feat(canvas): add mixer drag-resize and mixer->render bake

tests/image-pipeline/backend-router.test.ts

@@ -17,6 +17,13 @@ const sourceLoaderMocks = vi.hoisted(() => ({
 
 vi.mock("@/lib/image-pipeline/source-loader", () => ({
   loadSourceBitmap: sourceLoaderMocks.loadSourceBitmap,
+  loadRenderSourceBitmap: ({ sourceUrl }: { sourceUrl?: string }) => {
+    if (!sourceUrl) {
+      throw new Error("Render source is required.");
+    }
+
+    return sourceLoaderMocks.loadSourceBitmap(sourceUrl);
+  },
 }));
 
 function createPreviewPixels(): Uint8ClampedArray {

tests/image-pipeline/image-pipeline.worker.test.ts

@@ -0,0 +1,113 @@
+import { beforeEach, describe, expect, it, vi } from "vitest";
+
+import type { RenderFullResult, RenderSourceComposition } from "@/lib/image-pipeline/render-types";
+
+const bridgeMocks = vi.hoisted(() => ({
+  renderFull: vi.fn(),
+}));
+
+const previewRendererMocks = vi.hoisted(() => ({
+  renderPreview: vi.fn(),
+}));
+
+vi.mock("@/lib/image-pipeline/bridge", () => ({
+  renderFull: bridgeMocks.renderFull,
+}));
+
+vi.mock("@/lib/image-pipeline/preview-renderer", () => ({
+  renderPreview: previewRendererMocks.renderPreview,
+}));
+
+type WorkerMessage = {
+  kind: "full";
+  requestId: number;
+  payload: {
+    sourceUrl?: string;
+    sourceComposition?: RenderSourceComposition;
+    steps: [];
+    render: {
+      resolution: "original";
+      format: "png";
+    };
+  };
+};
+
+type WorkerScopeMock = {
+  postMessage: ReturnType<typeof vi.fn>;
+  onmessage: ((event: MessageEvent<WorkerMessage>) => void) | null;
+};
+
+function createFullResult(): RenderFullResult {
+  return {
+    blob: new Blob(["rendered"]),
+    width: 64,
+    height: 64,
+    mimeType: "image/png",
+    format: "png",
+    quality: null,
+    sizeBytes: 8,
+    sourceWidth: 64,
+    sourceHeight: 64,
+    wasSizeClamped: false,
+  };
+}
+
+function createWorkerScope(): WorkerScopeMock {
+  return {
+    postMessage: vi.fn(),
+    onmessage: null,
+  };
+}
+
+describe("image-pipeline.worker full render", () => {
+  beforeEach(() => {
+    vi.resetModules();
+    vi.unstubAllGlobals();
+    bridgeMocks.renderFull.mockReset();
+    bridgeMocks.renderFull.mockResolvedValue(createFullResult());
+    previewRendererMocks.renderPreview.mockReset();
+  });
+
+  it("forwards sourceComposition to renderFull for full requests", async () => {
+    const workerScope = createWorkerScope();
+    vi.stubGlobal("self", workerScope);
+    await import("@/lib/image-pipeline/image-pipeline.worker");
+
+    const sourceComposition: RenderSourceComposition = {
+      kind: "mixer",
+      baseUrl: "https://cdn.example.com/base.png",
+      overlayUrl: "https://cdn.example.com/overlay.png",
+      blendMode: "overlay",
+      opacity: 0.5,
+      overlayX: 32,
+      overlayY: 16,
+      overlayWidth: 128,
+      overlayHeight: 64,
+    };
+
+    workerScope.onmessage?.({
+      data: {
+        kind: "full",
+        requestId: 41,
+        payload: {
+          sourceComposition,
+          steps: [],
+          render: {
+            resolution: "original",
+            format: "png",
+          },
+        },
+      },
+    } as MessageEvent<WorkerMessage>);
+
+    await vi.waitFor(() => {
+      expect(bridgeMocks.renderFull).toHaveBeenCalledTimes(1);
+    });
+
+    expect(bridgeMocks.renderFull).toHaveBeenCalledWith(
+      expect.objectContaining({
+        sourceComposition,
+      }),
+    );
+  });
+});

tests/image-pipeline/source-loader.test.ts

@@ -355,4 +355,105 @@ describe("loadSourceBitmap", () => {
     expect(createImageBitmap).toHaveBeenCalledWith(fakeVideo);
     expect(revokeObjectUrl).toHaveBeenCalledWith("blob:video-source");
   });
+
+  it("renders mixer overlays with object-cover semantics instead of stretching", async () => {
+    const baseBlob = new Blob(["base"]);
+    const overlayBlob = new Blob(["overlay"]);
+    const baseBitmap = { width: 100, height: 100 } as ImageBitmap;
+    const overlayBitmap = { width: 200, height: 100 } as ImageBitmap;
+    const composedBitmap = { width: 100, height: 100 } as ImageBitmap;
+
+    const drawImage = vi.fn();
+    const context = {
+      clearRect: vi.fn(),
+      drawImage,
+      globalCompositeOperation: "source-over" as GlobalCompositeOperation,
+      globalAlpha: 1,
+    };
+    const canvas = {
+      width: 0,
+      height: 0,
+      getContext: vi.fn().mockReturnValue(context),
+    } as unknown as HTMLCanvasElement;
+
+    const nativeCreateElement = document.createElement.bind(document);
+    vi.spyOn(document, "createElement").mockImplementation((tagName: string) => {
+      if (tagName.toLowerCase() === "canvas") {
+        return canvas;
+      }
+
+      return nativeCreateElement(tagName);
+    });
+
+    vi.stubGlobal(
+      "fetch",
+      vi.fn().mockImplementation(async (input: string | URL | Request) => {
+        const url = String(input);
+        if (url.includes("base.png")) {
+          return {
+            ok: true,
+            status: 200,
+            headers: { get: vi.fn().mockReturnValue("image/png") },
+            blob: vi.fn().mockResolvedValue(baseBlob),
+          };
+        }
+
+        return {
+          ok: true,
+          status: 200,
+          headers: { get: vi.fn().mockReturnValue("image/png") },
+          blob: vi.fn().mockResolvedValue(overlayBlob),
+        };
+      }),
+    );
+
+    vi.stubGlobal(
+      "createImageBitmap",
+      vi.fn().mockImplementation(async (input: unknown) => {
+        if (input === baseBlob) {
+          return baseBitmap;
+        }
+        if (input === overlayBlob) {
+          return overlayBitmap;
+        }
+        if (input === canvas) {
+          return composedBitmap;
+        }
+
+        throw new Error("Unexpected createImageBitmap input in mixer cover-fit test.");
+      }),
+    );
+
+    const { loadRenderSourceBitmap } = await importSubject();
+
+    await expect(
+      loadRenderSourceBitmap({
+        sourceComposition: {
+          kind: "mixer",
+          baseUrl: "https://cdn.example.com/base.png",
+          overlayUrl: "https://cdn.example.com/overlay.png",
+          blendMode: "overlay",
+          opacity: 80,
+          overlayX: 0.1,
+          overlayY: 0.2,
+          overlayWidth: 0.25,
+          overlayHeight: 0.5,
+        },
+      }),
+    ).resolves.toBe(composedBitmap);
+
+    expect(drawImage).toHaveBeenNthCalledWith(1, baseBitmap, 0, 0, 100, 100);
+    expect(drawImage).toHaveBeenNthCalledWith(
+      2,
+      overlayBitmap,
+      75,
+      0,
+      50,
+      100,
+      10,
+      20,
+      25,
+      50,
+    );
+  });
 });

tests/image-pipeline/webgl-backend-poc.test.ts

@@ -341,6 +341,7 @@ describe("webgl backend poc", () => {
 
     vi.doMock("@/lib/image-pipeline/source-loader", () => ({
       loadSourceBitmap: vi.fn().mockResolvedValue({ width: 2, height: 2 }),
+      loadRenderSourceBitmap: vi.fn().mockResolvedValue({ width: 2, height: 2 }),
     }));
 
     vi.spyOn(HTMLCanvasElement.prototype, "getContext").mockReturnValue({