This document discusses recursion, translation, and rotation in Processing. It provides examples of: 1) Recursion and how it requires an exit condition to avoid infinite loops. An example of recursive square function is given. 2) The translate() function, which shifts the origin temporarily for drawing, and examples of translating shapes. 3) Drawing vertex shapes using beginShape(), vertex(), and endShape() methods. Examples include a trapezoid and pyramid top. 4) Rotating shapes using the rotation() method and how the origin can be moved with translate() before rotating. A rotating pyramid example is shown.

1. From last time…
• Solar System (with 2 constructors)!
• Using sin() on size, color, and position!
• Using Perlin noise() in 2 and 3 dimensions!
• Let’s talk about recursion…

2. Recursion
• A method which calls itself…
myMethod() {
doSomething();
}
doSomething() {
print(“Hey!”);
}
myMethod() {
myMethod();
}
myMethod() {
myMethod();
}
myMethod() {
myMethod();
}
myMethod() {
myMethod();
}
An infinite loop. FOREVER.!
This is bad.

3. Recursion
• Therefore you must provide an exit condition!
• “I’m going to keep calling myself until I reach my
exit condition.”!
• This is similar to while and for loops!
• Demo: Recursive Square

4. CAP
Translation &!
Rotation I

5. The Z Axis
+ x– x
+ y
– y
+ z
– z

6. translate()
• translate() shifts the origin of our sketch
temporarily–for the current draw loop!
• Use P3D or OPENGL rendering:!
! size(500, 500, P3D);
• Tell it how far you want to move the origin:!
translate(moveX, moveY, moveZ);

7. Demo!
Translate

8. Vertex Shapes
• To draw arbitrary shapes, use three methods:!
beginShape();
// POINTS, LINES, TRIANGLES, TRIANGLE_FAN,
TRIANGLE_STRIP, QUADS, or QUAD_STRIP
vertex(); OR curveVertex();
endShape(); OR endShape(CLOSE);

9. Demo!
Trapezoid

10. Vertex Shapes
In 3D!In 3D!
• Basically the same method, but compose a 3D
volume out of component shapes in 3D space!
• For example, a cube would be 6 squares placed
in 3D space

11. Demo!
Top of the Pyramid

12. ‘Simple’ Rotation
• Rotating using the rotation(); method!
• Processing rotates around the point of origin!
• But the point of origin can move with the
translate() method…

13. Demo!
Pyramid Rotation

14. For next time…
• Iteration 2: present on Monday!!
• Shiffman, p. 239–252 (Translation/Rotation II)!
• Homework 4: moved until after Iteration 2