LibWeb: Implement basics for OffscreenCanvas

This implements the basic interface, classes and functions for OffscreenCanvas. Many are still stubbed out and have many FIXMEs in them, but it is a basic skeleton.
Author: https://github.com/Totto16 Commit: 2ad3ce5d37 Pull-request: https://github.com/LadybirdBrowser/ladybird/pull/3788 Reviewed-by: https://github.com/ADKaster ✅ Reviewed-by: https://github.com/tcl3
2025-07-31 21:29:06 +00:00 · 2025-03-07 00:19:45 +01:00 · 2025-03-07 00:19:45 +01:00 · 2ad3ce5d37 · 2025-06-30 15:47:43 +00:00
commit 2ad3ce5d37
parent 193ab3757b
14 changed files with 1094 additions and 4 deletions
--- a/Libraries/LibWeb/HTML/OffscreenCanvas.h
+++ b/Libraries/LibWeb/HTML/OffscreenCanvas.h
@ -0,0 +1,91 @@
+/*
+ * Copyright (c) 2025, Ladybird contributors
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <LibGfx/Bitmap.h>
+#include <LibWeb/Bindings/PlatformObject.h>
+#include <LibWeb/Bindings/Transferable.h>
+#include <LibWeb/DOM/EventTarget.h>
+#include <LibWeb/Forward.h>
+#include <LibWeb/WebIDL/Types.h>
+
+namespace Web::HTML {
+
+// https://html.spec.whatwg.org/multipage/canvas.html#offscreenrenderingcontext
+// NOTE: This is the Variant created by the IDL wrapper generator, and needs to be updated accordingly.
+using OffscreenRenderingContext = Variant<GC::Root<OffscreenCanvasRenderingContext2D>, GC::Root<WebGL::WebGLRenderingContext>, GC::Root<WebGL::WebGL2RenderingContext>, Empty>;
+
+// https://html.spec.whatwg.org/multipage/canvas.html#imageencodeoptions
+struct ImageEncodeOptions {
+    FlyString type { "image/png"_fly_string };
+    Optional<double> quality;
+};
+
+// https://html.spec.whatwg.org/multipage/canvas.html#offscreencanvas
+class OffscreenCanvas : public DOM::EventTarget
+    , public Web::Bindings::Transferable {
+    WEB_PLATFORM_OBJECT(OffscreenCanvas, DOM::EventTarget);
+    GC_DECLARE_ALLOCATOR(OffscreenCanvas);
+
+public:
+    static GC::Ref<OffscreenCanvas> create(JS::Realm&, WebIDL::UnsignedLong width,
+        WebIDL::UnsignedLong height);
+
+    static WebIDL::ExceptionOr<GC::Ref<OffscreenCanvas>> construct_impl(
+        JS::Realm&,
+        WebIDL::UnsignedLong width,
+        WebIDL::UnsignedLong height);
+
+    virtual ~OffscreenCanvas() override;
+
+    // ^Web::Bindings::Transferable
+    virtual WebIDL::ExceptionOr<void> transfer_steps(HTML::TransferDataHolder&) override;
+    virtual WebIDL::ExceptionOr<void> transfer_receiving_steps(HTML::TransferDataHolder&) override;
+    virtual HTML::TransferType primary_interface() const override;
+
+    WebIDL::UnsignedLong width() const;
+    WebIDL::UnsignedLong height() const;
+
+    NonnullRefPtr<Gfx::Bitmap> bitmap() const;
+
+    WebIDL::ExceptionOr<void> set_width(WebIDL::UnsignedLong);
+    WebIDL::ExceptionOr<void> set_height(WebIDL::UnsignedLong);
+
+    Gfx::IntSize bitmap_size_for_canvas() const;
+
+    JS::ThrowCompletionOr<OffscreenRenderingContext> get_context(Bindings::OffscreenRenderingContextId contextId, JS::Value options);
+
+    WebIDL::ExceptionOr<GC::Ref<ImageBitmap>> transfer_to_image_bitmap();
+
+    GC::Ref<WebIDL::Promise> convert_to_blob(Optional<ImageEncodeOptions> options);
+
+    void set_oncontextlost(GC::Ptr<WebIDL::CallbackType>);
+    GC::Ptr<WebIDL::CallbackType> oncontextlost();
+    void set_oncontextrestored(GC::Ptr<WebIDL::CallbackType>);
+    GC::Ptr<WebIDL::CallbackType> oncontextrestored();
+
+private:
+    OffscreenCanvas(JS::Realm&, NonnullRefPtr<Gfx::Bitmap> bitmap);
+
+    virtual void initialize(JS::Realm&) override;
+    virtual void visit_edges(Cell::Visitor&) override;
+
+    enum class HasOrCreatedContext {
+        No,
+        Yes,
+    };
+    JS::ThrowCompletionOr<HasOrCreatedContext> create_2d_context(JS::Value options);
+
+    void reset_context_to_default_state();
+    void set_new_bitmap_size(Gfx::IntSize new_size);
+
+    Variant<GC::Ref<HTML::OffscreenCanvasRenderingContext2D>, GC::Ref<WebGL::WebGLRenderingContext>, GC::Ref<WebGL::WebGL2RenderingContext>, Empty> m_context;
+
+    NonnullRefPtr<Gfx::Bitmap> m_bitmap;
+};
+
+}