From 08afe2611228f4a252049b49da41778e1c464ca1 Mon Sep 17 00:00:00 2001
From: Joshua Barretto <joshua.s.barretto@gmail.com>
Date: Tue, 11 Apr 2023 11:49:10 +0100
Subject: [PATCH] Directly compare rtism resources to avoid unnecessary hooks

---
 common/src/rtsim.rs     | 2 +-
 server/src/lib.rs       | 7 ++++---
 server/src/rtsim/mod.rs | 2 ++
 3 files changed, 7 insertions(+), 4 deletions(-)

diff --git a/common/src/rtsim.rs b/common/src/rtsim.rs
index e6d13d8533..aee3d932a0 100644
--- a/common/src/rtsim.rs
+++ b/common/src/rtsim.rs
@@ -233,7 +233,7 @@ pub enum NpcAction {
 
 // Note: the `serde(name = "...")` is to minimise the length of field
 // identifiers for the sake of rtsim persistence
-#[derive(Copy, Clone, Debug, Serialize, Deserialize, enum_map::Enum)]
+#[derive(Copy, Clone, Debug, Serialize, Deserialize, PartialEq, Eq, enum_map::Enum)]
 pub enum ChunkResource {
     #[serde(rename = "0")]
     Grass,
diff --git a/server/src/lib.rs b/server/src/lib.rs
index e47d3e412f..e108015a27 100644
--- a/server/src/lib.rs
+++ b/server/src/lib.rs
@@ -700,9 +700,10 @@ impl Server {
 
         fn on_block_update(ecs: &specs::World, changes: Vec<BlockDiff>) {
             // When a resource block updates, inform rtsim
-            if changes.iter().any(|c| {
-                c.old.get_rtsim_resource().is_some() || c.new.get_rtsim_resource().is_some()
-            }) {
+            if changes
+                .iter()
+                .any(|c| c.old.get_rtsim_resource() != c.new.get_rtsim_resource())
+            {
                 ecs.write_resource::<rtsim::RtSim>().hook_block_update(
                     &ecs.read_resource::<Arc<world::World>>(),
                     ecs.read_resource::<world::IndexOwned>().as_index_ref(),
diff --git a/server/src/rtsim/mod.rs b/server/src/rtsim/mod.rs
index 27ad649538..ed807d9f4e 100644
--- a/server/src/rtsim/mod.rs
+++ b/server/src/rtsim/mod.rs
@@ -159,6 +159,8 @@ impl RtSim {
         }
     }
 
+    // Note that this hook only needs to be invoked if the block change results in a
+    // change to the rtsim resource produced by [`Block::get_rtsim_resource`].
     pub fn hook_block_update(&mut self, world: &World, index: IndexRef, changes: Vec<BlockDiff>) {
         self.state
             .emit(event::OnBlockChange { changes }, world, index);