Add some spiral examples

examples/fibonacci.rs

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+//Faux-bonacci Spiral Example
+//Maybe ot quite a true Fibonacci spiral but pretty close
+use turtle::{Drawing, ExportError};
+
+
+ fn main() -> Result<(), ExportError> {
+
+ let mut fval = 0.0;
+ let mut drawing = Drawing::new();
+ let mut turtle = drawing.add_turtle();
+
+     for i in 0..=960 {
+         turtle.forward(fval);
+         turtle.right(1.0);
+
+	//Adjust the tightness of the spiral ex. 0.00001-0.00003
+	//Change sign to change direction.
+
+        fval += 0.0000168 * i as f64;
+
+           }
+
+	turtle.hide();
+    drawing.save_svg("fibspiral.svg")?;
+    Ok(())
+ }

examples/logspiral.rs

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+//Logarithmic Spiral Example
+
+use turtle::{Drawing, ExportError};
+
+fn main() -> Result<(), ExportError> { 
+ let mut fval = 0.0;
+ let mut drawing = Drawing::new();
+ let mut turtle = drawing.add_turtle();	
+  turtle.set_speed("instant");
+
+
+     for _i in 0..=8192 {
+         turtle.forward(fval);
+         turtle.right(1.0);
+
+	//Adjust the tightness of the spiral ex. 0.0011 - 0.0009
+	//Change sign to change direction
+        fval -= 0.001;
+           }
+
+	turtle.hide();
+    drawing.save_svg("logspiral.svg")?;
+    Ok(())	
+ }

examples/three_d_logspirals.rs

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+//3d Logarithmic Spiral Example
+//This takes a little while so 
+// turtle.set_speed("instant");
+
+use turtle::{Drawing, ExportError};
+
+fn main() -> Result<(), ExportError> { 
+
+ let mut fval = 0.0;
+ let tval = 1.0;
+ let mut drawing = Drawing::new();
+ let mut turtle = drawing.add_turtle();	
+ turtle.set_speed("instant");
+	for _j in 0..=3 {
+     for _i in 0..=8192 {
+         turtle.forward(fval);
+         turtle.right(tval);
+
+	//Adjust the tightness of the spiral
+        fval -= 0.0009;
+           }
+	 turtle.right(90.0);
+	 turtle.forward(0.1);
+	 turtle.right(90.0);
+
+	 for _i in 0..=8192 {
+         turtle.forward(fval);
+         turtle.left(tval);
+
+	//Adjust the tightness of the spiral
+        fval += 0.0009;
+           }
+          turtle.left(90.0);
+	 turtle.forward(0.1);
+	 turtle.left(90.0); 
+	 }
+	turtle.hide();
+    drawing.save_svg("three_d_logspiral.svg")?;
+    Ok(())	
+ }

examples/ulamspiral.rs

@@ -0,0 +1,111 @@
+//Ulam Spiral
+//A plot of primes along a square spiral as such
+//where each side length is repeated once then 1
+//space is added to grow.
+//
+//55555555555555555
+//5
+//5  3.3.3.3.3.4
+//5  3         4
+//5  3  111    4
+//5  3  1 2    4
+//5  3    2    4
+//5  322222    4
+//5            4
+//44444444444444
+use turtle::{Drawing, ExportError};
+
+ fn main() -> Result<(), ExportError> {
+ //Each ring half grows by 1.0 per 'next' which is
+ //described in the above image. Each half is 2 sides.
+
+ //step is the ring spacing size.
+
+ //count is the total steps drawn and what
+ //is determined to be prime or not.
+
+	let mut drawing = Drawing::new();
+	let mut turtle = drawing.add_turtle();	
+	turtle.set_speed("instant");
+	let mut count: f64 = 1.0;
+	let step = 4.0;
+	let mut next = 1;
+
+	//size of spiral in lines x2
+     for _i in 0..=192 {		//Adjust to size
+		let mut cvr = next.clone();		//a clean copy
+		while cvr != 0 {		//decrementor for count against the side len
+			let mut result = true;		//holds prime check
+			if count >= 2.0 {		//min check value
+				let sqrt = count.sqrt();		//Find square root of count
+				let mut trsqrt = sqrt.clone().trunc() + 1.0; //truncate, round up
+				while trsqrt >= 2.0 {
+				//Check all the modulus of the real values from the 
+				//rounded up square root down to 2.
+				//If any == 0.0 then it is composite, else prime.
+					if count % trsqrt == 0.0 {
+						result = false;
+						}
+					trsqrt -= 1.0;	//down to 2
+					}
+				if count == 2.0 {	// 2 is prime
+					result = true;
+				}
+			}
+		if count <= 1.0 { // 1 is not prime
+			result = false;
+		}
+
+	//If prime then draw a larger space then for the other spaces.
+	//Then restore the size for the next draw.
+	//If composite then just draw normally.
+		if result == true {
+		turtle.set_pen_size(2.0);
+		turtle.forward(step);
+		turtle.set_pen_size(1.0);
+		} else { 
+         turtle.forward(step);
+         }
+         cvr -= 1;	//decrementor to zer0
+         count += 1.0;	//increment the total count
+         }
+
+	//When done with the side above then turn and repeat.
+		turtle.right(90.0);
+		cvr = next.clone();
+		while cvr != 0 {
+		let mut result2 = true;
+		if count >= 2.0 {
+			let sqrt = count.sqrt();
+			let mut trsqrt = sqrt.clone().trunc() + 1.0; 
+			while trsqrt >= 2.0 {				
+				if count % trsqrt == 0.0 {
+					result2 = false;
+				}
+				trsqrt -= 1.0;
+			}
+			if count == 2.0 {
+				result2 = true;
+			}
+		}
+		if count <= 1.0 {
+				result2 = false;
+			}
+		if result2 == true {
+		turtle.set_pen_size(2.0);
+		turtle.forward(step);
+		turtle.set_pen_size(1.0);
+		} else { 
+		turtle.forward(step);
+		}
+		cvr -= 1;
+		count += 1.0;
+		}
+		turtle.right(90.0);
+        next += 1;//Increment the side counter
+	}
+//Save the picture.
+	turtle.hide();
+    drawing.save_svg("ulamspiral.svg")?;
+    Ok(())
+ }