GTK plugin: Support OpenGL/WGL on Windows

This attempts to implement the gtkglsink element on Windows using WGL,
as there were some more gotchas that are along the way, since we need to
juggle with libepoxy along the way, meaning that we need a recent
GTK+-3.24.x for this to work properly, i.e. the upcoming GTK+-3.24.43.

Since we are essentially using an overlay compositor only during
rendering, move its initialization and destruction into the
gtk_gst_gl_widget_render() function, so that things are safer as we are
doing things across threads between gstreamer (gst-gl) and GTK, as GL
operations, as above, have more gotchas on Windows.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/4289>

subprojects/gst-plugins-good/ext/gtk/gtkgstglwidget.c

@@ -39,6 +39,10 @@
 #include <gst/gl/wayland/gstgldisplay_wayland.h>
 #endif
 
+#if GST_GL_HAVE_WINDOW_WIN32 && defined (GDK_WINDOWING_WIN32)
+#include <gdk/gdkwin32.h>
+#endif
+
 /**
  * SECTION:gtkgstglwidget
  * @title: GtkGstGlWidget
@@ -65,10 +69,10 @@ struct _GtkGstGLWidgetPrivate
   GLint attr_position;
   GLint attr_texture;
   GLuint current_tex;
-  GstGLOverlayCompositor *overlay_compositor;
   GstVideoOrientationMethod rotate_method;
   GstVideoOrientationMethod current_rotate_method;
   const gfloat *transform_matrix;
+  gboolean is_wgl;
 };
 
 static const GLfloat vertices[] = {
@@ -160,9 +164,6 @@ gtk_gst_gl_widget_init_redisplay (GtkGstGLWidget * gst_widget)
 
   gl->BindBuffer (GL_ARRAY_BUFFER, 0);
 
-  priv->overlay_compositor =
-      gst_gl_overlay_compositor_new (priv->other_context);
-
   priv->initted = TRUE;
 }
 
@@ -325,6 +326,7 @@ gtk_gst_gl_widget_render (GtkGLArea * widget, GdkGLContext * context)
 {
   GtkGstGLWidgetPrivate *priv = GTK_GST_GL_WIDGET (widget)->priv;
   GtkGstBaseWidget *base_widget = GTK_GST_BASE_WIDGET (widget);
+  GstGLOverlayCompositor *overlay_compositor = NULL;
 
   GTK_GST_BASE_WIDGET_LOCK (widget);
 
@@ -341,6 +343,8 @@ gtk_gst_gl_widget_render (GtkGLArea * widget, GdkGLContext * context)
     goto done;
   }
 
+  overlay_compositor = gst_gl_overlay_compositor_new (priv->other_context);
+
   /* Upload latest buffer */
   if (base_widget->pending_buffer) {
     GstBuffer *buffer = base_widget->pending_buffer;
@@ -357,8 +361,7 @@ gtk_gst_gl_widget_render (GtkGLArea * widget, GdkGLContext * context)
     gst_gl_insert_debug_marker (priv->other_context, "redrawing texture %u",
         priv->current_tex);
 
-    gst_gl_overlay_compositor_upload_overlays (priv->overlay_compositor,
-        buffer);
+    gst_gl_overlay_compositor_upload_overlays (overlay_compositor, buffer);
 
     sync_meta = gst_buffer_get_gl_sync_meta (buffer);
     if (sync_meta) {
@@ -381,12 +384,15 @@ gtk_gst_gl_widget_render (GtkGLArea * widget, GdkGLContext * context)
       base_widget->buffer, context);
 
   _redraw_texture (GTK_GST_GL_WIDGET (widget), priv->current_tex);
-  gst_gl_overlay_compositor_draw_overlays (priv->overlay_compositor);
+  gst_gl_overlay_compositor_draw_overlays (overlay_compositor);
 
   gst_gl_insert_debug_marker (priv->other_context, "texture %u redrawn",
       priv->current_tex);
 
 done:
+  if (overlay_compositor)
+    gst_object_unref (overlay_compositor);
+
   if (priv->other_context)
     gst_gl_context_activate (priv->other_context, FALSE);
 
@@ -429,9 +435,6 @@ _reset_gl (GtkGstGLWidget * gst_widget)
     priv->shader = NULL;
   }
 
-  if (priv->overlay_compositor)
-    gst_object_unref (priv->overlay_compositor);
-
   gst_gl_context_activate (priv->other_context, FALSE);
 
   gst_object_unref (priv->other_context);
@@ -502,6 +505,12 @@ gtk_gst_gl_widget_init (GtkGstGLWidget * gst_widget)
         gst_gl_display_wayland_new_with_display (wayland_display);
   }
 #endif
+#if GST_GL_HAVE_WINDOW_WIN32 && defined (GDK_WINDOWING_WIN32)
+  if (GDK_IS_WIN32_DISPLAY (display)) {
+    priv->display = (GstGLDisplay *)
+        gst_gl_display_new_with_type (GST_GL_DISPLAY_TYPE_WIN32);
+  }
+#endif
 
   (void) display;
 
@@ -579,6 +588,26 @@ _get_gl_context (GtkGstGLWidget * gst_widget)
           platform, gl_api);
   }
 #endif
+#if GST_GL_HAVE_WINDOW_WIN32 && (GST_GL_HAVE_PLATFORM_WGL || GST_GL_HAVE_PLATFORM_EGL) && defined (GDK_WINDOWING_WIN32)
+  if (GDK_IS_WIN32_DISPLAY (gdk_gl_context_get_display (priv->gdk_context))) {
+    gboolean is_gles = gdk_gl_context_get_use_es (priv->gdk_context);
+
+    /* for WGL, we need the updates in GdkWin32GLContext for this to work safely */
+    if (is_gles || GTK_CHECK_VERSION (3, 24, 43)) {
+      platform = is_gles ? GST_GL_PLATFORM_EGL : GST_GL_PLATFORM_WGL;
+      gl_api = gst_gl_context_get_current_gl_api (platform, NULL, NULL);
+      gl_handle = gst_gl_context_get_current_gl_context (platform);
+
+      if (gl_handle)
+        priv->other_context =
+            gst_gl_context_new_wrapped (priv->display, gl_handle,
+            platform, gl_api);
+
+      if (priv->other_context && !is_gles)
+        priv->is_wgl = TRUE;
+    }
+  }
+#endif
 
   (void) platform;
   (void) gl_api;
@@ -639,6 +668,21 @@ gtk_gst_gl_widget_init_winsys (GtkGstGLWidget * gst_widget)
   }
 
   GST_OBJECT_LOCK (priv->display);
+
+  /* If there's no wglCreateContextAttribsARB() support, then we would fallback to
+   * wglShareLists() which will fail with ERROR_BUSY (0xaa) if either of the GL
+   * contexts are current in any other thread.
+   *
+   * The workaround here is to temporarily disable GDK's GL context while we
+   * set up our own, and then make the GDK GL Context current again after we are done
+   *
+   * Sometimes wglCreateContextAttribsARB()
+   * exists, but isn't functional (some Intel drivers), so it's easiest to do this
+   * unconditionally.
+   */
+  if (priv->gdk_context && priv->is_wgl)
+    gdk_gl_context_clear_current ();
+
   if (!gst_gl_display_create_context (priv->display, priv->other_context,
           &priv->context, &error)) {
     GST_WARNING ("Could not create OpenGL context: %s",
@@ -648,6 +692,10 @@ gtk_gst_gl_widget_init_winsys (GtkGstGLWidget * gst_widget)
     GTK_GST_BASE_WIDGET_UNLOCK (gst_widget);
     return FALSE;
   }
+
+  if (priv->gdk_context && priv->is_wgl)
+    gdk_gl_context_make_current (priv->gdk_context);
+
   gst_gl_display_add_context (priv->display, priv->context);
   GST_OBJECT_UNLOCK (priv->display);
 

subprojects/gst-plugins-good/ext/gtk/meson.build

@@ -34,6 +34,15 @@ if gtk_dep.found()
       endif
     endif
 
+    if gst_gl_have_window_win32 and gst_gl_have_platform_wgl
+      # FIXME: automagic
+      gtk_win32_dep = dependency('gtk+-win32-3.0', required : false)
+      if gtk_win32_dep.found() and gtk_win32_dep.version().version_compare('>=3.24.43')
+        optional_deps += [gtk_win32_dep]
+        have_gtk3_gl_windowing = true
+      endif
+    endif
+
     if have_gtk3_gl_windowing
       gtk_sources += [
         'gstgtkglsink.c',