gstreamer/ext/gl/gstglvideomixer.c

/*
 * GStreamer
 * Copyright (C) 2009 Julien Isorce <julien.isorce@gmail.com>
 *
 * 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., 51 Franklin St, Fifth Floor,
 * Boston, MA 02110-1301, USA.
 */

/**
 * SECTION:element-glvideomixer
 *
 * Composites a number of streams into a single output scene using OpenGL in
 * a similar fashion to compositor and videomixer.
 *
 * <refsect2>
 * <title>Examples</title>
 * |[
 * gst-launch-1.0  glvideomixer name=m ! glimagesink \
 *     videotestsrc ! video/x-raw, format=YUY2 ! m. \
 *     videotestsrc pattern=12 ! video/x-raw, format=I420, framerate=5/1, width=100, height=200 ! queue ! m. \
 *     videotestsrc ! video/x-raw, format=RGB, framerate=15/1, width=1500, height=1500 ! gleffects effect=3 ! queue ! m. \
 *     videotestsrc ! gleffects effect=2 ! queue ! m.  \
 *     videotestsrc ! glfiltercube ! queue ! m. \
 *     videotestsrc ! gleffects effect=6 ! queue ! m.
 * ]|
 * </refsect2>
 */

#ifdef HAVE_CONFIG_H
#include "config.h"
#endif

#include "gstglvideomixer.h"

#define GST_CAT_DEFAULT gst_gl_video_mixer_debug
GST_DEBUG_CATEGORY_STATIC (GST_CAT_DEFAULT);

enum
{
  PROP_0,
  PROP_BACKGROUND,
};
#define DEFAULT_BACKGROUND GST_GL_VIDEO_MIXER_BACKGROUND_CHECKER

#define DEBUG_INIT \
    GST_DEBUG_CATEGORY_INIT (gst_gl_video_mixer_debug, "glvideomixer", 0, "glvideomixer element");

G_DEFINE_TYPE_WITH_CODE (GstGLVideoMixer, gst_gl_video_mixer, GST_TYPE_GL_MIXER,
    DEBUG_INIT);

static void gst_gl_video_mixer_set_property (GObject * object, guint prop_id,
    const GValue * value, GParamSpec * pspec);
static void gst_gl_video_mixer_get_property (GObject * object, guint prop_id,
    GValue * value, GParamSpec * pspec);

static gboolean _update_info (GstVideoAggregator * vagg, GstVideoInfo * info);
static void gst_gl_video_mixer_reset (GstGLMixer * mixer);
static gboolean gst_gl_video_mixer_init_shader (GstGLMixer * mixer,
    GstCaps * outcaps);

static gboolean gst_gl_video_mixer_process_textures (GstGLMixer * mixer,
    GPtrArray * in_frames, guint out_tex);
static void gst_gl_video_mixer_callback (gpointer stuff);

/* *INDENT-OFF* */
/* vertex source */
static const gchar *video_mixer_v_src =
    "attribute vec4 a_position;                                   \n"
    "attribute vec2 a_texCoord;                                   \n"
    "varying vec2 v_texCoord;                                     \n"
    "void main()                                                  \n"
    "{                                                            \n"
    "   gl_Position = a_position;                                 \n"
    "   v_texCoord = a_texCoord;                                  \n" "}";

/* fragment source */
static const gchar *video_mixer_f_src =
    "#ifdef GL_ES\n"
    "precision mediump float;\n"
    "#endif\n"
    "uniform sampler2D texture;                     \n"
    "uniform float alpha;\n"
    "varying vec2 v_texCoord;                            \n"
    "void main()                                         \n"
    "{                                                   \n"
    "  vec4 rgba = texture2D( texture, v_texCoord );\n"
    "  gl_FragColor = vec4(rgba.rgb, rgba.a * alpha);\n"
    "}                                                   \n";

/* checker vertex source */
static const gchar *checker_v_src =
    "attribute vec4 a_position;\n"
    "void main()\n"
    "{\n"
    "   gl_Position = a_position;\n"
    "}\n";

/* checker fragment source */
static const gchar *checker_f_src =
    "#ifdef GL_ES\n"
    "precision mediump float;\n"
    "#endif\n"
    "const float blocksize = 8.0;\n"
    "void main ()\n"
    "{\n"
    "  vec4 high = vec4(0.667, 0.667, 0.667, 1.0);\n"
    "  vec4 low = vec4(0.333, 0.333, 0.333, 1.0);\n"
    "  if (mod(gl_FragCoord.x, blocksize * 2.0) >= blocksize) {\n"
    "    if (mod(gl_FragCoord.y, blocksize * 2.0) >= blocksize)\n"
    "      gl_FragColor = low;\n"
    "    else\n"
    "      gl_FragColor = high;\n"
    "  } else {\n"
    "    if (mod(gl_FragCoord.y, blocksize * 2.0) < blocksize)\n"
    "      gl_FragColor = low;\n"
    "    else\n"
    "      gl_FragColor = high;\n"
    "  }\n"
    "}\n";
/* *INDENT-ON* */

#define GST_TYPE_GL_VIDEO_MIXER_PAD (gst_gl_video_mixer_pad_get_type())
#define GST_GL_VIDEO_MIXER_PAD(obj) \
        (G_TYPE_CHECK_INSTANCE_CAST((obj),GST_TYPE_GL_VIDEO_MIXER_PAD, GstGLVideoMixerPad))
#define GST_GL_VIDEO_MIXER_PAD_CLASS(klass) \
        (G_TYPE_CHECK_CLASS_CAST((klass),GST_TYPE_GL_VIDEO_MIXER_PAD, GstGLVideoMixerPadClass))
#define GST_IS_GL_VIDEO_MIXER_PAD(obj) \
        (G_TYPE_CHECK_INSTANCE_TYPE((obj),GST_TYPE_GL_VIDEO_MIXER_PAD))
#define GST_IS_GL_VIDEO_MIXER_PAD_CLASS(klass) \
        (G_TYPE_CHECK_CLASS_TYPE((klass),GST_TYPE_GL_VIDEO_MIXER_PAD))

typedef struct _GstGLVideoMixerPad GstGLVideoMixerPad;
typedef struct _GstGLVideoMixerPadClass GstGLVideoMixerPadClass;
typedef struct _GstGLVideoMixerCollect GstGLVideoMixerCollect;

/**
 * GstGLVideoMixerPad:
 *
 * The opaque #GstGLVideoMixerPad structure.
 */
struct _GstGLVideoMixerPad
{
  GstGLMixerPad parent;

  /* < private > */
  /* properties */
  gint xpos, ypos;
  gint width, height;
  gdouble alpha;
};

struct _GstGLVideoMixerPadClass
{
  GstGLMixerPadClass parent_class;
};

GType gst_gl_video_mixer_pad_get_type (void);
G_DEFINE_TYPE (GstGLVideoMixerPad, gst_gl_video_mixer_pad,
    GST_TYPE_GL_MIXER_PAD);

static void gst_gl_video_mixer_pad_set_property (GObject * object,
    guint prop_id, const GValue * value, GParamSpec * pspec);
static void gst_gl_video_mixer_pad_get_property (GObject * object,
    guint prop_id, GValue * value, GParamSpec * pspec);

#define DEFAULT_PAD_XPOS   0
#define DEFAULT_PAD_YPOS   0
#define DEFAULT_PAD_WIDTH  0
#define DEFAULT_PAD_HEIGHT 0
#define DEFAULT_PAD_ALPHA  1.0
enum
{
  PROP_PAD_0,
  PROP_PAD_XPOS,
  PROP_PAD_YPOS,
  PROP_PAD_WIDTH,
  PROP_PAD_HEIGHT,
  PROP_PAD_ALPHA
};

static void
gst_gl_video_mixer_pad_init (GstGLVideoMixerPad * pad)
{
  pad->alpha = 1.0;
}

static void
gst_gl_video_mixer_pad_class_init (GstGLVideoMixerPadClass * klass)
{
  GObjectClass *gobject_class = (GObjectClass *) klass;

  gobject_class->set_property = gst_gl_video_mixer_pad_set_property;
  gobject_class->get_property = gst_gl_video_mixer_pad_get_property;

  g_object_class_install_property (gobject_class, PROP_PAD_XPOS,
      g_param_spec_int ("xpos", "X Position", "X Position of the picture",
          G_MININT, G_MAXINT, DEFAULT_PAD_XPOS,
          G_PARAM_READWRITE | GST_PARAM_CONTROLLABLE | G_PARAM_STATIC_STRINGS));
  g_object_class_install_property (gobject_class, PROP_PAD_YPOS,
      g_param_spec_int ("ypos", "Y Position", "Y Position of the picture",
          G_MININT, G_MAXINT, DEFAULT_PAD_YPOS,
          G_PARAM_READWRITE | GST_PARAM_CONTROLLABLE | G_PARAM_STATIC_STRINGS));
  g_object_class_install_property (gobject_class, PROP_PAD_WIDTH,
      g_param_spec_int ("width", "Width", "Width of the picture",
          G_MININT, G_MAXINT, DEFAULT_PAD_WIDTH,
          G_PARAM_READWRITE | GST_PARAM_CONTROLLABLE | G_PARAM_STATIC_STRINGS));
  g_object_class_install_property (gobject_class, PROP_PAD_HEIGHT,
      g_param_spec_int ("height", "Height", "Height of the picture",
          G_MININT, G_MAXINT, DEFAULT_PAD_HEIGHT,
          G_PARAM_READWRITE | GST_PARAM_CONTROLLABLE | G_PARAM_STATIC_STRINGS));
  g_object_class_install_property (gobject_class, PROP_PAD_ALPHA,
      g_param_spec_double ("alpha", "Alpha", "Alpha of the picture", 0.0, 1.0,
          DEFAULT_PAD_ALPHA,
          G_PARAM_READWRITE | GST_PARAM_CONTROLLABLE | G_PARAM_STATIC_STRINGS));
}

static void
gst_gl_video_mixer_pad_get_property (GObject * object, guint prop_id,
    GValue * value, GParamSpec * pspec)
{
  GstGLVideoMixerPad *pad = GST_GL_VIDEO_MIXER_PAD (object);

  switch (prop_id) {
    case PROP_PAD_XPOS:
      g_value_set_int (value, pad->xpos);
      break;
    case PROP_PAD_YPOS:
      g_value_set_int (value, pad->ypos);
      break;
    case PROP_PAD_WIDTH:
      g_value_set_int (value, pad->width);
      break;
    case PROP_PAD_HEIGHT:
      g_value_set_int (value, pad->height);
      break;
    case PROP_PAD_ALPHA:
      g_value_set_double (value, pad->alpha);
      break;
    default:
      G_OBJECT_WARN_INVALID_PROPERTY_ID (object, prop_id, pspec);
      break;
  }
}

static void
gst_gl_video_mixer_pad_set_property (GObject * object, guint prop_id,
    const GValue * value, GParamSpec * pspec)
{
  GstGLVideoMixerPad *pad = GST_GL_VIDEO_MIXER_PAD (object);
  GstGLMixer *mix = GST_GL_MIXER (gst_pad_get_parent (GST_PAD (pad)));

  switch (prop_id) {
    case PROP_PAD_XPOS:
      pad->xpos = g_value_get_int (value);
      break;
    case PROP_PAD_YPOS:
      pad->ypos = g_value_get_int (value);
      break;
    case PROP_PAD_WIDTH:
      pad->width = g_value_get_int (value);
      break;
    case PROP_PAD_HEIGHT:
      pad->height = g_value_get_int (value);
      break;
    case PROP_PAD_ALPHA:
      pad->alpha = g_value_get_double (value);
      break;
    default:
      G_OBJECT_WARN_INVALID_PROPERTY_ID (object, prop_id, pspec);
      break;
  }

  gst_object_unref (mix);
}

#define GST_GL_TYPE_VIDEO_MIXER_BACKGROUND (gst_gl_video_mixer_background_get_type())
static GType
gst_gl_video_mixer_background_get_type (void)
{
  static GType mixer_background_type = 0;

  static const GEnumValue mixer_background[] = {
    {GST_GL_VIDEO_MIXER_BACKGROUND_CHECKER, "Checker pattern", "checker"},
    {GST_GL_VIDEO_MIXER_BACKGROUND_BLACK, "Black", "black"},
    {GST_GL_VIDEO_MIXER_BACKGROUND_WHITE, "White", "white"},
    {GST_GL_VIDEO_MIXER_BACKGROUND_TRANSPARENT,
        "Transparent Background to enable further compositing", "transparent"},
    {0, NULL, NULL},
  };

  if (!mixer_background_type) {
    mixer_background_type =
        g_enum_register_static ("GstGLVideoMixerBackground", mixer_background);
  }
  return mixer_background_type;
}

static void
gst_gl_video_mixer_class_init (GstGLVideoMixerClass * klass)
{
  GObjectClass *gobject_class;
  GstElementClass *element_class;
  GstAggregatorClass *agg_class = (GstAggregatorClass *) klass;
  GstVideoAggregatorClass *vagg_class = (GstVideoAggregatorClass *) klass;

  gobject_class = (GObjectClass *) klass;
  element_class = GST_ELEMENT_CLASS (klass);

  gobject_class->set_property = gst_gl_video_mixer_set_property;
  gobject_class->get_property = gst_gl_video_mixer_get_property;

  gst_element_class_set_metadata (element_class, "OpenGL video_mixer",
      "Filter/Effect/Video/Compositor", "OpenGL video_mixer",
      "Julien Isorce <julien.isorce@gmail.com>");

  g_object_class_install_property (gobject_class, PROP_BACKGROUND,
      g_param_spec_enum ("background", "Background", "Background type",
          GST_GL_TYPE_VIDEO_MIXER_BACKGROUND,
          DEFAULT_BACKGROUND, G_PARAM_READWRITE | G_PARAM_STATIC_STRINGS));

  GST_GL_MIXER_CLASS (klass)->set_caps = gst_gl_video_mixer_init_shader;
  GST_GL_MIXER_CLASS (klass)->reset = gst_gl_video_mixer_reset;
  GST_GL_MIXER_CLASS (klass)->process_textures =
      gst_gl_video_mixer_process_textures;

  vagg_class->update_info = _update_info;

  agg_class->sinkpads_type = GST_TYPE_GL_VIDEO_MIXER_PAD;
}

static void
gst_gl_video_mixer_init (GstGLVideoMixer * video_mixer)
{
  video_mixer->background = DEFAULT_BACKGROUND;
  video_mixer->shader = NULL;
  video_mixer->input_frames = NULL;
}

static void
gst_gl_video_mixer_set_property (GObject * object, guint prop_id,
    const GValue * value, GParamSpec * pspec)
{
  GstGLVideoMixer *mixer = GST_GL_VIDEO_MIXER (object);

  switch (prop_id) {
    case PROP_BACKGROUND:
      mixer->background = g_value_get_enum (value);
      break;
    default:
      G_OBJECT_WARN_INVALID_PROPERTY_ID (object, prop_id, pspec);
      break;
  }
}

static void
gst_gl_video_mixer_get_property (GObject * object, guint prop_id,
    GValue * value, GParamSpec * pspec)
{
  GstGLVideoMixer *mixer = GST_GL_VIDEO_MIXER (object);

  switch (prop_id) {
    case PROP_BACKGROUND:
      g_value_set_enum (value, mixer->background);
      break;
    default:
      G_OBJECT_WARN_INVALID_PROPERTY_ID (object, prop_id, pspec);
      break;
  }
}

static gboolean
_update_info (GstVideoAggregator * vagg, GstVideoInfo * info)
{
  GList *l;
  gint best_width = -1, best_height = -1;
  gboolean ret = FALSE;

  GST_OBJECT_LOCK (vagg);
  for (l = GST_ELEMENT (vagg)->sinkpads; l; l = l->next) {
    GstVideoAggregatorPad *vaggpad = l->data;
    GstGLVideoMixerPad *mixer_pad = GST_GL_VIDEO_MIXER_PAD (vaggpad);
    gint this_width, this_height;
    gint width, height;

    if (mixer_pad->width > 0)
      width = mixer_pad->width;
    else
      width = GST_VIDEO_INFO_WIDTH (&vaggpad->info);

    if (mixer_pad->height > 0)
      height = mixer_pad->height;
    else
      height = GST_VIDEO_INFO_HEIGHT (&vaggpad->info);

    if (width == 0 || height == 0)
      continue;

    this_width = width + MAX (mixer_pad->xpos, 0);
    this_height = height + MAX (mixer_pad->ypos, 0);

    if (best_width < this_width)
      best_width = this_width;
    if (best_height < this_height)
      best_height = this_height;
  }
  GST_OBJECT_UNLOCK (vagg);

  if (best_width > 0 && best_height > 0) {
    info->width = best_width;
    info->height = best_height;
    ret = TRUE;
  }

  return ret;
}

static void
gst_gl_video_mixer_reset (GstGLMixer * mixer)
{
  GstGLVideoMixer *video_mixer = GST_GL_VIDEO_MIXER (mixer);

  video_mixer->input_frames = NULL;

  if (video_mixer->shader)
    gst_gl_context_del_shader (mixer->context, video_mixer->shader);
  video_mixer->shader = NULL;

  if (video_mixer->checker)
    gst_gl_context_del_shader (mixer->context, video_mixer->checker);
  video_mixer->checker = NULL;
}

static gboolean
gst_gl_video_mixer_init_shader (GstGLMixer * mixer, GstCaps * outcaps)
{
  GstGLVideoMixer *video_mixer = GST_GL_VIDEO_MIXER (mixer);

  if (video_mixer->shader)
    gst_gl_context_del_shader (mixer->context, video_mixer->shader);

  return gst_gl_context_gen_shader (mixer->context, video_mixer_v_src,
      video_mixer_f_src, &video_mixer->shader);
}

static gboolean
gst_gl_video_mixer_process_textures (GstGLMixer * mix, GPtrArray * frames,
    guint out_tex)
{
  GstGLVideoMixer *video_mixer = GST_GL_VIDEO_MIXER (mix);

  video_mixer->input_frames = frames;

  gst_gl_context_use_fbo_v2 (mix->context,
      GST_VIDEO_INFO_WIDTH (&GST_VIDEO_AGGREGATOR (mix)->info),
      GST_VIDEO_INFO_HEIGHT (&GST_VIDEO_AGGREGATOR (mix)->info),
      mix->fbo, mix->depthbuffer,
      out_tex, gst_gl_video_mixer_callback, (gpointer) video_mixer);

  return TRUE;
}

static gboolean
_draw_checker_background (GstGLVideoMixer * video_mixer)
{
  GstGLMixer *mixer = GST_GL_MIXER (video_mixer);
  const GstGLFuncs *gl = mixer->context->gl_vtable;
  gint attr_position_loc = 0;

  const GLushort indices[] = {
    0, 1, 2,
    0, 2, 3
  };
  /* *INDENT-OFF* */
  gfloat v_vertices[] = {
    -1.0,-1.0,-1.0f,
     1.0,-1.0,-1.0f,
     1.0, 1.0,-1.0f,
    -1.0, 1.0,-1.0f,
  };
  /* *INDENT-ON* */

  if (!video_mixer->checker) {
    if (!gst_gl_context_gen_shader (mixer->context, checker_v_src,
            checker_f_src, &video_mixer->checker))
      return FALSE;
  }

  gst_gl_shader_use (video_mixer->checker);
  attr_position_loc =
      gst_gl_shader_get_attribute_location (video_mixer->checker, "a_position");

  gl->VertexAttribPointer (attr_position_loc, 3, GL_FLOAT,
      GL_FALSE, 3 * sizeof (GLfloat), &v_vertices[0]);

  gl->EnableVertexAttribArray (attr_position_loc);

  gl->DrawElements (GL_TRIANGLES, 6, GL_UNSIGNED_SHORT, indices);

  return TRUE;
}

static gboolean
_draw_background (GstGLVideoMixer * video_mixer)
{
  GstGLMixer *mixer = GST_GL_MIXER (video_mixer);
  const GstGLFuncs *gl = mixer->context->gl_vtable;

  switch (video_mixer->background) {
    case GST_GL_VIDEO_MIXER_BACKGROUND_BLACK:
      gl->ClearColor (0.0, 0.0, 0.0, 1.0);
      gl->Clear (GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
      break;
    case GST_GL_VIDEO_MIXER_BACKGROUND_WHITE:
      gl->ClearColor (1.0, 1.0, 1.0, 1.0);
      gl->Clear (GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
      break;
    case GST_GL_VIDEO_MIXER_BACKGROUND_TRANSPARENT:
      gl->ClearColor (0.0, 0.0, 0.0, 0.0);
      gl->Clear (GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
      break;
    case GST_GL_VIDEO_MIXER_BACKGROUND_CHECKER:
      return _draw_checker_background (video_mixer);
      break;
    default:
      break;
  }

  return TRUE;
}

/* opengl scene, params: input texture (not the output mixer->texture) */
static void
gst_gl_video_mixer_callback (gpointer stuff)
{
  GstGLVideoMixer *video_mixer = GST_GL_VIDEO_MIXER (stuff);
  GstGLMixer *mixer = GST_GL_MIXER (video_mixer);
  GstGLFuncs *gl = mixer->context->gl_vtable;

  GLint attr_position_loc = 0;
  GLint attr_texture_loc = 0;
  guint out_width, out_height;

  const GLushort indices[] = {
    0, 1, 2,
    0, 2, 3
  };

  guint count = 0;

  out_width = GST_VIDEO_INFO_WIDTH (&GST_VIDEO_AGGREGATOR (stuff)->info);
  out_height = GST_VIDEO_INFO_HEIGHT (&GST_VIDEO_AGGREGATOR (stuff)->info);

  gst_gl_context_clear_shader (mixer->context);
  gl->BindTexture (GL_TEXTURE_2D, 0);
  gl->Disable (GL_TEXTURE_2D);

  gl->Disable (GL_DEPTH_TEST);
  gl->Disable (GL_CULL_FACE);

  if (!_draw_background (video_mixer))
    return;

  gst_gl_shader_use (video_mixer->shader);

  attr_position_loc =
      gst_gl_shader_get_attribute_location (video_mixer->shader, "a_position");
  attr_texture_loc =
      gst_gl_shader_get_attribute_location (video_mixer->shader, "a_texCoord");

  gl->Enable (GL_BLEND);

  while (count < video_mixer->input_frames->len) {
    GstGLMixerFrameData *frame;
    GstGLVideoMixerPad *pad;
    /* *INDENT-OFF* */
    gfloat v_vertices[] = {
      /* front face */
      -1.0,-1.0,-1.0f, 0.0f, 0.0f,
       1.0,-1.0,-1.0f, 1.0f, 0.0f,
       1.0, 1.0,-1.0f, 1.0f, 1.0f,
      -1.0, 1.0,-1.0f, 0.0f, 1.0f,
    };
    /* *INDENT-ON* */
    guint in_tex;
    guint in_width, in_height;
    guint pad_width, pad_height;
    gfloat w, h;

    frame = g_ptr_array_index (video_mixer->input_frames, count);
    if (!frame) {
      GST_DEBUG ("skipping texture, null frame");
      count++;
      continue;
    }
    pad = (GstGLVideoMixerPad *) frame->pad;
    in_width = GST_VIDEO_INFO_WIDTH (&GST_VIDEO_AGGREGATOR_PAD (pad)->info);
    in_height = GST_VIDEO_INFO_HEIGHT (&GST_VIDEO_AGGREGATOR_PAD (pad)->info);

    if (!frame->texture || in_width <= 0 || in_height <= 0
        || pad->alpha == 0.0f) {
      GST_DEBUG ("skipping texture:%u frame:%p width:%u height:%u alpha:%f",
          frame->texture, frame, in_width, in_height, pad->alpha);
      count++;
      continue;
    }

    in_tex = frame->texture;
    pad_width = pad->width <= 0 ? in_width : pad->width;
    pad_height = pad->height <= 0 ? in_height : pad->height;

    w = ((gfloat) pad_width / (gfloat) out_width);
    h = ((gfloat) pad_height / (gfloat) out_height);

    /* top-left */
    v_vertices[0] = v_vertices[15] =
        2.0f * (gfloat) pad->xpos / (gfloat) out_width - 1.0f;
    /* bottom-left */
    v_vertices[1] = v_vertices[6] =
        2.0f * (gfloat) pad->ypos / (gfloat) out_height - 1.0f;
    /* top-right */
    v_vertices[5] = v_vertices[10] = v_vertices[0] + 2.0f * w;
    /* bottom-right */
    v_vertices[11] = v_vertices[16] = v_vertices[1] + 2.0f * h;
    GST_TRACE ("processing texture:%u dimensions:%ux%u, at %f,%f %fx%f with "
        "alpha:%f", in_tex, in_width, in_height, v_vertices[0], v_vertices[1],
        v_vertices[5], v_vertices[11], pad->alpha);

    gl->VertexAttribPointer (attr_position_loc, 3, GL_FLOAT,
        GL_FALSE, 5 * sizeof (GLfloat), &v_vertices[0]);

    gl->VertexAttribPointer (attr_texture_loc, 2, GL_FLOAT,
        GL_FALSE, 5 * sizeof (GLfloat), &v_vertices[3]);

    gl->EnableVertexAttribArray (attr_position_loc);
    gl->EnableVertexAttribArray (attr_texture_loc);

    gl->BlendFunc (GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
    gl->BlendEquation (GL_FUNC_ADD);

    gl->ActiveTexture (GL_TEXTURE0);
    gl->BindTexture (GL_TEXTURE_2D, in_tex);
    gst_gl_shader_set_uniform_1i (video_mixer->shader, "texture", 0);
    gst_gl_shader_set_uniform_1f (video_mixer->shader, "alpha", pad->alpha);

    gl->DrawElements (GL_TRIANGLES, 6, GL_UNSIGNED_SHORT, indices);

    ++count;
  }

  gl->DisableVertexAttribArray (attr_position_loc);
  gl->DisableVertexAttribArray (attr_texture_loc);

  gl->BindTexture (GL_TEXTURE_2D, 0);

  gl->Disable (GL_BLEND);

  gst_gl_context_clear_shader (mixer->context);
}