A line of circles follows the mouse pointer
From Physical Programming
Image:Source code with descriptions.pdf
/* A line of circles follows the mouse pointer */
/** global variables, x and y are the coordinates of
* each circle, i.e. position of circle 1 = x[1], y[2], with
* maximum amount of circles equal 10
*/
float[] x = new float[10];
float[] y = new float[10];
/** With this function the main window is constructed, size
* determines the windows size and smooth controls the drawing
* of new objects for a smooth animation
*/
void setup() {
size(600, 600);
smooth();
}
/** With function draw() the background is set to black.
* Function circleline will draw each circle in a line after
* the mouse pointer. For this, it gets for circle 0 the
* coordinates of the actual mousepointer position.
* In the for-loop circles 1-10 will be created with their
* calculated position.
*/
void draw() {
background(0);
circleline(0, mouseX, mouseY); // first circle
// For-Loop for the next circles
for(int i=0; i<x.length-1; i++) {
circleline(i+1, x[i], y[i]);
}
}
/** This function calculates the position for circle i.
* dx,dy ist the distance between circle i and its predecessor.
* With atan, cos, sin it calculates the angle between the
* circles, so its not just a static line, but a snake.
* After that it starts function circle which will draw the
* circle with given position, angle to predecessor and position
*/
void circleline(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) * 25;
y[i] = yin - sin(angle) * 25;
circle(x[i], y[i], angle, i);
}
/** Function circle actually draws the circle with standart
* methods
* Last fill sets color and the transparency by given position i
*/
void circle(float x, float y, float a, int i) {
pushMatrix(); /**Pushes the current transformation matrix onto
*the matrix stack. Understanding pushMatrix()
*and popMatrix() requires understanding the
*concept of a matrix stack. The pushMatrix()
*function saves the current coordinate system
*to the stack and popMatrix() restores the
*prior coordinate system. pushMatrix() and
*popMatrix() are used in conjuction with the
*other transformation methods and may be
*embedded to control the scope of the
*transformations.
*/
translate(x, y); /** Specifies an amount to displace objects
*within the display window. The x parameter
*specifies left/right translation, the y
*parameter specifies up/down translation, and
*the z parameter specifies translations
*toward/away from the screen. Transformations
*apply to everything that happens after and
*subsequent calls to the function accumulates
*the effect. For example, calling translate(50, 0)
*and then translate(20, 0) is the same as
*translate(70, 0). If translate() is called
*within draw(), the transformation is reset
*when the loop begins again. This function can
*be further controlled by the pushMatrix() and
*popMatrix().
*/
rotate(a); /**Rotates a shape the amount specified by the
*angle parameter. Objects are always rotated
*around their relative position to the origin
*and positive numbers rotate objects in a
*clockwise direction. Transformations apply
*to everything that happens after and
*subsequent calls to the function accumulates
*the effect.
*Technically, rotate() multiplies the current
*transformation matrix by a rotation matrix.
*This function can be further controlled by
*the pushMatrix() and popMatrix().
*/
popMatrix(); /**Pops the current transformation matrix off
*the matrix stack.
*/
ellipse(x, y, 15, 15); // circles
fill(255,0,0,100-i*10); // color with transparenz
}
