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Auto merge of #19807 - emilio:calc-font-size, r=Manishearth

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style: Make the Gecko font-size calc() code do what it means to do.

It makes no sense to pass a custom base size of zero in presence of rem, ex, or
ch units.

Bug: 1431031
Reviewed-by: Manishearth
MozReview-Commit-ID: 7ZZwRzQKREX

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This commit is contained in:
bors-servo 2018-01-18 09:36:51 -06:00 • committed by GitHub
commit 671b69c0b7
3 changed files with 61 additions and 29 deletions
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7
components/style/properties/gecko.mako.rs
View file

@ -2505,9 +2505,12 @@ fn static_assert() {
/// Set font size, taking into account scriptminsize and scriptlevel
/// Returns Some(size) if we have to recompute the script unconstrained size
pub fn apply_font_size(&mut self, v: FontSize,
pub fn apply_font_size(
&mut self,
v: FontSize,
parent: &Self,
device: &Device) -> Option<NonNegativeLength> {
device: &Device,
) -> Option<NonNegativeLength> {
let (adjusted_size, adjusted_unconstrained_size) =
self.calculate_script_level_size(parent, device);
// In this case, we have been unaffected by scriptminsize, ignore it

28
components/style/values/specified/font.rs
View file

@ -593,15 +593,25 @@ impl FontSize {
// Extract the ratio/offset and compose it
if (calc.em.is_some() || calc.percentage.is_some()) && parent.keyword_info.is_some() {
let ratio = calc.em.unwrap_or(0.) + calc.percentage.map_or(0., |pc| pc.0);
// Compute it, but shave off the font-relative part (em, %)
// This will mean that other font-relative units like ex and ch will be computed against
// the old font even when the font changes. There's no particular "right answer" for what
// to do here -- Gecko recascades as if the font had changed, we instead track the changes
// and reapply, which means that we carry over old computed ex/ch values whilst Gecko
// recomputes new ones. This is enough of an edge case to not really matter.
let abs = calc.to_computed_value_zoomed(context, FontBaseSize::Custom(Au(0).into()))
.length_component().into();
info = parent.keyword_info.map(|i| i.compose(ratio, abs));
// Compute it, but shave off the font-relative part (em, %).
//
// This will mean that other font-relative units like ex and
// ch will be computed against the old parent font even when
// the font changes.
//
// There's no particular "right answer" for what to do here,
// Gecko recascades as if the font had changed, we instead
// track the changes and reapply, which means that we carry
// over old computed ex/ch values whilst Gecko recomputes
// new ones.
//
// This is enough of an edge case to not really matter.
let abs = calc.to_computed_value_zoomed(
context,
FontBaseSize::InheritedStyleButStripEmUnits,
).length_component();
info = parent.keyword_info.map(|i| i.compose(ratio, abs.into()));
}
let calc = calc.to_computed_value_zoomed(context, base_size);
calc.to_used_value(Some(base_size.resolve(context))).unwrap().into()

45
components/style/values/specified/length.rs
View file

@ -71,11 +71,17 @@ pub enum FontRelativeLength {
/// A source to resolve font-relative units against
#[derive(Clone, Copy, Debug, PartialEq)]
pub enum FontBaseSize {
/// Use the font-size of the current element
/// Use the font-size of the current element.
CurrentStyle,
/// Use the inherited font-size
/// Use the inherited font-size.
InheritedStyle,
/// Use a custom base size
/// Use the inherited font-size, but strip em units.
///
/// FIXME(emilio): This is very complex, and should go away.
InheritedStyleButStripEmUnits,
/// Use a custom base size.
///
/// FIXME(emilio): This is very dubious, and only used for MathML.
Custom(Au),
}
@ -85,6 +91,7 @@ impl FontBaseSize {
match *self {
FontBaseSize::Custom(size) => size,
FontBaseSize::CurrentStyle => context.style().get_font().clone_font_size().size(),
FontBaseSize::InheritedStyleButStripEmUnits |
FontBaseSize::InheritedStyle => context.style().get_parent_font().clone_font_size().size(),
}
}
@ -99,36 +106,48 @@ impl FontRelativeLength {
CSSPixelLength::new(pixel)
}
/// Return reference font size. We use the base_size flag to pass a different size
/// for computing font-size and unconstrained font-size.
/// This returns a pair, the first one is the reference font size, and the second one is the
/// unpacked relative length.
/// Return reference font size.
///
/// We use the base_size flag to pass a different size for computing
/// font-size and unconstrained font-size.
///
/// This returns a pair, the first one is the reference font size, and the
/// second one is the unpacked relative length.
fn reference_font_size_and_length(
&self,
context: &Context,
base_size: FontBaseSize,
) -> (Au, CSSFloat) {
fn query_font_metrics(context: &Context, reference_font_size: Au) -> FontMetricsQueryResult {
context.font_metrics_provider.query(context.style().get_font(),
fn query_font_metrics(
context: &Context,
reference_font_size: Au,
) -> FontMetricsQueryResult {
context.font_metrics_provider.query(
context.style().get_font(),
reference_font_size,
context.style().writing_mode,
context.in_media_query,
context.device())
context.device(),
)
}
let reference_font_size = base_size.resolve(context);
match *self {
FontRelativeLength::Em(length) => {
if context.for_non_inherited_property.is_some() {
if matches!(base_size, FontBaseSize::CurrentStyle) {
if base_size == FontBaseSize::CurrentStyle {
context.rule_cache_conditions.borrow_mut()
.set_font_size_dependency(
reference_font_size.into()
);
}
}
if base_size == FontBaseSize::InheritedStyleButStripEmUnits {
(Au(0), length)
} else {
(reference_font_size, length)
}
},
FontRelativeLength::Ex(length) => {
if context.for_non_inherited_property.is_some() {
@ -182,7 +201,7 @@ impl FontRelativeLength {
// https://drafts.csswg.org/css-values/#rem:
//
// When specified on the font-size property of the root
// element, the rem units refer to the property’s initial
// element, the rem units refer to the property's initial
// value.
//
let reference_size = if context.is_root_element || context.in_media_query {