kiln/src/render.rs

use eframe::egui;
use egui::{Align2, FontId, Pos2, Rect, vec2};

use crate::game::{Board, Glyph, Player};

/// Width of one board cell in pixels.
pub(crate) const CELL_W: f32 = 14.0;
/// Height of one board cell in pixels.
pub(crate) const CELL_H: f32 = 20.0;

/// Approximate height of the egui menu bar in pixels, used for window sizing.
pub(crate) const MENU_H: f32 = 24.0;
/// Default inner margin that egui's CentralPanel adds on all sides, in pixels.
pub(crate) const PANEL_MARGIN: f32 = 8.0;
/// Default width of the editor side panel in pixels. The panel is resizable.
pub(crate) const PALETTE_PANEL_W: f32 = 200.0;
/// Default window width in pixels. Independent of map size.
pub(crate) const DEFAULT_WINDOW_W: f32 = 840.0;
/// Default window height in pixels. Independent of map size.
pub(crate) const DEFAULT_WINDOW_H: f32 = 524.0;
/// Minimum window width: enough room for 10 cells plus margins.
pub(crate) const MIN_WINDOW_W: f32 = CELL_W * 10.0 + 2.0 * PANEL_MARGIN;
/// Minimum window height: enough room for 5 cells plus menu and margins.
pub(crate) const MIN_WINDOW_H: f32 = CELL_H * 5.0 + MENU_H + 2.0 * PANEL_MARGIN;

/// Draws a single cell at grid position `(x, y)` using the given glyph.
///
/// Each cell is rendered as two layers:
/// 1. A filled rectangle in `glyph.bg` covering the full cell area.
/// 2. A monospace character (`glyph.ch`) in `glyph.fg`, centered in the cell.
///
/// `origin` is the pixel position of cell `(0, 0)` — the top-left corner of
/// the board within the panel. Cell positions are computed from `origin` using
/// [`CELL_W`] and [`CELL_H`].
pub(crate) fn draw_glyph(painter: &egui::Painter, origin: Pos2, x: usize, y: usize, glyph: &Glyph) {
    let tl = origin + vec2(x as f32 * CELL_W, y as f32 * CELL_H);
    let rect = Rect::from_min_size(tl, vec2(CELL_W, CELL_H));
    let center = rect.center();
    painter.rect_filled(rect, 0.0, glyph.bg);
    painter.text(center, Align2::CENTER_CENTER, glyph.ch, FontId::monospace(CELL_H), glyph.fg);
}

/// Draws all board cells then the player overlay at `origin`.
pub(crate) fn draw_board(painter: &egui::Painter, origin: Pos2, board: &Board) {
    for y in 0..board.height {
        for x in 0..board.width {
            let (glyph, _) = board.get(x, y);
            draw_glyph(painter, origin, x, y, glyph);
        }
    }
    // The player is not a board cell; it is rendered on top as an overlay.
    // This separate draw will be removed once the player becomes a scripted object.
    let player_glyph = Glyph::player();
    draw_glyph(painter, origin, board.player.x as usize, board.player.y as usize, &player_glyph);
}

/// Converts a pixel position to cell coordinates relative to `origin`.
///
/// Uses floor so positions above or left of `origin` produce negative values —
/// callers must guard `>= 0` before treating the result as a valid cell index.
pub(crate) fn pos_to_cell(origin: Pos2, pos: Pos2) -> (i32, i32) {
    let rel = pos - origin;
    ((rel.x / CELL_W).floor() as i32, (rel.y / CELL_H).floor() as i32)
}

/// Computes the pixel position of board cell (0, 0) within `available`.
///
/// If the board fits along an axis, it is centered. If it overflows, the
/// viewport is centered on the player and clamped so no empty space appears
/// at the board edges.
pub(crate) fn board_origin(available: Rect, board_w: usize, board_h: usize, player: Player) -> Pos2 {
    let board_px_w = board_w as f32 * CELL_W;
    let board_px_h = board_h as f32 * CELL_H;

    let origin_x = if board_px_w <= available.width() {
        // Board fits: center it horizontally.
        available.min.x + (available.width() - board_px_w) / 2.0
    } else {
        // Board overflows: keep player at viewport center, clamp to board edges.
        let player_px_x = player.x as f32 * CELL_W + CELL_W / 2.0;
        (available.center().x - player_px_x)
            .max(available.max.x - board_px_w)  // right edge must reach viewport right
            .min(available.min.x)               // left edge must reach viewport left
    };

    let origin_y = if board_px_h <= available.height() {
        available.min.y + (available.height() - board_px_h) / 2.0
    } else {
        let player_px_y = player.y as f32 * CELL_H + CELL_H / 2.0;
        (available.center().y - player_px_y)
            .max(available.max.y - board_px_h)
            .min(available.min.y)
    };

    Pos2::new(origin_x, origin_y)
}