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Bug 1890531 - Remove automatic adjustment for "centered operators". r=emilio

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The MathML code adjust vertical position of basic binary operators with
the NS_MATHML_OPERATOR_CENTERED flag set (e.g. plus, equal or minus
signs) so that their centers align with the math axis. This behavior
is not defined in MathML Core and is not necessary in practice for math
fonts (which are already designed with the desired vertical alignments).
This patch tries and removes this by placing that legacy behavior
under a disabled-by-default runtime flag.

Intent-to-ship: https://groups.google.com/a/mozilla.org/g/dev-platform/c/nlA0t4J0gzo

Differential Revision: https://phabricator.services.mozilla.com/D207026
This commit is contained in:
Frédéric Wang 2024-04-10 08:57:31 +00:00
parent 5ae6b66c22
commit 22ec186a63
4 changed files with 63 additions and 9 deletions
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21
layout/mathml/nsMathMLmoFrame.cpp
View File

@ -8,6 +8,7 @@
#include "gfxContext.h"
#include "mozilla/PresShell.h"
#include "mozilla/StaticPrefs_mathml.h"
#include "nsCSSValue.h"
#include "nsLayoutUtils.h"
#include "nsPresContext.h"
@ -145,15 +146,17 @@ void nsMathMLmoFrame::ProcessTextData() {
mFlags |= allFlags & NS_MATHML_OPERATOR_ACCENT;
mFlags |= allFlags & NS_MATHML_OPERATOR_MOVABLELIMITS;
// see if this is an operator that should be centered to cater for
// fonts that are not math-aware
if (1 == length) {
if ((ch == '+') || (ch == '=') || (ch == '*') ||
(ch == 0x2212) || // −
(ch == 0x2264) || // ≤
(ch == 0x2265) || // ≥
(ch == 0x00D7)) { // ×
mFlags |= NS_MATHML_OPERATOR_CENTERED;
if (!StaticPrefs::mathml_centered_operators_disabled()) {
// see if this is an operator that should be centered to cater for
// fonts that are not math-aware
if (1 == length) {
if ((ch == '+') || (ch == '=') || (ch == '*') ||
(ch == 0x2212) || // −
(ch == 0x2264) || // ≤
(ch == 0x2265) || // ≥
(ch == 0x00D7)) { // ×
mFlags |= NS_MATHML_OPERATOR_CENTERED;
}
}
}

7
modules/libpref/init/StaticPrefList.yaml
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@ -9548,6 +9548,13 @@
mirror: always
rust: true
# Whether to disable forced centering of binary operators (+, =, ...).
- name: mathml.centered_operators.disabled
type: bool
value: true
mirror: always
rust: true
#---------------------------------------------------------------------------
# Prefs starting with "media."
#---------------------------------------------------------------------------

5
testing/web-platform/mozilla/meta/mathml/fonts/opentype-axis-height.html.ini Normal file
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@ -0,0 +1,5 @@
# This test verifies that the AxisHeight parameter is used to adjust vertical
# positions of NS_MATHML_OPERATOR_CENTERED operators. It should be removed once
# the code for this legacy behavior is completely deleted.
[opentype-axis-height.html]
prefs: [mathml.centered_operators.disabled: false]

39
testing/web-platform/tests/mathml/presentation-markup/operators/mo-no-vertical-adjustment-for-basic-binary-operators.html Normal file
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@ -0,0 +1,39 @@
<!DOCTYPE html>
<meta charset="utf-8">
<title>No vertical adjustment for basic binary operators</title>
<link rel="stylesheet" type="text/css" href="/fonts/ahem.css" />
<link rel="help" href="https://bugzilla.mozilla.org/show_bug.cgi?id=1890531" />
<meta name="assert" content="Verify vertical alignement of basic binary operators is not adjusted to align their centers with the math axis.">
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<script src="/mathml/support/fonts.js"></script>
<style>
@font-face {
font-family: operators;
/* AxisHeight == 0, so the math axis matches the baseline */
src: url("/fonts/math/operators.woff");
}
math {
font: 25px operators;
}
</style>
<math>
<mn id="ref">↯</mn>
<mo>+</mo><mo>=</mo><mo>*</mo><mo>−</mo><mo>≤</mo><mo>≥</mo><mo>×</mo>
</math>
<script>
promise_test(async () => {
await new Promise(r => { window.addEventListener("DOMContentLoaded", r) });
await loadAllFonts();
function centerOf(element) {
const box = element.getBoundingClientRect();
return (box.top + box.bottom) / 2;
}
const ref = centerOf(document.getElementById("ref"));
const epsilon = 1;
Array.from(document.getElementsByTagName("mo")).forEach(mo => {
assert_approx_equals(centerOf(mo), ref, epsilon,
`Position of "${mo.textContent}"`);
});
}, "Vertical alignment of basic binary operators is not adjusted.");
</script>