From eb5529e4334483068caec416a7d2e8682d39d859 Mon Sep 17 00:00:00 2001
From: Andreas Monitzer <a.monitzer@dungeonfog.com>
Date: Sun, 2 Oct 2022 20:59:21 +0200
Subject: [PATCH] Implemented support for creating a render surface from canvas
 or offscreencanvas elements on the wasm target.

---
 crates/bevy_render/src/lib.rs         | 11 +++++++++++
 crates/bevy_render/src/view/window.rs | 15 +++++++++++++++
 crates/bevy_window/src/window.rs      | 24 ++++++++++++++++++++++++
 3 files changed, 50 insertions(+)

diff --git a/crates/bevy_render/src/lib.rs b/crates/bevy_render/src/lib.rs
index adf5a97c19a8d7..0cd77ea856aa62 100644
--- a/crates/bevy_render/src/lib.rs
+++ b/crates/bevy_render/src/lib.rs
@@ -147,6 +147,17 @@ impl Plugin for RenderPlugin {
             let surface = {
                 let windows = app.world.resource_mut::<bevy_window::Windows>();
                 let raw_handle = windows.get_primary().map(|window| unsafe {
+                    #[cfg(target_arch = "wasm32")]
+                    if let Some(canvas) = &window.canvas_element {
+                        return match canvas {
+                            bevy_window::Canvas::HtmlCanvas(canvas) => {
+                                instance.create_surface_from_canvas(canvas)
+                            }
+                            bevy_window::Canvas::OffscreenCanvas(canvas) => {
+                                instance.create_surface_from_offscreen_canvas(canvas)
+                            }
+                        };
+                    }
                     let handle = window.raw_window_handle().get_handle();
                     instance.create_surface(&handle)
                 });
diff --git a/crates/bevy_render/src/view/window.rs b/crates/bevy_render/src/view/window.rs
index 6fe1bc8627fdaf..1488d51a90848c 100644
--- a/crates/bevy_render/src/view/window.rs
+++ b/crates/bevy_render/src/view/window.rs
@@ -47,6 +47,8 @@ pub struct ExtractedWindow {
     pub swap_chain_texture: Option<TextureView>,
     pub size_changed: bool,
     pub present_mode_changed: bool,
+    #[cfg(target_arch = "wasm32")]
+    pub canvas: Option<bevy_window::Canvas>,
 }
 
 #[derive(Default, Resource)]
@@ -92,6 +94,8 @@ fn extract_windows(
                     swap_chain_texture: None,
                     size_changed: false,
                     present_mode_changed: false,
+                    #[cfg(target_arch = "wasm32")]
+                    canvas: window.canvas_element.clone(),
                 });
 
         // NOTE: Drop the swap chain frame here
@@ -168,6 +172,17 @@ pub fn prepare_windows(
             .surfaces
             .entry(window.id)
             .or_insert_with(|| unsafe {
+                #[cfg(target_arch = "wasm32")]
+                if let Some(canvas) = &window.canvas {
+                    return match canvas {
+                        bevy_window::Canvas::HtmlCanvas(canvas) => {
+                            render_instance.create_surface_from_canvas(canvas)
+                        }
+                        bevy_window::Canvas::OffscreenCanvas(canvas) => {
+                            render_instance.create_surface_from_offscreen_canvas(canvas)
+                        }
+                    };
+                }
                 // NOTE: On some OSes this MUST be called from the main thread.
                 render_instance.create_surface(&window.handle.get_handle())
             });
diff --git a/crates/bevy_window/src/window.rs b/crates/bevy_window/src/window.rs
index 127eb4ca5a2cae..4de575e44cb11f 100644
--- a/crates/bevy_window/src/window.rs
+++ b/crates/bevy_window/src/window.rs
@@ -210,6 +210,8 @@ pub struct Window {
     focused: bool,
     mode: WindowMode,
     canvas: Option<String>,
+    #[cfg(target_arch = "wasm32")]
+    pub canvas_element: Option<Canvas>,
     fit_canvas_to_parent: bool,
     command_queue: Vec<WindowCommand>,
 }
@@ -339,6 +341,8 @@ impl Window {
             focused: true,
             mode: window_descriptor.mode,
             canvas: window_descriptor.canvas.clone(),
+            #[cfg(target_arch = "wasm32")]
+            canvas_element: window_descriptor.canvas_element.clone(),
             fit_canvas_to_parent: window_descriptor.fit_canvas_to_parent,
             command_queue: Vec::new(),
         }
@@ -781,6 +785,17 @@ pub enum MonitorSelection {
     Index(usize),
 }
 
+#[cfg(target_arch = "wasm32")]
+#[derive(Clone, Debug, PartialEq, Eq)]
+pub enum Canvas {
+    HtmlCanvas(web_sys::HtmlCanvasElement),
+    OffscreenCanvas(web_sys::OffscreenCanvas),
+}
+#[cfg(target_arch = "wasm32")]
+unsafe impl Send for Canvas {}
+#[cfg(target_arch = "wasm32")]
+unsafe impl Sync for Canvas {}
+
 /// Describes the information needed for creating a window.
 ///
 /// This should be set up before adding the [`WindowPlugin`](crate::WindowPlugin).
@@ -859,6 +874,8 @@ pub struct WindowDescriptor {
     ///
     /// This value has no effect on non-web platforms.
     pub canvas: Option<String>,
+    #[cfg(target_arch = "wasm32")]
+    pub canvas_element: Option<Canvas>,
     /// Whether or not to fit the canvas element's size to its parent element's size.
     ///
     /// **Warning**: this will not behave as expected for parents that set their size according to the size of their
@@ -869,6 +886,11 @@ pub struct WindowDescriptor {
     pub fit_canvas_to_parent: bool,
 }
 
+#[cfg(target_arch = "wasm32")]
+unsafe impl Send for WindowDescriptor {}
+#[cfg(target_arch = "wasm32")]
+unsafe impl Sync for WindowDescriptor {}
+
 impl Default for WindowDescriptor {
     fn default() -> Self {
         WindowDescriptor {
@@ -887,6 +909,8 @@ impl Default for WindowDescriptor {
             mode: WindowMode::Windowed,
             transparent: false,
             canvas: None,
+            #[cfg(target_arch = "wasm32")]
+            canvas_element: None,
             fit_canvas_to_parent: false,
         }
     }