/**
* Pure geometry helpers for ALTO polygon hit-testing and coordinate transforms.
*/
import type { TextLine } from "./types";
/** Parsed polygon ready for hit-testing */
export interface PolygonHit {
lineId: string;
points: number[];
line: TextLine;
}
/** Parse ALTO polygon "x1,y1 x2,y2 ..." into flat [x1,y1,x2,y2,...] */
export function parsePolygonPoints(polygon: string): number[] {
const pts: number[] = [];
for (const pair of polygon.trim().split(/\s+/)) {
const [x, y] = pair.split(",").map(Number);
if (!isNaN(x) && !isNaN(y)) pts.push(x, y);
}
return pts;
}
/** Ray-casting point-in-polygon test */
export function pointInPolygon(px: number, py: number, pts: number[]): boolean {
let inside = false;
for (let i = 0, j = pts.length - 2; i < pts.length; j = i, i += 2) {
const xi = pts[i], yi = pts[i + 1];
const xj = pts[j], yj = pts[j + 1];
if (yi > py !== yj > py && px < ((xj - xi) * (py - yi)) / (yj - yi) + xi) {
inside = !inside;
}
}
return inside;
}
/** Find which polygon (text line) contains the given image-space coordinate */
export function findHitAtImageCoord(
imgX: number,
imgY: number,
polygons: PolygonHit[],
): PolygonHit | null {
for (const p of polygons) {
if (pointInPolygon(imgX, imgY, p.points)) return p;
}
return null;
}
/** Build PolygonHit array from ALTO text lines (filters lines with <6 polygon points) */
export function buildPolygonHits(textLines: TextLine[]): PolygonHit[] {
const hits: PolygonHit[] = [];
for (const line of textLines) {
const points = parsePolygonPoints(line.polygon);
if (points.length >= 6) {
hits.push({ lineId: line.id, points, line });
}
}
return hits;
}
