Advance Blender 5.2 web parity through M12-03D

web/app/src/assets/AssetPreviewDisplay.ts

@@ -0,0 +1,87 @@
+import { planAssetPreviewDecode } from "../../../protocol/asset-preview-decode";
+import type { AssetPreviewIdentityIR } from "../../../protocol/asset-preview";
+
+export type AssetPreviewDisplayBackend = "MAIN_THREAD_CANVAS_2D" | "OFFSCREEN_CANVAS_2D";
+
+export interface AssetPreviewDisplayReceiptIR {
+  schemaVersion: 1;
+  status: "READY";
+  backend: AssetPreviewDisplayBackend;
+  identitySha256: string;
+  contentSha256: string;
+  width: number;
+  height: number;
+  pixelByteLength: number;
+  pixelSha256: string;
+  nonTransparentPixels: number;
+  bitmapClosed: true;
+}
+
+export interface AssetPreviewDisplayResultIR {
+  receipt: AssetPreviewDisplayReceiptIR;
+  pixels: Uint8Array;
+}
+
+type PreviewCanvas = HTMLCanvasElement | OffscreenCanvas;
+
+async function sha256Bytes(value: Uint8Array): Promise<string> {
+  const digest = await crypto.subtle.digest("SHA-256", Uint8Array.from(value).buffer);
+  return Array.from(new Uint8Array(digest), (byte) => byte.toString(16).padStart(2, "0")).join("");
+}
+
+export async function displayAssetPreview(
+  canvas: PreviewCanvas,
+  backend: AssetPreviewDisplayBackend,
+  identityValue: unknown,
+  encodedBytes: ArrayBuffer,
+): Promise<AssetPreviewDisplayResultIR> {
+  const plan = await planAssetPreviewDecode(identityValue, encodedBytes);
+  if (typeof createImageBitmap !== "function") throw new Error("CAPABILITY_MISSING: createImageBitmap is unavailable");
+  const identity = identityValue as AssetPreviewIdentityIR;
+  const bitmap = await createImageBitmap(new Blob([encodedBytes], { type: plan.mimeType }), {
+    colorSpaceConversion: "none",
+    premultiplyAlpha: "none",
+    imageOrientation: "none",
+  });
+  try {
+    if (bitmap.width !== plan.width || bitmap.height !== plan.height) {
+      throw new Error("ASSET_PREVIEW_IDENTITY_MISMATCH: decoded preview dimensions changed");
+    }
+    canvas.width = plan.width;
+    canvas.height = plan.height;
+    const context = canvas.getContext("2d", { alpha: true, willReadFrequently: true }) as
+      | CanvasRenderingContext2D
+      | OffscreenCanvasRenderingContext2D
+      | null;
+    if (!context) throw new Error("CAPABILITY_MISSING: preview Canvas2D context is unavailable");
+    context.clearRect(0, 0, plan.width, plan.height);
+    context.imageSmoothingEnabled = false;
+    context.globalCompositeOperation = "copy";
+    context.drawImage(bitmap, 0, 0, plan.width, plan.height);
+    const pixels = new Uint8Array(context.getImageData(0, 0, plan.width, plan.height).data);
+    let nonTransparentPixels = 0;
+    for (let offset = 3; offset < pixels.byteLength; offset += 4) if (pixels[offset] !== 0) nonTransparentPixels++;
+    const receipt: AssetPreviewDisplayReceiptIR = {
+      schemaVersion: 1,
+      status: "READY",
+      backend,
+      identitySha256: identity.identitySha256,
+      contentSha256: identity.content.sha256,
+      width: plan.width,
+      height: plan.height,
+      pixelByteLength: pixels.byteLength,
+      pixelSha256: await sha256Bytes(pixels),
+      nonTransparentPixels,
+      bitmapClosed: true,
+    };
+    if (typeof HTMLCanvasElement !== "undefined" && canvas instanceof HTMLCanvasElement) {
+      canvas.dataset.assetPreviewStatus = "ready";
+      canvas.dataset.assetPreviewBackend = backend;
+      canvas.dataset.assetPreviewPixelSha256 = receipt.pixelSha256;
+    }
+    return { receipt, pixels };
+  }
+  finally {
+    bitmap.close();
+  }
+}