
          "Text to be display.", "", G_PARAM_WRITABLE));
  g_object_class_install_property (G_OBJECT_CLASS (klass), ARG_VALIGN,
      g_param_spec_string ("valign", "vertical alignment",
          "Vertical alignment of the text. "
          "Can be either 'baseline', 'bottom', or 'top'",
          "baseline", G_PARAM_WRITABLE));
  g_object_class_install_property (G_OBJECT_CLASS (klass), ARG_HALIGN,
      g_param_spec_string ("halign", "horizontal alignment",
          "Horizontal alignment of the text. "
          "Can be either 'left', 'right', or 'center'",
          "center", G_PARAM_WRITABLE));
  g_object_class_install_property (G_OBJECT_CLASS (klass), ARG_X0,
      g_param_spec_int ("x0", "X position",
          "Initial X position."
          " Horizontal aligment takes this point"
          " as reference.", G_MININT, G_MAXINT, 0, G_PARAM_WRITABLE));
  g_object_class_install_property (G_OBJECT_CLASS (klass), ARG_Y0,
      g_param_spec_int ("y0", "Y position",
          "Initial Y position."
          " Vertical aligment takes this point"
          " as reference.", G_MININT, G_MAXINT, 0, G_PARAM_WRITABLE));
  g_object_class_install_property (G_OBJECT_CLASS (klass), ARG_FONT_DESC,
      g_param_spec_string ("font-desc", "font description",
          "Pango font description of font "
          "to be used for rendering. "
          "See documentation of "
          "pango_font_description_from_string"
          " for syntax.", "", G_PARAM_WRITABLE));
}


#if 0
static void
resize_bitmap (GstTextOverlay * overlay, int width, int height)
{
  FT_Bitmap *bitmap = &overlay->bitmap;
  int pitch = (width | 3) + 1;
  int size = pitch * height;

  /* no need to keep reallocating; just keep the maximum size so far */
  if (size <= overlay->bitmap_buffer_size) {
    bitmap->rows = height;
    bitmap->width = width;
    bitmap->pitch = pitch;
    memset (bitmap->buffer, 0, overlay->bitmap_buffer_size);
    return;
  }
  if (!bitmap->buffer) {
    /* initialize */
    bitmap->pixel_mode = ft_pixel_mode_grays;
    bitmap->num_grays = 256;
  }
  if (bitmap->buffer)
    bitmap->buffer = g_realloc (bitmap->buffer, size);
  else
    bitmap->buffer = g_malloc (size);
  bitmap->rows = height;
  bitmap->width = width;
  bitmap->pitch = pitch;
  memset (bitmap->buffer, 0, size);
  overlay->bitmap_buffer_size = size;
}
#endif

static void
gst_textoverlay_render_text (GstTextOverlay * overlay, gchar * text,
    int textlen)
{
  cairo_text_extents_t extents;
  char *string;
  double x, y;

  string = g_strndup (text, textlen);

  if (overlay->text_fill_image)
    g_free (overlay->text_fill_image);
  overlay->text_fill_image =
      g_malloc (4 * overlay->width * overlay->text_height);
  cairo_set_target_image (overlay->cr, overlay->text_fill_image,
      CAIRO_FORMAT_ARGB32, overlay->width, overlay->text_height,
      overlay->width * 4);

  cairo_save (overlay->cr);
  cairo_rectangle (overlay->cr, 0, 0, overlay->width, overlay->text_height);
  cairo_set_rgb_color (overlay->cr, 0, 0, 0);
  cairo_set_alpha (overlay->cr, 1.0);
  cairo_set_operator (overlay->cr, CAIRO_OPERATOR_SRC);
  cairo_fill (overlay->cr);
  cairo_restore (overlay->cr);

  cairo_save (overlay->cr);
  cairo_text_extents (overlay->cr, string, &extents);
  cairo_set_rgb_color (overlay->cr, 1, 1, 1);
  cairo_set_alpha (overlay->cr, 1.0);
  switch (overlay->halign) {
    case GST_TEXT_OVERLAY_HALIGN_LEFT:
      x = overlay->x0;
      break;
    case GST_TEXT_OVERLAY_HALIGN_CENTER:
      x = overlay->x0 - extents.width / 2;
      break;
    case GST_TEXT_OVERLAY_HALIGN_RIGHT:
      x = overlay->x0 - extents.width;
      break;
    default:
      x = 0;
  }
  y = overlay->text_height - 2;
  cairo_move_to (overlay->cr, x, y);
  cairo_show_text (overlay->cr, string);
  cairo_restore (overlay->cr);

  if (overlay->text_outline_image)
    g_free (overlay->text_outline_image);
  overlay->text_outline_image =
      g_malloc (4 * overlay->width * overlay->text_height);
  cairo_set_target_image (overlay->cr, overlay->text_outline_image,
      CAIRO_FORMAT_ARGB32, overlay->width, overlay->text_height,
      overlay->width * 4);

  cairo_save (overlay->cr);
  cairo_rectangle (overlay->cr, 0, 0, overlay->width, overlay->text_height);
  cairo_set_rgb_color (overlay->cr, 0, 0, 0);
  cairo_set_alpha (overlay->cr, 1.0);
  cairo_set_operator (overlay->cr, CAIRO_OPERATOR_SRC);
  cairo_fill (overlay->cr);
  cairo_restore (overlay->cr);

  cairo_save (overlay->cr);
  cairo_move_to (overlay->cr, x, y);
  cairo_set_rgb_color (overlay->cr, 1, 1, 1);
  cairo_set_alpha (overlay->cr, 1.0);
  cairo_set_line_width (overlay->cr, 1.0);
  cairo_text_path (overlay->cr, string);
  cairo_stroke (overlay->cr);
  cairo_restore (overlay->cr);

  g_free (string);
}

/* static GstPadLinkReturn */
/* gst_textoverlay_text_sinkconnect (GstPad *pad, GstCaps *caps) */
/* { */
/*     return GST_PAD_LINK_DONE; */
/* } */


static GstPadLinkReturn
gst_textoverlay_video_sinkconnect (GstPad * pad, const GstCaps * caps)
{
  GstTextOverlay *overlay;
  GstStructure *structure;

  overlay = GST_TEXTOVERLAY (gst_pad_get_parent (pad));

  structure = gst_caps_get_structure (caps, 0);
  overlay->width = overlay->height = 0;
  gst_structure_get_int (structure, "width", &overlay->width);
  gst_structure_get_int (structure, "height", &overlay->height);

  return gst_pad_try_set_caps (overlay->srcpad, caps);
}


static void
gst_text_overlay_blit_1 (GstTextOverlay * overlay, guchar * dest,
    guchar * text_image, int val)
{
  int i;
  int j;
  int x, a, y;
  int y0 = 0;

  y = val;

  for (i = 0; i < overlay->text_height; i++) {
    for (j = 0; j < overlay->width; j++) {
      x = dest[(i + y0) * overlay->width + j];
      a = text_image[4 * (i * overlay->width + j) + 1];
      dest[(i + y0) * overlay->width + j] = (y * a + x * (255 - a)) / 255;
    }
  }
}

static void
gst_text_overlay_blit_sub2x2 (GstTextOverlay * overlay, guchar * dest,
    guchar * text_image, int val)
{
  int i;
  int j;
  int x, a, y;
  int y0 = 0;

  y = val;

  for (i = 0; i < overlay->text_height; i += 2) {
    for (j = 0; j < overlay->width; j += 2) {
      x = dest[(i / 2 + y0) * (overlay->width / 2) + j / 2];
      a = (text_image[4 * (i * overlay->width + j) + 1] +
          text_image[4 * (i * overlay->width + j + 1) + 1] +
          text_image[4 * ((i + 1) * overlay->width + j) + 1] +
          text_image[4 * ((i + 1) * overlay->width + j + 1) + 1] + 2) / 4;
      dest[(i / 2 + y0) * (overlay->width / 2) + j / 2] =
          (y * a + x * (255 - a)) / 255;
    }
  }
}


static void
gst_textoverlay_video_chain (GstPad * pad, GstData * _data)
{
  GstBuffer *buf = GST_BUFFER (_data);
  GstTextOverlay *overlay;
  guchar *pixbuf;
  gint y;

  g_return_if_fail (pad != NULL);
  g_return_if_fail (GST_IS_PAD (pad));
  g_return_if_fail (buf != NULL);
  overlay = GST_TEXTOVERLAY (gst_pad_get_parent (pad));
  g_return_if_fail (overlay != NULL);
  g_return_if_fail (GST_IS_TEXTOVERLAY (overlay));

  if (!GST_IS_BUFFER (_data))
    return;

  pixbuf = GST_BUFFER_DATA (buf);

  y = overlay->y0;
  switch (overlay->valign) {
    case GST_TEXT_OVERLAY_VALIGN_BOTTOM:
      y -= overlay->text_height;
      break;
    case GST_TEXT_OVERLAY_VALIGN_BASELINE:
#define BASELINE 2
      y -= (overlay->text_height - BASELINE);
      break;
    case GST_TEXT_OVERLAY_VALIGN_TOP:
      break;
  }

  gst_text_overlay_blit_1 (overlay,
      pixbuf + y * overlay->width, overlay->text_outline_image, 0);
  gst_text_overlay_blit_sub2x2 (overlay,
      pixbuf + (overlay->height * overlay->width) +
      (y / 2) * overlay->width / 2, overlay->text_outline_image, 128);
  gst_text_overlay_blit_sub2x2 (overlay, pixbuf +
      (overlay->height * overlay->width) +
      (overlay->height * overlay->width) / 4 + (y / 2) * overlay->width / 2,
      overlay->text_outline_image, 128);

  gst_text_overlay_blit_1 (overlay, pixbuf + y * overlay->width,
      overlay->text_fill_image, 255);
  gst_text_overlay_blit_sub2x2 (overlay,
      pixbuf + (overlay->height * overlay->width) +
      (y / 2) * overlay->width / 2, overlay->text_fill_image, 128);
  gst_text_overlay_blit_sub2x2 (overlay,
      pixbuf + (overlay->height * overlay->width) +
      (overlay->height * overlay->width) / 4 + (y / 2) * overlay->width / 2,
      overlay->text_fill_image, 128);

  gst_pad_push (overlay->srcpad, GST_DATA (buf));
}

#define PAST_END(buffer, time) \
  (GST_BUFFER_TIMESTAMP (buffer) != GST_CLOCK_TIME_NONE && \
   GST_BUFFER_DURATION (buffer) != GST_CLOCK_TIME_NONE && \
   GST_BUFFER_TIMESTAMP (buffer) + GST_BUFFER_DURATION (buffer) \
     < (time))

static void
gst_textoverlay_loop (GstElement * element)
{
  GstTextOverlay *overlay;
  GstBuffer *video_frame;
  guint64 now;

  g_return_if_fail (element != NULL);
  g_return_if_fail (GST_IS_TEXTOVERLAY (element));
  overlay = GST_TEXTOVERLAY (element);

  do {
    GST_DEBUG ("Attempting to pull next video frame");
    video_frame = GST_BUFFER (gst_pad_pull (overlay->video_sinkpad));
    if (GST_IS_EVENT (video_frame)) {
      GstEvent *event = GST_EVENT (video_frame);
      GstEventType type = GST_EVENT_TYPE (event);

      gst_pad_event_default (overlay->video_sinkpad, event);
      GST_DEBUG ("Received event of type %d", type);
      if (type == GST_EVENT_EOS || type == GST_EVENT_INTERRUPT)
        return;
      video_frame = NULL;
    }
  } while (!video_frame);
  now = GST_BUFFER_TIMESTAMP (video_frame);
  GST_DEBUG ("Got video frame, time=%" GST_TIME_FORMAT, GST_TIME_ARGS (now));

  /*
   * This state machine has a bug that can't be resolved easily.
   * (Needs a more complicated state machine.)  Basically, if the
   * text that came from a buffer from the sink pad is being
   * displayed, and the default text is changed by set_parameter,
   * we'll incorrectly display the default text.
   *
   * Otherwise, this is a pretty decent state machine that handles
   * buffer timestamps and durations correctly.  (I think)
   */

  while ((!overlay->current_buffer ||
          PAST_END (overlay->current_buffer, now)) &&
      overlay->next_buffer == NULL) {
    GST_DEBUG ("attempting to pull a buffer");

    /* read all text buffers until we get one "in the future" */
    if (!GST_PAD_IS_USABLE (overlay->text_sinkpad)) {
      break;
    }
    do {
      overlay->next_buffer = GST_BUFFER (gst_pad_pull (overlay->text_sinkpad));
      if (GST_IS_EVENT (overlay->next_buffer)) {
        GstEvent *event = GST_EVENT (overlay->next_buffer);
        GstEventType type = GST_EVENT_TYPE (event);

        gst_pad_event_default (overlay->text_sinkpad, event);
        if (type == GST_EVENT_EOS || type == GST_EVENT_INTERRUPT)
          return;
        overlay->next_buffer = NULL;
      }
    } while (!overlay->next_buffer);

    if (PAST_END (overlay->next_buffer, now)) {
      GST_DEBUG ("Received buffer is past end (%" GST_TIME_FORMAT " + %"
          GST_TIME_FORMAT " < %" GST_TIME_FORMAT ")",
          GST_TIME_ARGS (GST_BUFFER_TIMESTAMP (overlay->next_buffer)),
          GST_TIME_ARGS (GST_BUFFER_DURATION (overlay->next_buffer)),
          GST_TIME_ARGS (now));
      gst_buffer_unref (overlay->next_buffer);
      overlay->next_buffer = NULL;
    } else {
      GST_DEBUG ("Received new text buffer of time %" GST_TIME_FORMAT
          "and duration %" GST_TIME_FORMAT,
          GST_TIME_ARGS (GST_BUFFER_TIMESTAMP (overlay->next_buffer)),
          GST_TIME_ARGS (GST_BUFFER_DURATION (overlay->next_buffer)));
    }
  }

  if (overlay->next_buffer &&
      (GST_BUFFER_TIMESTAMP (overlay->next_buffer) <= now ||
          GST_BUFFER_TIMESTAMP (overlay->next_buffer) == GST_CLOCK_TIME_NONE)) {
    GST_DEBUG ("using new buffer");

    if (overlay->current_buffer) {
      gst_buffer_unref (overlay->current_buffer);
    }
    overlay->current_buffer = overlay->next_buffer;
    overlay->next_buffer = NULL;

    GST_DEBUG ("rendering '%*s'",
        GST_BUFFER_SIZE (overlay->current_buffer),
        GST_BUFFER_DATA (overlay->current_buffer));
    gst_textoverlay_render_text (overlay,
        GST_BUFFER_DATA (overlay->current_buffer),
        GST_BUFFER_SIZE (overlay->current_buffer));
    overlay->need_render = FALSE;
  }

  if (overlay->current_buffer && PAST_END (overlay->current_buffer, now)) {
    GST_DEBUG ("dropping old buffer");

    gst_buffer_unref (overlay->current_buffer);
    overlay->current_buffer = NULL;

    overlay->need_render = TRUE;
  }

  if (overlay->need_render) {
    GST_DEBUG ("rendering '%s'", overlay->default_text);
    gst_textoverlay_render_text (overlay,
        overlay->default_text, strlen (overlay->default_text));

    overlay->need_render = FALSE;
  }

  gst_textoverlay_video_chain (overlay->srcpad, GST_DATA (video_frame));
}

static void
gst_textoverlay_font_init (GstTextOverlay * overlay)
{
  cairo_font_extents_t font_extents;

  cairo_select_font (overlay->cr, overlay->font, overlay->slant,
      overlay->weight);
  cairo_scale_font (overlay->cr, overlay->scale);

  cairo_current_font_extents (overlay->cr, &font_extents);
  overlay->text_height = font_extents.height;
  if (overlay->text_height & 1)
    overlay->text_height++;

  overlay->need_render = TRUE;
}

static GstStateChangeReturn
gst_textoverlay_change_state (GstElement * element, GstStateChange transition)
{
  GstTextOverlay *overlay;

  overlay = GST_TEXTOVERLAY (element);

  switch (transition) {
    case GST_STATE_CHANGE_PAUSED_TO_PLAYING:
      break;
    case GST_STATE_CHANGE_PLAYING_TO_PAUSED:
      break;
    case GST_STATE_CHANGE_PAUSED_TO_READY:
      break;
  }

  parent_class->change_state (element, transition);

  return GST_STATE_CHANGE_SUCCESS;
}

static void
gst_textoverlay_finalize (GObject * object)
{
  GstTextOverlay *overlay = GST_TEXTOVERLAY (object);

  if (overlay->cr) {
    cairo_destroy (overlay->cr);
  }

  G_OBJECT_CLASS (parent_class)->finalize (object);
}

static void
gst_textoverlay_init (GstTextOverlay * overlay)
{
  /* video sink */
  overlay->video_sinkpad =
      gst_pad_new_from_template (gst_static_pad_template_get
      (&video_sink_template_factory), "video_sink");
  gst_pad_set_link_function (overlay->video_sinkpad,
      gst_textoverlay_video_sinkconnect);
  gst_element_add_pad (GST_ELEMENT (overlay), overlay->video_sinkpad);

  /* text sink */
  overlay->text_sinkpad =
      gst_pad_new_from_template (gst_static_pad_template_get
      (&text_sink_template_factory), "text_sink");
  gst_element_add_pad (GST_ELEMENT (overlay), overlay->text_sinkpad);

  /* (video) source */
  overlay->srcpad =
      gst_pad_new_from_template (gst_static_pad_template_get
      (&textoverlay_src_template_factory), "src");
  gst_element_add_pad (GST_ELEMENT (overlay), overlay->srcpad);

  overlay->cr = cairo_create ();

  overlay->halign = GST_TEXT_OVERLAY_HALIGN_CENTER;
  overlay->valign = GST_TEXT_OVERLAY_VALIGN_BASELINE;
  overlay->x0 = overlay->y0 = 25;

  overlay->default_text = g_strdup ("");
  overlay->need_render = TRUE;

  overlay->font = g_strdup ("sans");
  overlay->slant = CAIRO_FONT_SLANT_NORMAL;
  overlay->weight = CAIRO_FONT_WEIGHT_NORMAL;
  overlay->scale = 20;
  gst_textoverlay_font_init (overlay);

  gst_element_set_loop_function (GST_ELEMENT (overlay), gst_textoverlay_loop);
}

static void
gst_textoverlay_set_property (GObject * object, guint prop_id,
    const GValue * value, GParamSpec * pspec)
{
  GstTextOverlay *overlay;

  g_return_if_fail (GST_IS_TEXTOVERLAY (object));
  overlay = GST_TEXTOVERLAY (object);

  switch (prop_id) {

    case ARG_TEXT:
      if (overlay->default_text) {
        g_free (overlay->default_text);
      }
      overlay->default_text = g_strdup (g_value_get_string (value));
      overlay->need_render = TRUE;
      break;

    case ARG_VALIGN:
      if (strcasecmp (g_value_get_string (value), "baseline") == 0)
        overlay->valign = GST_TEXT_OVERLAY_VALIGN_BASELINE;
      else if (strcasecmp (g_value_get_string (value), "bottom") == 0)
        overlay->valign = GST_TEXT_OVERLAY_VALIGN_BOTTOM;
      else if (strcasecmp (g_value_get_string (value), "top") == 0)
        overlay->valign = GST_TEXT_OVERLAY_VALIGN_TOP;
      else
        g_warning ("Invalid 'valign' property value: %s",
            g_value_get_string (value));
      overlay->need_render = TRUE;
      break;

    case ARG_HALIGN:
      if (strcasecmp (g_value_get_string (value), "left") == 0)
        overlay->halign = GST_TEXT_OVERLAY_HALIGN_LEFT;
      else if (strcasecmp (g_value_get_string (value), "right") == 0)
        overlay->halign = GST_TEXT_OVERLAY_HALIGN_RIGHT;
      else if (strcasecmp (g_value_get_string (value), "center") == 0)
        overlay->halign = GST_TEXT_OVERLAY_HALIGN_CENTER;
      else
        g_warning ("Invalid 'halign' property value: %s",
            g_value_get_string (value));
      overlay->need_render = TRUE;
      break;

    case ARG_X0:
      overlay->x0 = g_value_get_int (value);
      break;

    case ARG_Y0:
      overlay->y0 = g_value_get_int (value);
      break;

    case ARG_FONT_DESC:
      if (overlay->font)
        g_free (overlay->font);
      overlay->font = g_strdup (g_value_get_string (value));
      gst_textoverlay_font_init (overlay);
      break;

    default:
      break;
  }
}

static void
gst_textoverlay_get_property (GObject * object, guint prop_id, GValue * value,
    GParamSpec * pspec)
{
  GstTextOverlay *overlay;

  g_return_if_fail (GST_IS_TEXTOVERLAY (object));
  overlay = GST_TEXTOVERLAY (object);

  switch (prop_id) {
    default:
      G_OBJECT_WARN_INVALID_PROPERTY_ID (object, prop_id, pspec);
      break;
  }
}