webgpu: implement get image for webgpu canvas (#35237)

* Implement `get_image_data` for WebGPU canvas

Signed-off-by: sagudev <16504129+sagudev@users.noreply.github.com>

* Update expectations

Signed-off-by: sagudev <16504129+sagudev@users.noreply.github.com>

* Add docs

Signed-off-by: sagudev <16504129+sagudev@users.noreply.github.com>

---------

Signed-off-by: sagudev <16504129+sagudev@users.noreply.github.com>

6 files changed, 50 insertions, 40 deletions

diff --git a/components/script/dom/htmlcanvaselement.rs b/components/script/dom/htmlcanvaselement.rs
index aee09ee4dd2..8fb2832915a 100644
--- a/components/script/dom/htmlcanvaselement.rs
+++ b/components/script/dom/htmlcanvaselement.rs
@@ -420,10 +420,7 @@ impl HTMLCanvasElement {
                 return None;
             },
             #[cfg(feature = "webgpu")]
-            Some(&CanvasContext::WebGPU(_)) => {
-                // TODO: add a method in GPUCanvasContext to get the pixels.
-                return None;
-            },
+            Some(CanvasContext::WebGPU(context)) => Some(context.get_ipc_image()),
             Some(CanvasContext::Placeholder(context)) => {
                 let (sender, receiver) =
                     ipc::channel(self.global().time_profiler_chan().clone()).unwrap();
@@ -450,9 +447,8 @@ impl HTMLCanvasElement {
             Some(CanvasContext::WebGL2(ref context)) => {
                 context.base_context().get_image_data(self.get_size())
             },
-            //TODO: Add method get_image_data to GPUCanvasContext
             #[cfg(feature = "webgpu")]
-            Some(CanvasContext::WebGPU(_)) => None,
+            Some(CanvasContext::WebGPU(ref context)) => Some(context.get_image_data()),
             Some(CanvasContext::Placeholder(_)) | None => {
                 // Each pixel is fully-transparent black.
                 Some(vec![0; (self.Width() * self.Height() * 4) as usize])
diff --git a/components/script/dom/webgpu/gpucanvascontext.rs b/components/script/dom/webgpu/gpucanvascontext.rs
index 51627071271..e1cfd4e5176 100644
--- a/components/script/dom/webgpu/gpucanvascontext.rs
+++ b/components/script/dom/webgpu/gpucanvascontext.rs
@@ -8,7 +8,7 @@ use std::cell::RefCell;
 use arrayvec::ArrayVec;
 use dom_struct::dom_struct;
 use euclid::default::Size2D;
-use ipc_channel::ipc;
+use ipc_channel::ipc::{self, IpcSharedMemory};
 use script_layout_interface::HTMLCanvasDataSource;
 use webgpu::swapchain::WebGPUContextId;
 use webgpu::wgc::id;
@@ -306,6 +306,28 @@ impl GPUCanvasContext {
                 .replace(Some(self.texture_descriptor_for_canvas(configuration)));
         }
     }
+
+    /// <https://gpuweb.github.io/gpuweb/#ref-for-abstract-opdef-get-a-copy-of-the-image-contents-of-a-context%E2%91%A5>
+    pub(crate) fn get_ipc_image(&self) -> IpcSharedMemory {
+        // 1. Return a copy of the image contents of context.
+        if self.drawing_buffer.borrow().cleared {
+            IpcSharedMemory::from_byte(0, self.size().area() as usize * 4)
+        } else {
+            let (sender, receiver) = ipc::channel().unwrap();
+            self.channel
+                .0
+                .send(WebGPURequest::GetImage {
+                    context_id: self.context_id,
+                    sender,
+                })
+                .unwrap();
+            receiver.recv().unwrap()
+        }
+    }
+
+    pub(crate) fn get_image_data(&self) -> Vec<u8> {
+        self.get_ipc_image().to_vec()
+    }
 }
 
 impl LayoutCanvasRenderingContextHelpers for LayoutDom<'_, GPUCanvasContext> {
diff --git a/components/webgpu/ipc_messages/recv.rs b/components/webgpu/ipc_messages/recv.rs
index 0ae97e4ec22..6355cb932a8 100644
--- a/components/webgpu/ipc_messages/recv.rs
+++ b/components/webgpu/ipc_messages/recv.rs
@@ -154,6 +154,11 @@ pub enum WebGPURequest {
         texture_id: id::TextureId,
         encoder_id: id::CommandEncoderId,
     },
+    /// Obtains image from latest presentation buffer (same as wr update)
+    GetImage {
+        context_id: WebGPUContextId,
+        sender: IpcSender<IpcSharedMemory>,
+    },
     ValidateTextureDescriptor {
         device_id: id::DeviceId,
         texture_id: id::TextureId,
diff --git a/components/webgpu/swapchain.rs b/components/webgpu/swapchain.rs
index b1512eae809..cc4a645aba9 100644
--- a/components/webgpu/swapchain.rs
+++ b/components/webgpu/swapchain.rs
@@ -9,7 +9,7 @@ use std::sync::{Arc, Mutex};
 
 use arrayvec::ArrayVec;
 use euclid::default::Size2D;
-use ipc_channel::ipc::IpcSender;
+use ipc_channel::ipc::{IpcSender, IpcSharedMemory};
 use log::{error, warn};
 use malloc_size_of::MallocSizeOf;
 use serde::{Deserialize, Serialize};
@@ -382,6 +382,22 @@ impl crate::WGPU {
         );
     }
 
+    pub(crate) fn get_image(&self, context_id: WebGPUContextId) -> IpcSharedMemory {
+        let webgpu_contexts = self.wgpu_image_map.lock().unwrap();
+        let context_data = webgpu_contexts.get(&context_id).unwrap();
+        let buffer_size = context_data.image_desc.buffer_size();
+        let data = if let Some(present_buffer) = context_data
+            .swap_chain
+            .as_ref()
+            .and_then(|swap_chain| swap_chain.data.as_ref())
+        {
+            IpcSharedMemory::from_bytes(present_buffer.slice())
+        } else {
+            IpcSharedMemory::from_byte(0, buffer_size as usize)
+        };
+        data
+    }
+
     pub(crate) fn update_context(
         &self,
         context_id: WebGPUContextId,
diff --git a/components/webgpu/wgpu_thread.rs b/components/webgpu/wgpu_thread.rs
index e03513a0dbb..63b7825723c 100644
--- a/components/webgpu/wgpu_thread.rs
+++ b/components/webgpu/wgpu_thread.rs
@@ -531,6 +531,9 @@ impl WGPU {
                             log::error!("Error occured in SwapChainPresent: {e:?}");
                         }
                     },
+                    WebGPURequest::GetImage { context_id, sender } => {
+                        sender.send(self.get_image(context_id)).unwrap()
+                    },
                     WebGPURequest::ValidateTextureDescriptor {
                         device_id,
                         texture_id,
diff --git a/tests/wpt/webgpu/meta/webgpu/cts.https.html.ini b/tests/wpt/webgpu/meta/webgpu/cts.https.html.ini
index bf265f02b54..d92953110f2 100644
--- a/tests/wpt/webgpu/meta/webgpu/cts.https.html.ini
+++ b/tests/wpt/webgpu/meta/webgpu/cts.https.html.ini
@@ -546023,48 +546023,32 @@
       if os == "linux" and not debug: FAIL
 
   [:format="bgra8unorm";alphaMode="opaque";colorSpace="display-p3";snapshotType="toBlob"]
-    expected:
-      if os == "linux" and not debug: FAIL
 
   [:format="bgra8unorm";alphaMode="opaque";colorSpace="display-p3";snapshotType="toDataURL"]
-    expected:
-      if os == "linux" and not debug: FAIL
 
   [:format="bgra8unorm";alphaMode="opaque";colorSpace="srgb";snapshotType="imageBitmap"]
     expected:
       if os == "linux" and not debug: FAIL
 
   [:format="bgra8unorm";alphaMode="opaque";colorSpace="srgb";snapshotType="toBlob"]
-    expected:
-      if os == "linux" and not debug: FAIL
 
   [:format="bgra8unorm";alphaMode="opaque";colorSpace="srgb";snapshotType="toDataURL"]
-    expected:
-      if os == "linux" and not debug: FAIL
 
   [:format="bgra8unorm";alphaMode="premultiplied";colorSpace="display-p3";snapshotType="imageBitmap"]
     expected:
       if os == "linux" and not debug: FAIL
 
   [:format="bgra8unorm";alphaMode="premultiplied";colorSpace="display-p3";snapshotType="toBlob"]
-    expected:
-      if os == "linux" and not debug: FAIL
 
   [:format="bgra8unorm";alphaMode="premultiplied";colorSpace="display-p3";snapshotType="toDataURL"]
-    expected:
-      if os == "linux" and not debug: FAIL
 
   [:format="bgra8unorm";alphaMode="premultiplied";colorSpace="srgb";snapshotType="imageBitmap"]
     expected:
       if os == "linux" and not debug: FAIL
 
   [:format="bgra8unorm";alphaMode="premultiplied";colorSpace="srgb";snapshotType="toBlob"]
-    expected:
-      if os == "linux" and not debug: FAIL
 
   [:format="bgra8unorm";alphaMode="premultiplied";colorSpace="srgb";snapshotType="toDataURL"]
-    expected:
-      if os == "linux" and not debug: FAIL
 
   [:format="rgba16float";alphaMode="opaque";colorSpace="display-p3";snapshotType="imageBitmap"]
     expected:
@@ -546119,48 +546103,32 @@
       if os == "linux" and not debug: FAIL
 
   [:format="rgba8unorm";alphaMode="opaque";colorSpace="display-p3";snapshotType="toBlob"]
-    expected:
-      if os == "linux" and not debug: FAIL
 
   [:format="rgba8unorm";alphaMode="opaque";colorSpace="display-p3";snapshotType="toDataURL"]
-    expected:
-      if os == "linux" and not debug: FAIL
 
   [:format="rgba8unorm";alphaMode="opaque";colorSpace="srgb";snapshotType="imageBitmap"]
     expected:
       if os == "linux" and not debug: FAIL
 
   [:format="rgba8unorm";alphaMode="opaque";colorSpace="srgb";snapshotType="toBlob"]
-    expected:
-      if os == "linux" and not debug: FAIL
 
   [:format="rgba8unorm";alphaMode="opaque";colorSpace="srgb";snapshotType="toDataURL"]
-    expected:
-      if os == "linux" and not debug: FAIL
 
   [:format="rgba8unorm";alphaMode="premultiplied";colorSpace="display-p3";snapshotType="imageBitmap"]
     expected:
       if os == "linux" and not debug: FAIL
 
   [:format="rgba8unorm";alphaMode="premultiplied";colorSpace="display-p3";snapshotType="toBlob"]
-    expected:
-      if os == "linux" and not debug: FAIL
 
   [:format="rgba8unorm";alphaMode="premultiplied";colorSpace="display-p3";snapshotType="toDataURL"]
-    expected:
-      if os == "linux" and not debug: FAIL
 
   [:format="rgba8unorm";alphaMode="premultiplied";colorSpace="srgb";snapshotType="imageBitmap"]
     expected:
       if os == "linux" and not debug: FAIL
 
   [:format="rgba8unorm";alphaMode="premultiplied";colorSpace="srgb";snapshotType="toBlob"]
-    expected:
-      if os == "linux" and not debug: FAIL
 
   [:format="rgba8unorm";alphaMode="premultiplied";colorSpace="srgb";snapshotType="toDataURL"]
-    expected:
-      if os == "linux" and not debug: FAIL
 
 
 [cts.https.html?q=webgpu:web_platform,canvas,readbackFromWebGPUCanvas:onscreenCanvas,uploadToWebGL:*]