Digital Games

Loops

Loops
While Loops
For Loops
Nested Loops
Example

Reading

Processing Basics (required: loops and nested loops)
Processing While and For (required)
Learning Processing: Chapter 6 (recommended)

Style is that which indicates how the writer takes himself and what he is saying. It is the mind skating circles around itself as it moves forward. [Robert Frost]

Loops

We use loops to repeatedly execute a block of code. There are two main types of loops:
counter controlled loops and sentinel controlled loops.

A counter controlled loop uses a counter to control the number of times it executes. We call each time a loop runs an iteration.

A sentinel-controlled loop uses a boolean expression or flag to indicate how many times to iterate. It will iterate until the boolean expression is false.

Note: You can use break; in any of these loops to exit out of a statement early.

Use loops to avoid copy and pasting code. Combine with a function for maximum impact.

while loops

The basic pattern:

Here is an example of a sentinel-controlled while loop.

Here is an example of a counter-controlled while loop.

Note: you can decided whether the counter should be updated before or after the code is executed. Beware of the difference.

Use while loops when you need to do something without counting.

for loops

A for loop is a counter-controlled loop. The counter declaration and increment are part of the loops syntax. The loop increments after each iteration.

You can do more than just increment the variable. You can decrement / multiply / divide, or use whatever arithmetic your design requires.

The loop increments after each iteration.

You can use any math in the loop increment portion of the syntax

Nested loops

A nested loop is simply a loop inside of loop. We can add a loop anywhere where we can put statements.

More on this later. . .

// global grid size
int rectSize = 25;
int halfRectSize = rectSize/2;
int gridSize = 40;

void setup() {
  size(fullWidth, fullHeight);
  background(255);
  fill(32);
}

void draw() {
  //clear background
  background(0);
  //no stroke called OUTSIDE LOOP! #perfmatters
  noStroke();
  for (int x = gridSize; x <= width - gridSize; x += gridSize) {
    for (int y = gridSize; y <= height - gridSize; y += gridSize) {
      pushMatrix();
      translate(x, y);
      rotate(atan2(mouseY - y, mouseX - x));
      //pay attention to how this rectangle is drawn
      //variables at top of sketch
      rect(-halfRectSize, -halfRectSize, rectSize, rectSize);
      popMatrix();
    }
  }
  //lines drawn after rectangles so they appear on top
  //splitting up looks like this will NOT slow down the program, why?
  for (int x = gridSize; x <= width - gridSize; x += gridSize) {
    for (int y = gridSize; y <= height - gridSize; y += gridSize) {
      //some things are better drawn directly...
      stroke(255, 64);
      line(x, y, mouseX, mouseY);
    }
  }
}