feat(web): improve OCR overlay text fitting, reactivity, and accessibility

- Precise font sizing using canvas measureText instead of character-count heuristic
- Fix overlay repositioning on viewport resize by computing metrics from reactive state instead of DOM reads
- Fix animation delay on resize by using transition-colors instead of transition-all
- Add keyboard accessibility: OCR boxes are focusable via Tab with reading-order sort
- Show text on focus (same styling as hover) with proper ARIA attributes

web/src/lib/components/asset-viewer/ocr-bounding-box.svelte

@@ -1,6 +1,6 @@
 <script lang="ts">
   import type { OcrBox } from '$lib/utils/ocr-utils';
-  import { calculateBoundingBoxMatrix } from '$lib/utils/ocr-utils';
+  import { calculateBoundingBoxMatrix, calculateFittedFontSize } from '$lib/utils/ocr-utils';
 
   type Props = {
     ocrBox: OcrBox;
@@ -11,16 +11,22 @@
   const dimensions = $derived(calculateBoundingBoxMatrix(ocrBox.points));
 
   const transform = $derived(`matrix3d(${dimensions.matrix.join(',')})`);
-  // Fits almost all strings within the box, depends on font family
   const fontSize = $derived(
-    `max(var(--text-sm), min(var(--text-6xl), ${(1.4 * dimensions.width) / ocrBox.text.length}px))`,
+    calculateFittedFontSize(ocrBox.text, dimensions.width, dimensions.height, ocrBox.isVertical) + 'px',
   );
 </script>
 
 <div class="absolute left-0 top-0">
   <div
-    class="absolute flex items-center justify-center text-transparent text-sm border-2 border-blue-500 bg-blue-500/10 px-2 py-1 pointer-events-auto cursor-text whitespace-pre-wrap wrap-break-word select-text transition-all hover:text-white hover:bg-black/60 hover:border-blue-600 hover:border-3"
-    style="font-size: {fontSize}; width: {dimensions.width}px; height: {dimensions.height}px; transform: {transform}; transform-origin: 0 0;"
+    class="absolute flex items-center justify-center text-transparent border-2 border-blue-500 bg-blue-500/10 px-2 py-1 pointer-events-auto cursor-text select-text transition-colors hover:z-1 hover:text-white hover:bg-black/60 hover:border-blue-600 hover:border-3 focus:z-1 focus:text-white focus:bg-black/60 focus:border-blue-600 focus:border-3 focus:outline-none {ocrBox.isVertical
+      ? ''
+      : 'whitespace-nowrap'}"
+    style="font-size: {fontSize}; width: {dimensions.width}px; height: {dimensions.height}px; transform: {transform}; transform-origin: 0 0;{ocrBox.isVertical
+      ? ' writing-mode: vertical-rl;'
+      : ''}"
+    tabindex="0"
+    role="button"
+    aria-label={ocrBox.text}
   >
     {ocrBox.text}
   </div>

web/src/lib/components/asset-viewer/photo-viewer.svelte

@@ -14,7 +14,7 @@
   import { SlideshowLook, SlideshowState, slideshowStore } from '$lib/stores/slideshow.store';
   import { handlePromiseError } from '$lib/utils';
   import { canCopyImageToClipboard, copyImageToClipboard } from '$lib/utils/asset-utils';
-  import { getNaturalSize, scaleToFit, type ContentMetrics } from '$lib/utils/container-utils';
+  import { type ContentMetrics, getNaturalSize, scaleToFit } from '$lib/utils/container-utils';
   import { handleError } from '$lib/utils/handle-error';
   import { getOcrBoundingBoxes } from '$lib/utils/ocr-utils';
   import { getBoundingBox } from '$lib/utils/people-utils';
@@ -73,12 +73,17 @@
     }
 
     const natural = getNaturalSize(assetViewerManager.imgRef);
-    const scaled = scaleToFit(natural, container);
+    const client = { width: containerWidth, height: containerHeight };
+    const scaled = scaleToFit(natural, client);
+    const offsetX = (client.width - scaled.width) / 2;
+    const offsetY = (client.height - scaled.height) / 2;
+    const { currentZoom, currentPositionX, currentPositionY } = assetViewerManager.zoomState;
+
     return {
-      contentWidth: scaled.width,
-      contentHeight: scaled.height,
-      offsetX: 0,
-      offsetY: 0,
+      contentWidth: scaled.width * currentZoom,
+      contentHeight: scaled.height * currentZoom,
+      offsetX: offsetX * currentZoom + currentPositionX,
+      offsetY: offsetY * currentZoom + currentPositionY,
     };
   });
 

web/src/lib/utils/ocr-utils.ts

@@ -1,18 +1,33 @@
 import type { OcrBoundingBox } from '$lib/stores/ocr.svelte';
 import type { ContentMetrics } from '$lib/utils/container-utils';
+import { clamp } from 'lodash-es';
 
 export type Point = {
   x: number;
   y: number;
 };
 
+const distance = (p1: Point, p2: Point) => Math.hypot(p2.x - p1.x, p2.y - p1.y);
+
 export interface OcrBox {
   id: string;
   points: Point[];
   text: string;
   confidence: number;
+  isVertical: boolean;
 }
 
+const CJK_PATTERN =
+  /[\u3000-\u303F\u3040-\u309F\u30A0-\u30FF\u3400-\u4DBF\u4E00-\u9FFF\uF900-\uFAFF\uAC00-\uD7AF\uFF00-\uFFEF]/;
+
+const VERTICAL_ASPECT_RATIO = 1.5;
+
+const containsCjk = (text: string): boolean => CJK_PATTERN.test(text);
+
+const isVerticalText = (width: number, height: number, text: string): boolean => {
+  return height / width >= VERTICAL_ASPECT_RATIO && containsCjk(text);
+};
+
 /**
  * Calculate bounding box transform from OCR points. Result matrix can be used as input for css matrix3d.
  * @param points - Array of 4 corner points of the bounding box
@@ -21,8 +36,6 @@ export interface OcrBox {
 export const calculateBoundingBoxMatrix = (points: Point[]): { matrix: number[]; width: number; height: number } => {
   const [topLeft, topRight, bottomRight, bottomLeft] = points;
 
-  // Approximate width and height to prevent text distortion as much as possible
-  const distance = (p1: Point, p2: Point) => Math.hypot(p2.x - p1.x, p2.y - p1.y);
   const width = Math.max(distance(topLeft, topRight), distance(bottomLeft, bottomRight));
   const height = Math.max(distance(topLeft, bottomLeft), distance(topRight, bottomRight));
 
@@ -55,6 +68,71 @@ export const calculateBoundingBoxMatrix = (points: Point[]): { matrix: number[];
   return { matrix, width, height };
 };
 
+const HORIZONTAL_PADDING = 16;
+const VERTICAL_PADDING = 8;
+const REFERENCE_FONT_SIZE = 100;
+const MIN_FONT_SIZE = 8;
+const MAX_FONT_SIZE = 96;
+const FALLBACK_FONT = `${REFERENCE_FONT_SIZE}px sans-serif`;
+
+let sharedCanvasContext: CanvasRenderingContext2D | null = null;
+let resolvedFont: string | undefined;
+
+const getCanvasContext = (): CanvasRenderingContext2D | null => {
+  if (sharedCanvasContext !== null) {
+    return sharedCanvasContext;
+  }
+  const canvas = document.createElement('canvas');
+  const context = canvas.getContext('2d');
+  if (!context) {
+    return null;
+  }
+  sharedCanvasContext = context;
+  return sharedCanvasContext;
+};
+
+const getReferenceFont = (): string => {
+  if (resolvedFont !== undefined) {
+    return resolvedFont;
+  }
+  const fontFamily = globalThis.getComputedStyle?.(document.documentElement).getPropertyValue('--font-sans').trim();
+  resolvedFont = fontFamily ? `${REFERENCE_FONT_SIZE}px ${fontFamily}` : FALLBACK_FONT;
+  return resolvedFont;
+};
+
+export const calculateFittedFontSize = (
+  text: string,
+  boxWidth: number,
+  boxHeight: number,
+  isVertical: boolean,
+): number => {
+  const availableWidth = boxWidth - HORIZONTAL_PADDING;
+  const availableHeight = boxHeight - VERTICAL_PADDING;
+
+  if (isVertical) {
+    const fontSize = Math.min(availableWidth, availableHeight / text.length);
+    return clamp(fontSize, MIN_FONT_SIZE, MAX_FONT_SIZE);
+  }
+
+  const context = getCanvasContext();
+  if (!context) {
+    return clamp((1.4 * availableWidth) / text.length, MIN_FONT_SIZE, MAX_FONT_SIZE);
+  }
+
+  // Unsupported in Safari iOS <16.6; falls back to default canvas font, giving less accurate but functional sizing
+  // eslint-disable-next-line tscompat/tscompat
+  context.font = getReferenceFont();
+
+  const metrics = context.measureText(text);
+  const measuredWidth = metrics.width;
+  const measuredHeight = metrics.actualBoundingBoxAscent + metrics.actualBoundingBoxDescent;
+
+  const scaleFromWidth = (availableWidth / measuredWidth) * REFERENCE_FONT_SIZE;
+  const scaleFromHeight = (availableHeight / measuredHeight) * REFERENCE_FONT_SIZE;
+
+  return clamp(Math.min(scaleFromWidth, scaleFromHeight), MIN_FONT_SIZE, MAX_FONT_SIZE);
+};
+
 export const getOcrBoundingBoxes = (ocrData: OcrBoundingBox[], metrics: ContentMetrics): OcrBox[] => {
   const boxes: OcrBox[] = [];
   for (const ocr of ocrData) {
@@ -68,13 +146,26 @@ export const getOcrBoundingBoxes = (ocrData: OcrBoundingBox[], metrics: ContentM
       y: point.y * metrics.contentHeight + metrics.offsetY,
     }));
 
+    const boxWidth = Math.max(distance(points[0], points[1]), distance(points[3], points[2]));
+    const boxHeight = Math.max(distance(points[0], points[3]), distance(points[1], points[2]));
+
     boxes.push({
       id: ocr.id,
       points,
       text: ocr.text,
       confidence: ocr.textScore,
+      isVertical: isVerticalText(boxWidth, boxHeight, ocr.text),
     });
   }
 
+  const rowThreshold = metrics.contentHeight * 0.02;
+  boxes.sort((a, b) => {
+    const yDifference = a.points[0].y - b.points[0].y;
+    if (Math.abs(yDifference) < rowThreshold) {
+      return a.points[0].x - b.points[0].x;
+    }
+    return yDifference;
+  });
+
   return boxes;
 };