@@ -13,9 +13,9 @@ import { NativeGestureRole } from '../web/interfaces';
 import { ButtonEventName } from '../web/tools/ButtonEvents';
 import { GestureLifecycleEvent } from '../web/tools/GestureLifecycleEvents';
 import {
-  calculateViewScale,
-  getEffectiveBoundingRect,
+  isPointerInBounds,
   PointerTypeMapping,
+  viewportToLocal,
 } from '../web/utils';
 
 const prefersReducedMotion = (): boolean =>
@@ -31,25 +31,21 @@ type ButtonPointerEvent = NativeSyntheticEvent<{
 }>;
 
 // Same coordinate basis as the press path (see PointerEventManager's
-// `mapEvent`), so the two payloads agree. Both reads below force a layout flush,
+// `mapEvent`), so the two payloads agree. The reads below force a layout flush,
 // hence the caller-side gate on a hover callback existing.
 const buttonEventFromPointerEvent = (
   event: ButtonPointerEvent
 ): ButtonEvent => {
   const view = event.currentTarget as unknown as HTMLElement;
-  const rect = getEffectiveBoundingRect(view);
-  const { scaleX, scaleY } = calculateViewScale(view);
   const absoluteX = event.nativeEvent.clientX ?? 0;
   const absoluteY = event.nativeEvent.clientY ?? 0;
+  const absolute = { x: absoluteX, y: absoluteY };
+  const local = viewportToLocal(view, absolute);
 
   return {
-    pointerInside:
-      absoluteX >= rect.left &&
-      absoluteX <= rect.right &&
-      absoluteY >= rect.top &&
-      absoluteY <= rect.bottom,
-    x: (absoluteX - rect.left) / scaleX,
-    y: (absoluteY - rect.top) / scaleY,
+    pointerInside: isPointerInBounds(view, absolute),
+    x: local.x,
+    y: local.y,
     absoluteX,
     absoluteY,
     numberOfPointers: 1,
 
@@ -0,0 +1,312 @@
+import { viewportToLocal } from '../utils';
+
+type Matrix = [number, number, number, number];
+
+type FakeViewOptions = {
+  matrix?: Matrix;
+  transform?: string;
+  scale?: string;
+  svg?: boolean;
+  // An svg root has a client box even though it has no offset size.
+  svgRoot?: boolean;
+  // Transforms of the ancestors, outermost first.
+  ancestors?: Matrix[];
+  parentDisplay?: string;
+};
+
+function multiply([a1, b1, c1, d1]: Matrix, [a2, b2, c2, d2]: Matrix): Matrix {
+  return [
+    a1 * a2 + c1 * b2,
+    b1 * a2 + d1 * b2,
+    a1 * c2 + c1 * d2,
+    b1 * c2 + d1 * d2,
+  ];
+}
+
+function fakeAncestor(
+  matrix: Matrix,
+  parentElement: unknown,
+  display = 'block'
+) {
+  return {
+    parentElement,
+    computedStyle: {
+      display,
+      scale: 'none',
+      transform: `matrix(${matrix.join(', ')}, 0, 0)`,
+    },
+  };
+}
+
+// A 100x50 view laid out at (200, 100), transformed around its center by its
+// own transform and those of its ancestors. The bounding rect is the one the
+// browser reports for the transformed box.
+function fakeView({
+  matrix = [1, 0, 0, 1],
+  transform,
+  scale = 'none',
+  svg = false,
+  svgRoot = false,
+  ancestors = [],
+  parentDisplay,
+}: FakeViewOptions = {}) {
+  const width = 100;
+  const height = 50;
+  const centerX = 250;
+  const centerY = 125;
+
+  let [a, b, c, d] = matrix;
+
+  if (scale !== 'none') {
+    const [scaleX, scaleY = scaleX] = scale.split(' ').map(parseFloat);
+    [a, b, c, d] = [a * scaleX, b * scaleY, c * scaleX, d * scaleY];
+  }
+
+  let parentElement: unknown = null;
+
+  for (const ancestor of ancestors) {
+    parentElement = fakeAncestor(ancestor, parentElement, parentDisplay);
+  }
+
+  if (parentDisplay !== 'contents') {
+    // The innermost ancestor applies first.
+    for (const ancestor of [...ancestors].reverse()) {
+      [a, b, c, d] = multiply(ancestor, [a, b, c, d]);
+    }
+  }
+
+  const rectWidth = Math.abs(a) * width + Math.abs(c) * height;
+  const rectHeight = Math.abs(b) * width + Math.abs(d) * height;
+
+  return {
+    style: {},
+    children: [],
+    parentElement,
+    // SVG elements have no offset size.
+    ...(svg ? {} : { offsetWidth: width, offsetHeight: height }),
+    ...(svgRoot ? { clientWidth: width, clientHeight: height } : {}),
+    computedStyle: {
+      display: 'block',
+      scale,
+      transform: transform ?? `matrix(${matrix.join(', ')}, 0, 0)`,
+    },
+    getBoundingClientRect: () => ({
+      left: centerX - rectWidth / 2,
+      top: centerY - rectHeight / 2,
+      right: centerX + rectWidth / 2,
+      bottom: centerY + rectHeight / 2,
+      width: rectWidth,
+      height: rectHeight,
+    }),
+  } as unknown as HTMLElement;
+}
+
+// The Jest environment is node, stub the DOM bits the helper touches.
+beforeAll(() => {
+  (globalThis as Record<string, unknown>).getComputedStyle = (
+    view: ReturnType<typeof fakeView>
+  ) => (view as unknown as { computedStyle: unknown }).computedStyle;
+  (globalThis as Record<string, unknown>).DOMRect = function (
+    left: number,
+    top: number,
+    width: number,
+    height: number
+  ) {
+    return { left, top, width, height };
+  };
+});
+
+afterAll(() => {
+  delete (globalThis as Record<string, unknown>).getComputedStyle;
+  delete (globalThis as Record<string, unknown>).DOMRect;
+});
+
+describe('viewportToLocal', () => {
+  // The point 10px right of and 10px below the view's top-left corner, when
+  // the view is not transformed.
+  const point = { x: 210, y: 110 };
+
+  test('an untransformed view', () => {
+    expect(viewportToLocal(fakeView(), point)).toEqual({ x: 10, y: 10 });
+    expect(viewportToLocal(fakeView({ transform: 'none' }), point)).toEqual({
+      x: 10,
+      y: 10,
+    });
+  });
+
+  test('a scaled view', () => {
+    // The box grows to 200x100 around its center, the point is 60px right of
+    // and 35px below the scaled corner.
+    expect(viewportToLocal(fakeView({ matrix: [2, 0, 0, 2] }), point)).toEqual({
+      x: 30,
+      y: 17.5,
+    });
+  });
+
+  test('a mirrored view', () => {
+    // The x axis runs from the right edge.
+    expect(viewportToLocal(fakeView({ matrix: [-1, 0, 0, 1] }), point)).toEqual(
+      { x: 90, y: 10 }
+    );
+  });
+
+  test('a view rotated by 180 degrees', () => {
+    expect(
+      viewportToLocal(fakeView({ matrix: [-1, 0, 0, -1] }), point)
+    ).toEqual({ x: 90, y: 40 });
+  });
+
+  test('a view rotated by 90 degrees', () => {
+    // The 100x50 box turns into a 50x100 one at (225, 75), the view's top-left
+    // corner lands on the top-right corner of the rotated box, its x axis runs
+    // downwards and its y axis leftwards.
+    const view = fakeView({ matrix: [0, 1, -1, 0] });
+
+    expect(viewportToLocal(view, { x: 275, y: 75 })).toEqual({ x: 0, y: 0 });
+    expect(viewportToLocal(view, { x: 265, y: 85 })).toEqual({ x: 10, y: 10 });
+  });
+
+  test('a mirrored and stretched view', () => {
+    const view = fakeView({ matrix: [-1, 0, 0, 1], scale: '2 1' });
+
+    // The box is 200px wide at (150, 100) and the x axis runs from the right
+    // edge: the point is 60px in, that is 30 view pixels from the right.
+    expect(viewportToLocal(view, point)).toEqual({ x: 70, y: 10 });
+  });
+
+  test('the scale property', () => {
+    expect(viewportToLocal(fakeView({ scale: '2' }), point)).toEqual({
+      x: 30,
+      y: 17.5,
+    });
+  });
+
+  test('a 3d transform matrix', () => {
+    const view = fakeView({
+      matrix: [2, 0, 0, 2],
+      transform: 'matrix3d(2, 0, 0, 0, 0, 2, 0, 0, 0, 0, 1, 0, 0, 0, 0, 1)',
+    });
+
+    expect(viewportToLocal(view, point)).toEqual({ x: 30, y: 17.5 });
+  });
+
+  test('an SVG element', () => {
+    expect(
+      viewportToLocal(fakeView({ matrix: [2, 0, 0, 2], svg: true }), point)
+    ).toEqual({ x: 30, y: 17.5 });
+    expect(
+      viewportToLocal(fakeView({ matrix: [0, 1, -1, 0], svg: true }), {
+        x: 265,
+        y: 85,
+      })
+    ).toEqual({ x: 10, y: 10 });
+  });
+
+  test('a view inside a scaled ancestor', () => {
+    // Same bounds as a scaled view, but the view's own space is unscaled.
+    const view = fakeView({ ancestors: [[2, 0, 0, 2]] });
+
+    expect(viewportToLocal(view, point)).toEqual({ x: 30, y: 17.5 });
+  });
+
+  test('a mirrored view inside a rotated ancestor', () => {
+    // Mirrored, then rotated by 90 degrees: the view's x axis runs upwards and
+    // its y axis leftwards from the bottom-right corner of the 50x100 box.
+    const view = fakeView({
+      matrix: [-1, 0, 0, 1],
+      ancestors: [[0, 1, -1, 0]],
+    });
+
+    expect(viewportToLocal(view, { x: 275, y: 175 })).toEqual({ x: 0, y: 0 });
+    expect(viewportToLocal(view, { x: 265, y: 165 })).toEqual({ x: 10, y: 10 });
+  });
+
+  test('a view inside nested scaled ancestors', () => {
+    // Scaled by 2, then by 0.5 horizontally: the box ends up 100x100.
+    const view = fakeView({
+      ancestors: [
+        [2, 0, 0, 2],
+        [0.5, 0, 0, 1],
+      ],
+    });
+
+    expect(viewportToLocal(view, point)).toEqual({ x: 10, y: 17.5 });
+  });
+
+  test('a transformed display: contents ancestor has no effect', () => {
+    const view = fakeView({
+      ancestors: [[2, 0, 0, 2]],
+      parentDisplay: 'contents',
+    });
+
+    expect(viewportToLocal(view, point)).toEqual({ x: 10, y: 10 });
+  });
+
+  test('a display: contents wrapper around a transformed view', () => {
+    const child = fakeView({ matrix: [-1, 0, 0, 1] });
+    const wrapper = {
+      style: { display: 'contents' },
+      children: [child],
+      childElementCount: 1,
+      computedStyle: { display: 'contents', scale: 'none', transform: 'none' },
+      getBoundingClientRect: () => ({ left: 0, top: 0, width: 0, height: 0 }),
+    } as unknown as HTMLElement;
+
+    expect(viewportToLocal(wrapper, point)).toEqual({ x: 90, y: 10 });
+  });
+
+  test('a display: contents wrapper around several views', () => {
+    const wrapper = {
+      style: { display: 'contents' },
+      children: [fakeView({ matrix: [-1, 0, 0, 1] }), fakeView()],
+      childElementCount: 2,
+      computedStyle: { display: 'contents', scale: 'none', transform: 'none' },
+      getBoundingClientRect: () => ({ left: 0, top: 0, width: 0, height: 0 }),
+    } as unknown as HTMLElement;
+
+    // The point is mapped against the union of the children's bounds.
+    expect(viewportToLocal(wrapper, point)).toEqual({ x: 10, y: 10 });
+  });
+
+  test('an svg root rotated by 45 degrees', () => {
+    // The bounds alone cannot tell the sides apart at 45 degrees, the size
+    // comes from the client box instead.
+    const s = Math.SQRT1_2;
+    const view = fakeView({ matrix: [s, s, -s, s], svg: true, svgRoot: true });
+    const corner = { x: 250 - 50 * s + 25 * s, y: 125 - 50 * s - 25 * s };
+
+    const local = viewportToLocal(view, corner);
+
+    expect(local.x).toBeCloseTo(0);
+    expect(local.y).toBeCloseTo(0);
+  });
+
+  test('a display: contents wrapper around several views in a scaled ancestor', () => {
+    const ancestor = fakeAncestor([2, 0, 0, 2], null);
+    const wrapper = {
+      style: { display: 'contents' },
+      children: [
+        fakeView({ ancestors: [[2, 0, 0, 2]] }),
+        fakeView({ ancestors: [[2, 0, 0, 2]] }),
+      ],
+      childElementCount: 2,
+      parentElement: ancestor,
+      // A contents element reports zeros, not its children's size.
+      offsetWidth: 0,
+      offsetHeight: 0,
+      computedStyle: { display: 'contents', scale: 'none', transform: 'none' },
+      getBoundingClientRect: () => ({ left: 0, top: 0, width: 0, height: 0 }),
+    } as unknown as HTMLElement;
+
+    // The union of the children is a scaled 100x50 box.
+    expect(viewportToLocal(wrapper, point)).toEqual({ x: 30, y: 17.5 });
+  });
+
+  test('a view scaled to zero', () => {
+    // Nothing to invert, fall back to the bounds.
+    expect(viewportToLocal(fakeView({ matrix: [0, 0, 0, 0] }), point)).toEqual({
+      x: -40,
+      y: -15,
+    });
+  });
+});