Skip to content
Snippets Groups Projects
Commit 0e69f1ac authored by Igor Oliveira's avatar Igor Oliveira Committed by Pier Angelo Vendrame
Browse files

Bug 23104: Add a default line height compensation 

Many fonts have issues with their vertical metrics. they
are used to influence the height of ascenders and depth
of descenders. Gecko uses it to calculate the line height
(font height + ascender + descender), however because of
that idiosyncratic behavior across multiple operating
systems, it can be used to identify the user's OS.

The solution proposed in the patch uses a default factor
to be multiplied with the font size, simulating the concept
of ascender and descender. This way all operating
systems will have the same line height.
parent 33eacb5e
No related branches found
No related tags found
1 merge request!126MB 310: Rebased MB 13.0 onto 115.12.0esr
Show whitespace changes
Inline Side-by-side
layout/generic/ReflowInput.cpp
+ 6
− 3
View file @ 0e69f1ac
......@@ -34,6 +34,7 @@
#include "nsTableCellFrame.h"
#include "nsTableFrame.h"
#include "StickyScrollContainer.h"
#include "nsContentUtils.h"
using namespace mozilla;
using namespace mozilla::css;
......@@ -2723,12 +2724,12 @@ void ReflowInput::CalculateBlockSideMargins() {
// This is necessary because without this compensation, normal line height might
// look too tight.
constexpr float kNormalLineHeightFactor = 1.2f;
static nscoord GetNormalLineHeight(nsFontMetrics* aFontMetrics) {
static nscoord GetNormalLineHeight(nsFontMetrics* aFontMetrics, bool aRFP) {
MOZ_ASSERT(aFontMetrics, "no font metrics");
nscoord externalLeading = aFontMetrics->ExternalLeading();
nscoord internalLeading = aFontMetrics->InternalLeading();
nscoord emHeight = aFontMetrics->EmHeight();
if (!internalLeading && !externalLeading) {
if ((!internalLeading && !externalLeading) || aRFP) {
return NSToCoordRound(emHeight * kNormalLineHeightFactor);
}
return emHeight + internalLeading + externalLeading;
......@@ -2768,7 +2769,9 @@ static inline nscoord ComputeLineHeight(const StyleLineHeight& aLh,
RefPtr<nsFontMetrics> fm = nsLayoutUtils::GetMetricsFor(
aPresContext, aIsVertical, &aRelativeToFont, size,
/* aUseUserFontSet = */ true);
return GetNormalLineHeight(fm);
return GetNormalLineHeight(
fm, aPresContext->Document()->ShouldResistFingerprinting(
RFPTarget::Unknown));
}
// If we don't have a pres context, use a 1.2em fallback.
size.ScaleBy(kNormalLineHeightFactor);
......
layout/generic/test/mochitest.ini
+ 1
− 0
View file @ 0e69f1ac
......@@ -164,3 +164,4 @@ support-files =
[test_scroll_on_display_contents.html]
support-files = !/gfx/layers/apz/test/mochitest/apz_test_native_event_utils.js
[test_bug1803209.html]
[test_tor_bug23104.html]
layout/generic/test/test_tor_bug23104.html 0 → 100644
+ 50
− 0
View file @ 0e69f1ac
<!DOCTYPE HTML>
<meta charset="UTF-8">
<html>
<head>
<title>Test for Tor Bug #23104: CSS line-height reveals the platform Tor browser is running</title>
<script type="application/javascript" src="/tests/SimpleTest/SimpleTest.js"></script>
<script type="application/javascript" src="/tests/SimpleTest/SpawnTask.js"></script>
<style type="text/css">
span {
background-color: #000;
color: #fff;
font-size: 16.5px;
}
</style>
</head>
<body>
<span id="test1">Test1</span>
<span id="test2">كلمة</span>
<span id="test3">ação</span>
<script>
let setPref = async function (key, value) {
await SpecialPowers.pushPrefEnv({"set": [[key, value]]});
}
function getStyle(el, styleprop) {
el = document.getElementById(el);
return document.defaultView.getComputedStyle(el, null).getPropertyValue(styleprop);
}
function validateElement(elementName, isFingerprintResistent) {
var fontSize = getStyle(elementName, 'font-size');
var lineHeight = getStyle(elementName, 'line-height');
var validationCb = isFingerprintResistent ? is : isnot;
validationCb(parseFloat(lineHeight), Math.round(parseFloat(fontSize)) * 1.2, 'Line Height validation');
}
add_task(async function() {
await setPref("layout.css.line-height.normal-as-resolved-value.enabled", false);
for (let resistFingerprintingValue of [true, false]) {
await setPref("privacy.resistFingerprinting", resistFingerprintingValue);
for (let elementId of ['test1', 'test2', 'test3']) {
validateElement(elementId, resistFingerprintingValue);
}
}
});
</script>
</body>
</html>
0% or .
You are about to add 0 people to the discussion. Proceed with caution.
Please register or to comment