add xmas_tree

examples/xmas_tree.scad

@@ -0,0 +1,40 @@
+use <line2d.scad>;
+use <starburst.scad>;
+use <util/rand.scad>;
+
+base = 100;
+segments = 150;
+
+xmas_tree(base, segments);
+
+module xmas_tree(base, segments) {
+	half_base = base / 2;
+	height = PI * half_base;
+	slope = height / half_base;
+	dx = half_base / segments;
+	dh = height / segments;
+	a = dh / (2 * PI * half_base) * 360 * 3;
+	base_h = dh * 2;
+	seg_w = base_h * 3;
+
+	for(i = [0:segments]) {
+		x = i * dx - half_base;
+		
+		color(c = [0, rand(), 0])
+		rotate(a * i)
+		translate([0, 0, dx * i * slope + base_h])
+		linear_extrude(dh)
+			line2d([x, 0], [-x, 0], width = seg_w);
+	}
+
+	color("Sienna")
+	linear_extrude(base_h)
+		circle(half_base + base_h + seg_w, $fn = 48);
+
+	color("yellow")
+	translate([0, 0, height + dh * 6])
+	rotate([90, 0, 540]) {
+		starburst(seg_w * 2.75, seg_w * 1.25, 8, seg_w);
+		mirror([0, 0, 1]) starburst(seg_w * 2.75, seg_w * 1.25, 8, seg_w);
+	}
+}