web: draw each landing photo cut to its own box, not to its own shape

docker/frontend/src/Landing.tsx

@@ -25,6 +25,10 @@ const SAMPLE = (n: number) => `/assets/samples/s${n}.jpg`;
 // that smaller bitmap is what the tag carries, so a saved copy is a screen-sized
 // one and not the uploader's 4000px original. The save gestures are turned off
 // on top of it. `data-full` keeps the original address for tests and debugging.
+//
+// The redraw covers what `object-fit: cover` will show, not the whole frame: a
+// 4:3 upload in a 4:5 card would otherwise be handed a stubby bitmap that the
+// card had to blow up again — the soft thumbnails the strip used to show.
 function Shot({ src, alt, filter }: { src: string; alt: string; filter?: string }) {
   const tag = useRef<HTMLImageElement>(null);
   const [shown, setShown] = useState(src);
@@ -33,16 +37,25 @@ function Shot({ src, alt, filter }: { src: string; alt: string; filter?: string
     let alive = true;
     const source = new Image();
     source.onload = () => {
-      const box = tag.current?.clientWidth ?? 0;
+      const boxW = tag.current?.clientWidth ?? 0;
+      const boxH = tag.current?.clientHeight ?? 0;
       const scale = Math.min(2, Math.max(1, window.devicePixelRatio || 1));
-      const width = Math.min(source.naturalWidth, Math.round(box * scale));
+      const width = Math.round(boxW * scale);
-      if (!alive || box === 0 || width >= source.naturalWidth) return;
+      const height = Math.round(boxH * scale);
+      if (!alive || width === 0 || height === 0) return;
+      if (width >= source.naturalWidth && height >= source.naturalHeight) return;
+      // The centred slice `cover` would show, cut to exactly the box: scale up
+      // to fill both sides, keep the middle of the overflow.
+      const grow = Math.max(width / source.naturalWidth, height / source.naturalHeight);
+      const sw = width / grow;
+      const sh = height / grow;
       const canvas = document.createElement('canvas');
       canvas.width = width;
-      canvas.height = Math.max(1, Math.round((source.naturalHeight * width) / source.naturalWidth));
+      canvas.height = height;
       const ctx = canvas.getContext('2d');
       if (!ctx) return;
-      ctx.drawImage(source, 0, 0, canvas.width, canvas.height);
+      ctx.imageSmoothingQuality = 'high';
+      ctx.drawImage(source, (source.naturalWidth - sw) / 2, (source.naturalHeight - sh) / 2, sw, sh, 0, 0, width, height);
       setShown(canvas.toDataURL('image/jpeg', 0.85));
     };
     source.src = src;