Move anchor, point and transform to JS

support/transform.js

@@ -0,0 +1,43 @@
+"use strict";
+
+module.exports = class Transform {
+	constructor(xx, yx, xy, yy, x, y) {
+		this.xx = xx;
+		this.yx = yx;
+		this.xy = xy;
+		this.yy = yy;
+		this.x = x;
+		this.y = y;
+	}
+
+	static Id() {
+		return new Transform(1, 0, 0, 1, 0, 0);
+	}
+
+	apply(pt) {
+		return {
+			x: pt.x * this.xx + pt.y * this.yx + this.x,
+			y: pt.x * this.xy + pt.y * this.yy + this.y
+		};
+	}
+	unapply(pt) {
+		const xx = pt.x - this.x;
+		const yy = pt.y - this.y;
+		const denom = this.xx * this.yy - this.xy * this.yx;
+		return {
+			x: (xx * this.yy - yy * this.yx) / denom,
+			y: (yy * this.xx - xx * this.xy) / denom
+		};
+	}
+	inverse() {
+		const denom = this.xx * this.yy - this.xy * this.yx;
+		return new Transform(
+			this.yy / denom,
+			-this.yx / denom,
+			-this.xy / denom,
+			this.xx / denom,
+			-(this.x * this.yy - this.y * this.yx) / denom,
+			-(-this.x * this.xy + this.y * this.xx) / denom
+		);
+	}
+};