LibWeb: Use discrete interpolation for degenerate ratios

Degenerate ratios cannot be interpolated.
Author: https://github.com/tcl3 Commit: f07a3fe6da Pull-request: https://github.com/LadybirdBrowser/ladybird/pull/4316 Reviewed-by: https://github.com/AtkinsSJ ✅
2025-08-02 06:09:08 +00:00 · 2025-04-11 09:59:25 +01:00 · 2025-04-11 09:59:25 +01:00 · f07a3fe6da · 2025-04-11 10:39:08 +00:00
commit f07a3fe6da
parent b3980d40f7
3 changed files with 387 additions and 0 deletions
--- a/Libraries/LibWeb/CSS/Interpolation.cpp
+++ b/Libraries/LibWeb/CSS/Interpolation.cpp
@ -616,6 +616,11 @@ NonnullRefPtr<CSSStyleValue const> interpolate_value(DOM::Element& element, Calc
        auto from_ratio = from.as_ratio().ratio();
        auto to_ratio = to.as_ratio().ratio();

+        // https://drafts.csswg.org/css-values/#combine-ratio
+        // If either <ratio> is degenerate, the values cannot be interpolated.
+        if (from_ratio.is_degenerate() || to_ratio.is_degenerate())
+            return delta >= 0.5f ? to : from;
+
        // The interpolation of a <ratio> is defined by converting each <ratio> to a number by dividing the first value
        // by the second (so a ratio of 3 / 2 would become 1.5), taking the logarithm of that result (so the 1.5 would
        // become approximately 0.176), then interpolating those values. The result during the interpolation is