# 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;
float[] y = new float;
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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