qmlgloverlay: make depth buffer optional

allow dropping depth/stencil buffer for
qmlgloverlay element. Shows considerable
drop in memory bandwidth consumption of
the element on windows platforms.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/7677>

subprojects/gst-plugins-base/gst-libs/gst/gl/glprototypes/all_functions.h

@@ -32,3 +32,4 @@
 #include "buffers.h"
 #include "query.h"
 #include "buffer_storage.h"
+#include "invalidate_subdata.h"

subprojects/gst-plugins-base/gst-libs/gst/gl/glprototypes/invalidate_subdata.h

@@ -0,0 +1,66 @@
+/*
+ * GStreamer
+ * Copyright (C) 2024 Andreas Wittmann <andreas.wittmann@zeiss.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.
+ */
+
+GST_GL_EXT_BEGIN (invalidate_subdata,
+                  GST_GL_API_OPENGL3 |
+                  GST_GL_API_GLES2,
+                  4, 3,
+                  3, 0,
+                  "ARB:\0",
+                  "invalidate_subdata\0")
+GST_GL_EXT_FUNCTION (void, InvalidateFramebuffer,
+                     (GLenum        target,
+                      GLsizei       numAttachments,
+                      const GLenum* attachments))
+GST_GL_EXT_FUNCTION (void, InvalidateSubFramebuffer,
+                     (GLenum        target,
+                      GLsizei       numAttachments,
+                      const GLenum* attachments,
+                      GLint         x,
+                      GLint         y,
+                      GLsizei       width,
+                      GLsizei       height))
+GST_GL_EXT_END ()
+
+GST_GL_EXT_BEGIN (invalidate_subdata_no_gles,
+                  GST_GL_API_OPENGL3,
+                  4, 3,
+                  255, 255,
+                  "ARB:\0",
+                  "invalidate_subdata\0")
+GST_GL_EXT_FUNCTION (void, InvalidateTexSubImage,
+                     (GLuint        texture,
+                      GLint         level,
+                      GLint         xoffset,
+                      GLint         yoffset,
+                      GLint         zoffset,
+                      GLsizei       width,
+                      GLsizei       height,
+                      GLsizei       depth))
+GST_GL_EXT_FUNCTION (void, InvalidateTexImage,
+                     (GLuint        texture,
+                      GLint         level))
+GST_GL_EXT_FUNCTION (void, InvalidateBufferSubData,
+                     (GLuint        buffer,
+                      GLintptr      offset,
+                      GLsizeiptr    length))
+GST_GL_EXT_FUNCTION (void, InvalidateBufferData,
+                     (GLuint        buffer))
+GST_GL_EXT_END ()

subprojects/gst-plugins-base/gst-libs/gst/gl/gstglfuncs.h

@@ -99,7 +99,7 @@ G_BEGIN_DECLS
 struct _GstGLFuncs
 {
 #include <gst/gl/glprototypes/all_functions.h>
-  gpointer padding[GST_PADDING_LARGE*6-2];
+  gpointer padding[GST_PADDING_LARGE*6-8];
 };
 
 #undef GST_GL_EXT_BEGIN

subprojects/gst-plugins-base/gst-libs/gst/gl/meson.build

@@ -103,6 +103,7 @@ gl_prototype_headers = files([
   'glprototypes/gles.h',
   'glprototypes/gstgl_compat.h',
   'glprototypes/gstgl_gles2compat.h',
+  'glprototypes/invalidate_subdata.h',
   'glprototypes/opengl.h',
   'glprototypes/query.h',
   'glprototypes/shaders.h',

subprojects/gst-plugins-good/docs/gst_plugins_cache.json

@@ -12450,6 +12450,18 @@
                         "type": "GstGLContext",
                         "writable": false
                     },
+                    "depth-buffer": {
+                        "blurb": "Use depth and stencil buffer for the rendering of the scene. Might corrupt the rendering when set to FALSE! Only set to FALSE after carefully checking the targeted QML scene.",
+                        "conditionally-available": false,
+                        "construct": false,
+                        "construct-only": false,
+                        "controllable": false,
+                        "default": "true",
+                        "mutable": "ready",
+                        "readable": true,
+                        "type": "gboolean",
+                        "writable": true
+                    },
                     "qml-scene": {
                         "blurb": "The contents of the QML scene",
                         "conditionally-available": false,

subprojects/gst-plugins-good/ext/qt/gstqtoverlay.cc

@@ -145,6 +145,7 @@ enum
   PROP_WIDGET,
   PROP_QML_SCENE,
   PROP_ROOT_ITEM,
+  PROP_DEPTH_AND_STENCIL_BUFFER,
 };
 
 enum
@@ -204,6 +205,23 @@ gst_qt_overlay_class_init (GstQtOverlayClass * klass)
           "The root QQuickItem from the qml-scene used to render",
           (GParamFlags) (G_PARAM_READABLE | G_PARAM_STATIC_STRINGS)));
 
+  /**
+   * GstQtOverlay:depth-buffer:
+   *
+   * Instructs QML to not use a depth or stencil buffer when rendering.
+   *
+   * WARNING: Disabling the depth and stencil buffer may cause QML to
+   * incorrectly render the provided scene.
+   *
+   * Since: 1.26
+   */
+  g_object_class_install_property (gobject_class, PROP_DEPTH_AND_STENCIL_BUFFER,
+      g_param_spec_boolean ("depth-buffer", "Depth and Stencil Buffer",
+          "Use depth and stencil buffer for the rendering of the scene. "
+          "Might corrupt the rendering when set to FALSE! "
+          "Only set to FALSE after carefully checking the targeted QML scene.", TRUE,
+          (GParamFlags) (G_PARAM_READWRITE | G_PARAM_STATIC_STRINGS | GST_PARAM_MUTABLE_READY)));
+
   /**
    * GstQmlGLOverlay::qml-scene-initialized
    * @element: the #GstQmlGLOverlay
@@ -243,6 +261,7 @@ static void
 gst_qt_overlay_init (GstQtOverlay * qt_overlay)
 {
   qt_overlay->widget = QSharedPointer<QtGLVideoItemInterface>();
+  qt_overlay->depth_buffer = TRUE;
   qt_overlay->qml_scene = NULL;
 }
 
@@ -278,6 +297,9 @@ gst_qt_overlay_set_property (GObject * object, guint prop_id,
       g_free (qt_overlay->qml_scene);
       qt_overlay->qml_scene = g_value_dup_string (value);
       break;
+    case PROP_DEPTH_AND_STENCIL_BUFFER:
+      qt_overlay->depth_buffer = g_value_get_boolean (value);
+      break;
     default:
       G_OBJECT_WARN_INVALID_PROPERTY_ID (object, prop_id, pspec);
       break;
@@ -316,6 +338,9 @@ gst_qt_overlay_get_property (GObject * object, guint prop_id,
       }
       GST_OBJECT_UNLOCK (qt_overlay);
       break;
+     case PROP_DEPTH_AND_STENCIL_BUFFER:
+      g_value_set_boolean(value, qt_overlay->depth_buffer);
+      break;
     default:
       G_OBJECT_WARN_INVALID_PROPERTY_ID (object, prop_id, pspec);
       break;
@@ -341,7 +366,7 @@ gst_qt_overlay_gl_start (GstGLBaseFilter * bfilter)
 
   GST_OBJECT_LOCK (bfilter);
   qt_overlay->renderer = new GstQuickRenderer;
-  if (!qt_overlay->renderer->init (bfilter->context, &error)) {
+  if (!qt_overlay->renderer->init (bfilter->context, qt_overlay->depth_buffer, &error)) {
     GST_ELEMENT_ERROR (GST_ELEMENT (bfilter), RESOURCE, NOT_FOUND,
         ("%s", error->message), (NULL));
     delete qt_overlay->renderer;

subprojects/gst-plugins-good/ext/qt/gstqtoverlay.h

@@ -51,6 +51,8 @@ struct _GstQtOverlay
   /* <private> */
   GstGLFilter           parent;
 
+  gboolean              depth_buffer;
+
   gchar                *qml_scene;
 
   GstQuickRenderer     *renderer;

subprojects/gst-plugins-good/ext/qt/qtglrenderer.cc

@@ -21,6 +21,14 @@
 #define GST_CAT_DEFAULT gst_qt_gl_renderer_debug
 GST_DEBUG_CATEGORY_STATIC (GST_CAT_DEFAULT);
 
+// from GL_EXT_discard_framebuffer
+#ifndef GL_DEPTH_EXT
+#define GL_DEPTH_EXT 0x1801
+#endif
+#ifndef GL_STENCIL_EXT
+#define GL_STENCIL_EXT 0x1802
+#endif
+
 static void
 init_debug (void)
 {
@@ -217,6 +225,7 @@ GstQuickRenderer::GstQuickRenderer()
       gl_allocator(NULL),
       gl_params(NULL),
       gl_mem(NULL),
+      m_useDepthBuffer(TRUE),
       m_sharedRenderData(NULL)
 {
   init_debug ();
@@ -292,7 +301,7 @@ bool CreateSurfaceWorker::event(QEvent * ev)
     return QObject::event(ev);
 }
 
-bool GstQuickRenderer::init (GstGLContext * context, GError ** error)
+bool GstQuickRenderer::init (GstGLContext * context, const gboolean use_depth_buffer, GError ** error)
 {
     g_return_val_if_fail (GST_IS_GL_CONTEXT (context), false);
     g_return_val_if_fail (gst_gl_context_get_current () == context, false);
@@ -306,6 +315,9 @@ bool GstQuickRenderer::init (GstGLContext * context, GError ** error)
         return false;
     }
 
+    m_useDepthBuffer = use_depth_buffer;
+    GST_DEBUG ("%s", m_useDepthBuffer ? "Use depth and stencil buffer" : "Discard depth and stencil buffer");
+
     struct SharedRenderData *render_data = NULL, *old_render_data;
     do {
         if (render_data)
@@ -551,7 +563,8 @@ void GstQuickRenderer::ensureFbo()
 
     if (!m_fbo) {
         m_fbo = new QOpenGLFramebufferObject(m_sharedRenderData->m_surface->size(),
-                QOpenGLFramebufferObject::CombinedDepthStencil);
+            m_useDepthBuffer ? QOpenGLFramebufferObject::CombinedDepthStencil :
+                QOpenGLFramebufferObject::NoAttachment);
         m_quickWindow->setRenderTarget(m_fbo);
         GST_DEBUG ("%p new framebuffer created with size %ix%i", this,
             m_fbo->size().width(), m_fbo->size().height());
@@ -584,6 +597,23 @@ GstQuickRenderer::renderGstGL ()
     /* Meanwhile on this thread continue with the actual rendering. */
     m_renderControl->render();
 
+    {
+        GLint currentFbo = -1;
+        gl->GetIntegerv(GL_DRAW_FRAMEBUFFER_BINDING, &currentFbo);
+
+        if ((GLuint)currentFbo == m_fbo->handle()) {
+            if (gl->InvalidateFramebuffer) {
+                const GLenum attachments[] = { GL_DEPTH_ATTACHMENT, GL_STENCIL_ATTACHMENT };
+                gl->InvalidateFramebuffer(GL_FRAMEBUFFER, sizeof(attachments) / sizeof(*attachments), attachments);
+            } else if (gl->DiscardFramebuffer) {
+                const GLenum attachments[] = { GL_DEPTH_EXT, GL_STENCIL_EXT };
+                gl->DiscardFramebuffer(GL_FRAMEBUFFER, sizeof(attachments) / sizeof(*attachments), attachments);
+            } else {
+                GST_DEBUG ("Context lacks both - GL_ARB_invalidate_subdata and GL_EXT_discard_framebuffer, cannot discard");
+            }
+        }
+    }
+
     GST_DEBUG ("wrapping Qfbo %p with texture %u", m_fbo, m_fbo->texture());
     struct FBOUserData *data = g_new0 (struct FBOUserData, 1);
     data->context = (GstGLContext *) gst_object_ref (gl_context);

subprojects/gst-plugins-good/ext/qt/qtglrenderer.h

@@ -44,11 +44,10 @@ public:
     GstQuickRenderer();
     ~GstQuickRenderer();
 
-    /* initialize the GStreamer/Qt integration.  On failure returns false
+    /* initialize the GStreamer/Qt integration and determine wether to attach depth/stencil buffer to fbo. On failure
-     * and fills @error.
+     * returns false and fills @error. Must be called with @context not wrapped and current in the current thread
-     * Must be called with @context not wrapped and current in the current
+     */
-     * thread  */
+    bool init (GstGLContext * context, const gboolean use_depth_buffer, GError ** error);
-    bool init (GstGLContext * context, GError ** error);
 
     /* set the qml scene.  returns false and fills @error on failure */
     bool setQmlScene (const gchar * scene, GError ** error);
@@ -101,7 +100,7 @@ private:
     GstGLAllocationParams *gl_params;
     GstVideoInfo v_info;
     GstGLMemory *gl_mem;
-
+    gboolean m_useDepthBuffer;
     QString m_errorString;
     struct SharedRenderData *m_sharedRenderData;
 };