lock proportion for corners

app.py

@@ -757,10 +757,37 @@ function init() {
     } else {
       let {x1,y1,x2,y2} = {...o};
       const t = dragType;
-      if (t.includes('l')) x1 = clamp01(o.x1+dx);
-      if (t.includes('r')) x2 = clamp01(o.x2+dx);
-      if (t.includes('t')) y1 = clamp01(o.y1+dy);
-      if (t.includes('b')) y2 = clamp01(o.y2+dy);
+      const isCorner = (t==='tl'||t==='tr'||t==='bl'||t==='br');
+      const freeResize = e && e.shiftKey;
+
+      if (isCorner && !freeResize) {
+        // Aspect-locked resize; opposite corner is the anchor
+        const origW = o.x2 - o.x1, origH = o.y2 - o.y1;
+        if (origW < 1e-6 || origH < 1e-6) return;
+        const aspect = origW / origH;
+        const ax = t.includes('l') ? o.x2 : o.x1;
+        const ay = t.includes('t') ? o.y2 : o.y1;
+        const mx = x / dispW, my = y / dispH;
+        let newW = Math.abs(mx - ax);
+        let newH = Math.abs(my - ay);
+        if (newW / aspect > newH) newH = newW / aspect;
+        else newW = newH * aspect;
+        const sx = t.includes('l') ? -1 : 1;
+        const sy = t.includes('t') ? -1 : 1;
+        const maxW = sx > 0 ? (1 - ax) : ax;
+        const maxH = sy > 0 ? (1 - ay) : ay;
+        const k = Math.min(1, maxW / newW, maxH / newH);
+        newW *= k; newH *= k;
+        x1 = sx > 0 ? ax : ax - newW;
+        x2 = sx > 0 ? ax + newW : ax;
+        y1 = sy > 0 ? ay : ay - newH;
+        y2 = sy > 0 ? ay + newH : ay;
+      } else {
+        if (t.includes('l')) x1 = clamp01(o.x1+dx);
+        if (t.includes('r')) x2 = clamp01(o.x2+dx);
+        if (t.includes('t')) y1 = clamp01(o.y1+dy);
+        if (t.includes('b')) y2 = clamp01(o.y2+dy);
+      }
       if (x1>x2) {const tmp=x1;x1=x2;x2=tmp;}
       if (y1>y2) {const tmp=y1;y1=y2;y2=tmp;}
       if (Math.abs(x2-x1)<0.01||Math.abs(y2-y1)<0.01) return;