From 9ccb4a7bc728fd0e85c04fddb802fde02b73cfe2 Mon Sep 17 00:00:00 2001
From: sanine <sanine.not@pm.me>
Date: Sun, 29 May 2022 20:44:11 -0500
Subject: add basic color brushing demo

---
 src/Terrain.js | 111 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 111 insertions(+)
 create mode 100644 src/Terrain.js

(limited to 'src/Terrain.js')

diff --git a/src/Terrain.js b/src/Terrain.js
new file mode 100644
index 0000000..c287063
--- /dev/null
+++ b/src/Terrain.js
@@ -0,0 +1,111 @@
+'use strict';
+
+import Voronoi from './3rdparty/rhill-voronoi-core.js';
+
+import { useAverage } from './modules/Util.js';
+import { AABB, QuadTree } from './modules/Geometry.js';
+
+
+/* from here on up, we always assume that points live in the range [(0,0), (1,1)) */
+
+function lloydRelax(point_set, density) {
+	/* setup quadtree and averages */
+	let tree = new QuadTree(1,1);
+	let averages = {};
+	for (let i=0; i<point_set.length; i++) {
+		const point = point_set[i];
+		point.index = i;
+		tree.insert(point);
+
+		let [avg, append] = useAverage();
+		const cent_x = { avg, append };
+		[avg, append] = useAverage();
+		const cent_y = { avg, append };
+		averages[i] = { cent_x, cent_y };
+	}
+
+	/* compute average centroids */
+	for (let x=0; x<1; x += 1/density) {
+		for (let y=0; y<1; y += 1/density) {
+			const point = { x, y };
+			const closest = tree.closest(point);
+			const { cent_x, cent_y } = averages[closest.index];
+			cent_x.append(point.x);
+			cent_y.append(point.y);
+		}
+	}
+
+	/* return centroid points */
+	const result = [];
+	for (let i=0; i<point_set.length; i++) {
+		const point = { x: averages[i].cent_x.avg(), y: averages[i].cent_y.avg() };
+		result.push(point);
+	}
+	return result;
+}
+
+
+class Terrain {
+	constructor() {
+		const N_SEED_POINTS = 2**12;
+		const N_RELAX_ITERATIONS = 1;
+		const RELAX_DENSITY = 400;
+		const randomPoint = () => ({x: Math.random(), y: Math.random()});
+
+		this.min_height = 0;
+		this.max_height = 0;
+
+		let seed_points = [];
+		for (let i=0; i<N_SEED_POINTS; i++) seed_points.push(randomPoint());
+
+		for (let i=0; i<N_RELAX_ITERATIONS; i++)
+			lloydRelax(seed_points, RELAX_DENSITY);
+
+		const v = new Voronoi();
+		this.graph = v.compute(seed_points, {xl: 0, xr: 1, yt: 0, yb: 1});
+
+		this.tree = new QuadTree(1,1);
+		for (let v of this.graph.vertices) {
+			v.hue = 0;
+			this.tree.insert(v);
+		}
+	}
+
+
+	applyBrush(x, y, f, strength, radius) {
+		const region = new AABB(x-radius, y-radius, 2*radius, 2*radius);
+		const points = this.tree.root.getPointsInRegion(region);
+		
+		const dist2 = (a, b) => (a.x - b.x)**2 + (a.y - b.y)**2;
+
+		const sigma = radius/3;
+		const beta = 1/(2*sigma*sigma);
+		const center = { x, y };
+		const power = pt => Math.exp(-beta * dist2(pt, center));
+		
+		for (let pt of points) f(pt, strength * power(pt));
+	}
+
+
+	renderGrid(ct) {
+		ct.save();
+		ct.lineWidth = 0.001;
+		for (let edge of this.graph.edges) {
+			ct.fillStyle = `hsl(${edge.va.hue}, 100%, 50%)`;
+			ct.beginPath();
+			ct.arc(edge.va.x, edge.va.y, 0.005, 0, 2*Math.PI);
+			ct.closePath();
+			ct.fill();
+
+			ct.beginPath();
+			ct.moveTo(edge.va.x, edge.va.y);
+			ct.lineTo(edge.vb.x, edge.vb.y);
+			ct.closePath();
+			ct.stroke();
+		}
+		ct.restore();
+	}
+}
+
+export { lloydRelax };
+export default Terrain;
-- 
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