Get moving with timers

Let’s go a step further – instead of having a static scene, we’ll add some animation. It is a normal thing for the Sun to ascend in the morning. To achieve the effect of sunrise, the form must be repainted. We are going to change the Y coordinate that is used for painting the Sun’s circle and rays. To do this, we’ll add a private member called FSunPosY: double to our TFormSun class that will store the current vertical position of the Sun.

The simplest way to change our scene over time is with the TTimer component. To do so, drop a timer on the form. It has only one event, OnTimer. The frequency of this event is controlled by the Interval property, which specifies the number of milliseconds between firing the OnTimer event. The default value of the Interval property is 1000, which means that the timer fires its event every second. For a smooth animation, this is too slow. Change the Interval property to 20 and double-click...