2d.text.measure.actualBoundingBox.small-font.html

Enable keyboard shortcuts

This test has a WPT meta file that expects 1 subtest issues.
This WPT test may be referenced by the following Test IDs:
- /html/canvas/element/text/2d.text.measure.actualBoundingBox.small-font.html - WPT Dashboard Interop Dashboard

<!DOCTYPE html>

<!-- DO NOT EDIT! This test has been generated by /html/canvas/tools/gentest.py. -->

<meta charset="UTF-8">

<title>Canvas test: 2d.text.measure.actualBoundingBox.small-font</title>

<script src="/resources/testharness.js"></script>

<script src="/resources/testharnessreport.js"></script>

<script src="/html/canvas/resources/canvas-tests.js"></script>

<link rel="stylesheet" href="/html/canvas/resources/canvas-tests.css">

<style>

@font-face {

  font-family: CanvasTest;

  src: url("/fonts/CanvasTest.ttf");

</style>

<body class="show_output">

<h1>2d.text.measure.actualBoundingBox.small-font</h1>

<p class="desc">Testing that actualBoundingBox metrics are precise at small font sizes</p>

<span style="font-family: CanvasTest; position: absolute; visibility: hidden">A</span>

<p class="output">Actual output:</p>

<canvas id="c" class="output" width="100" height="50"><p class="fallback">FAIL (fallback content)</p></canvas>

<ul id="d"></ul>

<script>

promise_test(async t => {

  var canvas = document.getElementById('c');

  var ctx = canvas.getContext('2d');

  await document.fonts.ready;

  ctx.font = '1.5px CanvasTest';

  ctx.direction = 'ltr';

  ctx.textAlign = 'left';

  ctx.textBaseline = 'alphabetic';

  // At small font sizes, Skia may store glyph bounds as integers, causing

  // loss of precision (crbug.com/479240778). The CanvasTest 'E' glyph fills

  // the em square (0, -0.25em) to (1em, 0.75em), so at 1.5px:

  //   actualBoundingBoxRight  ≈ 1.5   (1em)

  //   actualBoundingBoxAscent ≈ 1.125 (0.75em)

  //   actualBoundingBoxDescent≈ 0.375 (0.25em)

  // With integer quantization these would snap to 2, 2, 1 respectively.

  // Use ±0.25 tolerances so quantized values are reliably caught.

  var m = ctx.measureText('E');

  _assert(m.actualBoundingBoxRight > 1.25, "m.actualBoundingBoxRight > 1.25");

  _assert(m.actualBoundingBoxRight < 1.75, "m.actualBoundingBoxRight < 1.75");

  _assert(m.actualBoundingBoxAscent > 0.875, "m.actualBoundingBoxAscent > 0.875");

  _assert(m.actualBoundingBoxAscent < 1.375, "m.actualBoundingBoxAscent < 1.375");

  _assert(m.actualBoundingBoxDescent > 0.125, "m.actualBoundingBoxDescent > 0.125");

  _assert(m.actualBoundingBoxDescent < 0.625, "m.actualBoundingBoxDescent < 0.625");

}, "Testing that actualBoundingBox metrics are precise at small font sizes");

</script>