cranpose_render_common/
text_paint.rs

1//! What a renderer reads of a text's style to draw its glyphs, worked out
2//! once per text node so that drawing a plain text never loads its style.
3
4use std::cell::Cell;
5
6use cranpose_ui::{
7    Brush, Color, TextStyle,
8    text::{RangeStyle, SpanStyle, TextDecoration, TextDrawStyle},
9};
10
11/// The paint of a text node's glyphs.
12#[derive(Clone, Copy, Debug, PartialEq)]
13pub struct TextPaint {
14    /// Whether the glyphs in `color` are all the text draws: no background,
15    /// shadow, brush, stroke or decoration, and no span that paints its own
16    /// range.
17    pub plain: bool,
18    /// The style's colour, or its solid brush, times its alpha; white when
19    /// it names neither.
20    pub color: Color,
21    /// How far the style's baseline shift moves the glyphs down.
22    pub baseline_shift: f32,
23}
24
25impl TextPaint {
26    /// The paint of a text in `style` with `spans`, at `font_size`.
27    pub fn of(style: &TextStyle, spans: &[RangeStyle<SpanStyle>], font_size: f32) -> Self {
28        let span_style = &style.span_style;
29        let plain = span_style.background.is_none()
30            && span_style.shadow.is_none()
31            && span_style.brush.is_none()
32            && !matches!(
33                span_style.draw_style,
34                Some(TextDrawStyle::Stroke { width }) if width.is_finite() && width > 0.0
35            )
36            && !spans_override_foreground(spans)
37            && !has_visible_decoration(spans, style);
38        Self {
39            plain,
40            color: resolve_text_color_without_gradient_fallback(style, Color::WHITE),
41            baseline_shift: span_style
42                .baseline_shift
43                .filter(|shift| shift.is_specified())
44                .map_or(0.0, |shift| -(shift.0 * font_size)),
45        }
46    }
47}
48
49/// A text node's [`TextPaint`], set when the scene builds the node or when a
50/// renderer first asks for it. It is derived data, so two caches always
51/// compare equal.
52#[derive(Clone, Debug, Default)]
53pub struct TextPaintCache(Cell<Option<TextPaint>>);
54
55impl TextPaintCache {
56    /// A cache holding `paint`.
57    pub fn holding(paint: TextPaint) -> Self {
58        Self(Cell::new(Some(paint)))
59    }
60
61    /// The cached paint, or the one `compute` returns, which the cache then
62    /// keeps.
63    pub fn get_or(&self, compute: impl FnOnce() -> TextPaint) -> TextPaint {
64        if let Some(paint) = self.0.get() {
65            return paint;
66        }
67        let paint = compute();
68        self.0.set(Some(paint));
69        paint
70    }
71}
72
73impl PartialEq for TextPaintCache {
74    fn eq(&self, _other: &Self) -> bool {
75        true
76    }
77}
78
79/// The text colour a style names, its solid brush's colour, or `default`,
80/// times the style's alpha.
81pub fn resolve_text_color_without_gradient_fallback(
82    text_style: &TextStyle,
83    default: Color,
84) -> Color {
85    let mut color = text_style
86        .span_style
87        .color
88        .or(match text_style.span_style.brush.as_ref() {
89            Some(Brush::Solid(color)) => Some(*color),
90            _ => None,
91        })
92        .unwrap_or(default);
93    if let Some(alpha) = text_style.span_style.alpha {
94        color.3 *= alpha.clamp(0.0, 1.0);
95    }
96    color
97}
98
99fn span_has_foreground_override(span_style: &SpanStyle) -> bool {
100    matches!(
101        span_style.brush.as_ref(),
102        Some(
103            Brush::LinearGradient { .. }
104                | Brush::RadialGradient { .. }
105                | Brush::SweepGradient { .. }
106        )
107    ) || span_style.alpha.is_some()
108        || span_style.draw_style.is_some()
109}
110
111/// Whether a span paints its range with a gradient, an alpha or a draw
112/// style of its own.
113pub fn spans_override_foreground(spans: &[RangeStyle<SpanStyle>]) -> bool {
114    spans
115        .iter()
116        .any(|span| span_has_foreground_override(&span.item))
117}
118
119/// Whether a span gives its range a colour or a solid brush of its own.
120pub fn spans_override_foreground_color(spans: &[RangeStyle<SpanStyle>]) -> bool {
121    spans
122        .iter()
123        .any(|span| span.item.color.is_some() || matches!(span.item.brush, Some(Brush::Solid(_))))
124}
125
126/// Whether the style or a span draws an underline or a line-through.
127pub fn has_visible_decoration(spans: &[RangeStyle<SpanStyle>], global_style: &TextStyle) -> bool {
128    let visible = |decoration: Option<TextDecoration>| {
129        decoration.is_some_and(|decoration| decoration != TextDecoration::NONE)
130    };
131    visible(global_style.span_style.text_decoration)
132        || spans.iter().any(|span| visible(span.item.text_decoration))
133}
cranpose_render_common/text_paint.rs

cranpose_render_common/
text_paint.rs
