1 files changed, 163 insertions, 0 deletions
diff --git a/rust/crates/text/src/layout.rs b/rust/crates/text/src/layout.rs
new file mode 100644
index 00000000..c0e3a198
--- /dev/null
+++ b/rust/crates/text/src/layout.rs
@@ -0,0 +1,163 @@
+use crate::params::{
+    FONT_SIZE_SCALE_REFERENCE, TextAlign, TextBackground, TextDecoration, TextLayoutParams,
+};
+
+pub const TEXT_DECORATION_THICKNESS_RATIO: f64 = 0.07;
+pub const STRIKETHROUGH_VERTICAL_RATIO: f64 = 0.35;
+
+#[derive(Clone, Copy, Debug, PartialEq)]
+pub struct ResolvedTextLayout {
+    pub scaled_font_size: f64,
+    pub letter_spacing: f64,
+    pub line_height_px: f64,
+    pub font_size_ratio: f64,
+    pub text_align: TextAlign,
+    pub text_decoration: TextDecoration,
+}
+
+pub fn resolve_text_layout(text: &TextLayoutParams, canvas_height: f64) -> ResolvedTextLayout {
+    let scaled_font_size = text.font_size * (canvas_height / FONT_SIZE_SCALE_REFERENCE);
+    ResolvedTextLayout {
+        scaled_font_size,
+        letter_spacing: text.letter_spacing,
+        line_height_px: scaled_font_size * text.line_height,
+        font_size_ratio: text.font_size / 15.0,
+        text_align: text.text_align,
+        text_decoration: text.text_decoration,
+    }
+}
+
+#[derive(Clone, Copy, Debug, Default, PartialEq)]
+pub struct LineMetrics {
+    pub width: f64,
+    pub ascent: f64,
+    pub descent: f64,
+}
+
+#[derive(Clone, Copy, Debug, Default, PartialEq)]
+pub struct TextBlockMeasurement {
+    pub visual_center_offset: f64,
+    pub height: f64,
+    pub max_width: f64,
+}
+
+pub fn measure_text_block(
+    line_metrics: &[LineMetrics],
+    line_height_px: f64,
+) -> TextBlockMeasurement {
+    let max_width = line_metrics
+        .iter()
+        .fold(0.0_f64, |max, metrics| max.max(metrics.width));
+    let line_count = line_metrics.len() as f64;
+    TextBlockMeasurement {
+        visual_center_offset: ((line_count - 1.0) * line_height_px) / 2.0,
+        height: line_count * line_height_px,
+        max_width,
+    }
+}
+
+#[derive(Clone, Copy, Debug, Default, PartialEq)]
+pub struct Rect {
+    pub left: f64,
+    pub top: f64,
+    pub width: f64,
+    pub height: f64,
+}
+
+impl Rect {
+    pub fn right(self) -> f64 {
+        self.left + self.width
+    }
+
+    pub fn bottom(self) -> f64 {
+        self.top + self.height
+    }
+}
+
+pub fn align_offset(text_align: TextAlign, line_width: f64) -> f64 {
+    match text_align {
+        TextAlign::Left => 0.0,
+        TextAlign::Center => -line_width / 2.0,
+        TextAlign::Right => -line_width,
+    }
+}
+
+pub fn text_rect(text_align: TextAlign, block: &TextBlockMeasurement) -> Rect {
+    Rect {
+        left: align_offset(text_align, block.max_width),
+        top: -block.height / 2.0,
+        width: block.max_width,
+        height: block.height,
+    }
+}
+
+fn background_visible(background: &TextBackground) -> bool {
+    background.enabled && !background.color.is_empty() && background.color != "transparent"
+}
+
+pub fn text_background_rect(
+    text_align: TextAlign,
+    block: &TextBlockMeasurement,
+    background: &TextBackground,
+    font_size_ratio: f64,
+) -> Option<Rect> {
+    if !background_visible(background) {
+        return None;
+    }
+    let rect = text_rect(text_align, block);
+    let padding_x = background.padding_x * font_size_ratio;
+    let padding_y = background.padding_y * font_size_ratio;
+    Some(Rect {
+        left: rect.left - padding_x + background.offset_x,
+        top: rect.top - padding_y + background.offset_y,
+        width: rect.width + padding_x * 2.0,
+        height: rect.height + padding_y * 2.0,
+    })
+}
+
+pub fn text_visual_rect(
+    text_align: TextAlign,
+    block: &TextBlockMeasurement,
+    background: &TextBackground,
+    font_size_ratio: f64,
+) -> Rect {
+    let rect = text_rect(text_align, block);
+    let Some(background_rect) = text_background_rect(text_align, block, background, font_size_ratio)
+    else {
+        return rect;
+    };
+    let left = rect.left.min(background_rect.left);
+    let top = rect.top.min(background_rect.top);
+    Rect {
+        left,
+        top,
+        width: rect.right().max(background_rect.right()) - left,
+        height: rect.bottom().max(background_rect.bottom()) - top,
+    }
+}
+
+pub fn decoration_rect(
+    text_decoration: TextDecoration,
+    text_align: TextAlign,
+    line_width: f64,
+    line_y: f64,
+    ascent: f64,
+    descent: f64,
+    scaled_font_size: f64,
+) -> Option<Rect> {
+    if text_decoration == TextDecoration::None {
+        return None;
+    }
+    let thickness = (scaled_font_size * TEXT_DECORATION_THICKNESS_RATIO).max(1.0);
+    let top = match text_decoration {
+        TextDecoration::Underline => line_y + descent + thickness,
+        TextDecoration::LineThrough => line_y - (ascent - descent) * STRIKETHROUGH_VERTICAL_RATIO,
+        TextDecoration::None => unreachable!(),
+    };
+    Some(Rect {
+        left: align_offset(text_align, line_width),
+        top,
+        width: line_width,
+        height: thickness,
+    })
+}