var draw = function() {
    // draw the "computer screen" outline
    noFill(); // don't want a colored inside to the screen, it'll overwrite drawings
    rect(50, 50, 300, 300);
    
    // this equals true if the mouse is in the rectangle
    // and false if it's outside of the rectangle
    var mouseIsOnScreen = (mouseX > 50) && (mouseX < 350) && (mouseY > 50) && (mouseY < 350);
    
    // this does the same as the above line, but
    // with the mouse's coordinates from the last frame
    var mouseWasOnScreen = (pmouseX > 50) && (pmouseX < 350) && (pmouseY > 50) && (pmouseY < 350);
    
    // draw the line if the mouse is pressed and in the rectangle
    if(mouseIsOnScreen && mouseWasOnScreen) {
        line(pmouseX, pmouseY, mouseX, mouseY);
    }
};