int w = 600;
int h = 400;
void setup()
{
  size(w, h);
  background(300);
  smooth();
}

void draw() 
{
  int xpos = w / 2;
  int ypos = h / 2;
  variableEllipse(xpos, ypos, mouseX, mouseX);
}

void variableEllipse(int x, int y, int px, int py) 
{
  float speedx = 100 + abs(mouseX-pmouseX) * 10;
  float speedy = 100 + abs(mouseY-pmouseY) * 10;
  noStroke();
  fill(speedx, speedy, 100, 20);
  ellipse(x, y, px, py);

}