core: move damage ring related fields in session_t into a separate struct

Signed-off-by: Yuxuan Shui <yshuiv7@gmail.com>

src/backend/backend.c

@@ -42,17 +42,7 @@ region_t get_damage(session_t *ps, bool all_damage) {
 	}
 
 	pixman_region32_init(&region);
-	if (buffer_age == -1 || buffer_age > ps->ndamage) {
-		pixman_region32_copy(&region, &ps->screen_reg);
-	} else {
-		for (int i = 0; i < buffer_age; i++) {
-			auto curr = ((ps->damage - ps->damage_ring) + i) % ps->ndamage;
-			log_trace("damage index: %d, damage ring offset: %td", i, curr);
-			dump_region(&ps->damage_ring[curr]);
-			pixman_region32_union(&region, &region, &ps->damage_ring[curr]);
-		}
-		pixman_region32_intersect(&region, &region, &ps->screen_reg);
-	}
+	damage_ring_collect(&ps->damage_ring, &ps->screen_reg, &region, buffer_age);
 	return region;
 }
 
@@ -529,11 +519,7 @@ bool paint_all_new(session_t *ps, struct managed_win *const t) {
 	}
 
 	// Move the head of the damage ring
-	ps->damage = ps->damage - 1;
-	if (ps->damage < ps->damage_ring) {
-		ps->damage = ps->damage_ring + ps->ndamage - 1;
-	}
-	pixman_region32_clear(ps->damage);
+	damage_ring_advance(&ps->damage_ring);
 
 	if (ps->backend_data->ops->present) {
 		// Present the rendered scene

src/common.h

@@ -134,6 +134,18 @@ struct shader_info {
 	UT_hash_handle hh;
 };
 
+struct damage_ring {
+	/// Cache a xfixes region so we don't need to allocate it every time.
+	/// A workaround for yshui/picom#301
+	xcb_xfixes_region_t x_region;
+	/// The region needs to painted on next paint.
+	int cursor;
+	/// The region damaged on the last paint.
+	region_t *damages;
+	/// Number of damage regions we track
+	int count;
+};
+
 /// Structure containing all necessary data for a session.
 typedef struct session {
 	// === Event handlers ===
@@ -250,16 +262,8 @@ typedef struct session {
 	/// to the screen that's neither included in the current render, nor on the
 	/// screen.
 	bool render_queued;
-
-	/// Cache a xfixes region so we don't need to allocate it every time.
-	/// A workaround for yshui/picom#301
-	xcb_xfixes_region_t damaged_region;
-	/// The region needs to painted on next paint.
-	region_t *damage;
-	/// The region damaged on the last paint.
-	region_t *damage_ring;
-	/// Number of damage regions we track
-	int ndamage;
+	/// For tracking damage regions
+	struct damage_ring damage_ring;
 	/// Whether all windows are currently redirected.
 	bool redirected;
 	/// Pre-generated alpha pictures.
@@ -518,3 +522,24 @@ static inline void wintype_arr_enable(bool arr[]) {
 		arr[i] = true;
 	}
 }
+
+static inline void damage_ring_advance(struct damage_ring *ring) {
+	ring->cursor--;
+	if (ring->cursor < 0) {
+		ring->cursor += ring->count;
+	}
+	pixman_region32_clear(&ring->damages[ring->cursor]);
+}
+
+static inline void damage_ring_collect(struct damage_ring *ring, region_t *all_region,
+                                       region_t *region, int buffer_age) {
+	if (buffer_age == -1 || buffer_age > ring->count) {
+		pixman_region32_copy(region, all_region);
+	} else {
+		for (int i = 0; i < buffer_age; i++) {
+			auto curr = (ring->cursor + i) % ring->count;
+			pixman_region32_union(region, region, &ring->damages[curr]);
+		}
+		pixman_region32_intersect(region, region, all_region);
+	}
+}

src/event.c

@@ -629,12 +629,12 @@ static inline void repair_win(session_t *ps, struct managed_win *w) {
 		}
 		win_extents(w, &parts);
 	} else {
-		auto cookie =
-		    xcb_damage_subtract(ps->c.c, w->damage, XCB_NONE, ps->damaged_region);
+		auto cookie = xcb_damage_subtract(ps->c.c, w->damage, XCB_NONE,
+		                                  ps->damage_ring.x_region);
 		if (!ps->o.show_all_xerrors) {
 			set_ignore_cookie(&ps->c, cookie);
 		}
-		x_fetch_region(&ps->c, ps->damaged_region, &parts);
+		x_fetch_region(&ps->c, ps->damage_ring.x_region, &parts);
 		pixman_region32_translate(&parts, w->g.x + w->g.border_width,
 		                          w->g.y + w->g.border_width);
 	}

src/picom.c

@@ -464,7 +464,9 @@ void add_damage(session_t *ps, const region_t *damage) {
 	}
 	log_trace("Adding damage: ");
 	dump_region(damage);
-	pixman_region32_union(ps->damage, ps->damage, (region_t *)damage);
+
+	auto cursor = &ps->damage_ring.damages[ps->damage_ring.cursor];
+	pixman_region32_union(cursor, cursor, (region_t *)damage);
 }
 
 // === Fading ===
@@ -853,10 +855,10 @@ static void configure_root(session_t *ps) {
 	}
 
 	if (ps->redirected) {
-		for (int i = 0; i < ps->ndamage; i++) {
-			pixman_region32_clear(&ps->damage_ring[i]);
+		for (int i = 0; i < ps->damage_ring.count; i++) {
+			pixman_region32_clear(&ps->damage_ring.damages[i]);
 		}
-		ps->damage = ps->damage_ring + ps->ndamage - 1;
+		ps->damage_ring.cursor = ps->damage_ring.count - 1;
 #ifdef CONFIG_OPENGL
 		// GLX root change callback
 		if (BKEND_GLX == ps->o.backend && ps->o.legacy_backends) {
@@ -1531,15 +1533,15 @@ static bool redirect_start(session_t *ps) {
 
 	if (!ps->o.legacy_backends) {
 		assert(ps->backend_data);
-		ps->ndamage = ps->backend_data->ops->max_buffer_age;
+		ps->damage_ring.count = ps->backend_data->ops->max_buffer_age;
 	} else {
-		ps->ndamage = maximum_buffer_age(ps);
+		ps->damage_ring.count = maximum_buffer_age(ps);
 	}
-	ps->damage_ring = ccalloc(ps->ndamage, region_t);
-	ps->damage = ps->damage_ring + ps->ndamage - 1;
+	ps->damage_ring.damages = ccalloc(ps->damage_ring.count, region_t);
+	ps->damage_ring.cursor = ps->damage_ring.count - 1;
 
-	for (int i = 0; i < ps->ndamage; i++) {
-		pixman_region32_init(&ps->damage_ring[i]);
+	for (int i = 0; i < ps->damage_ring.count; i++) {
+		pixman_region32_init(&ps->damage_ring.damages[i]);
 	}
 
 	ps->frame_pacing = !ps->o.no_frame_pacing && ps->o.vsync;
@@ -1613,12 +1615,13 @@ static void unredirect(session_t *ps) {
 	}
 
 	// Free the damage ring
-	for (int i = 0; i < ps->ndamage; ++i) {
-		pixman_region32_fini(&ps->damage_ring[i]);
+	for (int i = 0; i < ps->damage_ring.count; ++i) {
+		pixman_region32_fini(&ps->damage_ring.damages[i]);
 	}
-	ps->ndamage = 0;
-	free(ps->damage_ring);
-	ps->damage_ring = ps->damage = NULL;
+	ps->damage_ring.count = 0;
+	free(ps->damage_ring.damages);
+	ps->damage_ring.cursor = 0;
+	ps->damage_ring.damages = NULL;
 
 	if (ps->vblank_scheduler) {
 		vblank_scheduler_free(ps->vblank_scheduler);
@@ -2209,8 +2212,9 @@ static session_t *session_init(int argc, char **argv, Display *dpy,
 	                                                    XCB_XFIXES_MINOR_VERSION)
 	                               .sequence);
 
-	ps->damaged_region = x_new_id(&ps->c);
-	if (!XCB_AWAIT_VOID(xcb_xfixes_create_region, ps->c.c, ps->damaged_region, 0, NULL)) {
+	ps->damage_ring.x_region = x_new_id(&ps->c);
+	if (!XCB_AWAIT_VOID(xcb_xfixes_create_region, ps->c.c, ps->damage_ring.x_region,
+	                    0, NULL)) {
 		log_fatal("Failed to create a XFixes region");
 		goto err;
 	}
@@ -2706,9 +2710,9 @@ static void session_destroy(session_t *ps) {
 		ps->debug_window = XCB_NONE;
 	}
 
-	if (ps->damaged_region != XCB_NONE) {
-		xcb_xfixes_destroy_region(ps->c.c, ps->damaged_region);
-		ps->damaged_region = XCB_NONE;
+	if (ps->damage_ring.x_region != XCB_NONE) {
+		xcb_xfixes_destroy_region(ps->c.c, ps->damage_ring.x_region);
+		ps->damage_ring.x_region = XCB_NONE;
 	}
 
 	if (!ps->o.legacy_backends) {

src/render.c

@@ -1009,16 +1009,7 @@ void paint_all(session_t *ps, struct managed_win *t) {
 
 	region_t region;
 	pixman_region32_init(&region);
-	int buffer_age = get_buffer_age(ps);
-	if (buffer_age == -1 || buffer_age > ps->ndamage) {
-		pixman_region32_copy(&region, &ps->screen_reg);
-	} else {
-		for (int i = 0; i < get_buffer_age(ps); i++) {
-			auto curr = ((ps->damage - ps->damage_ring) + i) % ps->ndamage;
-			pixman_region32_union(&region, &region, &ps->damage_ring[curr]);
-		}
-	}
-
+	damage_ring_collect(&ps->damage_ring, &ps->screen_reg, &region, get_buffer_age(ps));
 	if (!pixman_region32_not_empty(&region)) {
 		return;
 	}
@@ -1219,11 +1210,7 @@ void paint_all(session_t *ps, struct managed_win *t) {
 	pixman_region32_fini(&reg_shadow_clip);
 
 	// Move the head of the damage ring
-	ps->damage = ps->damage - 1;
-	if (ps->damage < ps->damage_ring) {
-		ps->damage = ps->damage_ring + ps->ndamage - 1;
-	}
-	pixman_region32_clear(ps->damage);
+	damage_ring_advance(&ps->damage_ring);
 
 	// Do this as early as possible
 	set_tgt_clip(ps, &ps->screen_reg);