gl-renderer: try to create a GLES3 context

GL drivers might allow using GLES3 features even in GLES2 contexts, but
that's not always the case. To make sure we can use GLES3, first try to
create a GLES3 context and then fallback to GLES2 on failure.

The reported GL version is used to determine which GLES version is
actually available.

Signed-off-by: Arnaud Vrac <avrac@freebox.fr>
Reviewed-by: Derek Foreman <derekf@osg.samsung.com>
Reviewed-by: Daniel Stone <daniels@collabora.com>

libweston/gl-renderer.c

@@ -3618,8 +3618,8 @@ gl_renderer_setup(struct weston_compositor *ec, EGLSurface egl_surface)
 	EGLConfig context_config;
 	EGLBoolean ret;
 
-	static const EGLint context_attribs[] = {
+	EGLint context_attribs[] = {
-		EGL_CONTEXT_CLIENT_VERSION, 2,
+		EGL_CONTEXT_CLIENT_VERSION, 0,
 		EGL_NONE
 	};
 
@@ -3634,13 +3634,23 @@ gl_renderer_setup(struct weston_compositor *ec, EGLSurface egl_surface)
 	if (gr->has_configless_context)
 		context_config = EGL_NO_CONFIG_KHR;
 
+	/* try to create an OpenGLES 3 context first */
+	context_attribs[1] = 3;
 	gr->egl_context = eglCreateContext(gr->egl_display, context_config,
 					   EGL_NO_CONTEXT, context_attribs);
+	if (gr->egl_context == NULL) {
+		/* and then fallback to OpenGLES 2 */
+		context_attribs[1] = 2;
+		gr->egl_context = eglCreateContext(gr->egl_display,
+						   context_config,
+						   EGL_NO_CONTEXT,
+						   context_attribs);
 		if (gr->egl_context == NULL) {
 			weston_log("failed to create context\n");
 			gl_renderer_print_egl_error_state();
 			return -1;
 		}
+	}
 
 	ret = eglMakeCurrent(gr->egl_display, egl_surface,
 			     egl_surface, gr->egl_context);