kiln/kiln-tui/src/utils.rs

use color::Rgba8;
use kiln_core::glyph::Glyph;
use ratatui::layout::Rect;
use ratatui::prelude::Color;
use ratatui::style::Style;
use ratatui::text::Span;

/// Converts a core [`Rgba8`] color into a ratatui truecolor [`Color`].
///
/// The alpha channel is dropped — terminals have no per-cell alpha. Truecolor
/// requires terminal support; terminals limited to 256 colors approximate it.
pub fn rgba8_to_color(c: Rgba8) -> Color {
    Color::Rgb(c.r, c.g, c.b)
}

/// The character this terminal front-end draws for `glyph`.
///
/// A glyph carries its character directly, so this is almost the identity — the
/// one case that needs handling is the transparent sentinel `'\0'`, which means
/// "draw nothing". By the time a glyph reaches a renderer, `Board::glyph_at` has
/// already exhausted its precedence chain, so there is nothing underneath left to
/// reveal and the cell is simply blank. Writing the NUL through to the terminal
/// buffer would emit an unprintable character instead.
///
/// How a sentinel looks on screen is a front-end decision, which is why this
/// lives here rather than in kiln-core.
pub fn glyph_char(glyph: Glyph) -> char {
    if glyph.is_visible() { glyph.tile } else { ' ' }
}

/// Converts a [`Glyph`] to a single-character styled [`Span`], applying fg and bg.
pub fn glyph_to_span(glyph: Glyph) -> Span<'static> {
    let style = Style::default()
        .fg(rgba8_to_color(glyph.fg))
        .bg(rgba8_to_color(glyph.bg));
    Span::styled(glyph_char(glyph).to_string(), style)
}

/// Returns true if two `Rect`s share at least one cell.
pub fn rects_overlap(a: Rect, b: Rect) -> bool {
    a.x < b.x + b.width && b.x < a.x + a.width && a.y < b.y + b.height && b.y < a.y + a.height
}