diff --git a/ewext/src/lib.rs b/ewext/src/lib.rs
index e86f7073..fe3cd9c1 100644
--- a/ewext/src/lib.rs
+++ b/ewext/src/lib.rs
@@ -39,6 +39,7 @@ extern "C" fn init_particle_world_state(lua: *mut lua_State) -> c_int {
             _world_ptr: world_pointer as *mut c_void,
             chunk_map_ptr: chunk_map_pointer as *mut c_void,
             material_list_ptr: material_list_pointer as _,
+            runner: Default::default(),
         });
     });
     0
@@ -52,8 +53,8 @@ extern "C" fn encode_area(lua: *mut lua_State) -> c_int {
     let encoded_buffer = unsafe { LUA.lua_tointeger(lua, 5) } as *mut NoitaPixelRun;
 
     STATE.with(|state| {
-        let state = state.borrow_mut();
-        let pws = state.particle_world_state.as_ref().unwrap();
+        let mut state = state.borrow_mut();
+        let pws = state.particle_world_state.as_mut().unwrap();
         let runs = unsafe { pws.encode_area(start_x, start_y, end_x, end_y, encoded_buffer) };
         unsafe { LUA.lua_pushinteger(lua, runs as isize) };
     });
diff --git a/ewext/src/noita.rs b/ewext/src/noita.rs
index 1342b2e1..e746d92a 100644
--- a/ewext/src/noita.rs
+++ b/ewext/src/noita.rs
@@ -27,7 +27,7 @@ struct PixelRun<Pixel> {
 
 /// Copied from proxy.
 /// Converts a normal sequence of pixels to a run-length-encoded one.
-struct PixelRunner<Pixel> {
+pub(crate) struct PixelRunner<Pixel> {
     current_pixel: Option<Pixel>,
     current_run_len: u32,
     runs: Vec<PixelRun<Pixel>>,
@@ -64,14 +64,20 @@ impl<Pixel: Eq + Copy> PixelRunner<Pixel> {
             self.current_run_len = 1;
         }
     }
-    fn build(mut self) -> Vec<PixelRun<Pixel>> {
+    fn build(&mut self) -> &[PixelRun<Pixel>] {
         if self.current_run_len > 0 {
             self.runs.push(PixelRun {
                 length: self.current_run_len,
                 data: self.current_pixel.expect("has current pixel"),
             });
         }
-        self.runs
+        &mut self.runs
+    }
+
+    fn clear(&mut self) {
+        self.current_pixel = None;
+        self.current_run_len = 0;
+        self.runs.clear();
     }
 }
 
@@ -79,6 +85,8 @@ pub(crate) struct ParticleWorldState {
     pub(crate) _world_ptr: *mut c_void,
     pub(crate) chunk_map_ptr: *mut c_void,
     pub(crate) material_list_ptr: *const c_void,
+
+    pub(crate) runner: PixelRunner<RawPixel>,
 }
 
 impl ParticleWorldState {
@@ -115,14 +123,13 @@ impl ParticleWorldState {
     }
 
     pub(crate) unsafe fn encode_area(
-        &self,
+        &mut self,
         start_x: i32,
         start_y: i32,
         end_x: i32,
         end_y: i32,
         pixel_runs: *mut NoitaPixelRun,
     ) -> usize {
-        let mut runner = PixelRunner::default();
         for y in start_y..end_y {
             for x in start_x..end_x {
                 let mut raw_pixel = RawPixel {
@@ -148,12 +155,12 @@ impl ParticleWorldState {
                         ntypes::CellType::Invalid => {}
                     }
                 }
-                runner.put_pixel(raw_pixel);
+                self.runner.put_pixel(raw_pixel);
             }
         }
 
         let mut pixel_runs = pixel_runs;
-        let built_runner = runner.build();
+        let built_runner = self.runner.build();
         let runs = built_runner.len();
         for run in built_runner {
             let noita_pixel_run = pixel_runs.as_mut().unwrap();
@@ -162,6 +169,7 @@ impl ParticleWorldState {
             noita_pixel_run.flags = run.data.flags;
             pixel_runs = pixel_runs.offset(1);
         }
+        self.runner.clear();
         runs
     }
 }