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Preserve (don't clamp) negative half-leading #743

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Preserve (don't clamp) negative half-leading #743

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90 changes: 58 additions & 32 deletions parley/src/layout/line_break.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -97,14 +97,29 @@ struct Extents {

impl Default for Extents {
fn default() -> Self {
// Initialized to negative infinity so that content with negative extents (e.g. text with
// negative half-leading from a small `line-height`) is not floored at zero. Lines with no
// contributing content resolve to zero via [`Self::or_zero`], keeping the sentinel
// internal.
//
// Ideally, a line's initial extents should be sourced from the primary font.
Self {
// NOTE: these should be `f32::NEG_INFINITY`, but that's currently causing
// `tests::test_builders::builders_empty` to fail with a `NaN`.
//
// And even more ideally, a line's initial extents should be sourced from the primary
// font.
over: 0.,
under: 0.,
over: f32::NEG_INFINITY,
under: f32::NEG_INFINITY,
}
}
}

impl Extents {
/// Resolve unset (default) extents to zero.
fn or_zero(self) -> Self {
if self.over == f32::NEG_INFINITY && self.under == f32::NEG_INFINITY {
Self {
over: 0.,
under: 0.,
}
} else {
self
}
}
}
Expand All @@ -113,7 +128,8 @@ impl LineBoxMetrics {
/// The line height seen so far.
#[inline(always)]
fn line_height(self) -> f32 {
self.line_box.over + self.line_box.under
let line_box = self.line_box.or_zero();
line_box.over + line_box.under
}

fn add_text(&mut self, metrics: &FontMetrics, line_height: f32, quantize: bool) {
Expand Down Expand Up @@ -625,26 +641,36 @@ impl<'a, B: Brush> BreakLines<'a, B> {
// and the portion below to its descent. By default (no explicit baseline) the
// bottom of the box is aligned with the text baseline, i.e. the box is all
// ascent and zero descent. Out-of-flow boxes contribute nothing.
let (width_contribution, height_contribution, resolved_baseline) =
match inline_box.kind {
InlineBoxKind::InFlow => {
let baseline = inline_box.baseline.unwrap_or(inline_box.height);
(inline_box.width, inline_box.height, baseline)
}
InlineBoxKind::OutOfFlow => (0.0, 0.0, 0.0),
// If the box is a `CustomOutOfFlow` box then we yield control flow back to the caller.
// It is then the caller's responsibility to handle placement of the box.
InlineBoxKind::CustomOutOfFlow => {
return Some(YieldData::InlineBoxBreak(BoxBreakData {
inline_box_id: inline_box.id,
inline_box_index: item.index,
advance: self.state.line.x,
}));
}
};

let ascent_contribution = resolved_baseline;
let descent_contribution = height_contribution - resolved_baseline;
let (
width_contribution,
height_contribution,
ascent_contribution,
descent_contribution,
) = match inline_box.kind {
InlineBoxKind::InFlow => {
let baseline = inline_box.baseline.unwrap_or(inline_box.height);
(
inline_box.width,
inline_box.height,
baseline,
inline_box.height - baseline,
)
}
// Negative infinity extents are a no-op when maxed into the line's
// extents, so out-of-flow boxes truly contribute nothing.
InlineBoxKind::OutOfFlow => {
(0.0, 0.0, f32::NEG_INFINITY, f32::NEG_INFINITY)
}
// If the box is a `CustomOutOfFlow` box then we yield control flow back to the caller.
// It is then the caller's responsibility to handle placement of the box.
InlineBoxKind::CustomOutOfFlow => {
return Some(YieldData::InlineBoxBreak(BoxBreakData {
inline_box_id: inline_box.id,
inline_box_index: item.index,
advance: self.state.line.x,
}));
}
};

// Compute the x position of the content being currently processed
let next_x = self.state.line.x + width_contribution;
Expand Down Expand Up @@ -941,8 +967,8 @@ impl<'a, B: Brush> BreakLines<'a, B> {
if inline_box.kind != InlineBoxKind::InFlow {
self.state.append_inline_box_to_line(
self.state.line.x,
0.0,
0.0,
f32::NEG_INFINITY,
f32::NEG_INFINITY,
self.layout.data.quantize,
);
continue;
Expand Down Expand Up @@ -1223,8 +1249,8 @@ impl<'a, B: Brush> BreakLines<'a, B> {
// Whether metrics should be quantized to pixel boundaries
let quantize = self.layout.data.quantize;

let mut line_box_extents = self.state.line.box_metrics.line_box;
let mut content_box_extents = self.state.line.box_metrics.content_box;
let mut line_box_extents = self.state.line.box_metrics.line_box.or_zero();
let mut content_box_extents = self.state.line.box_metrics.content_box.or_zero();
if !have_metrics
&& line.item_range.is_empty()
&& let Some(metrics) = prev_line_metrics
Expand Down
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