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LibWeb: Avoid early conversion to CSSPixels when simplifying calculation

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Converting to CSSPixels caused us to lose precision and the sign of
signed zeroes.

The values we resolve against in Length::ResolutionContext are still
themselves rounded too early but this is in the right direction.
This commit is contained in:
Callum Law 2025-10-22 20:18:07 +13:00 • committed by Sam Atkins
parent 43b06cbbdd
commit 0b45a68423
Notes: github-actions[bot] 2025-10-23 08:35:32 +00:00
6 changed files with 63 additions and 39 deletions
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46
Libraries/LibWeb/CSS/Length.cpp
View file

@ -38,74 +38,84 @@ Length Length::percentage_of(Percentage const& percentage) const
}
CSSPixels Length::font_relative_length_to_px(Length::FontMetrics const& font_metrics, Length::FontMetrics const& root_font_metrics) const
{
return CSSPixels::nearest_value_for(font_relative_length_to_px_without_rounding(font_metrics, root_font_metrics));
}
double Length::font_relative_length_to_px_without_rounding(Length::FontMetrics const& font_metrics, Length::FontMetrics const& root_font_metrics) const
{
switch (m_unit) {
case LengthUnit::Em:
return CSSPixels::nearest_value_for(m_value * font_metrics.font_size.to_double());
return m_value * font_metrics.font_size.to_double();
case LengthUnit::Rem:
return CSSPixels::nearest_value_for(m_value * root_font_metrics.font_size.to_double());
return m_value * root_font_metrics.font_size.to_double();
case LengthUnit::Ex:
return CSSPixels::nearest_value_for(m_value * font_metrics.x_height.to_double());
return m_value * font_metrics.x_height.to_double();
case LengthUnit::Rex:
return CSSPixels::nearest_value_for(m_value * root_font_metrics.x_height.to_double());
return m_value * root_font_metrics.x_height.to_double();
case LengthUnit::Cap:
return CSSPixels::nearest_value_for(m_value * font_metrics.cap_height.to_double());
return m_value * font_metrics.cap_height.to_double();
case LengthUnit::Rcap:
return CSSPixels::nearest_value_for(m_value * root_font_metrics.cap_height.to_double());
return m_value * root_font_metrics.cap_height.to_double();
case LengthUnit::Ch:
return CSSPixels::nearest_value_for(m_value * font_metrics.zero_advance.to_double());
return m_value * font_metrics.zero_advance.to_double();
case LengthUnit::Rch:
return CSSPixels::nearest_value_for(m_value * root_font_metrics.zero_advance.to_double());
return m_value * root_font_metrics.zero_advance.to_double();
case LengthUnit::Ic:
// FIXME: Use the "advance measure of the “水” (CJK water ideograph, U+6C34) glyph"
return CSSPixels::nearest_value_for(m_value * font_metrics.font_size.to_double());
return m_value * font_metrics.font_size.to_double();
case LengthUnit::Ric:
// FIXME: Use the "advance measure of the “水” (CJK water ideograph, U+6C34) glyph"
return CSSPixels::nearest_value_for(m_value * root_font_metrics.font_size.to_double());
return m_value * root_font_metrics.font_size.to_double();
case LengthUnit::Lh:
return CSSPixels::nearest_value_for(m_value * font_metrics.line_height.to_double());
return m_value * font_metrics.line_height.to_double();
case LengthUnit::Rlh:
return CSSPixels::nearest_value_for(m_value * root_font_metrics.line_height.to_double());
return m_value * root_font_metrics.line_height.to_double();
default:
VERIFY_NOT_REACHED();
}
}
CSSPixels Length::viewport_relative_length_to_px(CSSPixelRect const& viewport_rect) const
{
return CSSPixels::nearest_value_for(viewport_relative_length_to_px_without_rounding(viewport_rect));
}
double Length::viewport_relative_length_to_px_without_rounding(CSSPixelRect const& viewport_rect) const
{
switch (m_unit) {
case LengthUnit::Vw:
case LengthUnit::Svw:
case LengthUnit::Lvw:
case LengthUnit::Dvw:
return viewport_rect.width() * (CSSPixels::nearest_value_for(m_value) / 100);
return viewport_rect.width() * m_value / 100;
case LengthUnit::Vh:
case LengthUnit::Svh:
case LengthUnit::Lvh:
case LengthUnit::Dvh:
return viewport_rect.height() * (CSSPixels::nearest_value_for(m_value) / 100);
return viewport_rect.height() * m_value / 100;
case LengthUnit::Vi:
case LengthUnit::Svi:
case LengthUnit::Lvi:
case LengthUnit::Dvi:
// FIXME: Select the width or height based on which is the inline axis.
return viewport_rect.width() * (CSSPixels::nearest_value_for(m_value) / 100);
return viewport_rect.width() * m_value / 100;
case LengthUnit::Vb:
case LengthUnit::Svb:
case LengthUnit::Lvb:
case LengthUnit::Dvb:
// FIXME: Select the width or height based on which is the block axis.
return viewport_rect.height() * (CSSPixels::nearest_value_for(m_value) / 100);
return viewport_rect.height() * m_value / 100;
case LengthUnit::Vmin:
case LengthUnit::Svmin:
case LengthUnit::Lvmin:
case LengthUnit::Dvmin:
return min(viewport_rect.width(), viewport_rect.height()) * (CSSPixels::nearest_value_for(m_value) / 100);
return min(viewport_rect.width(), viewport_rect.height()) * m_value / 100;
case LengthUnit::Vmax:
case LengthUnit::Svmax:
case LengthUnit::Lvmax:
case LengthUnit::Dvmax:
return max(viewport_rect.width(), viewport_rect.height()) * (CSSPixels::nearest_value_for(m_value) / 100);
return max(viewport_rect.width(), viewport_rect.height()) * m_value / 100;
default:
VERIFY_NOT_REACHED();
}