gl-renderer: Always setup gl-renderer

Currently, the gl-renderer setup is being done on per-output
basis. This isn't desirable when trying to make weston run
with zero outputs.

When there are no outputs present, there is no surface available
to attach an EGLContext to with eglMakeCurrent, which makes
any EGL command fail.

The problem is solved by using EGL_KHR_surfaceless_context to
bind an EGLContext to EGL_NO_SURFACE, or if that is
unavailable, creating a dummy PbufferSurface and binding an
EGLContext to it, so EGL gets set up properly.

v2:

- Move PbufferSurface creation into its own function
- Introduce a new EGLConfig with EGL_PBUFFER_BIT set
  and use it to create a PbufferSurface
- Make PbufferSurface attributes definition static
- Check for return of gl_renderer_setup and terminate
  in case it fails
- Remove redundant gl_renderer_setup call from
  gl_renderer_output_create
- Only destroy the dummy surface if it is valid

This patch causes a warning from Mesa when using the i965 driver:
libEGL warning: FIXME: egl/x11 doesn't support front buffer rendering.
A bug has been filed about it since it seems to be spurious:
https://bugs.freedesktop.org/show_bug.cgi?id=96694

Signed-off-by: Armin Krezović <krezovic.armin@gmail.com>
[Pekka: filed a Mesa bug and added the note in commit msg]
Reviewed-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>

libweston/gl-renderer.c

@@ -175,6 +175,8 @@ struct gl_renderer {
 	EGLContext egl_context;
 	EGLConfig egl_config;
 
+	EGLSurface dummy_surface;
+
 	struct wl_array vertices;
 	struct wl_array vtxcnt;
 
@@ -201,6 +203,8 @@ struct gl_renderer {
 
 	int has_configless_context;
 
+	int has_surfaceless_context;
+
 	int has_dmabuf_import;
 	struct wl_list dmabuf_images;
 
@@ -2597,12 +2601,6 @@ gl_renderer_output_create(struct weston_output *output,
 		return -1;
 	}
 
-	if (gr->egl_context == NULL)
-		if (gl_renderer_setup(ec, go->egl_surface) < 0) {
-			free(go);
-			return -1;
-		}
-
 	for (i = 0; i < BUFFER_DAMAGE_COUNT; i++)
 		pixman_region32_init(&go->buffer_damage[i]);
 
@@ -2654,6 +2652,9 @@ gl_renderer_destroy(struct weston_compositor *ec)
 	wl_list_for_each_safe(image, next, &gr->dmabuf_images, link)
 		dmabuf_image_destroy(image);
 
+	if (gr->dummy_surface != EGL_NO_SURFACE)
+		eglDestroySurface(gr->egl_display, gr->dummy_surface);
+
 	eglTerminate(gr->egl_display);
 	eglReleaseThread();
 
@@ -2765,6 +2766,9 @@ gl_renderer_setup_egl_extensions(struct weston_compositor *ec)
 		gr->has_configless_context = 1;
 #endif
 
+	if (check_extension(extensions, "EGL_KHR_surfaceless_context"))
+		gr->has_surfaceless_context = 1;
+
 #ifdef EGL_EXT_image_dma_buf_import
 	if (check_extension(extensions, "EGL_EXT_image_dma_buf_import"))
 		gr->has_dmabuf_import = 1;
@@ -2795,6 +2799,7 @@ static const EGLint gl_renderer_alpha_attribs[] = {
 	EGL_NONE
 };
 
+
 /** Checks whether a platform EGL client extension is supported
  *
  * \param ec The weston compositor
@@ -2872,6 +2877,43 @@ platform_to_extension(EGLenum platform)
 	}
 }
 
+static int
+gl_renderer_create_pbuffer_surface(struct gl_renderer *gr) {
+	EGLConfig pbuffer_config;
+
+	static const EGLint pbuffer_config_attribs[] = {
+		EGL_SURFACE_TYPE, EGL_PBUFFER_BIT,
+		EGL_RED_SIZE, 1,
+		EGL_GREEN_SIZE, 1,
+		EGL_BLUE_SIZE, 1,
+		EGL_ALPHA_SIZE, 0,
+		EGL_RENDERABLE_TYPE, EGL_OPENGL_ES2_BIT,
+		EGL_NONE
+	};
+
+	static const EGLint pbuffer_attribs[] = {
+		EGL_WIDTH, 10,
+		EGL_HEIGHT, 10,
+		EGL_NONE
+	};
+
+	if (egl_choose_config(gr, pbuffer_config_attribs, NULL, 0, &pbuffer_config) < 0) {
+		weston_log("failed to choose EGL config for PbufferSurface");
+		return -1;
+	}
+
+	gr->dummy_surface = eglCreatePbufferSurface(gr->egl_display,
+						    pbuffer_config,
+						    pbuffer_attribs);
+
+	if (gr->dummy_surface == EGL_NO_SURFACE) {
+		weston_log("failed to create PbufferSurface\n");
+		return -1;
+	}
+
+	return 0;
+}
+
 static int
 gl_renderer_create(struct weston_compositor *ec, EGLenum platform,
 	void *native_window, const EGLint *attribs,
@@ -2956,10 +2998,27 @@ gl_renderer_create(struct weston_compositor *ec, EGLenum platform,
 	if (gr->has_dmabuf_import)
 		gr->base.import_dmabuf = gl_renderer_import_dmabuf;
 
+	if (gr->has_surfaceless_context) {
+		weston_log("EGL_KHR_surfaceless_context available\n");
+		gr->dummy_surface = EGL_NO_SURFACE;
+	} else {
+		weston_log("EGL_KHR_surfaceless_context unavailable. "
+			   "Trying PbufferSurface\n");
+
+		if (gl_renderer_create_pbuffer_surface(gr) < 0)
+			goto fail_with_error;
+	}
+
 	wl_display_add_shm_format(ec->wl_display, WL_SHM_FORMAT_RGB565);
 
 	wl_signal_init(&gr->destroy_signal);
 
+	if (gl_renderer_setup(ec, gr->dummy_surface) < 0) {
+		if (gr->dummy_surface != EGL_NO_SURFACE)
+			eglDestroySurface(gr->egl_display, gr->dummy_surface);
+		goto fail_with_error;
+	}
+
 	return 0;
 
 fail_with_error: