glvideomixer: add a background property

That's compatible with the compositor/videomixer property

https://bugzilla.gnome.org/show_bug.cgi?id=731954

ext/gl/gstglvideomixer.c

@@ -47,7 +47,9 @@ 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");
@@ -69,6 +71,7 @@ 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"
@@ -93,6 +96,38 @@ static const gchar *video_mixer_f_src =
     "  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))
@@ -247,6 +282,28 @@ gst_gl_video_mixer_pad_set_property (GObject * object, guint prop_id,
   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)
 {
@@ -265,6 +322,11 @@ gst_gl_video_mixer_class_init (GstGLVideoMixerClass * klass)
       "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 =
@@ -278,6 +340,7 @@ gst_gl_video_mixer_class_init (GstGLVideoMixerClass * klass)
 static void
 gst_gl_video_mixer_init (GstGLVideoMixer * video_mixer)
 {
+  video_mixer->background = DEFAULT_BACKGROUND;
   video_mixer->shader = NULL;
   video_mixer->input_frames = NULL;
 }
@@ -286,7 +349,12 @@ 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;
@@ -297,7 +365,12 @@ 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;
@@ -360,6 +433,10 @@ gst_gl_video_mixer_reset (GstGLMixer * mixer)
   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
@@ -391,6 +468,76 @@ gst_gl_video_mixer_process_textures (GstGLMixer * mix, GPtrArray * frames,
   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* */
+
+  attr_position_loc =
+      gst_gl_shader_get_attribute_location (video_mixer->shader, "a_position");
+
+  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);
+
+  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)
@@ -420,8 +567,8 @@ gst_gl_video_mixer_callback (gpointer stuff)
   gl->Disable (GL_DEPTH_TEST);
   gl->Disable (GL_CULL_FACE);
 
-  gl->ClearColor (0.0, 0.0, 0.0, 0.0);
-  gl->Clear (GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
+  if (!_draw_background (video_mixer))
+    return;
 
   gst_gl_shader_use (video_mixer->shader);
 

ext/gl/gstglvideomixer.h

@@ -36,11 +36,32 @@ G_BEGIN_DECLS
 typedef struct _GstGLVideoMixer GstGLVideoMixer;
 typedef struct _GstGLVideoMixerClass GstGLVideoMixerClass;
 
+/**
+ * GstGLVideoMixerBackground:
+ * @GST_GL_VIDEO_MIXER_BACKGROUND_CHECKER: checker pattern background
+ * @GST_GL_VIDEO_MIXER_BACKGROUND_BLACK: solid color black background
+ * @GST_GL_VIDEO_MIXER_BACKGROUND_WHITE: solid color white background
+ * @GST_GL_VIDEO_MIXER_BACKGROUND_TRANSPARENT: background is left transparent and layers are composited using "A OVER B" composition rules. This is only applicable to AYUV and ARGB (and variants) as it preserves the alpha channel and allows for further mixing.
+ *
+ * The different backgrounds compositor can blend over.
+ */
+typedef enum
+{
+  GST_GL_VIDEO_MIXER_BACKGROUND_CHECKER,
+  GST_GL_VIDEO_MIXER_BACKGROUND_BLACK,
+  GST_GL_VIDEO_MIXER_BACKGROUND_WHITE,
+  GST_GL_VIDEO_MIXER_BACKGROUND_TRANSPARENT,
+}
+GstGLVideoMixerBackground;
+
 struct _GstGLVideoMixer
 {
     GstGLMixer mixer;
 
+    GstGLVideoMixerBackground background;
+
     GstGLShader *shader;
+    GstGLShader *checker;
     GPtrArray *input_frames;
 };