fix native and web screenshot rendering

frontend/package.json

@@ -9,7 +9,8 @@
   "scripts": {
     "dev": "vite",
     "build": "vite build",
-    "preview": "vite preview"
+    "preview": "vite preview",
+    "test": "node --test tests/**/*.test.mjs"
   },
   "dependencies": {
     "@xyflow/react": "^12.0.0",

frontend/src/App.jsx

@@ -13,6 +13,7 @@ import FileBrowser from './FileBrowser';
 import * as api from './api';
 import { toBlob } from 'html-to-image';
 import { embedWorkflow, extractWorkflow } from './pngMetadata';
+import { serializeWorkflowState } from './workflowSerialization';
 
 // ── Constants ─────────────────────────────────────────────────────────
 
@@ -51,29 +52,94 @@ function blobToDataUrl(blob) {
   });
 }
 
-function serializeWorkflowState(nodes, edges) {
-  return {
-    version: 1,
-    nodes: nodes.map((node) => ({
-      id: node.id,
-      type: node.type || 'custom',
-      position: node.position,
-      dragHandle: node.dragHandle || '.drag-handle',
-      data: {
-        label: node.data?.label || node.data?.className || 'Node',
-        className: node.data?.className || '',
-        widgetValues: node.data?.widgetValues || {},
-      },
-    })),
-    edges: edges.map((edge) => ({
-      id: edge.id,
-      source: edge.source,
-      sourceHandle: edge.sourceHandle,
-      target: edge.target,
-      targetHandle: edge.targetHandle,
-      style: edge.style,
-    })),
-  };
+async function waitForImageElement(img) {
+  if (img.complete && img.naturalWidth > 0) return;
+  if (typeof img.decode === 'function') {
+    try {
+      await img.decode();
+      return;
+    } catch {
+      // Fall back to load/error listeners below.
+    }
+  }
+  await new Promise((resolve) => {
+    const done = () => {
+      img.removeEventListener('load', done);
+      img.removeEventListener('error', done);
+      resolve();
+    };
+    img.addEventListener('load', done, { once: true });
+    img.addEventListener('error', done, { once: true });
+  });
+}
+
+function createCapturePlaceholder(el, dataUrl) {
+  const rect = el.getBoundingClientRect();
+  const style = window.getComputedStyle(el);
+  const placeholder = document.createElement('div');
+
+  placeholder.style.display = style.display === 'inline' ? 'inline-block' : style.display;
+  placeholder.style.width = `${el.clientWidth || rect.width}px`;
+  placeholder.style.height = `${el.clientHeight || rect.height}px`;
+  placeholder.style.maxWidth = style.maxWidth;
+  placeholder.style.maxHeight = style.maxHeight;
+  placeholder.style.minWidth = style.minWidth;
+  placeholder.style.minHeight = style.minHeight;
+  placeholder.style.borderRadius = style.borderRadius;
+  placeholder.style.backgroundImage = `url("${dataUrl}")`;
+  placeholder.style.backgroundRepeat = 'no-repeat';
+  placeholder.style.backgroundPosition = 'center';
+  placeholder.style.backgroundSize = el.tagName === 'CANVAS' ? '100% 100%' : 'contain';
+  placeholder.style.flexShrink = style.flexShrink;
+
+  return placeholder;
+}
+
+async function captureViewportBlob(viewportEl, options) {
+  const restorers = [];
+  const images = Array.from(viewportEl.querySelectorAll('img'));
+  await Promise.all(images.map(waitForImageElement));
+
+  for (const img of images) {
+    const dataUrl = img.currentSrc || img.src;
+    if (!dataUrl || !img.parentNode) continue;
+    const placeholder = createCapturePlaceholder(img, dataUrl);
+    img.parentNode.replaceChild(placeholder, img);
+    restorers.push(() => {
+      if (placeholder.parentNode) {
+        placeholder.parentNode.replaceChild(img, placeholder);
+      }
+    });
+  }
+
+  const canvases = Array.from(viewportEl.querySelectorAll('canvas'));
+  for (const canvas of canvases) {
+    if (!canvas.parentNode) continue;
+    let dataUrl = 'data:,';
+    try {
+      dataUrl = canvas.toDataURL('image/png');
+    } catch {
+      dataUrl = 'data:,';
+    }
+    if (dataUrl === 'data:,') continue;
+
+    const placeholder = createCapturePlaceholder(canvas, dataUrl);
+    canvas.parentNode.replaceChild(placeholder, canvas);
+    restorers.push(() => {
+      if (placeholder.parentNode) {
+        placeholder.parentNode.replaceChild(canvas, placeholder);
+      }
+    });
+  }
+
+  await new Promise((resolve) => requestAnimationFrame(() => resolve()));
+  await new Promise((resolve) => requestAnimationFrame(() => resolve()));
+
+  try {
+    return await toBlob(viewportEl, options);
+  } finally {
+    restorers.reverse().forEach((restore) => restore());
+  }
 }
 
 // ── Graph serialisation → backend prompt format ───────────────────────
@@ -505,7 +571,7 @@ function Flow() {
     const imageHeight = Math.ceil(bounds.height * (1 + pad * 2));
     const vp = getViewportForBounds(bounds, imageWidth, imageHeight, 0.5, 1, pad);
 
-    const blob = await toBlob(viewportEl, {
+    const blob = await captureViewportBlob(viewportEl, {
       backgroundColor: '#1a1a1a',
       width: imageWidth,
       height: imageHeight,

frontend/src/SurfaceView.jsx

@@ -28,7 +28,11 @@ export default function SurfaceView({ meshData }) {
     const width = container.clientWidth;
     const height = width; // 1:1 aspect
 
-    const renderer = new THREE.WebGLRenderer({ antialias: true, alpha: false });
+    const renderer = new THREE.WebGLRenderer({
+      antialias: true,
+      alpha: false,
+      preserveDrawingBuffer: true,
+    });
     renderer.setSize(width, height);
     renderer.setPixelRatio(window.devicePixelRatio);
     renderer.setClearColor(0x0f172a);

frontend/src/workflowSerialization.js

@@ -0,0 +1,24 @@
+export function serializeWorkflowState(nodes, edges) {
+  return {
+    version: 1,
+    nodes: nodes.map((node) => ({
+      id: node.id,
+      type: node.type || 'custom',
+      position: node.position,
+      dragHandle: node.dragHandle || '.drag-handle',
+      data: {
+        label: node.data?.label || node.data?.className || 'Node',
+        className: node.data?.className || '',
+        widgetValues: node.data?.widgetValues || {},
+      },
+    })),
+    edges: edges.map((edge) => ({
+      id: edge.id,
+      source: edge.source,
+      sourceHandle: edge.sourceHandle,
+      target: edge.target,
+      targetHandle: edge.targetHandle,
+      style: edge.style,
+    })),
+  };
+}

frontend/tests/pngMetadata.test.mjs

@@ -0,0 +1,109 @@
+import test from 'node:test';
+import assert from 'node:assert/strict';
+
+import { embedWorkflow, extractWorkflow } from '../src/pngMetadata.js';
+
+const PNG_BASE64 = 'iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCAQAAAC1HAwCAAAAC0lEQVR42mP8/x8AAwMCAO+aF9sAAAAASUVORK5CYII=';
+
+function makePngBlob() {
+  return new Blob([Buffer.from(PNG_BASE64, 'base64')], { type: 'image/png' });
+}
+
+function crc32(bytes) {
+  const table = new Uint32Array(256);
+  for (let i = 0; i < 256; i++) {
+    let c = i;
+    for (let j = 0; j < 8; j++) {
+      c = (c & 1) ? (0xEDB88320 ^ (c >>> 1)) : (c >>> 1);
+    }
+    table[i] = c;
+  }
+
+  let crc = 0xFFFFFFFF;
+  for (let i = 0; i < bytes.length; i++) {
+    crc = table[(crc ^ bytes[i]) & 0xFF] ^ (crc >>> 8);
+  }
+  return (crc ^ 0xFFFFFFFF) >>> 0;
+}
+
+function buildChunk(type, payload) {
+  const typeBytes = new TextEncoder().encode(type);
+  const crcInput = new Uint8Array(4 + payload.length);
+  crcInput.set(typeBytes, 0);
+  crcInput.set(payload, 4);
+
+  const chunk = new Uint8Array(12 + payload.length);
+  const view = new DataView(chunk.buffer);
+  view.setUint32(0, payload.length);
+  chunk.set(typeBytes, 4);
+  chunk.set(payload, 8);
+  view.setUint32(8 + payload.length, crc32(crcInput));
+  return chunk;
+}
+
+async function insertTextChunk(blob, workflow) {
+  const png = new Uint8Array(await blob.arrayBuffer());
+  const encoder = new TextEncoder();
+  const key = encoder.encode('workflow');
+  const text = encoder.encode(JSON.stringify(workflow));
+  const payload = new Uint8Array(key.length + 1 + text.length);
+  payload.set(key, 0);
+  payload.set(text, key.length + 1);
+  const chunk = buildChunk('tEXt', payload);
+
+  let pos = 8;
+  while (pos < png.length) {
+    const len = new DataView(png.buffer, pos, 4).getUint32(0);
+    const type = String.fromCharCode(png[pos + 4], png[pos + 5], png[pos + 6], png[pos + 7]);
+    if (type === 'IEND') break;
+    pos += 12 + len;
+  }
+
+  const out = new Uint8Array(png.length + chunk.length);
+  out.set(png.subarray(0, pos), 0);
+  out.set(chunk, pos);
+  out.set(png.subarray(pos), pos + chunk.length);
+  return new Blob([out], { type: 'image/png' });
+}
+
+test('embedWorkflow roundtrips workflow data through an iTXt chunk', async () => {
+  const workflow = {
+    version: 1,
+    nodes: [
+      {
+        id: '1',
+        type: 'custom',
+        position: { x: 12, y: 34 },
+        data: { className: 'DemoNode', widgetValues: { title: 'naïve café', sigma: 'β' } },
+      },
+    ],
+    edges: [],
+  };
+
+  const embedded = await embedWorkflow(makePngBlob(), workflow);
+  const extracted = await extractWorkflow(embedded);
+  const bytes = new Uint8Array(await embedded.arrayBuffer());
+
+  assert.deepEqual(extracted, workflow);
+  assert.match(Buffer.from(bytes).toString('latin1'), /iTXt/);
+});
+
+test('extractWorkflow still supports legacy tEXt metadata chunks', async () => {
+  const workflow = { version: 1, legacy: true, nodes: [], edges: [] };
+  const legacyBlob = await insertTextChunk(makePngBlob(), workflow);
+
+  const extracted = await extractWorkflow(legacyBlob);
+
+  assert.deepEqual(extracted, workflow);
+});
+
+test('extractWorkflow returns the last workflow chunk when an image is re-saved', async () => {
+  const first = { version: 1, name: 'old', nodes: [], edges: [] };
+  const second = { version: 1, name: 'new', nodes: [], edges: [] };
+
+  const once = await embedWorkflow(makePngBlob(), first);
+  const twice = await embedWorkflow(once, second);
+  const extracted = await extractWorkflow(twice);
+
+  assert.deepEqual(extracted, second);
+});

frontend/tests/workflowSerialization.test.mjs

@@ -0,0 +1,91 @@
+import test from 'node:test';
+import assert from 'node:assert/strict';
+
+import { serializeWorkflowState } from '../src/workflowSerialization.js';
+
+test('serializeWorkflowState keeps only stable workflow fields needed for reload', () => {
+  const nodes = [
+    {
+      id: '1',
+      type: 'custom',
+      position: { x: 100, y: 200 },
+      dragHandle: '.node-header',
+      selected: true,
+      width: 320,
+      data: {
+        label: 'Demo Label',
+        className: 'DemoNode',
+        widgetValues: { threshold: 0.42, mode: 'fast' },
+        definition: { input: { required: { threshold: ['FLOAT', { default: 0.5 }] } } },
+        previewImage: 'data:image/png;base64,abc',
+        tableRows: [{ a: 1 }],
+        meshData: { vertices: [1, 2, 3] },
+        overlay: { active: true },
+      },
+    },
+    {
+      id: '2',
+      position: { x: 10, y: 20 },
+      data: {
+        className: 'NoLabelNode',
+      },
+    },
+  ];
+
+  const edges = [
+    {
+      id: 'e1-2',
+      source: '1',
+      sourceHandle: 'output::0::IMAGE',
+      target: '2',
+      targetHandle: 'input::image::IMAGE',
+      style: { stroke: '#fff', strokeWidth: 2 },
+      selected: true,
+      animated: true,
+    },
+  ];
+
+  const serialized = serializeWorkflowState(nodes, edges);
+
+  assert.deepEqual(serialized, {
+    version: 1,
+    nodes: [
+      {
+        id: '1',
+        type: 'custom',
+        position: { x: 100, y: 200 },
+        dragHandle: '.node-header',
+        data: {
+          label: 'Demo Label',
+          className: 'DemoNode',
+          widgetValues: { threshold: 0.42, mode: 'fast' },
+        },
+      },
+      {
+        id: '2',
+        type: 'custom',
+        position: { x: 10, y: 20 },
+        dragHandle: '.drag-handle',
+        data: {
+          label: 'NoLabelNode',
+          className: 'NoLabelNode',
+          widgetValues: {},
+        },
+      },
+    ],
+    edges: [
+      {
+        id: 'e1-2',
+        source: '1',
+        sourceHandle: 'output::0::IMAGE',
+        target: '2',
+        targetHandle: 'input::image::IMAGE',
+        style: { stroke: '#fff', strokeWidth: 2 },
+      },
+    ],
+  });
+
+  assert.equal('definition' in serialized.nodes[0].data, false);
+  assert.equal('previewImage' in serialized.nodes[0].data, false);
+  assert.equal('selected' in serialized.edges[0], false);
+});

package.json

@@ -10,6 +10,7 @@
     "dev": "npm --prefix frontend run dev",
     "build": "npm --prefix frontend run build",
     "preview": "npm --prefix frontend run preview",
+    "test:frontend": "npm --prefix frontend test",
     "backend": "python -m backend.main",
     "desktop": "python desktop.py",
     "build:windows": "powershell -ExecutionPolicy Bypass -File scripts\\build-windows.ps1",