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LibWeb: Correctly round non-integer z-indexes

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Previously we would just cast to an int.

Gains us 3 WPT tests.
This commit is contained in:
Callum Law 2025-08-01 15:07:07 +12:00 • committed by Tim Ledbetter
commit 15cee5cc15
Notes: github-actions[bot] 2025-08-05 05:39:02 +00:00
3 changed files with 73 additions and 2 deletions
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5
Libraries/LibWeb/CSS/ComputedProperties.cpp
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@ -338,7 +338,7 @@ Optional<int> ComputedProperties::z_index() const
return {};
// Clamp z-index to the range of a signed 32-bit integer for consistency with other engines.
auto clamp = [](auto number) -> int {
auto clamp = [](long number) -> int {
if (number >= NumericLimits<int>::max())
return NumericLimits<int>::max();
if (number <= NumericLimits<int>::min())
@ -352,7 +352,8 @@ Optional<int> ComputedProperties::z_index() const
if (value.is_calculated()) {
auto maybe_double = value.as_calculated().resolve_number_deprecated({});
if (maybe_double.has_value()) {
return clamp(maybe_double.value());
// Round up on half
return clamp(floor(maybe_double.value() + 0.5f));
}
}
return {};

11
Tests/LibWeb/Text/expected/wpt-import/css/css-values/calc-z-index-fractions-001.txt Normal file
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@ -0,0 +1,11 @@
Harness status: OK
Found 6 tests
6 Pass
Pass testing z-index: calc(2.5 / 2)
Pass testing z-index: calc(3 / 2)
Pass testing z-index: calc(3.5 / 2)
Pass testing z-index: calc(-2.5 / 2)
Pass testing z-index: calc(-3 / 2)
Pass testing z-index: calc(-3.5 / 2)

59
Tests/LibWeb/Text/input/wpt-import/css/css-values/calc-z-index-fractions-001.html Normal file
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@ -0,0 +1,59 @@
<!DOCTYPE html>
<meta charset="UTF-8">
<title>CSS Values and Units Test: computed value of 'z-index' when specified with calc() function and fractional values</title>
<link rel="author" title="Gérard Talbot" href="http://www.gtalbot.org/BrowserBugsSection/css21testsuite/">
<link rel="help" href="https://www.w3.org/TR/css-values-4/#calc-range">
<meta content="This test verifies how 2 calc() functions are computed for 'z-index' when involved expressions end up being numbers halfway between adjacent integers." name="assert">
<script src="../../resources/testharness.js"></script>
<script src="../../resources/testharnessreport.js"></script>
<div id="target"></div>
<script>
function startTesting()
{
var targetElement = document.getElementById("target");
function verifyComputedStyle(property_name, initial_value, specified_value, expected_value)
{
test(function()
{
targetElement.style.setProperty(property_name, initial_value);
/*
The purpose of the initial_value is to act as a fallback
value in case the calc() function in the specified value
fails or in case it generates an invalid value. Since we
are running 2 consecutive tests on the same element,
then it is necessary to reset its property to an initial
value.
*/
targetElement.style.setProperty(property_name, specified_value);
assert_equals(getComputedStyle(targetElement)[property_name], expected_value);
}, `testing ${property_name}: ${specified_value}`);
}
/* verifyComputedStyle(property_name, initial_value, specified_value, expected_value) */
verifyComputedStyle("z-index", "auto", "calc(2.5 / 2)", "1");
verifyComputedStyle("z-index", "auto", "calc(3 / 2)", "2");
verifyComputedStyle("z-index", "auto", "calc(3.5 / 2)", "2");
verifyComputedStyle("z-index", "auto", "calc(-2.5 / 2)", "-1");
verifyComputedStyle("z-index", "auto", "calc(-3 / 2)", "-1");
verifyComputedStyle("z-index", "auto", "calc(-3.5 / 2)", "-2");
}
startTesting();
</script>