// spiral.pde
// (c) 2013 Marie desJardins
//
// This is my spiffy new program -- can you tell what it does?!
// Try changing the parameters (spiralSize and spiralIncrement) to see
// how its behavior changes!
//
// Mini-challenge:  How would you change this program to draw a spiral
// that's more stretched out vertically than horizontally?


// VARIABLE AND CONSTANT DEFINITIONS

// Screen size and spiral parameter (constants)
final int width = 700;
final int height = 700;
final int spiralIncrement = 3;

// Current and previous cursor location to let us draw lines
int curX = width/2;
int curY = height/2;
int prevX, prevY;

// Variables to keep track of which direction we're going
// and how far to move
int dir = 0;   // 0=east, 1=south, 2=west, 3=north
int xDir, yDir;
int spiralSize = 1;


// MAIN FUNCTION -- setup()

void setup () {
  // Set the screen size
  size (width, height);

  // Draw the spiral - Keep going until we run out of room!
  while ( curX>0 && curX<width && curY>0 && curY<height ) {
    // Call the magic function that tells us which way to go
    setDir();
    prevX = curX;
    prevY = curY;
    curX = curX + (xDir * spiralSize);
    curY = curY + (yDir * spiralSize);
    // Draw the next line and update the spiral size to grow
    line (prevX, prevY, curX, curY);
    spiralSize = spiralSize + spiralIncrement;
  }
}

// setDir() - turn by 90 degrees.  dir tells us which way to go
// (using the code 0=east, 1=south, 2=west, 3=north) and xDir and yDir
// are the x and y directions - +1 (move forward along that axis),
// -1 (move backward along that axis), or 0 (don't move in that direction
// this time)

void setDir () {
  if ( dir == 0 ) { // east
    xDir = 1;
    yDir = 0;
    dir = 1;
  } 
  else if ( dir == 1 ) { // south
    xDir = 0;
    yDir = 1;
    dir = 2;
  } 
  else if ( dir == 2 ) { // west
    xDir = -1;
    yDir = 0;
    dir = 3;
  } 
  else if ( dir == 3 ) { // north
    xDir = 0;
    yDir = -1;
    dir = 0;
  } 
  else { 
    println ("How on earth did I get to direction " + dir + "??");
    exit();
  }
}