COMP 202 Review with robots on Processing

Pixel coordinate system

Going back to Assignment 2

point(x,y) draws a point centered at pixel coordinates (x,y)

strokeWeight(pixels) lets you set the size of the point

Shapes

Color

• stroke(val) sets the color of lines to val in grayscale

• fill(val) sets the color inside a shape to val in grayscale

• background(val) sets the color of the background to val in grayscale

• stroke(r,g,b) sets the color of lines to r,g,b in the red-green-blue scale

• fill(r,g,b) sets the color inside a shape to r,g,b in the red-green-blue scale

• background(r,g,b) sets the color of the background to r,g,b in red-green-blue scale

Interaction

Making things animated and interactive

• The setup method specifies what will happen at the beginning of the program, and will be executed only once

• The draw method specifies what will happen continuously, during your program's execution. This is known as the drawing loop.

The speed of the drawing loop can be set with the frameRate(fps), where fps is the desired number of frames per second

Interaction

Making things animated and interactive

Mouse input:

• The mousePressed global variable is a boolean that is set to true when the user clicks a mouse button. Before every call to the draw method it is set to false by default.

• The global variables mouseX and mouseY give you the pixel coordintates of the mouse pointer in the canvas. These are of type int.

Using Objects and Classes in Processing

Processing is based on Java, so we can use all of the things we learned during the COMP 202. Let's create a program that draws robots with the following rules:

• A Robot should be drawn as an ellipse. It has a position on the screen in pixel coordinates (x,y), and a diameter attribute. It will also have a speed attribute (in pixels per second).

• Every time the user clicks on the window, a new Robot will be drawn at the location of the click.

• Every time the user presses x, a Robot will be selected at random, and killed.

• Robot instances are scared of the last rule, so they should be shaking around their current location

Robot velocities, attraction and repulsion forces

All these have a magnitude and direction

• Let's modify the Point2D class from Assignment 3, to create a Vector2D class
• A vector has x and y components
• Since we want to accumulate forces, and velocities, the vector should have an add method.
• We will find useful to compute the angle and magnitude of a vector.
• We will find useful to multiply a vector by a number to change it's magnitude.

Robot velocities, attraction and repulsion forces

Let's modify the Robot class by adding the following attributes:

• The location vector will represent the Robot's position
• The velocity vector will control the direction in which the robot will move in the next frame.
• The acceleration vector will control how the velocity changes, depending on external forces.

Robot velocities, attraction and repulsion forces

The kinematics of our robot world ( the update method )

Using the vectors for the Robot and mouse pointer position, we will modify the Robot's velocity

• The update method will change the Robot's location, using its current velocity. It will also update it's current velocity using using its current acceleration

Robot velocities, attraction and repulsion forces

The dynamics of our robot world ( the applyForce method )

Using the vectors for the Robot and mouse pointer position, we will modify the Robot's velocity

• The update method will change the Robot's location, using its current velocity. It will also update it's current velocity using using its current acceleration
• The applyForce method will accumulate external forces that we apply to each robot. This will change the Robot's acceleration.

Robot velocities, attraction and repulsion forces

The dynamics of our robot world ( the applyForce method )

Using the vectors for the Robot and mouse pointer position, we will modify the Robot's velocity

• The update method will change the Robot's location, using its current velocity. It will also update it's current velocity using using its current acceleration
• The applyForce method will accumulate external forces that we apply to each robot. This will change the Robot's acceleration.

Robot velocities, attraction and repulsion forces

The dynamics of our robot world ( the applyForce method )

Using the vectors for the positions of every Robot, we will modify each Robot's velocity

• The update method will change the Robot's location, using its current velocity. It will also update it's current velocity using using its current acceleration
• The applyForce method will accumulate external forces that we apply to each robot. This will change the Robot's acceleration.

Saving a file of our current robot world

We want to store the location and velocity of every robot, so that we can reload it when we start the program:

• We need to implement the toString method of the Vector2D and Robot classes

• We need to implement a loadFromString method for the Robot class

• We will implement a method loadState that will try opening a file to load the state of the robot world

• We will implement a method saveState that will open a file with the robot world state, and recreate it.

• We will use the keyPressed method to save the world state, when the user presses the 'S' key.

Next class: Final Exam Review

Resources

• Processing:
  http://processing.org
• Very simple Processing Tutorial:
  http://hello.processing.org
• A book with far more advanced programming concepts on Processing:
  http://natureofcode.com/book/