1 files changed, 80 insertions, 0 deletions
diff --git a/packages/webapi/src/lib/OffscreenCanvas.ts b/packages/webapi/src/lib/OffscreenCanvas.ts
new file mode 100644
index 000000000..01ee5d34a
--- /dev/null
+++ b/packages/webapi/src/lib/OffscreenCanvas.ts
@@ -0,0 +1,80 @@
+import type { CanvasRenderingContext2D } from './CanvasRenderingContext2D'
+
+import * as _ from './utils'
+import { __createCanvasRenderingContext2D } from './CanvasRenderingContext2D'
+
+export class OffscreenCanvas extends EventTarget {
+	constructor(width: number, height: number) {
+		super()
+
+		if (arguments.length < 2) throw new TypeError(`Failed to construct 'OffscreenCanvas': 2 arguments required.`)
+
+		width = Number(width) || 0
+		height = Number(height) || 0
+
+		_.INTERNALS.set(this, { width, height } as OffscreenCanvasInternals)
+	}
+
+	get height(): number {
+		return _.internalsOf(this, 'OffscreenCanvas', 'height').height
+	}
+
+	set height(value) {
+		_.internalsOf(this, 'OffscreenCanvas', 'height').height = Number(value) || 0
+	}
+
+	get width(): number {
+		return _.internalsOf(this, 'OffscreenCanvas', 'width').width
+	}
+
+	set width(value) {
+		_.internalsOf(this, 'OffscreenCanvas', 'width').width = Number(value) || 0
+	}
+
+	getContext(contextType: PredefinedContextId): CanvasRenderingContext2D | null {
+		const internals = _.internalsOf<OffscreenCanvasInternals>(this, 'HTMLCanvasElement', 'getContext')
+
+		switch (contextType) {
+			case '2d':
+				if (internals.renderingContext2D) return internals.renderingContext2D
+
+				internals.renderingContext2D = __createCanvasRenderingContext2D(this)
+
+				return internals.renderingContext2D
+			default:
+				return null
+		}
+	}
+
+	convertToBlob(options: Partial<ConvertToBlobOptions>) {
+		options = Object(options)
+
+		const quality = Number(options.quality) || 0
+		const type = getImageType(String(options.type).trim().toLowerCase())
+
+		void quality
+
+		return Promise.resolve(
+			new Blob([], { type })
+		)
+	}
+}
+
+_.allowStringTag(OffscreenCanvas)
+
+const getImageType = (type: string): PredefinedImageType => type === 'image/avif' || type === 'image/jpeg' || type === 'image/png' || type === 'image/webp' ? type : 'image/png'
+
+interface OffscreenCanvasInternals {
+	height: number
+	renderingContext2D: CanvasRenderingContext2D
+	width: number
+}
+
+interface ConvertToBlobOptions {
+	quality: number
+	type: PredefinedImageType
+}
+
+type PredefinedContextId = '2d' | 'bitmaprenderer' | 'webgl' | 'webgl2' | 'webgpu'
+
+type PredefinedImageType = 'image/avif' | 'image/jpeg' | 'image/png' | 'image/webp'