From 600d995e94dc3892b727d787e722eadb4fcbad5e Mon Sep 17 00:00:00 2001
From: Alexander Orzechowski <alex@ozal.ski>
Date: Wed, 12 Jul 2023 23:08:34 -0400
Subject: [PATCH] wlr_damage_ring: Rework to use list instead of fixed length
 ring

When we add buffer support this model of keeping a fixed size list
simply won't be compatible.
---
 include/wlr/types/wlr_damage_ring.h |  9 ++--
 types/wlr_damage_ring.c             | 72 ++++++++++++++++++-----------
 2 files changed, 49 insertions(+), 32 deletions(-)

diff --git a/include/wlr/types/wlr_damage_ring.h b/include/wlr/types/wlr_damage_ring.h
index 3f1ad70ed..457448c20 100644
--- a/include/wlr/types/wlr_damage_ring.h
+++ b/include/wlr/types/wlr_damage_ring.h
@@ -13,14 +13,14 @@
 #include <stddef.h>
 #include <stdint.h>
 #include <pixman.h>
-
-/* For triple buffering, a history of two frames is required. */
-#define WLR_DAMAGE_RING_PREVIOUS_LEN 2
+#include <wayland-server-core.h>
 
 struct wlr_box;
 
 struct wlr_damage_ring_entry {
 	pixman_region32_t damage;
+
+	struct wl_list link; // struct wlr_damage_ring.previous
 };
 
 struct wlr_damage_ring {
@@ -31,8 +31,7 @@ struct wlr_damage_ring {
 
 	// private state
 
-	struct wlr_damage_ring_entry previous[WLR_DAMAGE_RING_PREVIOUS_LEN];
-	size_t previous_idx;
+	struct wl_list previous; // struct wlr_damage_ring_entry.link
 };
 
 void wlr_damage_ring_init(struct wlr_damage_ring *ring);
diff --git a/types/wlr_damage_ring.c b/types/wlr_damage_ring.c
index 361f4802f..0862d91fa 100644
--- a/types/wlr_damage_ring.c
+++ b/types/wlr_damage_ring.c
@@ -14,15 +14,21 @@ void wlr_damage_ring_init(struct wlr_damage_ring *ring) {
 	};
 
 	pixman_region32_init(&ring->current);
-	for (size_t i = 0; i < WLR_DAMAGE_RING_PREVIOUS_LEN; ++i) {
-		pixman_region32_init(&ring->previous[i].damage);
-	}
+	wl_list_init(&ring->previous);
+}
+
+static void entry_destroy(struct wlr_damage_ring_entry *entry) {
+	wl_list_remove(&entry->link);
+	pixman_region32_fini(&entry->damage);
+	free(entry);
 }
 
 void wlr_damage_ring_finish(struct wlr_damage_ring *ring) {
 	pixman_region32_fini(&ring->current);
-	for (size_t i = 0; i < WLR_DAMAGE_RING_PREVIOUS_LEN; ++i) {
-		pixman_region32_fini(&ring->previous[i].damage);
+
+	struct wlr_damage_ring_entry *entry, *tmp_entry;
+	wl_list_for_each_safe(entry, tmp_entry, &ring->previous, link) {
+		entry_destroy(entry);
 	}
 }
 
@@ -79,38 +85,50 @@ void wlr_damage_ring_add_whole(struct wlr_damage_ring *ring) {
 }
 
 void wlr_damage_ring_rotate(struct wlr_damage_ring *ring) {
-	// modular decrement
-	ring->previous_idx = ring->previous_idx +
-		WLR_DAMAGE_RING_PREVIOUS_LEN - 1;
-	ring->previous_idx %= WLR_DAMAGE_RING_PREVIOUS_LEN;
+	struct wlr_damage_ring_entry *last =
+		wl_container_of(ring->previous.prev, last, link);
+	wl_list_remove(&last->link);
+	wl_list_insert(&ring->previous, &last->link);
 
-	pixman_region32_copy(&ring->previous[ring->previous_idx].damage, &ring->current);
+	pixman_region32_copy(&last->damage, &ring->current);
 	pixman_region32_clear(&ring->current);
 }
 
 void wlr_damage_ring_get_buffer_damage(struct wlr_damage_ring *ring,
 		int buffer_age, pixman_region32_t *damage) {
-	if (buffer_age <= 0 || buffer_age - 1 > WLR_DAMAGE_RING_PREVIOUS_LEN) {
+	pixman_region32_copy(damage, &ring->current);
+
+	// Accumulate damage from old buffers
+	struct wlr_damage_ring_entry *entry;
+	wl_list_for_each(entry, &ring->previous, link) {
+		if (--buffer_age <= 0) {
+			break;
+		}
+
+		pixman_region32_union(damage, damage, &entry->damage);
+	}
+
+	// if our buffer age is older than anything we are keeping track of, increase
+	// the size
+	if (buffer_age > 0) {
 		pixman_region32_clear(damage);
 		pixman_region32_union_rect(damage, damage,
 			0, 0, ring->width, ring->height);
-	} else {
-		pixman_region32_copy(damage, &ring->current);
 
-		// Accumulate damage from old buffers
-		for (int i = 0; i < buffer_age - 1; ++i) {
-			int j = (ring->previous_idx + i) % WLR_DAMAGE_RING_PREVIOUS_LEN;
-			pixman_region32_union(damage, damage, &ring->previous[j].damage);
-		}
-
-		// Check the number of rectangles
-		int n_rects = pixman_region32_n_rects(damage);
-		if (n_rects > WLR_DAMAGE_RING_MAX_RECTS) {
-			pixman_box32_t *extents = pixman_region32_extents(damage);
-			pixman_region32_union_rect(damage, damage,
-				extents->x1, extents->y1,
-				extents->x2 - extents->x1,
-				extents->y2 - extents->y1);
+		struct wlr_damage_ring_entry *entry = calloc(1, sizeof(*entry));
+		if (entry) {
+			pixman_region32_init(&entry->damage);
+			wl_list_insert(ring->previous.prev, &entry->link);
 		}
 	}
+
+	// Check the number of rectangles
+	int n_rects = pixman_region32_n_rects(damage);
+	if (n_rects > WLR_DAMAGE_RING_MAX_RECTS) {
+		pixman_box32_t *extents = pixman_region32_extents(damage);
+		pixman_region32_union_rect(damage, damage,
+			extents->x1, extents->y1,
+			extents->x2 - extents->x1,
+			extents->y2 - extents->y1);
+	}
 }