render/egl: support config-less wlr_egl

When using wlr_swapchain, there's no need to select an EGLConfig. Add
support for creating config-less EGL contexts.

render/egl.c

@@ -319,10 +319,20 @@ bool wlr_egl_init(struct wlr_egl *egl, EGLenum platform, void *remote_display,
 			check_egl_ext(device_exts_str, "EGL_EXT_device_drm");
 	}
 
+	if (config_attribs != NULL) {
 		if (!egl_get_config(egl->display, config_attribs, &egl->config, visual_id)) {
 			wlr_log(WLR_ERROR, "Failed to get EGL config");
 			goto error;
 		}
+	} else {
+		if (!check_egl_ext(display_exts_str, "EGL_KHR_no_config_context") &&
+				!check_egl_ext(display_exts_str, "EGL_MESA_configless_context")) {
+			wlr_log(WLR_ERROR, "EGL_KHR_no_config_context or "
+				"EGL_MESA_configless_context not supported");
+			goto error;
+		}
+		egl->config = EGL_NO_CONFIG_KHR;
+	}
 
 	wlr_log(WLR_INFO, "Using EGL %d.%d", (int)major, (int)minor);
 	wlr_log(WLR_INFO, "Supported EGL client extensions: %s", client_exts_str);

render/wlr_renderer.c

@@ -268,7 +268,11 @@ struct wlr_renderer *wlr_renderer_autocreate(struct wlr_egl *egl,
 	memcpy(&all_config_attribs[config_attribs_len], gles2_config_attribs,
 		sizeof(gles2_config_attribs));
 
-	if (!wlr_egl_init(egl, platform, remote_display, all_config_attribs,
+	if (config_attribs != NULL) {
+		config_attribs = all_config_attribs;
+	}
+
+	if (!wlr_egl_init(egl, platform, remote_display, config_attribs,
 			visual_id)) {
 		wlr_log(WLR_ERROR, "Could not initialize EGL");
 		return NULL;