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.

3 files changed, 41 insertions, 4 deletions

diff --git a/include/wlr/render/interface.h b/include/wlr/render/interface.h
index 709ae481..c352efe1 100644
--- a/include/wlr/render/interface.h
+++ b/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,
diff --git a/include/wlr/render/wlr_renderer.h b/include/wlr/render/wlr_renderer.h
index 33668067..a150930c 100644
--- a/include/wlr/render/wlr_renderer.h
+++ b/include/wlr/render/wlr_renderer.h
@@ -162,13 +162,22 @@ 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_renderer *renderer, struct wlr_buffer *buffer);
+struct wlr_render_pass *wlr_renderer_begin_buffer_pass(struct wlr_renderer *renderer,
+	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
diff --git a/include/wlr/types/wlr_output.h b/include/wlr/types/wlr_output.h
index be8253af..e096a3ce 100644
--- a/include/wlr/types/wlr_output.h
+++ b/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);
 
 
 /**