output: add damage tracking via buffer age

backend/drm/drm.c

@@ -183,12 +183,13 @@ void wlr_drm_resources_free(struct wlr_drm_backend *drm) {
 	free(drm->planes);
 }
 
-static void wlr_drm_connector_make_current(struct wlr_output *output) {
+static bool wlr_drm_connector_make_current(struct wlr_output *output,
+		int *buffer_age) {
 	struct wlr_drm_connector *conn = (struct wlr_drm_connector *)output;
-	wlr_drm_surface_make_current(&conn->crtc->primary->surf);
+	return wlr_drm_surface_make_current(&conn->crtc->primary->surf, buffer_age);
 }
 
-static void wlr_drm_connector_swap_buffers(struct wlr_output *output) {
+static bool wlr_drm_connector_swap_buffers(struct wlr_output *output) {
 	struct wlr_drm_connector *conn = (struct wlr_drm_connector *)output;
 	struct wlr_drm_backend *drm = (struct wlr_drm_backend *)output->backend;
 
@@ -203,7 +204,7 @@ static void wlr_drm_connector_swap_buffers(struct wlr_output *output) {
 
 	if (conn->pageflip_pending) {
 		wlr_log(L_ERROR, "Skipping pageflip");
-		return;
+		return true;
 	}
 
 	if (drm->iface->crtc_pageflip(drm, conn, crtc, fb_id, NULL)) {
@@ -212,6 +213,8 @@ static void wlr_drm_connector_swap_buffers(struct wlr_output *output) {
 		wl_event_source_timer_update(conn->retry_pageflip,
 			1000000.0f / conn->output.current_mode->refresh);
 	}
+
+	return true;
 }
 
 static void wlr_drm_connector_set_gamma(struct wlr_output *output,
@@ -595,7 +598,7 @@ static bool wlr_drm_connector_set_cursor(struct wlr_output *output,
 		return false;
 	}
 
-	wlr_drm_surface_make_current(&plane->surf);
+	wlr_drm_surface_make_current(&plane->surf, NULL);
 
 	wlr_texture_upload_pixels(plane->wlr_tex, WL_SHM_FORMAT_ARGB8888,
 		stride, width, height, buf);

backend/drm/renderer.c

@@ -113,9 +113,9 @@ void wlr_drm_surface_finish(struct wlr_drm_surface *surf) {
 	memset(surf, 0, sizeof(*surf));
 }
 
-void wlr_drm_surface_make_current(struct wlr_drm_surface *surf) {
-	eglMakeCurrent(surf->renderer->egl.display, surf->egl, surf->egl,
-		surf->renderer->egl.context);
+bool wlr_drm_surface_make_current(struct wlr_drm_surface *surf,
+		int *buffer_damage) {
+	return wlr_egl_make_current(&surf->renderer->egl, surf->egl, buffer_damage);
 }
 
 struct gbm_bo *wlr_drm_surface_swap_buffers(struct wlr_drm_surface *surf) {
@@ -123,7 +123,9 @@ struct gbm_bo *wlr_drm_surface_swap_buffers(struct wlr_drm_surface *surf) {
 		gbm_surface_release_buffer(surf->gbm, surf->front);
 	}
 
-	eglSwapBuffers(surf->renderer->egl.display, surf->egl);
+	if (!eglSwapBuffers(surf->renderer->egl.display, surf->egl)) {
+		wlr_log(L_ERROR, "eglSwapBuffers failed");
+	}
 
 	surf->front = surf->back;
 	surf->back = gbm_surface_lock_front_buffer(surf->gbm);
@@ -135,7 +137,7 @@ struct gbm_bo *wlr_drm_surface_get_front(struct wlr_drm_surface *surf) {
 		return surf->front;
 	}
 
-	wlr_drm_surface_make_current(surf);
+	wlr_drm_surface_make_current(surf, NULL);
 	glViewport(0, 0, surf->width, surf->height);
 	glClearColor(0.0, 0.0, 0.0, 1.0);
 	glClear(GL_COLOR_BUFFER_BIT);
@@ -207,8 +209,9 @@ static struct wlr_texture *get_tex_for_bo(struct wlr_drm_renderer *renderer, str
 	return tex->tex;
 }
 
-struct gbm_bo *wlr_drm_surface_mgpu_copy(struct wlr_drm_surface *dest, struct gbm_bo *src) {
-	wlr_drm_surface_make_current(dest);
+struct gbm_bo *wlr_drm_surface_mgpu_copy(struct wlr_drm_surface *dest,
+		struct gbm_bo *src) {
+	wlr_drm_surface_make_current(dest, NULL);
 
 	struct wlr_texture *tex = get_tex_for_bo(dest->renderer, src);
 

backend/headless/output.c

@@ -48,18 +48,15 @@ static void output_transform(struct wlr_output *wlr_output,
 	output->wlr_output.transform = transform;
 }
 
-static void output_make_current(struct wlr_output *wlr_output) {
+static bool output_make_current(struct wlr_output *wlr_output, int *buffer_age) {
 	struct wlr_headless_output *output =
 		(struct wlr_headless_output *)wlr_output;
-	if (!eglMakeCurrent(output->backend->egl.display,
-		output->egl_surface, output->egl_surface,
-		output->backend->egl.context)) {
-		wlr_log(L_ERROR, "eglMakeCurrent failed: %s", egl_error());
-	}
+	return wlr_egl_make_current(&output->backend->egl, output->egl_surface,
+		buffer_age);
 }
 
-static void output_swap_buffers(struct wlr_output *wlr_output) {
-	// No-op
+static bool output_swap_buffers(struct wlr_output *wlr_output) {
+	return true; // No-op
 }
 
 static void output_destroy(struct wlr_output *wlr_output) {

backend/wayland/output.c

@@ -38,22 +38,27 @@ static bool wlr_wl_output_set_custom_mode(struct wlr_output *_output,
 	return true;
 }
 
-static void wlr_wl_output_make_current(struct wlr_output *_output) {
-	struct wlr_wl_backend_output *output = (struct wlr_wl_backend_output *)_output;
-	if (!eglMakeCurrent(output->backend->egl.display,
-		output->egl_surface, output->egl_surface,
-		output->backend->egl.context)) {
-		wlr_log(L_ERROR, "eglMakeCurrent failed: %s", egl_error());
-	}
+static bool wlr_wl_output_make_current(struct wlr_output *wlr_output,
+		int *buffer_age) {
+	struct wlr_wl_backend_output *output =
+		(struct wlr_wl_backend_output *)wlr_output;
+	return wlr_egl_make_current(&output->backend->egl, output->egl_surface,
+		buffer_age);
 }
 
-static void wlr_wl_output_swap_buffers(struct wlr_output *_output) {
-	struct wlr_wl_backend_output *output = (struct wlr_wl_backend_output *)_output;
+static bool wlr_wl_output_swap_buffers(struct wlr_output *wlr_output) {
+	struct wlr_wl_backend_output *output =
+		(struct wlr_wl_backend_output *)wlr_output;
+
 	output->frame_callback = wl_surface_frame(output->surface);
 	wl_callback_add_listener(output->frame_callback, &frame_listener, output);
+
 	if (!eglSwapBuffers(output->backend->egl.display, output->egl_surface)) {
 		wlr_log(L_ERROR, "eglSwapBuffers failed: %s", egl_error());
+		return false;
 	}
+
+	return true;
 }
 
 static void wlr_wl_output_transform(struct wlr_output *_output,

backend/x11/backend.c

@@ -379,28 +379,23 @@ static void output_destroy(struct wlr_output *wlr_output) {
 	// output has been allocated on the stack, do not free it
 }
 
-static void output_make_current(struct wlr_output *wlr_output) {
+static bool output_make_current(struct wlr_output *wlr_output, int *buffer_age) {
 	struct wlr_x11_output *output = (struct wlr_x11_output *)wlr_output;
 	struct wlr_x11_backend *x11 = output->x11;
 
-	if (!eglMakeCurrent(x11->egl.display, output->surf, output->surf, x11->egl.context)) {
-		wlr_log(L_ERROR, "eglMakeCurrent failed: %s", egl_error());
-	}
+	return wlr_egl_make_current(&x11->egl, output->surf, buffer_age);
 }
 
-static void output_swap_buffers(struct wlr_output *wlr_output) {
+static bool output_swap_buffers(struct wlr_output *wlr_output) {
 	struct wlr_x11_output *output = (struct wlr_x11_output *)wlr_output;
 	struct wlr_x11_backend *x11 = output->x11;
 
 	if (!eglSwapBuffers(x11->egl.display, output->surf)) {
 		wlr_log(L_ERROR, "eglSwapBuffers failed: %s", egl_error());
+		return false;
 	}
 
-	// Damage the whole output
-	// TODO: use the buffer age extension
-	pixman_region32_union_rect(&wlr_output->damage, &wlr_output->damage,
-		0, 0, wlr_output->width, wlr_output->height);
-	wlr_output_update_needs_swap(wlr_output);
+	return true;
 }
 
 static struct wlr_output_impl output_impl = {

examples/multi-pointer.c

@@ -56,7 +56,7 @@ static void handle_output_frame(struct output_state *output,
 	struct sample_state *sample = state->data;
 	struct wlr_output *wlr_output = output->output;
 
-	wlr_output_make_current(wlr_output);
+	wlr_output_make_current(wlr_output, NULL);
 
 	glClearColor(sample->clear_color[0], sample->clear_color[1],
 		sample->clear_color[2], sample->clear_color[3]);

examples/output-layout.c

@@ -100,7 +100,7 @@ static void handle_output_frame(struct output_state *output,
 	struct sample_state *sample = state->data;
 	struct wlr_output *wlr_output = output->output;
 
-	wlr_output_make_current(wlr_output);
+	wlr_output_make_current(wlr_output, NULL);
 	wlr_renderer_begin(sample->renderer, wlr_output);
 
 	animate_cat(sample, output->output);

examples/pointer.c

@@ -85,7 +85,7 @@ static void handle_output_frame(struct output_state *output,
 	struct sample_state *sample = state->data;
 	struct wlr_output *wlr_output = output->output;
 
-	wlr_output_make_current(wlr_output);
+	wlr_output_make_current(wlr_output, NULL);
 
 	glClearColor(sample->clear_color[0], sample->clear_color[1],
 		sample->clear_color[2], sample->clear_color[3]);

examples/rotation.c

@@ -42,7 +42,7 @@ static void handle_output_frame(struct output_state *output, struct timespec *ts
 	int32_t width, height;
 	wlr_output_effective_resolution(wlr_output, &width, &height);
 
-	wlr_output_make_current(wlr_output);
+	wlr_output_make_current(wlr_output, NULL);
 	wlr_renderer_begin(sample->renderer, wlr_output);
 
 	float matrix[16];

examples/simple.c

@@ -35,7 +35,7 @@ void handle_output_frame(struct output_state *output, struct timespec *ts) {
 		sample->dec = inc;
 	}
 
-	wlr_output_make_current(output->output);
+	wlr_output_make_current(output->output, NULL);
 
 	glClearColor(sample->color[0], sample->color[1], sample->color[2], 1.0);
 	glClear(GL_COLOR_BUFFER_BIT);

examples/tablet.c

@@ -42,7 +42,7 @@ static void handle_output_frame(struct output_state *output, struct timespec *ts
 	int32_t width, height;
 	wlr_output_effective_resolution(wlr_output, &width, &height);
 
-	wlr_output_make_current(wlr_output);
+	wlr_output_make_current(wlr_output, NULL);
 	wlr_renderer_begin(sample->renderer, wlr_output);
 
 	float matrix[16], view[16];

examples/touch.c

@@ -41,7 +41,7 @@ static void handle_output_frame(struct output_state *output, struct timespec *ts
 	int32_t width, height;
 	wlr_output_effective_resolution(wlr_output, &width, &height);
 
-	wlr_output_make_current(wlr_output);
+	wlr_output_make_current(wlr_output, NULL);
 	wlr_renderer_begin(sample->renderer, wlr_output);
 
 	float matrix[16];

include/backend/drm/renderer.h

@@ -45,7 +45,7 @@ bool wlr_drm_plane_surfaces_init(struct wlr_drm_plane *plane, struct wlr_drm_bac
 		int32_t width, uint32_t height, uint32_t format);
 
 void wlr_drm_surface_finish(struct wlr_drm_surface *surf);
-void wlr_drm_surface_make_current(struct wlr_drm_surface *surf);
+bool wlr_drm_surface_make_current(struct wlr_drm_surface *surf, int *buffer_age);
 struct gbm_bo *wlr_drm_surface_swap_buffers(struct wlr_drm_surface *surf);
 struct gbm_bo *wlr_drm_surface_get_front(struct wlr_drm_surface *surf);
 void wlr_drm_surface_post(struct wlr_drm_surface *surf);

include/rootston/output.h

@@ -5,6 +5,8 @@
 #include <pixman.h>
 #include <wayland-server.h>
 
+#define ROOTS_OUTPUT_PREVIOUS_DAMAGE_LEN 2
+
 struct roots_desktop;
 
 struct roots_output {
@@ -15,9 +17,12 @@ struct roots_output {
 	struct roots_view *fullscreen_view;
 
 	struct timespec last_frame;
-	pixman_region32_t damage, previous_damage;
+	pixman_region32_t damage;
 	bool frame_pending;
 
+	pixman_region32_t previous_damage[ROOTS_OUTPUT_PREVIOUS_DAMAGE_LEN];
+	size_t previous_damage_idx;
+
 	struct wl_listener frame;
 	struct wl_listener mode;
 	struct wl_listener needs_swap;

include/wlr/interfaces/wlr_output.h

@@ -18,8 +18,8 @@ struct wlr_output_impl {
 		int32_t hotspot_x, int32_t hotspot_y, bool update_pixels);
 	bool (*move_cursor)(struct wlr_output *output, int x, int y);
 	void (*destroy)(struct wlr_output *output);
-	void (*make_current)(struct wlr_output *output);
-	void (*swap_buffers)(struct wlr_output *output);
+	bool (*make_current)(struct wlr_output *output, int *buffer_age);
+	bool (*swap_buffers)(struct wlr_output *output);
 	void (*set_gamma)(struct wlr_output *output,
 		uint32_t size, uint16_t *r, uint16_t *g, uint16_t *b);
 	uint32_t (*get_gamma_size)(struct wlr_output *output);

include/wlr/render/egl.h

@@ -11,8 +11,12 @@ struct wlr_egl {
 	EGLConfig config;
 	EGLContext context;
 
-	const char *egl_exts;
-	const char *gl_exts;
+	const char *egl_exts_str;
+	const char *gl_exts_str;
+
+	struct {
+		bool buffer_age;
+	} egl_exts;
 
 	struct wl_display *wl_display;
 };
@@ -65,4 +69,10 @@ bool wlr_egl_destroy_image(struct wlr_egl *egl, EGLImageKHR image);
  */
 const char *egl_error(void);
 
+bool wlr_egl_make_current(struct wlr_egl *egl, EGLSurface surface,
+	int *buffer_age);
+
+// TODO: remove
+int wlr_egl_get_buffer_age(struct wlr_egl *egl, EGLSurface surface);
+
 #endif

include/wlr/types/wlr_output.h

@@ -33,6 +33,8 @@ struct wlr_output_cursor {
 	struct wl_listener surface_destroy;
 };
 
+#define WLR_OUTPUT_PREVIOUS_DAMAGE_COUNT 2
+
 struct wlr_output_impl;
 
 struct wlr_output {
@@ -55,7 +57,7 @@ struct wlr_output {
 	enum wl_output_transform transform;
 
 	bool needs_swap;
-	pixman_region32_t damage, previous_damage;
+	pixman_region32_t damage;
 	float transform_matrix[16];
 
 	// Note: some backends may have zero modes
@@ -104,13 +106,19 @@ void wlr_output_set_scale(struct wlr_output *output, float scale);
 void wlr_output_destroy(struct wlr_output *output);
 void wlr_output_effective_resolution(struct wlr_output *output,
 	int *width, int *height);
-void wlr_output_make_current(struct wlr_output *output);
+/**
+ * Makes the output GL context current.
+ *
+ * `buffer_age` is set to the drawing buffer age in number of frames or -1 if
+ * unknown.
+ */
+bool wlr_output_make_current(struct wlr_output *output, int *buffer_age);
 /**
  * Swaps the output buffers. If the time of the frame isn't known, set `when` to
  * NULL. If the compositor doesn't support damage tracking, set `damage` to
  * NULL.
  */
-void wlr_output_swap_buffers(struct wlr_output *output, struct timespec *when,
+bool wlr_output_swap_buffers(struct wlr_output *output, struct timespec *when,
 	pixman_region32_t *damage);
 void wlr_output_set_gamma(struct wlr_output *output,
 	uint32_t size, uint16_t *r, uint16_t *g, uint16_t *b);

render/egl.c

@@ -127,18 +127,23 @@ bool wlr_egl_init(struct wlr_egl *egl, EGLenum platform, void *remote_display,
 	}
 
 	eglMakeCurrent(egl->display, EGL_NO_SURFACE, EGL_NO_SURFACE, egl->context);
-	egl->egl_exts = eglQueryString(egl->display, EGL_EXTENSIONS);
-	if (strstr(egl->egl_exts, "EGL_WL_bind_wayland_display") == NULL ||
-			strstr(egl->egl_exts, "EGL_KHR_image_base") == NULL) {
+	egl->egl_exts_str = eglQueryString(egl->display, EGL_EXTENSIONS);
+	egl->gl_exts_str = (const char*) glGetString(GL_EXTENSIONS);
+
+	wlr_log(L_INFO, "Using EGL %d.%d", (int)major, (int)minor);
+	wlr_log(L_INFO, "Supported EGL extensions: %s", egl->egl_exts_str);
+	wlr_log(L_INFO, "Using %s", glGetString(GL_VERSION));
+	wlr_log(L_INFO, "Supported OpenGL ES extensions: %s", egl->gl_exts_str);
+
+	if (strstr(egl->egl_exts_str, "EGL_WL_bind_wayland_display") == NULL ||
+			strstr(egl->egl_exts_str, "EGL_KHR_image_base") == NULL) {
 		wlr_log(L_ERROR, "Required egl extensions not supported");
 		goto error;
 	}
 
-	egl->gl_exts = (const char*) glGetString(GL_EXTENSIONS);
-	wlr_log(L_INFO, "Using EGL %d.%d", (int)major, (int)minor);
-	wlr_log(L_INFO, "Supported EGL extensions: %s", egl->egl_exts);
-	wlr_log(L_INFO, "Using %s", glGetString(GL_VERSION));
-	wlr_log(L_INFO, "Supported OpenGL ES extensions: %s", egl->gl_exts);
+	egl->egl_exts.buffer_age =
+		strstr(egl->egl_exts_str, "EGL_EXT_buffer_age") != NULL;
+
 	return true;
 
 error:
@@ -208,3 +213,32 @@ EGLSurface wlr_egl_create_surface(struct wlr_egl *egl, void *window) {
 	}
 	return surf;
 }
+
+int wlr_egl_get_buffer_age(struct wlr_egl *egl, EGLSurface surface) {
+	if (!egl->egl_exts.buffer_age) {
+		return -1;
+	}
+
+	EGLint buffer_age;
+	EGLBoolean ok = eglQuerySurface(egl->display, surface,
+		EGL_BUFFER_AGE_EXT, &buffer_age);
+	if (!ok) {
+		wlr_log(L_ERROR, "Failed to get EGL surface buffer age: %s", egl_error());
+		return -1;
+	}
+
+	return buffer_age;
+}
+
+bool wlr_egl_make_current(struct wlr_egl *egl, EGLSurface surface,
+		int *buffer_age) {
+	if (!eglMakeCurrent(egl->display, surface, surface, egl->context)) {
+		wlr_log(L_ERROR, "eglMakeCurrent failed: %s", egl_error());
+		return false;
+	}
+
+	if (buffer_age != NULL) {
+		*buffer_age = wlr_egl_get_buffer_age(egl, surface);
+	}
+	return true;
+}

rootston/output.c

@@ -294,11 +294,26 @@ static void render_output(struct roots_output *output) {
 		wlr_output_set_fullscreen_surface(wlr_output, NULL);
 	}
 
+	int buffer_age = -1;
+	wlr_output_make_current(wlr_output, &buffer_age);
+
 	pixman_region32_t damage;
 	pixman_region32_init(&damage);
-	pixman_region32_union(&damage, &output->damage, &output->previous_damage);
-	pixman_region32_intersect_rect(&damage, &damage, 0, 0, wlr_output->width,
-		wlr_output->height);
+	if (buffer_age <= 0 || buffer_age - 1 > ROOTS_OUTPUT_PREVIOUS_DAMAGE_LEN) {
+		// Buffer new or too old, damage the whole output
+		pixman_region32_union_rect(&damage, &damage, 0, 0,
+			wlr_output->width, wlr_output->height);
+	} else {
+		pixman_region32_copy(&damage, &output->damage);
+
+		size_t idx = output->previous_damage_idx;
+		for (int i = 0; i < buffer_age - 1; i++) {
+			int j = (idx + i) % ROOTS_OUTPUT_PREVIOUS_DAMAGE_LEN;
+			pixman_region32_union(&damage, &damage, &output->previous_damage[j]);
+		}
+	}
+	pixman_region32_intersect_rect(&damage, &damage, 0, 0,
+		wlr_output->width, wlr_output->height);
 
 	if (!pixman_region32_not_empty(&damage) && !wlr_output->needs_swap) {
 		// Output doesn't need swap and isn't damaged, skip rendering completely
@@ -308,7 +323,6 @@ static void render_output(struct roots_output *output) {
 
 	wlr_log(L_DEBUG, "render");
 
-	wlr_output_make_current(wlr_output);
 	wlr_renderer_begin(server->renderer, wlr_output);
 	glEnable(GL_SCISSOR_TEST);
 
@@ -384,7 +398,10 @@ renderer_end:
 	wlr_renderer_end(server->renderer);
 	wlr_output_swap_buffers(wlr_output, &now, &damage);
 	output->frame_pending = true;
-	pixman_region32_copy(&output->previous_damage, &output->damage);
+	output->previous_damage_idx += ROOTS_OUTPUT_PREVIOUS_DAMAGE_LEN - 1;
+	output->previous_damage_idx %= ROOTS_OUTPUT_PREVIOUS_DAMAGE_LEN;
+	pixman_region32_copy(&output->previous_damage[output->previous_damage_idx],
+		&output->damage);
 	pixman_region32_clear(&output->damage);
 	output->last_frame = desktop->last_frame = now;
 
@@ -551,7 +568,9 @@ void output_add_notify(struct wl_listener *listener, void *data) {
 	output->wlr_output = wlr_output;
 	wl_list_insert(&desktop->outputs, &output->link);
 	pixman_region32_init(&output->damage);
-	pixman_region32_init(&output->previous_damage);
+	for (size_t i = 0; i < ROOTS_OUTPUT_PREVIOUS_DAMAGE_LEN; ++i) {
+		pixman_region32_init(&output->previous_damage[i]);
+	}
 
 	output->frame.notify = output_handle_frame;
 	wl_signal_add(&wlr_output->events.frame, &output->frame);
@@ -610,7 +629,9 @@ void output_remove_notify(struct wl_listener *listener, void *data) {
 	//	sample->compositor);
 
 	pixman_region32_fini(&output->damage);
-	pixman_region32_fini(&output->previous_damage);
+	for (size_t i = 0; i < ROOTS_OUTPUT_PREVIOUS_DAMAGE_LEN; ++i) {
+		pixman_region32_fini(&output->previous_damage[i]);
+	}
 	wl_list_remove(&output->link);
 	wl_list_remove(&output->frame.link);
 	wl_list_remove(&output->mode.link);

types/wlr_output.c

@@ -281,7 +281,6 @@ void wlr_output_init(struct wlr_output *output, struct wlr_backend *backend,
 	wl_signal_init(&output->events.transform);
 	wl_signal_init(&output->events.destroy);
 	pixman_region32_init(&output->damage);
-	pixman_region32_init(&output->previous_damage);
 
 	output->display_destroy.notify = handle_display_destroy;
 	wl_display_add_destroy_listener(display, &output->display_destroy);
@@ -310,7 +309,6 @@ void wlr_output_destroy(struct wlr_output *output) {
 	}
 
 	pixman_region32_fini(&output->damage);
-	pixman_region32_fini(&output->previous_damage);
 
 	if (output->impl && output->impl->destroy) {
 		output->impl->destroy(output);
@@ -332,8 +330,8 @@ void wlr_output_effective_resolution(struct wlr_output *output,
 	*height /= output->scale;
 }
 
-void wlr_output_make_current(struct wlr_output *output) {
-	output->impl->make_current(output);
+bool wlr_output_make_current(struct wlr_output *output, int *buffer_age) {
+	return output->impl->make_current(output, buffer_age);
 }
 
 static void output_fullscreen_surface_get_box(struct wlr_output *output,
@@ -466,17 +464,17 @@ surface_damage_finish:
 	pixman_region32_fini(&surface_damage);
 }
 
-void wlr_output_swap_buffers(struct wlr_output *output, struct timespec *when,
+bool wlr_output_swap_buffers(struct wlr_output *output, struct timespec *when,
 		pixman_region32_t *damage) {
 	wl_signal_emit(&output->events.swap_buffers, damage);
 
 	pixman_region32_t *render_damage = damage;
 	if (damage == NULL) {
+		// Damage tracking not supported, repaint the whole output
 		pixman_region32_t output_damage;
 		pixman_region32_init(&output_damage);
-		pixman_region32_copy(&output_damage, &output->damage);
-		pixman_region32_union(&output_damage, &output_damage,
-			&output->previous_damage);
+		pixman_region32_union_rect(&output_damage, &output_damage,
+			0, 0, output->width, output->height);
 		render_damage = &output_damage;
 	}
 
@@ -503,14 +501,18 @@ void wlr_output_swap_buffers(struct wlr_output *output, struct timespec *when,
 	}
 
 	// TODO: provide `damage` (not `render_damage`) to backend
-	output->impl->swap_buffers(output);
+	if (!output->impl->swap_buffers(output)) {
+		return false;
+	}
+
 	output->needs_swap = false;
-	pixman_region32_copy(&output->previous_damage, &output->damage);
 	pixman_region32_clear(&output->damage);
 
 	if (damage == NULL) {
 		pixman_region32_fini(render_damage);
 	}
+
+	return true;
 }
 
 void wlr_output_set_gamma(struct wlr_output *output,

types/wlr_screenshooter.c

@@ -47,7 +47,6 @@ static void output_frame_notify(struct wl_listener *listener, void *_data) {
 	struct wlr_renderer *renderer = state->screenshot->screenshooter->renderer;
 	struct wlr_output *output = state->screenshot->output;
 
-	wlr_output_make_current(output);
 	wlr_renderer_read_pixels(renderer, 0, 0, output->width, output->height,
 		state->pixels);