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docs/lib-bijection_offset.md

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+# bijection_offset
+
+Move 2D outlines outward or inward by a given amount. Each point of the offsetted shape is paired with exactly one point of the original shape.
+
+
+
+## Parameters
+
+- `pts` : Points of a shape.
+- `d` : Amount to offset the shape. When negative, the shape is offset inwards. 
+
+## Examples
+
+	include <bijection_offset.scad>;
+
+	shape = [
+		[15, 0],
+		[15, 30],
+		[0, 20],
+		[-15, 40],
+		[-15, 0]
+	];
+
+	color("red") polygon(bijection_offset(shape, 3));
+	color("orange") polygon(bijection_offset(shape, 2));
+	color("yellow") polygon(bijection_offset(shape, 1));
+	color("green") polygon(shape);
+	color("blue") polygon(bijection_offset(shape, -1));
+	color("indigo") polygon(bijection_offset(shape, -2));
+	color("purple") polygon(bijection_offset(shape, -3));
+
+![bijection_offset](images/lib-bijection_offset-1.JPG)
+
+	include <bijection_offset.scad>;
+	include <rotate_p.scad>;
+	include <polysections.scad>;
+	include <path_extrude.scad>;
+	include <bezier_curve.scad>;
+
+	shape = [
+		[5, 0],
+		[3, 9],
+		[0, 10],    
+		[-5, 0]
+	];
+	offsetted = bijection_offset(shape, 1);
+
+	offsetted2 = bijection_offset(shape, 2);
+	offsetted3 = bijection_offset(shape, 3);
+
+	t_step = 0.05;
+
+	p0 = [0, 0, 0];
+	p1 = [40, 60, 35];
+	p2 = [-50, 70, 0];
+	p3 = [20, 150, -35];
+	p4 = [30, 50, -3];
+
+	path_pts = bezier_curve(t_step, 
+		[p0, p1, p2, p3, p4]
+	);
+
+	path_extrude(concat(shape, offsetted), path_pts, "HOLLOW");
+	path_extrude(concat(offsetted2, offsetted3), path_pts, "HOLLOW");
+
+![bijection_offset](images/lib-bijection_offset-2.JPG)
+