Merge ~smspillaz/compiz:buffer-age-egl into compiz:master

[Sam Spilsbury]

Enable EGL_EXT_buffer_age on USE_GLES where it is advertised.

Enable EGL_EXT_buffer_age on USE_GLES

buffer_age is long-since supported on GLES platforms, we can also use it there too with minimal changes. Tested on vc4 (Rasberry Pi 4).

A nice side-effect of this is that we don't have to draw the whole scene into an fbo and then redraw it later, just so that we can get double-buffering. Which should be nice on fillrate-bound GPUs.

Probably this should be tested on a few other platforms before merging, I am unsure if there are drivers for which this is broken. At least cogl appears to support it, so maybe its not too bad on other drivers: https://gitlab.gnome.org/GNOME/mutter/-/blob/main/cogl/cogl/winsys/cogl-onscreen-egl.c#L165 .

[Dmitry Shachnev (mitya57)]

> Probably this should be tested on a few other platforms before merging

I don’t have any GLES hardware to test this on. Code changes look good, so if it works for you, let’s just merge it.

[Sam Spilsbury (smspillaz)]

OK!

FWIW, I think most of the mesa drivers + nvidia should support running on GLES these days. I think you just need to build with USE_GLES. But GLES isn't really the default, so I think this won't affect most users. Haven't tested that path though.

[Dmitry Shachnev (mitya57)]

Hi again Sam!

Unfortunately, this causes build failure when building without GLES.

I left an inline comment with error message.

review: Needs Fixing

[Sam Spilsbury (smspillaz)]

Hi! Thanks for the catch. Wasn't able to build with the OpenGL config locally, but it was a simple fix of just putting another local in the right place.

Pushed + rebased.

[Dmitry Shachnev (mitya57)]

I tested the build with -DBUILD_GLES=ON on my laptop today, and it worked fine. So thanks again.

diff --git a/plugins/opengl/include/opengl/opengl.h b/plugins/opengl/include/opengl/opengl.h
index 6e59a48..497eddb 100644
--- a/plugins/opengl/include/opengl/opengl.h
+++ b/plugins/opengl/include/opengl/opengl.h
@@ -44,7 +44,9 @@
  * to GLX_BACK_BUFFER_AGE_EXT but this is the token as defined
  * in the spec (https://www.opengl.org/registry/specs/EXT/glx_buffer_age.txt)
  */
+#ifndef GLX_BACK_BUFFER_AGE_EXT
 #define GLX_BACK_BUFFER_AGE_EXT 0x20F4
+#endif
 
 #endif
 
diff --git a/plugins/opengl/src/screen.cpp b/plugins/opengl/src/screen.cpp
index 1ed7588..ef645aa 100644
--- a/plugins/opengl/src/screen.cpp
+++ b/plugins/opengl/src/screen.cpp
@@ -372,7 +372,59 @@ class BufferAgeFrameProvider :
 	Display *mDisplay;
 	GLXDrawable mDrawable;
 };
+#else
+class BufferAgeFrameProvider :
+    public FrameProvider
+{
+    public:
+
+        BufferAgeFrameProvider (Display     *disp,
+                                EGLSurface   drawable) :
+            mDisplay (disp),
+            mDrawable (drawable)
+        {
+        }
+
+        unsigned int getCurrentFrame ()
+        {
+            EGLint age = 0;
+            eglQuerySurface (eglGetDisplay (mDisplay),
+                                 mDrawable,
+                                 EGL_BUFFER_AGE_EXT,
+                                 &age);
+            return (unsigned int) age;
+        }
+
+        void useCurrentFrame ()
+        {
+        }
+
+        void endFrame ()
+        {
+        }
+
+        void invalidateAll ()
+        {
+        }
+
+        bool providesPersistence ()
+        {
+            return true;
+        }
+
+        bool alwaysPostprocess ()
+        {
+            return false;
+        }
+
+    private:
+
+        Display    *mDisplay;
+        EGLSurface mDrawable;
+};
+#endif
 
+#ifndef USE_GLES
 namespace compiz
 {
 namespace opengl
@@ -729,6 +781,13 @@ GLScreen::glInitContext (XVisualInfo *visinfo)
 	return false;
     }
 
+    if (strstr (eglExtensions, "EGL_EXT_buffer_age"))
+    {
+        compLogMessage ("opengl", CompLogLevelInfo,
+                        "EGL_EXT_buffer_age is supported");
+        GL::bufferAge = true;
+    }
+
 // work around efika supporting GL_BGRA directly instead of via this extension
 #ifndef GL_BGRA
     if (!strstr (glExtensions, "GL_EXT_texture_format_BGRA8888"))
@@ -2663,15 +2722,18 @@ PrivateGLScreen::updateRenderMode ()
 void
 PrivateGLScreen::updateFrameProvider ()
 {
-#ifndef USE_GLES
-    const Window outputWindow = CompositeScreen::get (screen)->output ();
-
     if (GL::fboEnabled)
     {
 	if (GL::bufferAge)
 	{
+#ifndef USE_GLES
+	    const Window outputWindow = CompositeScreen::get (screen)->output ();
 	    FrameProvider::Ptr back (new BufferAgeFrameProvider (screen->dpy (),
 								 outputWindow));
+#else
+	    FrameProvider::Ptr back (new BufferAgeFrameProvider (screen->dpy (),
+								 surface));
+#endif
 	    FrameProvider::Ptr scratch (new PostprocessFrameProvider (scratchFbo.get ()));
 	    OptionalPostprocessFrameProvider::PostprocessRequired ppReq
 		    (boost::bind (&PrivateGLScreen::postprocessRequiredForCurrentFrame,
@@ -2689,14 +2751,18 @@ PrivateGLScreen::updateFrameProvider ()
     else
     {
 	if (GL::bufferAge)
+	{
+#ifndef USE_GLES
+	    const Window outputWindow = CompositeScreen::get (screen)->output ();
 	    frameProvider.reset (new BufferAgeFrameProvider (screen->dpy (),
 								   outputWindow));
+#else
+	    frameProvider.reset (new BufferAgeFrameProvider (screen->dpy (), surface));
+#endif
+	}
 	else
 	    frameProvider.reset (new UndefinedFrameProvider ());
     }
-#else
-    frameProvider.reset (new PostprocessFrameProvider (scratchFbo.get ()));
-#endif
 }
 
 void