qml: implement the required multiple GL context synchonisation

From GStreamer's GL context into the QML context

ext/qt/gstqsgtexture.cc

@@ -45,11 +45,13 @@ GstQSGTexture::GstQSGTexture ()
 
   gst_video_info_init (&this->v_info);
   this->buffer_ = NULL;
+  this->sync_buffer_ = gst_buffer_new ();
 }
 
 GstQSGTexture::~GstQSGTexture ()
 {
   gst_buffer_replace (&this->buffer_, NULL);
+  gst_buffer_replace (&this->sync_buffer_, NULL);
 }
 
 /* only called from the streaming thread with scene graph thread blocked */
@@ -62,18 +64,26 @@ GstQSGTexture::setCaps (GstCaps * caps)
 }
 
 /* only called from the streaming thread with scene graph thread blocked */
-void
+gboolean
 GstQSGTexture::setBuffer (GstBuffer * buffer)
 {
   GST_LOG ("%p setBuffer %" GST_PTR_FORMAT, this, buffer);
   /* FIXME: update more state here */
-  gst_buffer_replace (&this->buffer_, buffer);
+  if (!gst_buffer_replace (&this->buffer_, buffer))
+    return FALSE;
+
+  this->qt_context_ = gst_gl_context_get_current ();
+
+  return TRUE;
 }
 
 /* only called from qt's scene graph render thread */
 void
 GstQSGTexture::bind ()
 {
+  GstGLContext *context;
+  GstGLSyncMeta *sync_meta;
+  GstMemory *mem;
   guint tex_id;
 
   if (!this->buffer_)
@@ -81,6 +91,10 @@ GstQSGTexture::bind ()
   if (GST_VIDEO_INFO_FORMAT (&this->v_info) == GST_VIDEO_FORMAT_UNKNOWN)
     return;
 
+  this->mem_ = gst_buffer_peek_memory (this->buffer_, 0);
+  if (!this->mem_)
+    return;
+
   /* FIXME: should really lock the memory to prevent write access */
   if (!gst_video_frame_map (&this->v_frame, &this->v_info, this->buffer_,
         (GstMapFlags) (GST_MAP_READ | GST_MAP_GL))) {
@@ -88,6 +102,20 @@ GstQSGTexture::bind ()
     return;
   }
 
+  mem = gst_buffer_peek_memory (this->buffer_, 0);
+  g_assert (gst_is_gl_memory (mem));
+
+  context = ((GstGLBaseBuffer *)mem)->context;
+
+  sync_meta = gst_buffer_get_gl_sync_meta (this->sync_buffer_);
+  if (!sync_meta)
+    sync_meta = gst_buffer_add_gl_sync_meta (context, this->sync_buffer_);
+
+  gst_gl_sync_meta_set_sync_point (sync_meta, context);
+
+  g_assert (this->qt_context_);
+  gst_gl_sync_meta_wait (sync_meta, this->qt_context_);
+
   tex_id = *(guint *) this->v_frame.data[0];
   GST_LOG ("%p binding Qt texture %u", this, tex_id);
 

ext/qt/gstqsgtexture.h

@@ -25,6 +25,7 @@
 #include <QSGTexture>
 #include <QOpenGLFunctions>
 #include <gst/video/video.h>
+#include <gst/gl/gl.h>
 
 class GstQSGTexture : public QSGTexture, protected QOpenGLFunctions
 {
@@ -34,7 +35,7 @@ public:
     ~GstQSGTexture ();
 
     void setCaps (GstCaps * caps);
-    void setBuffer (GstBuffer * buffer);
+    gboolean setBuffer (GstBuffer * buffer);
 
     /* QSGTexture */
     void bind ();
@@ -45,6 +46,9 @@ public:
 
 private:
     GstBuffer * buffer_;
+    GstBuffer * sync_buffer_;
+    GstGLContext * qt_context_;
+    GstMemory * mem_;
     GstVideoInfo v_info;
     GstVideoFrame v_frame;
 };

ext/qt/qtitem.cc

@@ -171,6 +171,7 @@ QtGLVideoItem::updatePaintNode(QSGNode * oldNode,
   GstQSGTexture *tex;
 
   g_mutex_lock (&this->priv->lock);
+  gst_gl_context_activate (this->priv->other_context, TRUE);
 
   GST_TRACE ("%p updatePaintNode", this);
 
@@ -181,14 +182,15 @@ QtGLVideoItem::updatePaintNode(QSGNode * oldNode,
 
   if (!texNode) {
     texNode = new QSGSimpleTextureNode ();
-    tex = new GstQSGTexture ();
-    texNode->setTexture (tex);
+    texNode->setOwnsTexture (true);
   } else {
     tex = static_cast<GstQSGTexture *> (texNode->texture());
   }
 
+  tex = new GstQSGTexture ();
   tex->setCaps (this->priv->caps);
   tex->setBuffer (this->priv->buffer);
+  texNode->setTexture (tex);
 
   if (this->priv->force_aspect_ratio) {
     src.w = this->priv->display_width;
@@ -209,6 +211,7 @@ QtGLVideoItem::updatePaintNode(QSGNode * oldNode,
 
   texNode->setRect (QRectF (result.x, result.y, result.w, result.h));
 
+  gst_gl_context_activate (this->priv->other_context, FALSE);
   g_mutex_unlock (&this->priv->lock);
 
   return texNode;