Follow 3

Follow 3 based on code from Keith Peters.

A segmented line follows the mouse. The relative angle from each segment to the next is calculated with atan2() and the position of the next is calculated with sin() and cos().


float[] x = new float[20];
float[] y = new float[20];
float segLength = 18;

void setup() {
  size(640, 360);
  strokeWeight(9);
  stroke(255, 100);
}

void draw() {
  background(0);
  dragSegment(0, mouseX, mouseY);
  for(int i=0; i<x.length-1; i++) {
    dragSegment(i+1, x[i], y[i]);
  }
}

void dragSegment(int i, float xin, float yin) {
  float dx = xin - x[i];
  float dy = yin - y[i];
  float angle = atan2(dy, dx);  
  x[i] = xin - cos(angle) * segLength;
  y[i] = yin - sin(angle) * segLength;
  segment(x[i], y[i], angle);
}

void segment(float x, float y, float a) {
  pushMatrix();
  translate(x, y);
  rotate(a);
  line(0, 0, segLength, 0);
  popMatrix();
}

Functions Used

stroke()

Sets the color used to draw lines and borders around shapes

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size()

Defines the dimension of the display window width and height in units of pixels

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pushMatrix()

Pushes the current transformation matrix onto the matrix stack

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sin()

Calculates the sine of an angle

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popMatrix()

Pops the current transformation matrix off the matrix stack

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setup()

The setup() function is run once, when the program starts

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strokeWeight()

Sets the width of the stroke used for lines, points, and the border around shapes

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cos()

Calculates the cosine of an angle

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rotate()

Rotates the amount specified by the angle parameter

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translate()

Specifies an amount to displace objects within the display window

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draw()

Called directly after setup(), the draw() function continuously executes the lines of code contained inside its block until the program is stopped or noLoop() is called

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for

Controls a sequence of repetitions

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atan2()

Calculates the angle (in radians) from a specified point to the coordinate origin as measured from the positive x-axis

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line()

Draws a line (a direct path between two points) to the screen

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background()

The background() function sets the color used for the background of the Processing window

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