gl: add support for surfaceless display in GstGL

Use of the EGL_MESA_platform_surfaceless EGL extension to create an EGL
display that is not depending on any kind of windowing system.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/5511>

girs/GstGL-1.0.gir

@@ -3016,7 +3016,7 @@ a #GstGLDisplay.
 There are a number of environment variables that influence the choice of
 platform and window system specific functionality.
 - GST_GL_WINDOW influences the window system to use.  Common values are
-  'x11', 'wayland', 'win32' or 'cocoa'.
+  'x11', 'wayland', 'surfaceless', 'win32' or 'cocoa'.
 - GST_GL_PLATFORM influences the OpenGL platform to use.  Common values are
   'egl', 'glx', 'wgl' or 'cgl'.
 - GST_GL_API influences the OpenGL API requested by the OpenGL platform.
@@ -3453,6 +3453,8 @@ display's object lock held.</doc>
       </member>
       <member name="android" value="2048" c:identifier="GST_GL_DISPLAY_TYPE_ANDROID" glib:nick="android">
       </member>
+      <member name="egl_surfaceless" value="4096" c:identifier="GST_GL_DISPLAY_TYPE_EGL_SURFACELESS" glib:nick="egl-surfaceless">
+      </member>
       <member name="any" value="4294967295" c:identifier="GST_GL_DISPLAY_TYPE_ANY" glib:nick="any">
         <doc xml:space="preserve" filename="../subprojects/gst-plugins-base/gst-libs/gst/gl/gstgldisplay.h">any display type</doc>
       </member>

subprojects/gst-plugins-base/gst-libs/gst/gl/egl/gstgldisplay_egl.c

@@ -25,8 +25,8 @@
  * @see_also: #GstGLDisplay
  *
  * #GstGLDisplayEGL represents a connection to an EGL `EGLDisplay` handle created
- * internally (gst_gl_display_egl_new()) or wrapped by the application
+ * internally (gst_gl_display_egl_new() or gst_gl_display_egl_new_surfaceless())
- * (gst_gl_display_egl_new_with_egl_display())
+ * or wrapped by the application (gst_gl_display_egl_new_with_egl_display())
  */
 
 #ifdef HAVE_CONFIG_H
@@ -122,8 +122,8 @@ gst_gl_display_egl_finalize (GObject * object)
  * @display: pointer to a display (or 0)
  *
  * Attempts to create a new `EGLDisplay` from @display.  If @type is
- * %GST_GL_DISPLAY_TYPE_ANY, then @display must be 0. @type must not be
+ * %GST_GL_DISPLAY_TYPE_ANY or %GST_GL_DISPLAY_TYPE_EGL_SURFACELESS, then
- * %GST_GL_DISPLAY_TYPE_NONE.
+ * @display must be 0. @type must not be %GST_GL_DISPLAY_TYPE_NONE.
  *
  * Returns: (nullable): A `EGLDisplay` or `EGL_NO_DISPLAY`
  *
@@ -137,8 +137,11 @@ gst_gl_display_egl_get_from_native (GstGLDisplayType type, guintptr display)
   _gst_eglGetPlatformDisplay_type _gst_eglGetPlatformDisplay = NULL;
 
   g_return_val_if_fail (type != GST_GL_DISPLAY_TYPE_NONE, EGL_NO_DISPLAY);
-  g_return_val_if_fail ((type != GST_GL_DISPLAY_TYPE_ANY && display != 0)
+  g_return_val_if_fail ((type != GST_GL_DISPLAY_TYPE_ANY &&
-      || (type == GST_GL_DISPLAY_TYPE_ANY && display == 0), EGL_NO_DISPLAY);
+          type != GST_GL_DISPLAY_TYPE_EGL_SURFACELESS && display != 0)
+      || ((type == GST_GL_DISPLAY_TYPE_ANY ||
+              type == GST_GL_DISPLAY_TYPE_EGL_SURFACELESS) && display == 0),
+      EGL_NO_DISPLAY);
 
   init_debug ();
 
@@ -233,6 +236,11 @@ gst_gl_display_egl_get_from_native (GstGLDisplayType type, guintptr display)
         NULL);
   }
   /* android only has one winsys/display connection */
+  if (ret == EGL_NO_DISPLAY && (type & GST_GL_DISPLAY_TYPE_EGL_SURFACELESS) &&
+      gst_gl_check_extension ("EGL_MESA_platform_surfaceless", egl_exts)) {
+    ret = _gst_eglGetPlatformDisplay (EGL_PLATFORM_SURFACELESS_MESA,
+        (gpointer) display, NULL);
+  }
 
   if (ret != EGL_NO_DISPLAY)
     return ret;
@@ -272,6 +280,40 @@ gst_gl_display_egl_new (void)
   return ret;
 }
 
+/**
+ * gst_gl_display_egl_new_surfaceless:
+ *
+ * Create a new surfaceless #GstGLDisplayEGL using the Mesa3D
+ * EGL_PLATFORM_SURFACELESS_MESA extension.
+ *
+ * Returns: (transfer full) (nullable): a new #GstGLDisplayEGL or %NULL
+ *
+ * Since: 1.24
+ */
+GstGLDisplayEGL *
+gst_gl_display_egl_new_surfaceless (void)
+{
+  GstGLDisplayEGL *ret;
+  gpointer display;
+
+  init_debug ();
+
+  display =
+      gst_gl_display_egl_get_from_native (GST_GL_DISPLAY_TYPE_EGL_SURFACELESS,
+      0);
+
+  if (!display) {
+    GST_INFO ("Failed to create a surfaceless EGL display");
+    return NULL;
+  }
+
+  ret = g_object_new (GST_TYPE_GL_DISPLAY_EGL, NULL);
+  gst_object_ref_sink (ret);
+  ret->display = display;
+
+  return ret;
+}
+
 /**
  * gst_gl_display_egl_new_with_display:
  * @display: an existing and connected EGLDisplay

subprojects/gst-plugins-base/gst-libs/gst/gl/egl/gstgldisplay_egl.h

@@ -66,6 +66,9 @@ struct _GstGLDisplayEGLClass
 GST_GL_API
 GstGLDisplayEGL *gst_gl_display_egl_new (void);
 
+GST_GL_API
+GstGLDisplayEGL *gst_gl_display_egl_new_surfaceless (void);
+
 GST_GL_API
 GstGLDisplayEGL *gst_gl_display_egl_new_with_egl_display (gpointer display);
 

subprojects/gst-plugins-base/gst-libs/gst/gl/gstgldisplay.c

@@ -34,7 +34,7 @@
  * There are a number of environment variables that influence the choice of
  * platform and window system specific functionality.
  * - GST_GL_WINDOW influences the window system to use.  Common values are
- *   'x11', 'wayland', 'win32' or 'cocoa'.
+ *   'x11', 'wayland', 'surfaceless', 'win32' or 'cocoa'.
  * - GST_GL_PLATFORM influences the OpenGL platform to use.  Common values are
  *   'egl', 'glx', 'wgl' or 'cgl'.
  * - GST_GL_API influences the OpenGL API requested by the OpenGL platform.
@@ -310,6 +310,8 @@ gst_gl_display_type_from_environment (void)
       return GST_GL_DISPLAY_TYPE_EGL;
     } else if (g_strstr_len (env, 5, "winrt")) {
       return GST_GL_DISPLAY_TYPE_EGL;
+    } else if (g_strstr_len (env, 11, "surfaceless")) {
+      return GST_GL_DISPLAY_TYPE_EGL_SURFACELESS;
     } else {
       return GST_GL_DISPLAY_TYPE_NONE;
     }
@@ -393,9 +395,14 @@ gst_gl_display_new_with_type (GstGLDisplayType type)
   if (!display && (type & GST_GL_DISPLAY_TYPE_EGL)) {
     display = GST_GL_DISPLAY (gst_gl_display_egl_new ());
   }
+
+  if (!display && (type & GST_GL_DISPLAY_TYPE_EGL_SURFACELESS)) {
+    display = GST_GL_DISPLAY (gst_gl_display_egl_new_surfaceless ());
+  }
 #endif
   custom_new_types |= GST_GL_DISPLAY_TYPE_EGL_DEVICE;
   custom_new_types |= GST_GL_DISPLAY_TYPE_EGL;
+  custom_new_types |= GST_GL_DISPLAY_TYPE_EGL_SURFACELESS;
   custom_new_types |= GST_GL_DISPLAY_TYPE_DISPMANX;
   custom_new_types |= GST_GL_DISPLAY_TYPE_WINRT;
   custom_new_types |= GST_GL_DISPLAY_TYPE_ANDROID;

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

@@ -80,6 +80,14 @@ GType gst_gl_display_get_type (void);
  *
  * Since: 1.20
  */
+/**
+ * GST_GL_DISPLAY_TYPE_EGL_SURFACELESS:
+ *
+ * Mesa3D surfaceless display using the EGL_PLATFORM_SURFACELESS_MESA
+ * extension.
+ *
+ * Since: 1.24
+ */
 typedef enum
 {
   GST_GL_DISPLAY_TYPE_NONE = 0,
@@ -95,6 +103,7 @@ typedef enum
   GST_GL_DISPLAY_TYPE_EAGL = (1 << 9),
   GST_GL_DISPLAY_TYPE_WINRT = (1 << 10),
   GST_GL_DISPLAY_TYPE_ANDROID = (1 << 11),
+  GST_GL_DISPLAY_TYPE_EGL_SURFACELESS = (1 << 12),
 
   GST_GL_DISPLAY_TYPE_ANY = G_MAXUINT32
 } GstGLDisplayType;

subprojects/gst-plugins-base/gst-libs/gst/gl/gstglwindow.c

@@ -334,6 +334,9 @@ gst_gl_window_new (GstGLDisplay * display)
   if (!window && (!user_choice || g_strstr_len (user_choice, 5, "winrt")))
     window = GST_GL_WINDOW (gst_gl_window_winrt_egl_new (display));
 #endif
+  if (!window && (!user_choice
+          || g_strstr_len (user_choice, 11, "surfaceless")))
+    window = GST_GL_WINDOW (gst_gl_dummy_window_new ());
 
   if (!window) {
     /* subclass returned a NULL window */

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

@@ -253,6 +253,7 @@ if gl_winsys.contains('auto')
   need_win_winrt = 'auto'
   need_win_cocoa = 'auto'
   need_win_egl = 'auto'
+  need_win_surfaceless = 'auto'
   need_win_eagl = 'auto'
   need_win_dispmanx = 'auto'
   need_win_viv_fb = 'auto'
@@ -265,6 +266,7 @@ else
   need_win_winrt = 'no'
   need_win_cocoa = 'no'
   need_win_egl = 'no'
+  need_win_surfaceless = 'no'
   need_win_eagl = 'no'
   need_win_dispmanx = 'no'
   need_win_viv_fb = 'no'
@@ -283,6 +285,8 @@ else
       need_win_cocoa = 'yes'
     elif winsys == 'egl'
       need_win_egl = 'yes'
+    elif winsys == 'surfaceless'
+      need_win_surfaceless = 'yes'
     elif winsys == 'eagl'
       need_win_eagl = 'yes'
     elif winsys == 'dispmanx'
@@ -578,16 +582,39 @@ if need_platform_egl != 'no'
 endif
 
 # winsys_egl checks
-if need_win_egl == 'yes'
+if need_win_egl != 'no'
   if need_platform_egl == 'no'
-    error('Impossible situation requested: Cannot use Winsys egl without EGL support')
+    if need_win_egl == 'yes'
+      error ('Impossible situation requested: Cannot use Winsys egl without EGL support')
+    endif
   elif not egl_dep.found()
-    error ('Could not find EGL libraries for Winsys egl')
+    if need_win_egl == 'yes'
+      error ('Could not find EGL libraries for Winsys egl')
+    else
+      message ('Could not find EGL libraries for Winsys egl')
+    endif
   else
     enabled_gl_winsys += 'egl'
   endif
 endif
 
+# winsys_surfaceless checks
+if need_win_surfaceless != 'no'
+  if need_platform_egl == 'no'
+    if need_win_surfaceless == 'yes'
+      error ('Impossible situation requested: Cannot use Winsys surfaceless without EGL support')
+    endif
+  elif not egl_dep.found()
+    if need_win_surfaceless == 'yes'
+      error ('Could not find EGL libraries for Winsys surfaceless')
+    else
+      message ('Could not find EGL libraries for Winsys surfaceless')
+    endif
+  else
+    enabled_gl_winsys += 'surfaceless'
+  endif
+endif
+
 # wayland checks
 wayland_client_dep = unneeded_dep
 wayland_cursor_dep = unneeded_dep

subprojects/gst-plugins-base/meson_options.txt

@@ -12,7 +12,7 @@ option('gl_platform', type : 'array',
        choices : ['glx', 'egl', 'cgl', 'wgl', 'eagl', 'auto'], value : ['auto'],
        description : 'A comma separated list of opengl platforms to enable building against')
 option('gl_winsys', type : 'array',
-       choices : ['x11', 'wayland', 'win32', 'winrt', 'cocoa', 'dispmanx', 'egl', 'viv-fb', 'gbm', 'android', 'auto'], value : ['auto'],
+       choices : ['x11', 'wayland', 'win32', 'winrt', 'cocoa', 'dispmanx', 'egl', 'surfaceless', 'viv-fb', 'gbm', 'android', 'auto'], value : ['auto'],
        description : 'A comma separated list of opengl windows systems to enable building against. Supported values are x11, wayland, win32, winrt, cocoa, dispmanx, egl, viv-fb, gbm, and android')
 option('egl_module_name', type : 'string', value : '',
        description : 'The file to pass to g_module_open to open the libEGL library (default: libEGL)')

subprojects/gstreamer/docs/gst/running.md

@@ -315,7 +315,7 @@ the encoding does not look like UTF-8.
 **`GST_GL_WINDOW`.**
 
 Influences the window system to use by the GStreamer OpenGL library.
-Common values are 'x11', 'wayland', 'win32' or 'cocoa'.
+Common values are 'x11', 'wayland', 'surfaceless', 'win32' or 'cocoa'.
 
 **`GST_GL_PLATFORM`.**
 

subprojects/gstreamer/docs/index.md

@@ -325,7 +325,7 @@ the encoding does not look like UTF-8.
 **GST_GL_WINDOW.**
 
 Influences the window system to use by the GStreamer OpenGL library.
-Common values are 'x11', 'wayland', 'win32' or 'cocoa'.
+Common values are 'x11', 'wayland', 'surfaceless', 'win32' or 'cocoa'.
 
 **GST_GL_PLATFORM.**