# thi-ng/umbrella

packages/rasterize/src/poly.ts

### Summary

A
3 hrs
###### Test Coverage
``````import type { IGrid2D, TypedArray } from "@thi.ng/api";
import type { Shader2D } from "./api.js";
import { ensureShader2D } from "./checks.js";

/**
* Draws a filled polygon (simple, no holes) into given grid. Each grid cell's
* value is obtained from user supplied shader function which will be called
* with the pixel's `x,y` coords.
*
* Based on Efficient Polygon Fill Algorithm by Darel Rex Finley
* http://alienryderflex.com/polygon_fill/
*
* Bounds calculation and clipping added by Karsten Schmidt
*
* @param grid -
* @param pts -
* @param val -
*/
export const fillPoly = <T extends any[] | TypedArray, P>(
grid: IGrid2D<T, P>,
pts: number[][],
val: P | Shader2D<P>
) => {
const numP = pts.length;
const [width, height] = grid.size;
let minX = Infinity;
let minY = Infinity;
let maxX = -Infinity;
let maxY = -Infinity;
for (let i = numP; i-- > 0; ) {
const { 0: x, 1: y } = pts[i];
minX = Math.min(minX, x);
maxX = Math.max(maxX, x);
minY = Math.min(minY, y);
maxY = Math.max(maxY, y);
}
minX = Math.max(minX | 0, 0);
maxX = Math.min(maxX | 0, width - 1);
minY = Math.max(minY | 0, 0);
maxY = Math.min(maxY | 0, height - 1);
if (minX >= width || maxX < 0 || minY >= height || maxY < 0) return;
let i = 0;
let k = 0;
let j: number;
const isec: number[] = [];
for (let y = Math.max(0, minY); y <= maxY; y++) {
i = k = 0;
j = numP - 1;
isec.length = 0;
for (; i < numP; j = i, i++) {
const { 0: pix, 1: piy } = pts[i];
const { 0: pjx, 1: pjy } = pts[j];
if ((piy < y && pjy >= y) || (pjy < y && piy >= y)) {
isec[k++] = (pix + ((y - piy) / (pjy - piy)) * (pjx - pix)) | 0;
}
}
isec.sort((a, b) => a - b);
for (i = 0; i < k; i += 2) {
let x1 = isec[i];
if (x1 > maxX) break;
let x2 = isec[i + 1];
if (x2 > minX) {
x1 < minX && (x1 = minX);
x2 > maxX && (x2 = maxX);
for (let x = x1; x <= x2; x++) {
grid.setAtUnsafe(x, y, shader(x, y));
}
}
}
}
};``````