backend/headless: add wlr_headless_backend_create_with_renderer

This allows one to create a headless backend with an existing renderer.

backend/headless/backend.c

@@ -62,7 +62,9 @@ static void backend_destroy(struct wlr_backend *wlr_backend) {
 	wlr_signal_emit_safe(&wlr_backend->events.destroy, backend);
 
 	wlr_renderer_destroy(backend->renderer);
-	wlr_egl_finish(&backend->egl);
+	if (backend->egl == &backend->priv_egl) {
+		wlr_egl_finish(&backend->priv_egl);
+	}
 	free(backend);
 }
 
@@ -85,6 +87,33 @@ static void handle_display_destroy(struct wl_listener *listener, void *data) {
 	backend_destroy(&backend->backend);
 }
 
+static bool backend_init(struct wlr_headless_backend *backend,
+		struct wl_display *display, struct wlr_renderer *renderer) {
+	wlr_backend_init(&backend->backend, &backend_impl);
+	backend->display = display;
+	wl_list_init(&backend->outputs);
+	wl_list_init(&backend->input_devices);
+
+	backend->renderer = renderer;
+	backend->egl = wlr_gles2_renderer_get_egl(renderer);
+
+	if (wlr_gles2_renderer_check_ext(backend->renderer, "GL_OES_rgb8_rgba8") ||
+			wlr_gles2_renderer_check_ext(backend->renderer,
+				"GL_OES_required_internalformat")) {
+		backend->internal_format = GL_RGBA8_OES;
+	} else {
+		wlr_log(WLR_INFO, "GL_RGBA_OES not supported, "
+			"falling back to GL_RGBA4 internal format "
+			"(performance may be affected)");
+		backend->internal_format = GL_RGBA4;
+	}
+
+	backend->display_destroy.notify = handle_display_destroy;
+	wl_display_add_destroy_listener(display, &backend->display_destroy);
+
+	return true;
+}
+
 struct wlr_backend *wlr_headless_backend_create(struct wl_display *display,
 		wlr_renderer_create_func_t create_renderer_func) {
 	wlr_log(WLR_INFO, "Creating headless backend");
@@ -95,10 +124,6 @@ struct wlr_backend *wlr_headless_backend_create(struct wl_display *display,
 		wlr_log(WLR_ERROR, "Failed to allocate wlr_headless_backend");
 		return NULL;
 	}
-	wlr_backend_init(&backend->backend, &backend_impl);
-	backend->display = display;
-	wl_list_init(&backend->outputs);
-	wl_list_init(&backend->input_devices);
 
 	static const EGLint config_attribs[] = {
 		EGL_SURFACE_TYPE, 0,
@@ -113,39 +138,41 @@ struct wlr_backend *wlr_headless_backend_create(struct wl_display *display,
 		create_renderer_func = wlr_renderer_autocreate;
 	}
 
-	backend->renderer = create_renderer_func(&backend->egl,
+	struct wlr_renderer *renderer = create_renderer_func(&backend->priv_egl,
 		EGL_PLATFORM_SURFACELESS_MESA, EGL_DEFAULT_DISPLAY,
 		(EGLint*)config_attribs, 0);
-	if (!backend->renderer) {
+	if (!renderer) {
 		wlr_log(WLR_ERROR, "Failed to create renderer");
-		goto error_backend;
+		free(backend);
+		return NULL;
 	}
 
-	if (!wlr_egl_make_current(&backend->egl, EGL_NO_SURFACE, NULL)) {
-		wlr_log(WLR_ERROR, "wlr_egl_make_current failed");
-		goto error_renderer;
+	if (!backend_init(backend, display, renderer)) {
+		wlr_renderer_destroy(backend->renderer);
+		free(backend);
+		return NULL;
 	}
 
-	if (wlr_gles2_renderer_check_ext(backend->renderer, "GL_OES_rgb8_rgba8") ||
-			wlr_gles2_renderer_check_ext(backend->renderer,
-				"GL_OES_required_internalformat")) {
-		backend->internal_format = GL_RGBA8_OES;
-	} else {
-		wlr_log(WLR_INFO, "GL_OES_rgb8_rgba8 not supported, "
-			"falling back to GL_RGBA4 internal format");
-		backend->internal_format = GL_RGBA4;
+	return &backend->backend;
+}
+
+struct wlr_backend *wlr_headless_backend_create_with_renderer(
+		struct wl_display *display, struct wlr_renderer *renderer) {
+	wlr_log(WLR_INFO, "Creating headless backend");
+
+	struct wlr_headless_backend *backend =
+		calloc(1, sizeof(struct wlr_headless_backend));
+	if (!backend) {
+		wlr_log(WLR_ERROR, "Failed to allocate wlr_headless_backend");
+		return NULL;
 	}
 
-	backend->display_destroy.notify = handle_display_destroy;
-	wl_display_add_destroy_listener(display, &backend->display_destroy);
+	if (!backend_init(backend, display, renderer)) {
+		free(backend);
+		return NULL;
+	}
 
 	return &backend->backend;
-
-error_renderer:
-	wlr_renderer_destroy(backend->renderer);
-error_backend:
-	free(backend);
-	return NULL;
 }
 
 bool wlr_backend_is_headless(struct wlr_backend *backend) {

backend/headless/output.c

@@ -16,7 +16,7 @@ static struct wlr_headless_output *headless_output_from_output(
 
 static bool create_fbo(struct wlr_headless_output *output,
 		unsigned int width, unsigned int height) {
-	if (!wlr_egl_make_current(&output->backend->egl, EGL_NO_SURFACE, NULL)) {
+	if (!wlr_egl_make_current(output->backend->egl, EGL_NO_SURFACE, NULL)) {
 		return false;
 	}
 
@@ -46,7 +46,7 @@ static bool create_fbo(struct wlr_headless_output *output,
 }
 
 static void destroy_fbo(struct wlr_headless_output *output) {
-	if (!wlr_egl_make_current(&output->backend->egl, EGL_NO_SURFACE, NULL)) {
+	if (!wlr_egl_make_current(output->backend->egl, EGL_NO_SURFACE, NULL)) {
 		return;
 	}
 
@@ -82,7 +82,7 @@ static bool output_attach_render(struct wlr_output *wlr_output,
 	struct wlr_headless_output *output =
 		headless_output_from_output(wlr_output);
 
-	if (!wlr_egl_make_current(&output->backend->egl, EGL_NO_SURFACE, NULL)) {
+	if (!wlr_egl_make_current(output->backend->egl, EGL_NO_SURFACE, NULL)) {
 		return false;
 	}
 
@@ -129,7 +129,7 @@ static bool output_commit(struct wlr_output *wlr_output) {
 		wlr_output_send_present(wlr_output, NULL);
 	}
 
-	wlr_egl_make_current(&output->backend->egl, EGL_NO_SURFACE, NULL);
+	wlr_egl_make_current(output->backend->egl, EGL_NO_SURFACE, NULL);
 	glBindFramebuffer(GL_FRAMEBUFFER, 0);
 
 	return true;
@@ -138,7 +138,7 @@ static bool output_commit(struct wlr_output *wlr_output) {
 static void output_rollback(struct wlr_output *wlr_output) {
 	struct wlr_headless_output *output =
 		headless_output_from_output(wlr_output);
-	wlr_egl_make_current(&output->backend->egl, EGL_NO_SURFACE, NULL);
+	wlr_egl_make_current(output->backend->egl, EGL_NO_SURFACE, NULL);
 	glBindFramebuffer(GL_FRAMEBUFFER, 0);
 }
 

include/backend/headless.h

@@ -9,7 +9,8 @@
 
 struct wlr_headless_backend {
 	struct wlr_backend backend;
-	struct wlr_egl egl;
+	struct wlr_egl priv_egl; // may be uninitialized
+	struct wlr_egl *egl;
 	struct wlr_renderer *renderer;
 	struct wl_display *display;
 	struct wl_list outputs;

include/wlr/backend/headless.h

@@ -19,6 +19,11 @@
  */
 struct wlr_backend *wlr_headless_backend_create(struct wl_display *display,
 	wlr_renderer_create_func_t create_renderer_func);
+/**
+ * Creates a headless backend with an existing renderer.
+ */
+struct wlr_backend *wlr_headless_backend_create_with_renderer(
+	struct wl_display *display, struct wlr_renderer *renderer);
 /**
  * Create a new headless output backed by an in-memory EGL framebuffer. You can
  * read pixels from this framebuffer via wlr_renderer_read_pixels but it is