widget/tests/test_textScaleFactor_system_font.html

   1 <!DOCTYPE HTML>
   2 <html>
   3 <head>
   4   <meta charset="utf-8">
   5   <title>Test that system font sizing is independent from ui.textScaleFactor</title>
   6   <script src="/tests/SimpleTest/SimpleTest.js"></script>
   7   <link rel="stylesheet" href="/tests/SimpleTest/test.css"/>
   8   <style>
   9     p { width: max-content }
  10     #menu { font: menu }
  11   </style>
  12 </head>
  13 <body>
  14   <p id="menu">"menu" text.</p>
  15   <p id="default">Default text.</p>
  16 </body>
  17 <script>
  18 "use strict";
  19
  20 const { AppConstants } = SpecialPowers.ChromeUtils.import(
  21   "resource://gre/modules/AppConstants.jsm"
  22 );
  23
  24 // Returns a Number for the font size in CSS pixels.
  25 function elementFontSize(element) {
  26   return parseFloat(getComputedStyle(element).getPropertyValue("font-size"));
  27 }
  28
  29 // "look-and-feel-changed" may be dispatched twice: once for the pref
  30 // change and once after receiving the new values from
  31 // ContentChild::RecvThemeChanged().
  32 // pushPrefEnv() resolves after the former. This resolves after the latter.
  33 function promiseNewFontSizeOnThemeChange(element) {
  34   return new Promise(resolve => {
  35     const lastSize = elementFontSize(element);
  36
  37     function ThemeChanged() {
  38       const size = elementFontSize(element);
  39       if (size != lastSize) {
  40         resolve(size);
  41       }
  42     }
  43     // "look-and-feel-changed" is dispatched before the style system is flushed,
  44     // https://searchfox.org/mozilla-central/rev/380fc5571b039fd453b45bbb64ed13146fe9b066/layout/base/nsPresContext.cpp#1684,1703-1705
  45     // so use an async observer to get a notification after style changes.
  46     SpecialPowers.addAsyncObserver(ThemeChanged, "look-and-feel-changed");
  47     SimpleTest.registerCleanupFunction(function() {
  48       SpecialPowers.removeAsyncObserver(ThemeChanged, "look-and-feel-changed");
  49     });
  50   });
  51 }
  52
  53 function fuzzyCompareLength(actual, expected, message, tolerance, expectFn) {
  54   expectFn(Math.abs(actual-expected) <= tolerance,
  55            `${message} - got ${actual}, expected ${expected} +/- ${tolerance}`);
  56 }
  57
  58 add_task(async () => {
  59   // MOZ_HEADLESS is set in content processes with GTK regardless of the
  60   // headless state of the parent process.  Check the parent state.
  61   const headless = await SpecialPowers.spawnChrome([], function get_headless() {
  62     return Services.env.get("MOZ_HEADLESS");
  63   });
  64   // LookAndFeel::TextScaleFactor::FloatID is implemented only for WINNT and
  65   // GTK.  ui.textScaleFactor happens to scale CSS pixels on other platforms
  66   // but system font integration has not been implemented.
  67   const expectSuccess = AppConstants.MOZ_WIDGET_TOOLKIT == "windows" ||
  68          (AppConstants.MOZ_WIDGET_TOOLKIT == "gtk" &&
  69           // Headless GTK doesn't get system font sizes from the system, but
  70           // uses sizes fixed in CSS pixels.
  71           !headless);
  72
  73   async function setScaleAndPromiseFontSize(scale, element) {
  74     const prefPromise = SpecialPowers.pushPrefEnv({
  75       set: [["ui.textScaleFactor", scale]],
  76     });
  77     if (!expectSuccess) {
  78       // The size is not expected to change but get it afresh to check our
  79       // assumption.
  80       await prefPromise;
  81       return elementFontSize(element);
  82     }
  83     const [size] = await Promise.all([
  84       promiseNewFontSizeOnThemeChange(element),
  85       prefPromise,
  86     ]);
  87     return size;
  88   }
  89
  90   const menu = document.getElementById("menu");
  91   const def = document.getElementById("default");
  92   // Choose a scaleFactor value different enough from possible default values
  93   // that app unit rounding does not prevent a change in devicePixelRatio.
  94   // A scaleFactor of 120 also has no rounding of app units per dev pixel.
  95   const referenceScale = 120;
  96   const menuSize1 = await setScaleAndPromiseFontSize(referenceScale, menu);
  97   const menuRect1 = menu.getBoundingClientRect();
  98   const defSize1 = elementFontSize(def);
  99   const defRect1 = def.getBoundingClientRect();
 100
 101   const expectFn = expectSuccess ? ok : todo;
 102   const menuSize2 = await setScaleAndPromiseFontSize(2*referenceScale, menu);
 103   {
 104     const singlePrecisionULP = Math.pow(2, -23);
 105     // Precision seems to be lost in the conversion to decimal string for the
 106     // property value.
 107     const reltolerance = 30 * singlePrecisionULP;
 108     fuzzyCompareLength(menuSize2, menuSize1/2, "size of menu font",
 109                        reltolerance*menuSize1/2, expectFn);
 110   }
 111   {
 112     const menuRect2 = menu.getBoundingClientRect();
 113     // The menu font text renders exactly the same and app-unit rects are
 114     // equal, but the DOMRect conversion is rounded to 1/65536 CSS pixels.
 115     // https://searchfox.org/mozilla-central/rev/380fc5571b039fd453b45bbb64ed13146fe9b066/dom/base/DOMRect.cpp#151-159
 116     // See also https://bugzilla.mozilla.org/show_bug.cgi?id=1640441#c28
 117     const absTolerance = 1/65536
 118     fuzzyCompareLength(menuRect2.width, menuRect1.width/2,
 119                        "width of menu font <p> in px", absTolerance, expectFn);
 120     fuzzyCompareLength(menuRect2.height, menuRect1.height/2,
 121                        "height of menu font <p> in px", absTolerance, expectFn);
 122   }
 123
 124   const defSize2 = elementFontSize(def);
 125   is(defSize2, defSize1, "size of default font");
 126   {
 127     const defRect2 = def.getBoundingClientRect();
 128     // Wider tolerance for hinting and snapping
 129     const relTolerance = 1/12;
 130     fuzzyCompareLength(defRect2.width, defRect1.width,
 131                        "width of default font <p> in px",
 132                        relTolerance*defRect1.width, ok);
 133     fuzzyCompareLength(defRect2.height, defRect1.height,
 134                        "height of default font <p> in px",
 135                        relTolerance*defRect1.height, ok);
 136   }
 137 });
 138 </script>
 139 </html>