glshaderelement: implement on-demand create-shader signalling

One may not have an GstGLContext available or current in the thread where one
would need to update the shader.  Support this by signalling create-shader
whenever the one-shot 'update-shader' is set to TRUE.

ext/gl/gstglfiltershader.c

@@ -47,6 +47,7 @@ enum
   PROP_SHADER,
   PROP_VERTEX,
   PROP_FRAGMENT,
+  PROP_UPDATE_SHADER,
   PROP_LAST,
 };
 
@@ -111,6 +112,20 @@ gst_gl_filtershader_class_init (GstGLFilterShaderClass * klass)
           G_PARAM_READWRITE | G_PARAM_STATIC_STRINGS));
   /* FIXME: add other stages */
 
+  g_object_class_install_property (gobject_class, PROP_UPDATE_SHADER,
+      g_param_spec_boolean ("update-shader", "Update Shader",
+          "Emit the \'create-shader\' signal for the next frame",
+          FALSE, G_PARAM_WRITABLE | G_PARAM_STATIC_STRINGS));
+
+  /*
+   * GstGLFilterShader::create-shader:
+   * @object: the #GstGLFilterShader
+   *
+   * Ask's the application for a shader to render with as a result of
+   * inititialization or setting the 'update-shader' property.
+   *
+   * Returns: a new #GstGLShader for use in the rendering pipeline
+   */
   gst_gl_shader_signals[SIGNAL_CREATE_SHADER] =
       g_signal_new ("create-shader", G_TYPE_FROM_CLASS (klass),
       G_SIGNAL_RUN_LAST, 0, NULL, NULL, g_cclosure_marshal_generic,
@@ -139,13 +154,6 @@ gst_gl_filtershader_init (GstGLFilterShader * filtershader)
 static void
 gst_gl_filtershader_finalize (GObject * object)
 {
-  GstGLFilterShader *filtershader = GST_GL_FILTERSHADER (object);
-
-  if (filtershader->shader_prop) {
-    gst_object_unref (filtershader->shader_prop);
-    filtershader->shader_prop = NULL;
-  }
-
   G_OBJECT_CLASS (gst_gl_filtershader_parent_class)->finalize (object);
 }
 
@@ -158,9 +166,9 @@ gst_gl_filtershader_set_property (GObject * object, guint prop_id,
   switch (prop_id) {
     case PROP_SHADER:
       GST_OBJECT_LOCK (filtershader);
-      gst_object_replace ((GstObject **) & filtershader->shader_prop,
+      gst_object_replace ((GstObject **) & filtershader->shader,
           g_value_dup_object (value));
-      filtershader->new_source = TRUE;
+      filtershader->new_source = FALSE;
       GST_OBJECT_UNLOCK (filtershader);
       break;
     case PROP_VERTEX:
@@ -179,6 +187,11 @@ gst_gl_filtershader_set_property (GObject * object, guint prop_id,
       filtershader->new_source = TRUE;
       GST_OBJECT_UNLOCK (filtershader);
       break;
+    case PROP_UPDATE_SHADER:
+      GST_OBJECT_LOCK (filtershader);
+      filtershader->update_shader = g_value_get_boolean (value);
+      GST_OBJECT_UNLOCK (filtershader);
+      break;
     default:
       G_OBJECT_WARN_INVALID_PROPERTY_ID (object, prop_id, pspec);
       break;
@@ -194,7 +207,7 @@ gst_gl_filtershader_get_property (GObject * object, guint prop_id,
   switch (prop_id) {
     case PROP_SHADER:
       GST_OBJECT_LOCK (filtershader);
-      g_value_set_object (value, filtershader->shader_prop);
+      g_value_set_object (value, filtershader->shader);
       GST_OBJECT_UNLOCK (filtershader);
       break;
     case PROP_VERTEX:
@@ -292,22 +305,29 @@ _maybe_recompile_shader (GstGLFilterShader * filtershader)
 
   GST_OBJECT_LOCK (filtershader);
 
-  if (filtershader->shader_prop) {
-    shader = gst_object_ref (filtershader->shader_prop);
+  if (!filtershader->shader || filtershader->update_shader) {
+    filtershader->update_shader = FALSE;
     GST_OBJECT_UNLOCK (filtershader);
-    return shader;
-  }
-  if (!filtershader->shader) {
     g_signal_emit (filtershader, gst_gl_shader_signals[SIGNAL_CREATE_SHADER], 0,
-        &filtershader->shader);
-    if (filtershader->shader) {
+        &shader);
+    GST_OBJECT_LOCK (filtershader);
+
+    if (shader) {
+      if (filtershader->shader)
+        gst_object_unref (filtershader->shader);
       filtershader->new_source = FALSE;
-      shader = gst_object_ref (filtershader->shader);
+      filtershader->shader = gst_object_ref (shader);
       GST_OBJECT_UNLOCK (filtershader);
       return shader;
     }
   }
 
+  if (filtershader->shader) {
+    shader = gst_object_ref (filtershader->shader);
+    GST_OBJECT_UNLOCK (filtershader);
+    return shader;
+  }
+
   if (filtershader->new_source) {
     GstGLSLStage *stage;
 

ext/gl/gstglfiltershader.h

@@ -39,12 +39,12 @@ struct _GstGLFilterShader
   GstGLFilter filter;
 
   /* properties */
-  GstGLShader *shader_prop;
+  GstGLShader *shader;
   gchar *vertex;
   gchar *fragment;
+  gboolean update_shader; /* update the shader on the next draw */
   GstStructure *uniforms;
 
-  GstGLShader *shader;
   gboolean new_source;
   gdouble time;
 

tests/examples/gtk/glliveshader.c

@@ -195,36 +195,36 @@ _new_shader (GstGLContext * context, struct shader_state *state)
   return shader;
 }
 
+static gboolean
+_set_compilation_state (struct shader_state *state)
+{
+  gtk_label_set_text (GTK_LABEL (state->label),
+      state->shader_linked ? "Success" : "Failure");
+
+  return G_SOURCE_REMOVE;
+}
+
 static GstGLShader *
 _create_shader (GstElement * element, struct shader_state *state)
 {
   GstGLContext *context;
-  GstGLShader *shader;
+  GstGLShader *shader, *new_shader;
 
-  g_object_get (G_OBJECT (element), "context", &context, NULL);
+  g_object_get (G_OBJECT (element), "context", &context, "shader", &shader,
+      NULL);
 
-  shader = _new_shader (context, state);
-  state->shader_linked = TRUE;
+  new_shader = _new_shader (context, state);
+  if (!shader && !new_shader)
+    g_warning ("Failed to create a shader!");
+  state->shader_linked = new_shader != NULL;
 
-  if (state->context)
-    gst_object_unref (state->context);
-  state->context = context;
+  if (shader)
+    gst_object_unref (shader);
+  gst_object_unref (context);
 
-  return shader;
-}
+  g_main_context_invoke (NULL, (GSourceFunc) _set_compilation_state, state);
 
-static void
-_modify_shader (GstGLContext * context, struct shader_state *state)
-{
-  GstGLShader *shader;
-
-  if (!(shader = _new_shader (context, state))) {
-    state->shader_linked = FALSE;
-    return;
-  }
-  state->shader_linked = TRUE;
-
-  g_object_set (state->shader, "shader", shader, NULL);
+  return new_shader;
 }
 
 static void
@@ -232,18 +232,11 @@ _on_text_changed (GtkTextBuffer * text, struct text_view_state *state)
 {
   GtkTextIter start, end;
 
-  if (!state->state->context)
-    return;
-
   gtk_text_buffer_get_bounds (text, &start, &end);
   if (state->str)
     g_free (state->str);
   state->str = gtk_text_buffer_get_text (text, &start, &end, FALSE);
-  gst_gl_context_thread_add (state->state->context,
-      (GstGLContextThreadFunc) _modify_shader, state->state);
-
-  gtk_label_set_text (GTK_LABEL (state->state->label),
-      state->state->shader_linked ? "Success" : "Failure");
+  g_object_set (state->state->shader, "update-shader", TRUE, NULL);
 }
 
 static GtkWidget *