add render timer API

Based on five calls:
wlr_render_timer_create - creates a timer which can be reused across
  frames on the same renderer
wlr_renderer_begin_buffer_pass - now takes a timer so that backends can
  record when the rendering starts and finishes
wlr_render_timer_get_time - should be called as late as possible so that
  queries can make their way back from the GPU
wlr_render_timer_destroy - self-explanatory

The timer is exposed as an opaque `struct wlr_render_timer` so that
backends can store whatever they want in there.

backend/drm/renderer.c

@@ -102,7 +102,7 @@ struct wlr_buffer *drm_surface_blit(struct wlr_drm_surface *surf,
 		goto error_tex;
 	}
 
-	struct wlr_render_pass *pass = wlr_renderer_begin_buffer_pass(renderer, dst);
+	struct wlr_render_pass *pass = wlr_renderer_begin_buffer_pass(renderer, dst, NULL);
 	if (pass == NULL) {
 		wlr_log(WLR_ERROR, "Failed to begin render pass with multi-GPU destination buffer");
 		goto error_dst;

examples/fullscreen-shell.c

@@ -90,7 +90,8 @@ static void output_handle_frame(struct wl_listener *listener, void *data) {
 	wlr_output_effective_resolution(output->wlr_output, &width, &height);
 
 	struct wlr_output_state state = {0};
-	struct wlr_render_pass *pass = wlr_output_begin_render_pass(output->wlr_output, &state, NULL);
+	struct wlr_render_pass *pass = wlr_output_begin_render_pass(output->wlr_output, &state, NULL,
+		NULL);
 	if (pass == NULL) {
 		return;
 	}

examples/output-layers.c

@@ -94,7 +94,8 @@ static void output_handle_frame(struct wl_listener *listener, void *data) {
 	wlr_output_effective_resolution(output->wlr_output, &width, &height);
 
 	struct wlr_output_state output_state = {0};
-	struct wlr_render_pass *pass = wlr_output_begin_render_pass(output->wlr_output, &output_state, NULL);
+	struct wlr_render_pass *pass = wlr_output_begin_render_pass(output->wlr_output, &output_state,
+		NULL, NULL);
 
 	wlr_render_pass_add_rect(pass, &(struct wlr_render_rect_options){
 		.box = { .width = width, .height = height },

examples/output-layout.c

@@ -115,7 +115,7 @@ static void output_frame_notify(struct wl_listener *listener, void *data) {
 	struct wlr_output *wlr_output = output->output;
 
 	struct wlr_output_state output_state = {0};
-	struct wlr_render_pass *pass = wlr_output_begin_render_pass(wlr_output, &output_state, NULL);
+	struct wlr_render_pass *pass = wlr_output_begin_render_pass(wlr_output, &output_state, NULL, NULL);
 
 	wlr_render_pass_add_rect(pass, &(struct wlr_render_rect_options){
 		.box = { .width = wlr_output->width, .height = wlr_output->height },

examples/pointer.c

@@ -102,7 +102,7 @@ static void output_frame_notify(struct wl_listener *listener, void *data) {
 	assert(renderer);
 
 	struct wlr_output_state output_state = {0};
-	struct wlr_render_pass *pass = wlr_output_begin_render_pass(wlr_output, &output_state, NULL);
+	struct wlr_render_pass *pass = wlr_output_begin_render_pass(wlr_output, &output_state, NULL, NULL);
 	wlr_render_pass_add_rect(pass, &(struct wlr_render_rect_options){
 		.box = { .width = wlr_output->width, .height = wlr_output->height },
 		.color = {

examples/rotation.c

@@ -60,7 +60,7 @@ static void output_frame_notify(struct wl_listener *listener, void *data) {
 	wlr_output_effective_resolution(wlr_output, &width, &height);
 
 	struct wlr_output_state output_state = {0};
-	struct wlr_render_pass *pass = wlr_output_begin_render_pass(wlr_output, &output_state, NULL);
+	struct wlr_render_pass *pass = wlr_output_begin_render_pass(wlr_output, &output_state, NULL, NULL);
 
 	wlr_render_pass_add_rect(pass, &(struct wlr_render_rect_options){
 		.box = { .width = wlr_output->width, .height = wlr_output->height },

examples/simple.c

@@ -63,7 +63,7 @@ static void output_frame_notify(struct wl_listener *listener, void *data) {
 	}
 
 	struct wlr_output_state state = {0};
-	struct wlr_render_pass *pass = wlr_output_begin_render_pass(wlr_output, &state, NULL);
+	struct wlr_render_pass *pass = wlr_output_begin_render_pass(wlr_output, &state, NULL, NULL);
 	wlr_render_pass_add_rect(pass, &(struct wlr_render_rect_options){
 		.box = { .width = wlr_output->width, .height = wlr_output->height },
 		.color = {

examples/tablet.c

@@ -88,7 +88,7 @@ static void output_frame_notify(struct wl_listener *listener, void *data) {
 	wlr_output_effective_resolution(wlr_output, &width, &height);
 
 	struct wlr_output_state output_state = {0};
-	struct wlr_render_pass *pass = wlr_output_begin_render_pass(wlr_output, &output_state, NULL);
+	struct wlr_render_pass *pass = wlr_output_begin_render_pass(wlr_output, &output_state, NULL, NULL);
 
 	wlr_render_pass_add_rect(pass, &(struct wlr_render_rect_options){
 		.box = { .width = wlr_output->width, .height = wlr_output->height },

examples/touch.c

@@ -77,7 +77,7 @@ static void output_frame_notify(struct wl_listener *listener, void *data) {
 	wlr_output_effective_resolution(wlr_output, &width, &height);
 
 	struct wlr_output_state output_state = {0};
-	struct wlr_render_pass *pass = wlr_output_begin_render_pass(wlr_output, &output_state, NULL);
+	struct wlr_render_pass *pass = wlr_output_begin_render_pass(wlr_output, &output_state, NULL, NULL);
 	wlr_render_pass_add_rect(pass, &(struct wlr_render_rect_options){
 		.box = { .width = width, .height = height },
 		.color = { 0.25, 0.25, 0.25, 1 },

include/wlr/render/interface.h

@@ -49,7 +49,8 @@ struct wlr_renderer_impl {
 	struct wlr_texture *(*texture_from_buffer)(struct wlr_renderer *renderer,
 		struct wlr_buffer *buffer);
 	struct wlr_render_pass *(*begin_buffer_pass)(struct wlr_renderer *renderer,
-		struct wlr_buffer *buffer);
+		struct wlr_buffer *buffer, struct wlr_buffer_pass_options *options);
+	struct wlr_render_timer *(*render_timer_create)(struct wlr_renderer *renderer);
 };
 
 void wlr_renderer_init(struct wlr_renderer *renderer,
@@ -79,6 +80,15 @@ struct wlr_render_pass_impl {
 		const struct wlr_render_rect_options *options);
 };
 
+struct wlr_render_timer {
+	const struct wlr_render_timer_impl *impl;
+};
+
+struct wlr_render_timer_impl {
+	int (*get_duration_ns)(struct wlr_render_timer *timer);
+	void (*destroy)(struct wlr_render_timer *timer);
+};
+
 void wlr_render_texture_options_get_src_box(const struct wlr_render_texture_options *options,
 	struct wlr_fbox *box);
 void wlr_render_texture_options_get_dst_box(const struct wlr_render_texture_options *options,

include/wlr/render/wlr_renderer.h

@@ -161,14 +161,23 @@ void wlr_renderer_destroy(struct wlr_renderer *renderer);
  */
 struct wlr_render_pass;
 
+/**
+ * An object that can be queried after a render to get the duration of the render.
+ */
+struct wlr_render_timer;
+
+struct wlr_buffer_pass_options {
+	struct wlr_render_timer *timer;
+};
+
 /**
  * Begin a new render pass with the supplied destination buffer.
  *
  * Callers must call wlr_render_pass_submit() once they are done with the
  * render pass.
  */
-struct wlr_render_pass *wlr_renderer_begin_buffer_pass(
+struct wlr_render_pass *wlr_renderer_begin_buffer_pass(struct wlr_renderer *renderer,
-	struct wlr_renderer *renderer, struct wlr_buffer *buffer);
+	struct wlr_buffer *buffer, struct wlr_buffer_pass_options *options);
 
 /**
  * Submit the render pass.
@@ -235,4 +244,21 @@ struct wlr_render_rect_options {
 void wlr_render_pass_add_rect(struct wlr_render_pass *render_pass,
 	const struct wlr_render_rect_options *options);
 
+/**
+ * Allocate and initialise a new render timer.
+ */
+struct wlr_render_timer *wlr_render_timer_create(struct wlr_renderer *renderer);
+
+/**
+ * Get the render duration in nanoseconds from the timer.
+ *
+ * Returns -1 if the duration is unavailable.
+ */
+int wlr_render_timer_get_duration_ns(struct wlr_render_timer *timer);
+
+/**
+ * Destroy the render timer.
+ */
+void wlr_render_timer_destroy(struct wlr_render_timer *timer);
+
 #endif

include/wlr/types/wlr_output.h

@@ -14,6 +14,7 @@
 #include <time.h>
 #include <wayland-server-protocol.h>
 #include <wayland-util.h>
+#include <wlr/render/wlr_renderer.h>
 #include <wlr/types/wlr_buffer.h>
 #include <wlr/util/addon.h>
 
@@ -590,7 +591,7 @@ bool wlr_output_configure_primary_swapchain(struct wlr_output *output,
  * Same as wlr_output_attach_render(), but returns a struct wlr_render_pass.
  */
 struct wlr_render_pass *wlr_output_begin_render_pass(struct wlr_output *output,
-	struct wlr_output_state *state, int *buffer_age);
+	struct wlr_output_state *state, int *buffer_age, struct wlr_render_timer *timer);
 
 
 /**

render/gles2/renderer.c

@@ -537,7 +537,7 @@ static void gles2_destroy(struct wlr_renderer *wlr_renderer) {
 }
 
 static struct wlr_render_pass *gles2_begin_buffer_pass(struct wlr_renderer *wlr_renderer,
-		struct wlr_buffer *wlr_buffer) {
+		struct wlr_buffer *wlr_buffer, struct wlr_buffer_pass_options *options) {
 	struct wlr_gles2_renderer *renderer = gles2_get_renderer(wlr_renderer);
 	if (!wlr_egl_make_current(renderer->egl)) {
 		return NULL;

render/pixman/renderer.c

@@ -494,7 +494,7 @@ static uint32_t pixman_get_render_buffer_caps(struct wlr_renderer *renderer) {
 }
 
 static struct wlr_render_pass *pixman_begin_buffer_pass(struct wlr_renderer *wlr_renderer,
-		struct wlr_buffer *wlr_buffer) {
+		struct wlr_buffer *wlr_buffer, struct wlr_buffer_pass_options *options) {
 	struct wlr_pixman_renderer *renderer = get_renderer(wlr_renderer);
 
 	struct wlr_pixman_buffer *buffer = get_buffer(renderer, wlr_buffer);

render/vulkan/renderer.c

@@ -1916,7 +1916,8 @@ static uint32_t vulkan_get_render_buffer_caps(struct wlr_renderer *wlr_renderer)
 	return WLR_BUFFER_CAP_DMABUF;
 }
 
-static struct wlr_render_pass *vulkan_begin_buffer_pass(struct wlr_renderer *wlr_renderer, struct wlr_buffer *buffer) {
+static struct wlr_render_pass *vulkan_begin_buffer_pass(struct wlr_renderer *wlr_renderer,
+		struct wlr_buffer *buffer, struct wlr_buffer_pass_options *options) {
 	struct wlr_vk_renderer *renderer = vulkan_get_renderer(wlr_renderer);
 
 	struct wlr_vk_render_buffer *render_buffer = get_render_buffer(renderer, buffer);

render/wlr_renderer.c

@@ -413,10 +413,31 @@ int wlr_renderer_get_drm_fd(struct wlr_renderer *r) {
 	return r->impl->get_drm_fd(r);
 }
 
-struct wlr_render_pass *wlr_renderer_begin_buffer_pass(
+struct wlr_render_pass *wlr_renderer_begin_buffer_pass(struct wlr_renderer *renderer,
-		struct wlr_renderer *renderer, struct wlr_buffer *buffer) {
+		struct wlr_buffer *buffer, struct wlr_buffer_pass_options *options) {
 	if (!renderer->impl->begin_buffer_pass) {
 		return begin_legacy_buffer_render_pass(renderer, buffer);
 	}
-	return renderer->impl->begin_buffer_pass(renderer, buffer);
+	return renderer->impl->begin_buffer_pass(renderer, buffer, options);
+}
+
+struct wlr_render_timer *wlr_render_timer_create(struct wlr_renderer *renderer) {
+	if (!renderer->impl->render_timer_create) {
+		return NULL;
+	}
+	return renderer->impl->render_timer_create(renderer);
+}
+
+int wlr_render_timer_get_duration_ns(struct wlr_render_timer *timer) {
+	if (!timer->impl->get_duration_ns) {
+		return -1;
+	}
+	return timer->impl->get_duration_ns(timer);
+}
+
+void wlr_render_timer_destroy(struct wlr_render_timer *timer) {
+	if (!timer->impl->destroy) {
+		return;
+	}
+	timer->impl->destroy(timer);
 }

types/output/cursor.c

@@ -318,7 +318,7 @@ static struct wlr_buffer *render_cursor_buffer(struct wlr_output_cursor *cursor)
 	wlr_box_transform(&dst_box, &dst_box, wlr_output_transform_invert(output->transform),
 		buffer->width, buffer->height);
 
-	struct wlr_render_pass *pass = wlr_renderer_begin_buffer_pass(renderer, buffer);
+	struct wlr_render_pass *pass = wlr_renderer_begin_buffer_pass(renderer, buffer, NULL);
 	if (pass == NULL) {
 		wlr_buffer_unlock(buffer);
 		return NULL;

types/output/render.c

@@ -249,7 +249,7 @@ uint32_t wlr_output_preferred_read_format(struct wlr_output *output) {
 }
 
 struct wlr_render_pass *wlr_output_begin_render_pass(struct wlr_output *output,
-		struct wlr_output_state *state, int *buffer_age) {
+		struct wlr_output_state *state, int *buffer_age, struct wlr_render_timer *timer) {
 	if (!wlr_output_configure_primary_swapchain(output, state, &output->swapchain)) {
 		return NULL;
 	}
@@ -261,7 +261,10 @@ struct wlr_render_pass *wlr_output_begin_render_pass(struct wlr_output *output,
 
 	struct wlr_renderer *renderer = output->renderer;
 	assert(renderer != NULL);
-	struct wlr_render_pass *pass = wlr_renderer_begin_buffer_pass(renderer, buffer);
+	struct wlr_render_pass *pass = wlr_renderer_begin_buffer_pass(renderer, buffer,
+			&(struct wlr_buffer_pass_options){
+		.timer = timer,
+	});
 	if (pass == NULL) {
 		return NULL;
 	}

types/scene/wlr_scene.c

@@ -1673,7 +1673,7 @@ bool wlr_scene_output_commit(struct wlr_scene_output *scene_output) {
 	wlr_damage_ring_get_buffer_damage(&scene_output->damage_ring,
 		buffer_age, &damage);
 
-	struct wlr_render_pass *render_pass = wlr_renderer_begin_buffer_pass(renderer, buffer);
+	struct wlr_render_pass *render_pass = wlr_renderer_begin_buffer_pass(renderer, buffer, NULL);
 	if (render_pass == NULL) {
 		pixman_region32_fini(&damage);
 		wlr_buffer_unlock(buffer);