From 12ccb7d72e928d687b0e8697e36bcad2795a524f Mon Sep 17 00:00:00 2001
From: daxpedda <daxpedda@gmail.com>
Date: Sun, 17 Dec 2023 23:10:20 +0100
Subject: [PATCH] Make sure pointer to `HtmlCanvasElement` doesn't change

---
 src/platform_impl/web/web_sys/canvas.rs  | 12 +++++++++---
 src/platform_impl/web/web_sys/pointer.rs |  4 ++--
 src/platform_impl/web/window.rs          |  1 +
 3 files changed, 12 insertions(+), 5 deletions(-)

diff --git a/src/platform_impl/web/web_sys/canvas.rs b/src/platform_impl/web/web_sys/canvas.rs
index 5cece3889ff..8d60f49a1ee 100644
--- a/src/platform_impl/web/web_sys/canvas.rs
+++ b/src/platform_impl/web/web_sys/canvas.rs
@@ -1,4 +1,5 @@
 use std::cell::Cell;
+use std::ops::Deref;
 use std::rc::Rc;
 use std::sync::{Arc, Mutex};
 
@@ -49,7 +50,8 @@ pub struct Common {
     pub window: web_sys::Window,
     pub document: Document,
     /// Note: resizing the HTMLCanvasElement should go through `backend::set_canvas_size` to ensure the DPI factor is maintained.
-    pub raw: HtmlCanvasElement,
+    /// Note: this is read-only because we use a pointer to this for [`WindowHandle`](rwh_06::WindowHandle).
+    raw: Rc<HtmlCanvasElement>,
     style: Style,
     old_size: Rc<Cell<PhysicalSize<u32>>>,
     current_size: Rc<Cell<PhysicalSize<u32>>>,
@@ -101,7 +103,7 @@ impl Canvas {
         let common = Common {
             window: window.clone(),
             document: document.clone(),
-            raw: canvas.clone(),
+            raw: Rc::new(canvas.clone()),
             style,
             old_size: Rc::default(),
             current_size: Rc::default(),
@@ -539,7 +541,11 @@ impl Common {
         E: 'static + AsRef<web_sys::Event> + wasm_bindgen::convert::FromWasmAbi,
         F: 'static + FnMut(E),
     {
-        EventListenerHandle::new(self.raw.clone(), event_name, Closure::new(handler))
+        EventListenerHandle::new(self.raw.deref().clone(), event_name, Closure::new(handler))
+    }
+
+    pub fn raw(&self) -> &HtmlCanvasElement {
+        &self.raw
     }
 }
 
diff --git a/src/platform_impl/web/web_sys/pointer.rs b/src/platform_impl/web/web_sys/pointer.rs
index 71f128a959e..dbfe3476a7f 100644
--- a/src/platform_impl/web/web_sys/pointer.rs
+++ b/src/platform_impl/web/web_sys/pointer.rs
@@ -117,7 +117,7 @@ impl PointerHandler {
         T: 'static + FnMut(ModifiersState, i32, PhysicalPosition<f64>, Force),
     {
         let window = canvas_common.window.clone();
-        let canvas = canvas_common.raw.clone();
+        let canvas = canvas_common.raw().clone();
         self.on_pointer_press = Some(canvas_common.add_event(
             "pointerdown",
             move |event: PointerEvent| {
@@ -174,7 +174,7 @@ impl PointerHandler {
         B: 'static + FnMut(ModifiersState, i32, PhysicalPosition<f64>, ButtonsState, MouseButton),
     {
         let window = canvas_common.window.clone();
-        let canvas = canvas_common.raw.clone();
+        let canvas = canvas_common.raw().clone();
         self.on_cursor_move = Some(canvas_common.add_event(
             "pointermove",
             move |event: PointerEvent| {
diff --git a/src/platform_impl/web/window.rs b/src/platform_impl/web/window.rs
index bd88f0763c3..8b7fb75949d 100644
--- a/src/platform_impl/web/window.rs
+++ b/src/platform_impl/web/window.rs
@@ -93,6 +93,7 @@ impl Window {
             .value()
             .map(|inner| {
                 let canvas = inner.canvas.borrow();
+                // SAFETY: This will only work if the reference to `HtmlCanvasElement` stays valid.
                 let canvas: &wasm_bindgen::JsValue = canvas.raw();
                 let window_handle =
                     rwh_06::WebCanvasWindowHandle::new(std::ptr::NonNull::from(canvas).cast());