From 765e2c32c81a113102ddbbf700208155d3573a12 Mon Sep 17 00:00:00 2001
From: Camden Dixie O'Brien <cdo@wip.sh>
Date: Sat, 4 Jan 2025 13:03:19 +0000
Subject: [PATCH] Implement drawlist updating for decreasing y

---
 game/main.c | 44 +++++++++++++++++++++++++++++++++++++++++---
 1 file changed, 41 insertions(+), 3 deletions(-)

diff --git a/game/main.c b/game/main.c
index 977b2b5..e94d1ad 100644
--- a/game/main.c
+++ b/game/main.c
@@ -646,6 +646,44 @@ static void update_drawlist(dynentity_t *e, entity_t **drawlist)
 			n->prev->next = (entity_t *)e;
 			n->prev = (entity_t *)e;
 		}
+	} else {
+		// The entity moved up -- this is mostly symmetric with the
+		// above case.
+		entity_t *n = e->e.prev;
+		if (n == NULL)
+			return;
+
+		const int y = dynentity_bottom(e);
+		int prevy = entity_bottom(n);
+		if (y >= prevy)
+			return;
+
+		while (n->prev != NULL && y < prevy) {
+			n = n->prev;
+			prevy = entity_bottom(n);
+		}
+		assert(n != NULL);
+
+		if (y < prevy) {
+			e->e.prev->next = e->e.next;
+			e->e.next->prev = e->e.prev;
+
+			e->e.prev = NULL;
+			e->e.next = n;
+			*drawlist = n->prev = (entity_t *)e;
+		} else {
+			if (e->e.next == NULL) {
+				e->e.prev->next = NULL;
+			} else {
+				e->e.next->prev = e->e.prev;
+				e->e.prev->next = e->e.next;
+			}
+
+			e->e.next = n->next;
+			e->e.prev = n;
+			n->next->prev = (entity_t *)e;
+			n->next = (entity_t *)e;
+		}
 	}
 }
 
@@ -675,7 +713,8 @@ static void update_dynentity(gamestate_t *state, dynentity_t *e, double dt)
 			e->svar = SPRITE_DIR_UP;
 	}
 
-	// Apply velocity (handling map collisions)
+	// Apply velocity, handling map collisions and updating the
+	// drawlist
 	const double nextx = e->pos.x + dt * e->speed * e->dir.x;
 	const double nexty = e->pos.y + dt * e->speed * e->dir.y;
 	const dvec_t pfb
@@ -692,8 +731,7 @@ static void update_dynentity(gamestate_t *state, dynentity_t *e, double dt)
 	if (valid) {
 		e->pos.x = nextx;
 		e->pos.y = nexty;
-
-		update_drawlist(e);
+		update_drawlist(e, &state->drawlist);
 	}
 }