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LibWeb: Handle inaccuracies resolving transformation matrix type

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Doing trigonometric calculations with floating point numbers can
introduce small inaccuracies. This meant that we would sometimes
incorrectly generate a 3d rather than 2d matrix for the resolved value
of `transform`.

Gains us 3 WPT tests.
This commit is contained in:
Callum Law
2025-10-22 15:39:40 +13:00
committed by Sam Atkins
parent 2d331b9176
commit 1977a976da
Notes: github-actions[bot] 2025-10-23 08:35:56 +00:00 
Author: https://github.com/Calme1709
Commit: https://github.com/LadybirdBrowser/ladybird/commit/1977a976da2
Pull-request: https://github.com/LadybirdBrowser/ladybird/pull/6544
Reviewed-by: https://github.com/AtkinsSJ ✅
3 changed files with 200 additions and 10 deletions
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21
Libraries/LibWeb/CSS/CSSStyleProperties.cpp
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@@ -826,18 +826,19 @@ RefPtr<StyleValue const> CSSStyleProperties::style_value_for_computed_property(L
// and m33, m44 are equal to 1.
// NB: We only care about 4x4 matrices here.
// NB: Our elements are 0-indexed not 1-indexed, and in the opposite order.
if (matrix[0, 2] != 0 // m31
|| matrix[1, 2] != 0 // m32
|| matrix[2, 0] != 0 // m13
|| matrix[2, 1] != 0 // m23
|| matrix[2, 3] != 0 // m43
|| matrix[3, 0] != 0 // m14
|| matrix[3, 1] != 0 // m24
|| matrix[3, 2] != 0) // m34
// NB: We use epsilon comparisons here to account for inaccuracies when doing trigonometric calculations.
if (abs(matrix[0, 2]) > AK::NumericLimits<float>::epsilon() // m31
|| abs(matrix[1, 2]) > AK::NumericLimits<float>::epsilon() // m32
|| abs(matrix[2, 0]) > AK::NumericLimits<float>::epsilon() // m13
|| abs(matrix[2, 1]) > AK::NumericLimits<float>::epsilon() // m23
|| abs(matrix[2, 3]) > AK::NumericLimits<float>::epsilon() // m43
|| abs(matrix[3, 0]) > AK::NumericLimits<float>::epsilon() // m14
|| abs(matrix[3, 1]) > AK::NumericLimits<float>::epsilon() // m24
|| abs(matrix[3, 2]) > AK::NumericLimits<float>::epsilon()) // m34
return false;
if (matrix[2, 2] != 1 // m33
|| matrix[3, 3] != 1) // m44
if (abs(matrix[2, 2]) - 1 > AK::NumericLimits<float>::epsilon() // m33
|| abs(matrix[3, 3]) - 1 > AK::NumericLimits<float>::epsilon()) // m44
return false;
return true;