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docs/lib2-t2d.md

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+# t2d
+
+An implementation of Turtle Graphics with Fluent API. It moves on the xy plane. You can get the cooridinate `[x, y]` or `angle` of its current position.
+
+## Parameters
+
+- `t` : The data of a turtle. If it's ignored, `t2d` creates a new turtle.
+- `cmd` : It accepts a string or a list of commands. 
+    - Given a string: `"turn"`, `"forward"`, `"point"` or `"angle"`. If `"turn"` is provided, the `angle` parameter is required. If `"forward"` is provided, `leng` is required. `"point"` and `"angle"` are used to get respective data from a turtle.
+    - Given a list: `[[cmd1, value], [cmd2, value2], ...]`. For example, `[["forward", 10], ["turn", 120]]` will forward a turtle 10mm and turn it 120 degrees. 
+- `point` : Set the position of a turtle.
+- `angle` : Set the angle of a turtle if `cmd` is not provided. Turn a turtle if `cmd` is `"turn"`. 
+- `leng` : Forward a turtle if `cmd` is `"forward"`.
+
+## Examples
+	    
+	include <line2d.scad>;
+	include <turtle/t2d.scad>;
+	
+	module turtle_spiral(t, times, side_leng, angle, width) {
+	    $fn = 24;
+	    if(times != 0) {
+	        t1 = t2d(t, "turn", angle = angle);
+	        t2 = t2d(t1, "forward", leng = side_leng);
+	
+	        line2d(
+	            t2d(t, "point"),
+	            t2d(t2, "point"),
+	            width,
+	            p1Style = "CAP_ROUND", 
+	            p2Style =  "CAP_ROUND"
+	        );
+	
+	        turtle_spiral(t2, times - 1, side_leng, angle, width);
+	    }
+	
+	}
+	
+	turtle_spiral(
+	    t2d(point = [0, 0], angle = 0), 
+	    times = 5, 
+	    side_leng = 10, 
+	    angle = 144, 
+	    width = 1
+	);
+
+![t2d](images/lib2-t2d-1.JPG)
+	
+	include <hull_polyline2d.scad>;
+	include <turtle/t2d.scad>;
+	
+	side_leng = 100;
+	min_leng = 4;
+	thickness = 0.5; 
+	
+	sierpinski_triangle(
+	    t2d(point = [0, 0], angle = 0),
+	    side_leng, min_leng, thickness, $fn = 3
+	);
+	
+	module triangle(t, side_leng, thickness) {    
+	    t2 = t2d(t, "forward", leng = side_leng);
+	    t3 = t2d(t2, [
+	        ["turn", 120],
+	        ["forward", side_leng]
+	    ]);
+	
+	    hull_polyline2d(
+	        [for(turtle = [t, t2, t3, t]) t2d(turtle, "point")], 
+	        thickness
+	    );
+	}
+	
+	module sierpinski_triangle(t, side_leng, min_leng, thickness) {
+	    triangle(t, side_leng, thickness);
+	
+	    if(side_leng >= min_leng) { 
+	        half_leng = side_leng / 2;
+	        t2 = t2d(t, "forward", leng = half_leng); 
+	        t3 = t2d(t, [
+	            ["turn", 60],
+	            ["forward", half_leng],
+	            ["turn", -60]
+	        ]);
+
+	        for(turtle = [t, t2, t3]) {
+	            sierpinski_triangle(turtle, half_leng, min_leng, thickness);
+	        }
+	    }
+	}
+
+![t2d](images/lib2-t2d-2.JPG)