Horizontal Hues

This original code allows processing to generate a series of vertical rectangles depends on the width of the rectangle and the width of the screen. By tracking the change of X coordinate of the mouse, it generates new rectangles with different hues and then overlay on top of the older ones.

In my modified code,  I changed the background color from Black to white by alternating the RBG value. I  also modified the code to generate horizontal rectangles instead of vertical ones. Moreover, it now tracks the Y coordinate of the mouse and populates hue values base on that coordinate.

Modified Code: 

// Change from int barWidth to barHeigth, and change the int to a value that can be divided by the screen height. 
int barHeight = 72;
int lastBar = -1;

void setup()
{
  size(640, 360);
// change HSB ( Hue, Saturation, and Brightness) of the color now depending on canvas width
  colorMode(HSB, width, width, width); 
  noStroke();
// background color change from black to white 
  background(255);
}

void draw()
{
//change from mouseX to mouseY, now the int whichBar is depended on the Y coordinate of the mouse.
  int whichBar = mouseY / barHeight;
  if (whichBar != lastBar) {
    int barY = whichBar * barHeight;
// change fill mouseX to mouseY now the hue will depend on the Y coordinate of the mouse
    fill(mouseY, width, width);
//change the rects from vertical to horizontal  
    rect(0, barY, width, barHeight);
    lastBar = whichBar;
  }
}

Original Code: 

int barWidth = 20;

int lastBar = -1;

void setup() 

{

  size(640, 360);

  colorMode(HSB, height, height, height);  

  noStroke();

  background(0);

}

void draw() 

{

  int whichBar = mouseX / barWidth;

  if (whichBar != lastBar) {

    int barX = whichBar * barWidth;

    fill(mouseY, height, height);

    rect(barX, 0, barWidth, height);

    lastBar = whichBar;

  }

}