feat: implement "Place on Face" feature with UI integration and translations

index.html

@@ -82,6 +82,7 @@
           <input type="checkbox" id="wireframe-toggle" />
           <span data-i18n="ui.wireframe">Wireframe</span>
         </label>
+
         <div class="viewport-controls-hint" data-i18n="ui.controlsHint">Left drag: orbit &nbsp;·&nbsp; Right drag: pan &nbsp;·&nbsp; Scroll: zoom</div>
       </div>
     </section>
@@ -91,10 +92,16 @@
 
       <!-- Load STL -->
       <section class="panel-section">
-        <label class="upload-btn" for="stl-file-input" style="width:100%;box-sizing:border-box;justify-content:center;">
+        <div class="load-stl-row">
-          <svg width="14" height="14" viewBox="0 0 24 24" fill="none"><path d="M12 2L2 7l10 5 10-5-10-5Z" stroke="currentColor" stroke-width="2" stroke-linejoin="round"/><path d="M2 17l10 5 10-5M2 12l10 5 10-5" stroke="currentColor" stroke-width="2" stroke-linejoin="round"/></svg>
+          <label class="upload-btn" for="stl-file-input" style="flex:1;justify-content:center;">
-          <span data-i18n="ui.loadStl">Load STL…</span>
+            <svg width="14" height="14" viewBox="0 0 24 24" fill="none"><path d="M12 2L2 7l10 5 10-5-10-5Z" stroke="currentColor" stroke-width="2" stroke-linejoin="round"/><path d="M2 17l10 5 10-5M2 12l10 5 10-5" stroke="currentColor" stroke-width="2" stroke-linejoin="round"/></svg>
-        </label>
+            <span data-i18n="ui.loadStl">Load STL…</span>
+          </label>
+          <button id="place-on-face-btn" class="place-on-face-btn" data-i18n-title="ui.placeOnFaceTitle" title="Click a face to orient it downward onto the print bed">
+            <svg width="14" height="14" viewBox="0 0 24 24" fill="none"><path d="M12 3v14m0 0l-5-5m5 5l5-5" stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round"/><path d="M4 21h16" stroke="currentColor" stroke-width="2" stroke-linecap="round"/></svg>
+            <span data-i18n="ui.placeOnFace">Place on Face</span>
+          </button>
+        </div>
       </section>
 
       <!-- Displacement Map -->

js/i18n.js

@@ -98,6 +98,10 @@ export const TRANSLATIONS = {
     // Displacement preview
     'labels.displacementPreview':    '3D Preview \u24d8',
     'tooltips.displacementPreview':  'Subdivides the mesh and displaces vertices in real-time so you can judge the actual depth. GPU-intensive on complex models.',
+
+    // Place on face
+    'ui.placeOnFace':                'Place on Face',
+    'ui.placeOnFaceTitle':           'Click a face to orient it downward onto the print bed',
     'progress.subdividingPreview':   'Preparing preview\u2026',
 
     // Amplitude overlap warning
@@ -242,6 +246,10 @@ export const TRANSLATIONS = {
     // Displacement preview
     'labels.displacementPreview':    '3D-Vorschau \u24d8',
     'tooltips.displacementPreview':  'Unterteilt das Netz und verschiebt Punkte in Echtzeit, damit die tats\u00e4chliche Tiefe sichtbar wird. GPU-intensiv bei komplexen Modellen.',
+
+    // Auf Fl\u00e4che platzieren
+    'ui.placeOnFace':                'Auf Fl\u00e4che platzieren',
+    'ui.placeOnFaceTitle':           'Klicken Sie auf eine Fl\u00e4che, um sie nach unten auf das Druckbett auszurichten',
     'progress.subdividingPreview':   'Vorschau wird vorbereitet\u2026',
 
     // Amplitude overlap warning

js/main.js

@@ -35,6 +35,7 @@ let bucketThreshold    = 20;
 let isPainting         = false;
 let selectionMode      = false;       // false = exclude painted faces; true = include only painted faces
 let _lastHoverTriIdx   = -1;          // last triangle index used for hover preview
+let placeOnFaceActive  = false;       // true while "Place on Face" mode is active
 const _raycaster       = new THREE.Raycaster();
 
 const settings = {
@@ -79,6 +80,7 @@ const exportProgPct    = document.getElementById('export-progress-pct');
 const exportProgLbl    = document.getElementById('export-progress-label');
 const triLimitWarning  = document.getElementById('tri-limit-warning');
 const wireframeToggle  = document.getElementById('wireframe-toggle');
+const placeOnFaceBtn   = document.getElementById('place-on-face-btn');
 
 const mappingSelect   = document.getElementById('mapping-mode');
 const scaleUSlider    = document.getElementById('scale-u');
@@ -337,6 +339,11 @@ function wireEvents() {
     toggleDisplacementPreview(dispPreviewToggle.checked);
   });
 
+  // ── Place on Face ──
+  placeOnFaceBtn.addEventListener('click', () => {
+    togglePlaceOnFace(!placeOnFaceActive);
+  });
+
   // ── License ──
   licenseLink.addEventListener('click', () => licenseOverlay.classList.remove('hidden'));
   licenseClose.addEventListener('click', () => licenseOverlay.classList.add('hidden'));
@@ -434,7 +441,16 @@ function wireEvents() {
 
   // ── Canvas mouse events for exclusion painting ────────────────────────────
   canvas.addEventListener('mousedown', (e) => {
-    if (!currentGeometry || !exclusionTool || e.button !== 0) return;
+    if (!currentGeometry || e.button !== 0) return;
+
+    // Place on Face mode
+    if (placeOnFaceActive) {
+      e.preventDefault();
+      handlePlaceOnFaceClick(e);
+      return;
+    }
+
+    if (!exclusionTool) return;
 
     if (exclusionTool === 'bucket') {
       e.preventDefault();
@@ -464,6 +480,10 @@ function wireEvents() {
   });
 
   canvas.addEventListener('mousemove', (e) => {
+    if (placeOnFaceActive && currentGeometry) {
+      updatePlaceOnFaceHover(e);
+      return;
+    }
     if (exclusionTool === 'brush' && brushIsRadius) {
       updateBrushCursor(e);
     }
@@ -493,6 +513,7 @@ function wireEvents() {
 
   document.addEventListener('keydown', (e) => {
     if (e.key === 'Escape') {
+      if (placeOnFaceActive) togglePlaceOnFace(false);
       if (exclusionTool) setExclusionTool(null);
       licenseOverlay.classList.add('hidden');
     }
@@ -522,6 +543,9 @@ function setExclusionTool(tool) {
   // Clicking the active tool toggles it off; passing null always deactivates
   exclusionTool = (exclusionTool === tool) ? null : tool;
 
+  // Deactivate place-on-face if an exclusion tool is being activated
+  if (exclusionTool && placeOnFaceActive) togglePlaceOnFace(false);
+
   // Exit 3D displacement preview when a masking tool is activated
   if (exclusionTool && settings.useDisplacement) {
     settings.useDisplacement = false;
@@ -624,6 +648,144 @@ function paintAt(e) {
   refreshExclusionOverlay();
 }
 
+// ── Place on Face ─────────────────────────────────────────────────────────────
+
+function togglePlaceOnFace(active) {
+  placeOnFaceActive = active;
+  placeOnFaceBtn.classList.toggle('active', active);
+
+  if (active) {
+    // Deactivate exclusion tool
+    if (exclusionTool) setExclusionTool(null);
+    canvas.style.cursor = 'crosshair';
+  } else {
+    if (!exclusionTool) canvas.style.cursor = '';
+    _lastHoverTriIdx = -1;
+    setHoverPreview(null);
+  }
+}
+
+function updatePlaceOnFaceHover(e) {
+  const mesh = getCurrentMesh();
+  if (!mesh) { setHoverPreview(null); return; }
+  _raycaster.setFromCamera(_canvasNDC(e), getCamera());
+  const hits = _raycaster.intersectObject(mesh);
+  const hit = getFrontFaceHit(hits, mesh);
+  if (!hit) { _lastHoverTriIdx = -1; setHoverPreview(null); return; }
+
+  let triIdx = hit.faceIndex;
+  if (dispPreviewGeometry && mesh.geometry === dispPreviewGeometry && dispPreviewParentMap) {
+    triIdx = dispPreviewParentMap[triIdx];
+  }
+  if (triIdx === _lastHoverTriIdx) return;
+  _lastHoverTriIdx = triIdx;
+  setHoverPreview(buildExclusionOverlayGeo(currentGeometry, new Set([triIdx])));
+}
+
+function handlePlaceOnFaceClick(e) {
+  const mesh = getCurrentMesh();
+  if (!mesh) return;
+  _raycaster.setFromCamera(_canvasNDC(e), getCamera());
+  const hits = _raycaster.intersectObject(mesh);
+  const hit = getFrontFaceHit(hits, mesh);
+  if (!hit) return;
+
+  // Get the face normal (mesh has identity transform)
+  const faceNormal = hit.face.normal.clone().normalize();
+
+  // Compute quaternion that rotates faceNormal to -Z (face down on print bed)
+  const targetDir = new THREE.Vector3(0, 0, -1);
+  const quat = new THREE.Quaternion().setFromUnitVectors(faceNormal, targetDir);
+
+  // Apply rotation to all vertex positions
+  const pos = currentGeometry.attributes.position.array;
+  const v = new THREE.Vector3();
+  for (let i = 0; i < pos.length; i += 3) {
+    v.set(pos[i], pos[i + 1], pos[i + 2]);
+    v.applyQuaternion(quat);
+    pos[i]     = v.x;
+    pos[i + 1] = v.y;
+    pos[i + 2] = v.z;
+  }
+
+  // Re-center geometry
+  currentGeometry.computeBoundingBox();
+  const center = new THREE.Vector3();
+  currentGeometry.boundingBox.getCenter(center);
+  currentGeometry.translate(-center.x, -center.y, -center.z);
+
+  // Recompute normals from scratch (fixes lighting + angle masking)
+  currentGeometry.computeVertexNormals();
+  // Delete stale faceNormal attribute so updateFaceMask() recomputes it
+  // from the new rotated positions (needed for correct angle masking in 2D preview)
+  if (currentGeometry.attributes.faceNormal) {
+    currentGeometry.deleteAttribute('faceNormal');
+  }
+
+  // Now reload as if this were a freshly loaded STL
+  currentBounds = computeBounds(currentGeometry);
+  checkAmplitudeWarning();
+
+  // Dispose old preview material so it gets fully recreated
+  if (previewMaterial) {
+    previewMaterial.dispose();
+    previewMaterial = null;
+  }
+
+  loadGeometry(currentGeometry);
+
+  // Reset displacement preview
+  if (dispPreviewGeometry) { dispPreviewGeometry.dispose(); dispPreviewGeometry = null; }
+  settings.useDisplacement = false;
+  dispPreviewToggle.checked = false;
+
+  // Deactivate tools but keep excludedFaces (face indices are stable after rotation)
+  exclusionTool     = null;
+  eraseMode         = false;
+  isPainting        = false;
+  exclBrushBtn.classList.remove('active');
+  exclBucketBtn.classList.remove('active');
+  exclBrushTypeRow.classList.add('hidden');
+  exclRadiusRow.classList.add('hidden');
+  exclThresholdRow.classList.add('hidden');
+  canvas.style.cursor = '';
+  setHoverPreview(null);
+  _lastHoverTriIdx = -1;
+
+  // Rebuild adjacency
+  const adjData = buildAdjacency(currentGeometry);
+  triangleAdjacency = adjData.adjacency;
+  triangleCentroids = adjData.centroids;
+
+  // Update edge length for new bounds
+  const maxDim = Math.max(currentBounds.size.x, currentBounds.size.y, currentBounds.size.z);
+  const defaultEdge = Math.max(0.05, Math.min(5.0, +(maxDim / 200).toFixed(2)));
+  settings.refineLength = defaultEdge;
+  refineLenSlider.value = defaultEdge;
+  refineLenVal.value = defaultEdge;
+
+  // Update mesh info
+  const triCount = getTriangleCount(currentGeometry);
+  const mb = ((currentGeometry.attributes.position.array.byteLength) / 1024 / 1024).toFixed(2);
+  const sx = currentBounds.size.x.toFixed(2);
+  const sy = currentBounds.size.y.toFixed(2);
+  const sz = currentBounds.size.z.toFixed(2);
+  meshInfo.textContent = t('ui.meshInfo', { n: triCount.toLocaleString(), mb, sx, sy, sz });
+
+  exportBtn.disabled = (activeMapEntry === null);
+  updatePreview();
+
+  // Rebuild exclusion overlay with new vertex positions (face indices unchanged)
+  if (excludedFaces.size > 0) {
+    refreshExclusionOverlay();
+  } else {
+    setExclusionOverlay(null);
+  }
+
+  // Exit place-on-face mode
+  togglePlaceOnFace(false);
+}
+
 function refreshExclusionOverlay() {
   if (!currentGeometry) return;
   if (selectionMode) {
@@ -799,6 +961,7 @@ function loadDefaultCube() {
   exclusionTool     = null;
   eraseMode         = false;
   isPainting        = false;
+  if (placeOnFaceActive) togglePlaceOnFace(false);
   exclBrushBtn.classList.remove('active');
   exclBucketBtn.classList.remove('active');
   exclBrushTypeRow.classList.add('hidden');
@@ -874,6 +1037,7 @@ async function handleSTL(file) {
     exclusionTool     = null;
     eraseMode         = false;
     isPainting        = false;
+    if (placeOnFaceActive) togglePlaceOnFace(false);
     exclBrushBtn.classList.remove('active');
     exclBucketBtn.classList.remove('active');
     exclBrushTypeRow.classList.add('hidden');

style.css

@@ -287,6 +287,36 @@ main {
   user-select: none;
 }
 
+.place-on-face-btn {
+  display: flex;
+  align-items: center;
+  gap: 5px;
+  font-size: 11px;
+  color: var(--text-muted);
+  background: var(--surface);
+  border: 1px solid var(--border);
+  border-radius: 4px;
+  cursor: pointer;
+  padding: 6px 10px;
+  user-select: none;
+  font-family: inherit;
+  white-space: nowrap;
+}
+.place-on-face-btn:hover {
+  color: var(--text);
+  border-color: var(--accent);
+}
+.place-on-face-btn.active {
+  color: var(--accent);
+  border-color: var(--accent);
+}
+
+.load-stl-row {
+  display: flex;
+  gap: 8px;
+  align-items: stretch;
+}
+
 /* ── Settings panel ──────────────────────────────────────────────────── */
 #settings-panel {
   width: var(--sidebar-w);