types: add wlr_damage_ring

wlr_damage_ring is effectively wlr_output_damage untied from wlr_output.

include/wlr/types/wlr_damage_ring.h

@@ -0,0 +1,81 @@
+/*
+ * 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_DAMAGE_RING_H
+#define WLR_TYPES_WLR_DAMAGE_RING_H
+
+#include <stdbool.h>
+
+/* For triple buffering, a history of two frames is required. */
+#define WLR_DAMAGE_RING_PREVIOUS_LEN 2
+
+struct wlr_box;
+
+struct wlr_damage_ring {
+	int32_t width, height;
+
+	// Difference between the current buffer and the previous one
+	pixman_region32_t current;
+
+	// private state
+
+	pixman_region32_t previous[WLR_DAMAGE_RING_PREVIOUS_LEN];
+	size_t previous_idx;
+};
+
+void wlr_damage_ring_init(struct wlr_damage_ring *ring);
+
+void wlr_damage_ring_finish(struct wlr_damage_ring *ring);
+
+/**
+ * Set ring bounds and damage the ring fully.
+ *
+ * Next time damage will be added, it will be cropped to the ring bounds.
+ * If at least one of the dimensions is 0, bounds are removed.
+ *
+ * By default, a damage ring doesn't have bounds.
+ */
+void wlr_damage_ring_set_bounds(struct wlr_damage_ring *ring,
+	int32_t width, int32_t height);
+
+/**
+ * Add a region to the current damage.
+ *
+ * Returns true if the region intersects the ring bounds, false otherwise.
+ */
+bool wlr_damage_ring_add(struct wlr_damage_ring *ring,
+	pixman_region32_t *damage);
+
+/**
+ * Add a box to the current damage.
+ *
+ * Returns true if the box intersects the ring bounds, false otherwise.
+ */
+bool wlr_damage_ring_add_box(struct wlr_damage_ring *ring,
+	const struct wlr_box *box);
+
+/**
+ * Damage the ring fully.
+ */
+void wlr_damage_ring_add_whole(struct wlr_damage_ring *ring);
+
+/**
+ * Rotate the damage ring. This needs to be called after using the accumulated
+ * damage, e.g. after rendering to an output's back buffer.
+ */
+void wlr_damage_ring_rotate(struct wlr_damage_ring *ring);
+
+/**
+ * Get accumulated damage, which is the difference between the current buffer
+ * and the buffer with age of buffer_age; in context of rendering, this is
+ * the region that needs to be redrawn.
+ */
+void wlr_damage_ring_get_buffer_damage(struct wlr_damage_ring *ring,
+	int buffer_age, pixman_region32_t *damage);
+
+#endif