3 files changed, 27 insertions, 13 deletions

diff --git a/backend/headless/backend.c b/backend/headless/backend.c
index 0138166d..cbc158f3 100644
--- a/backend/headless/backend.c
+++ b/backend/headless/backend.c
@@ -1,4 +1,4 @@
-#include "util/signal.h"
+#include <assert.h>
 #include <stdlib.h>
 #include <wlr/interfaces/wlr_input_device.h>
 #include <wlr/interfaces/wlr_output.h>
@@ -7,10 +7,17 @@
 #include <wlr/util/log.h>
 #include "backend/headless.h"
 #include "glapi.h"
+#include "util/signal.h"
+
+struct wlr_headless_backend *headless_backend_from_backend(
+		struct wlr_backend *wlr_backend) {
+	assert(wlr_backend_is_headless(wlr_backend));
+	return (struct wlr_headless_backend *)wlr_backend;
+}
 
 static bool backend_start(struct wlr_backend *wlr_backend) {
 	struct wlr_headless_backend *backend =
-		(struct wlr_headless_backend *)wlr_backend;
+		headless_backend_from_backend(wlr_backend);
 	wlr_log(WLR_INFO, "Starting headless backend");
 
 	struct wlr_headless_output *output;
@@ -34,7 +41,7 @@ static bool backend_start(struct wlr_backend *wlr_backend) {
 
 static void backend_destroy(struct wlr_backend *wlr_backend) {
 	struct wlr_headless_backend *backend =
-		(struct wlr_headless_backend *)wlr_backend;
+		headless_backend_from_backend(wlr_backend);
 	if (!wlr_backend) {
 		return;
 	}
@@ -62,7 +69,7 @@ static void backend_destroy(struct wlr_backend *wlr_backend) {
 static struct wlr_renderer *backend_get_renderer(
 		struct wlr_backend *wlr_backend) {
 	struct wlr_headless_backend *backend =
-		(struct wlr_headless_backend *)wlr_backend;
+		headless_backend_from_backend(wlr_backend);
 	return backend->renderer;
 }
 
@@ -107,9 +114,8 @@ struct wlr_backend *wlr_headless_backend_create(struct wl_display *display,
 		create_renderer_func = wlr_renderer_autocreate;
 	}
 
-	backend->renderer = create_renderer_func(&backend->egl, EGL_PLATFORM_SURFACELESS_MESA,
-		NULL, (EGLint*)config_attribs, 0);
-
+	backend->renderer = create_renderer_func(&backend->egl,
+		EGL_PLATFORM_SURFACELESS_MESA, NULL, (EGLint*)config_attribs, 0);
 	if (!backend->renderer) {
 		wlr_log(WLR_ERROR, "Failed to create renderer");
 		free(backend);
diff --git a/backend/headless/input_device.c b/backend/headless/input_device.c
index a2474aeb..ba251dd7 100644
--- a/backend/headless/input_device.c
+++ b/backend/headless/input_device.c
@@ -1,3 +1,4 @@
+#include <assert.h>
 #include <stdlib.h>
 #include <wlr/interfaces/wlr_input_device.h>
 #include <wlr/interfaces/wlr_keyboard.h>
@@ -18,7 +19,7 @@ bool wlr_input_device_is_headless(struct wlr_input_device *wlr_dev) {
 struct wlr_input_device *wlr_headless_add_input_device(
 		struct wlr_backend *wlr_backend, enum wlr_input_device_type type) {
 	struct wlr_headless_backend *backend =
-		(struct wlr_headless_backend *)wlr_backend;
+		headless_backend_from_backend(wlr_backend);
 
 	struct wlr_headless_input_device *device =
 		calloc(1, sizeof(struct wlr_headless_input_device));
diff --git a/backend/headless/output.c b/backend/headless/output.c
index 24fc3bfd..143900d4 100644
--- a/backend/headless/output.c
+++ b/backend/headless/output.c
@@ -1,3 +1,4 @@
+#include <assert.h>
 #include <EGL/egl.h>
 #include <EGL/eglext.h>
 #include <stdlib.h>
@@ -7,6 +8,12 @@
 #include "backend/headless.h"
 #include "util/signal.h"
 
+static struct wlr_headless_output *headless_output_from_output(
+		struct wlr_output *wlr_output) {
+	assert(wlr_output_is_headless(wlr_output));
+	return (struct wlr_headless_output *)wlr_output;
+}
+
 static EGLSurface egl_create_surface(struct wlr_egl *egl, unsigned int width,
 		unsigned int height) {
 	EGLint attribs[] = {EGL_WIDTH, width, EGL_HEIGHT, height, EGL_NONE};
@@ -22,7 +29,7 @@ static EGLSurface egl_create_surface(struct wlr_egl *egl, unsigned int width,
 static bool output_set_custom_mode(struct wlr_output *wlr_output, int32_t width,
 		int32_t height, int32_t refresh) {
 	struct wlr_headless_output *output =
-		(struct wlr_headless_output *)wlr_output;
+		headless_output_from_output(wlr_output);
 	struct wlr_headless_backend *backend = output->backend;
 
 	if (refresh <= 0) {
@@ -47,13 +54,13 @@ static bool output_set_custom_mode(struct wlr_output *wlr_output, int32_t width,
 static void output_transform(struct wlr_output *wlr_output,
 		enum wl_output_transform transform) {
 	struct wlr_headless_output *output =
-		(struct wlr_headless_output *)wlr_output;
+		headless_output_from_output(wlr_output);
 	output->wlr_output.transform = transform;
 }
 
 static bool output_make_current(struct wlr_output *wlr_output, int *buffer_age) {
 	struct wlr_headless_output *output =
-		(struct wlr_headless_output *)wlr_output;
+		headless_output_from_output(wlr_output);
 	return wlr_egl_make_current(&output->backend->egl, output->egl_surface,
 		buffer_age);
 }
@@ -65,7 +72,7 @@ static bool output_swap_buffers(struct wlr_output *wlr_output,
 
 static void output_destroy(struct wlr_output *wlr_output) {
 	struct wlr_headless_output *output =
-		(struct wlr_headless_output *)wlr_output;
+		headless_output_from_output(wlr_output);
 
 	wl_list_remove(&output->link);
 
@@ -97,7 +104,7 @@ static int signal_frame(void *data) {
 struct wlr_output *wlr_headless_add_output(struct wlr_backend *wlr_backend,
 		unsigned int width, unsigned int height) {
 	struct wlr_headless_backend *backend =
-		(struct wlr_headless_backend *)wlr_backend;
+		headless_backend_from_backend(wlr_backend);
 
 	struct wlr_headless_output *output =
 		calloc(1, sizeof(struct wlr_headless_output));