Struct TextMetrics 

pub struct TextMetrics {
    pub width: f64,
    pub height: f64,
    pub ascent: f64,
    pub cap_height: f64,
    pub ink: Rect,
}

Single-line text measurement in canvas points (Toolkit::measure_text, docs/fonts.md).

Two boxes, and the difference between them matters. width/height is the line box: the typographic slot the text occupies, the same for every string in a face at a size, and what TextAnchor positions. ink is the ink box: where the glyphs put marks. A line of digits leaves the descender space of its line box empty, so the two disagree, and which one is wanted depends on the question: laying text out in a column wants the line box, and centering it on a rule or keeping it clear of a mark wants the ink.

Fields

width: f64

The advance width of the whole string.

height: f64

The line box: ascent + descent at this size (plus the line gap where the engine reports one), which is the box TextAnchor positions.

ascent: f64

The baseline’s offset from the top of the line box.

cap_height: f64

The face’s cap height at this size: baseline to the top of a capital.

A property of the font, not of this string, reported here because it is what optical centering needs and asking for it separately would be a second measurement. Text made of capitals and digits looks centered on a rule when its cap box straddles it, not its line box: the line box reserves descender room that digits never use, so centering by it sits every label a little low. The cap middle is ascent - cap_height / 2.0 below the line box’s top.

ink: Rect

The ink box, the tight bounds of what is drawn, with its origin relative to the line box’s top-leading corner, so ink.origin is where the marks start inside the slot.

Empty (zero-size) for text that draws nothing, a space included. Where a toolkit cannot report ink it answers the whole line box, which is a superset: an overlap test against it can only be too cautious, never wrong.

Implementations

impl TextMetrics

pub fn approximate(text: &str, size: f64) -> TextMetrics

The portable guess day::measure_text falls back to when a toolkit cannot measure: 0.6 × size per character, 1.2 × size tall, the baseline at 0.9 × size, caps at 0.7 × size. Its ink is the whole line box, the safe direction to be wrong in (see ink).

pub fn from_slots(out: &[f64; 8]) -> TextMetrics

Read the eight-slot form the serializing backends (qt, xaml, arkui, web) fill across their C ABI: advance, line height, ascent, cap height, then the ink box relative to the line box’s top-leading corner. One definition so four shims cannot drift from each other.

pub fn from_baseline( width: f64, ascent: f64, descent: f64, cap_height: f64, ink: Rect, ) -> TextMetrics

The line box’s top-leading corner, given a baseline-relative measurement, the shape every backend’s metrics come in. ink_* are relative to the drawing origin on the baseline (ink_top negative above it), the convention Skia, Core Text and Qt all report in.

Trait Implementations

impl Clone for TextMetrics

fn clone(&self) -> TextMetrics

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Copy for TextMetrics

impl Debug for TextMetrics

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl PartialEq for TextMetrics

fn eq(&self, other: &TextMetrics) -> bool

Equality operator ==.

fn ne(&self, other: &Rhs) -> bool

Inequality operator !=.

impl StructuralPartialEq for TextMetrics