float left=50, right=350, top=50, bottom=250;
float ballX, ballY, ballDX=3, ballDY=2;
float mX, mY;
void draw () {
  //next frame
  scene();
  action();
}
void setup () {
 size(500,500);
 reset();
}
void reset () {
  // Reset
 ballX=  left+40; 
 ballY=  top+30;
}  
void scene() {
  //// Table
  rectMode(CORNERS);
  fill( 100,200,100 );
  strokeWeight(6);
  stroke( 100,30,0 );
  rect( left, top, right, bottom );
}
  
void action() {
  myball();
} 

void myball() {
  //// Check boundaries, move ball, draw it.

  if (ballX > right || ballX< left) ballDX= -ballDX; 

  ballX=  ballX + ballDX;
  ballY=  ballY + ballDY;

  fill( 255,0,255 );
  noStroke();
  ellipse( ballX, ballY, 30, 30 );
}