Add frame scheduler interface

include/wlr/interfaces/wlr_frame_scheduler.h

@@ -0,0 +1,26 @@
+/*
+ * This an unstable interface of wlroots. No guarantees are made regarding the
+ * future consistency of this API.
+ */
+#ifndef WLR_USE_UNSTABLE
+#error "Add -DWLR_USE_UNSTABLE to enable unstable wlroots features"
+#endif
+
+#ifndef WLR_INTERFACES_WLR_FRAME_SCHEDULER_H
+#define WLR_INTERFACES_WLR_FRAME_SCHEDULER_H
+
+struct wlr_frame_scheduler;
+struct wlr_output;
+
+struct wlr_frame_scheduler_impl {
+	/**
+	 * Ensure that the scheduler->frame signal will be fired in the future.
+	 */
+	void (*schedule_frame)(struct wlr_frame_scheduler *scheduler);
+	void (*destroy)(struct wlr_frame_scheduler *scheduler);
+};
+
+void wlr_frame_scheduler_init(struct wlr_frame_scheduler *scheduler,
+	const struct wlr_frame_scheduler_impl *impl, struct wlr_output *output);
+
+#endif

include/wlr/types/wlr_frame_scheduler.h

@@ -0,0 +1,58 @@
+/*
+ * This an unstable interface of wlroots. No guarantees are made regarding the
+ * future consistency of this API.
+ */
+#ifndef WLR_USE_UNSTABLE
+#error "Add -DWLR_USE_UNSTABLE to enable unstable wlroots features"
+#endif
+
+#ifndef WLR_TYPES_WLR_FRAME_SCHEDULER_H
+#define WLR_TYPES_WLR_FRAME_SCHEDULER_H
+
+#include <stdbool.h>
+#include <wayland-server-core.h>
+
+struct wlr_frame_scheduler_impl;
+
+struct wlr_frame_scheduler {
+	struct wlr_output *output;
+
+	struct {
+		struct wl_signal frame;
+	} events;
+
+	// Whether the render loop should be kept awake. True if wlr_frame_scheduler_schedule_frame()
+	// was called since the last frame event.
+	bool needs_frame;
+
+	// private state
+
+	const struct wlr_frame_scheduler_impl *impl;
+
+	struct wl_listener backend_needs_frame;
+};
+
+/**
+ * The present scheduler maintains a render loop based on `wlr_output.events.present`. To wake the
+ * render loop, it emits the frame signal when the compositor's event loop is idle.
+ */
+struct wlr_frame_scheduler *wlr_present_scheduler_create(struct wlr_output *output);
+
+/**
+ * Creates an appropriate frame scheduler for the given output's backend capabilities.
+ */
+struct wlr_frame_scheduler *wlr_frame_scheduler_autocreate(struct wlr_output *output);
+/**
+ * Inform the scheduler that a frame signal is needed. The scheduler implementation will choose a
+ * good time to emit the signal. The signal is emitted only if this function has been called at
+ * least once since the last signal.
+ */
+void wlr_frame_scheduler_schedule_frame(struct wlr_frame_scheduler *scheduler);
+/**
+ * Emits a frame signal if `wlr_frame_scheduler_schedule_frame()` has been called since the last
+ * frame signal.
+ */
+void wlr_frame_scheduler_emit_frame(struct wlr_frame_scheduler *scheduler);
+void wlr_frame_scheduler_destroy(struct wlr_frame_scheduler *scheduler);
+
+#endif