Trait TextService 

pub trait TextService {
    // Required methods
    fn prepare(
        &mut self,
        input: &TextInput,
        constraints: TextConstraints,
    ) -> (TextBlobId, TextMetrics);
    fn release(&mut self, blob: TextBlobId);

    // Provided methods
    fn prepare_str(
        &mut self,
        text: &str,
        style: &TextStyle,
        constraints: TextConstraints,
    ) -> (TextBlobId, TextMetrics) { ... }
    fn prepare_rich(
        &mut self,
        rich: &AttributedText,
        base_style: &TextStyle,
        constraints: TextConstraints,
    ) -> (TextBlobId, TextMetrics) { ... }
    fn measure(
        &mut self,
        input: &TextInput,
        constraints: TextConstraints,
    ) -> TextMetrics { ... }
    fn measure_str(
        &mut self,
        text: &str,
        style: &TextStyle,
        constraints: TextConstraints,
    ) -> TextMetrics { ... }
    fn measure_rich(
        &mut self,
        rich: &AttributedText,
        base_style: &TextStyle,
        constraints: TextConstraints,
    ) -> TextMetrics { ... }
    fn caret_x(&mut self, _blob: TextBlobId, _index: usize) -> Px { ... }
    fn hit_test_x(&mut self, _blob: TextBlobId, _x: Px) -> usize { ... }
    fn selection_rects(
        &mut self,
        _blob: TextBlobId,
        _range: (usize, usize),
        _out: &mut Vec<Rect>,
    ) { ... }
    fn first_line_metrics(
        &mut self,
        _blob: TextBlobId,
    ) -> Option<TextLineMetrics> { ... }
    fn first_line_ink_metrics(
        &mut self,
        _blob: TextBlobId,
    ) -> Option<TextInkMetrics> { ... }
    fn last_line_metrics(
        &mut self,
        _blob: TextBlobId,
    ) -> Option<TextLineMetrics> { ... }
    fn last_line_ink_metrics(
        &mut self,
        _blob: TextBlobId,
    ) -> Option<TextInkMetrics> { ... }
    fn selection_rects_clipped(
        &mut self,
        blob: TextBlobId,
        range: (usize, usize),
        clip: Rect,
        out: &mut Vec<Rect>,
    ) { ... }
    fn caret_stops(&mut self, _blob: TextBlobId, _out: &mut Vec<(usize, Px)>) { ... }
    fn caret_rect(
        &mut self,
        _blob: TextBlobId,
        _index: usize,
        _affinity: CaretAffinity,
    ) -> Rect { ... }
    fn hit_test_point(
        &mut self,
        _blob: TextBlobId,
        _point: Point,
    ) -> HitTestResult { ... }
}

Required Methods

fn prepare( &mut self, input: &TextInput, constraints: TextConstraints, ) -> (TextBlobId, TextMetrics)

fn release(&mut self, blob: TextBlobId)

Provided Methods

fn prepare_str( &mut self, text: &str, style: &TextStyle, constraints: TextConstraints, ) -> (TextBlobId, TextMetrics)

fn prepare_rich( &mut self, rich: &AttributedText, base_style: &TextStyle, constraints: TextConstraints, ) -> (TextBlobId, TextMetrics)

fn measure( &mut self, input: &TextInput, constraints: TextConstraints, ) -> TextMetrics

fn measure_str( &mut self, text: &str, style: &TextStyle, constraints: TextConstraints, ) -> TextMetrics

fn measure_rich( &mut self, rich: &AttributedText, base_style: &TextStyle, constraints: TextConstraints, ) -> TextMetrics

fn caret_x(&mut self, _blob: TextBlobId, _index: usize) -> Px

Returns the X offset (in logical px) of the caret at index within the prepared text blob.

Coordinate space: relative to the text origin (x=0 at the beginning of the line).

Notes:

• index is a byte offset into the UTF-8 text, clamped to valid char boundaries (ADR 0044).
• Implementations may clamp to the nearest representable caret position.

fn hit_test_x(&mut self, _blob: TextBlobId, _x: Px) -> usize

Performs hit-testing for a single-line text blob and returns the nearest caret byte index.

Coordinate space: x is relative to the text origin (x=0 at the beginning of the line).

fn selection_rects( &mut self, _blob: TextBlobId, _range: (usize, usize), _out: &mut Vec<Rect>, )

Computes selection rectangles for a single-line selection range.

Coordinate space: rects are relative to the text origin (x=0, y=0 at top of text box).

Geometry contract:

• For a non-empty range (start != end), conforming implementations should emit rectangles with positive height (and should avoid emitting zero-width rectangles).

fn first_line_metrics(&mut self, _blob: TextBlobId) -> Option<TextLineMetrics>

Best-effort first-line font extents for a prepared text blob.

This is primarily intended for mechanism-level vertical placement policies in fixed-height controls. Implementations should return None if the data is unavailable or expensive to compute.

fn first_line_ink_metrics( &mut self, _blob: TextBlobId, ) -> Option<TextInkMetrics>

Best-effort first-line ink extents (ascent/descent) for a prepared text blob.

This differs from first_line_metrics when the line box is fixed (e.g. TextLineHeightPolicy::FixedFromStyle) but the shaped content includes taller fallback glyphs (emoji/CJK/etc). Callers may use this to detect potential clipping and apply padding or a different line-height preset.

fn last_line_metrics(&mut self, _blob: TextBlobId) -> Option<TextLineMetrics>

Best-effort last-line font extents for a prepared multi-line text blob.

This is primarily intended for mechanism-level vertical placement and overflow handling policies. Implementations should return None if the data is unavailable or expensive to compute.

fn last_line_ink_metrics(&mut self, _blob: TextBlobId) -> Option<TextInkMetrics>

Best-effort last-line ink extents (ascent/descent) for a prepared multi-line text blob.

This is intended for avoiding bottom-edge clipping in fixed line-box layouts when the last line contains tall fallback glyphs (emoji/CJK/etc).

fn selection_rects_clipped( &mut self, blob: TextBlobId, range: (usize, usize), clip: Rect, out: &mut Vec<Rect>, )

Computes selection rectangles and clips them to clip in the same coordinate space.

This is intended for large multi-line selections where generating rectangles for off-screen lines is wasteful. Implementations may override this to cull work earlier.

Coordinate space: rects and clip are relative to the text origin (x=0, y=0 at top of text box).

fn caret_stops(&mut self, _blob: TextBlobId, _out: &mut Vec<(usize, Px)>)

Extracts the precomputed caret stop table (byte index -> x offset) for a single-line blob.

This is primarily intended for UI hit-testing in event handlers, which do not have access to the text service.

fn caret_rect( &mut self, _blob: TextBlobId, _index: usize, _affinity: CaretAffinity, ) -> Rect

Returns the caret rectangle (in logical px) for the given index.

Coordinate space: rect is relative to the text origin (x=0, y=0 at the top of the text box).

Notes:

• Single-line implementations may ignore affinity.
• Multi-line implementations should use affinity to disambiguate positions at line breaks.
• Conforming implementations should return a rectangle with positive height.

fn hit_test_point(&mut self, _blob: TextBlobId, _point: Point) -> HitTestResult

Hit-test a point in the text’s local coordinate space and return a caret index and affinity.

Coordinate space: point is relative to the text origin (x=0, y=0 at the top of the text box).

Implementors