If with and

sketch.js

function setup() {
  createCanvas(500,500);
}

function draw() {
  background(255,255,255);
  
  if (mouseY > height/2 && mouseX > width/2) {
      fill(255,0,0);
      ellipse(width/2, height/2, 50, 50);
  }

  if (mouseY > height/2 && mouseX < width/2) {
      fill(255,255,0);
      ellipse(width/2, height/2, 10, 10);
  }
  
  if (mouseY < height/2 && mouseX > width/2) {
      fill(0,0,255);
      rect(width/2, height/2, 50, 50);
  }
  
  if (mouseY < height/2 && mouseX < width/2) {
      fill(0,255,0);
      triangle(0, height, width/2, 0, width, height);
  }
  
}