How to simulate an analog stop watch in Android Watch Face? - android-wear-2.0

Question

I'm developing a realistic chronograph watch with Android Wear OS. I already have a seconds hand watch working well, and a stoped chronograph hand. When I tap on the watch, I want my chronograph hand start from zero, but it is starting from the actual second.
My question is: How can I apply a shift value to my chronograph rotate in order to discount the actual second, and the hand start from 0 position?
Here is the actual behavior:
Here is the code that rotate the small seconds hand:
private float getSecondsRotation() {
final float seconds =
(mCalendar.get(Calendar.SECOND) + mCalendar.get(Calendar.MILLISECOND) / 1000f);
return seconds * 6f;
}
Is there any way to passing a shift parameter for that method and discount from the result?

Answer 1

I haven't actually tried to run this code, but hopefully it gives you an idea of how to approach your problem.
// True when the chronograph is running, false otherwise
private boolean isChronographRunning = false;
// The second when the chronograph is started
private float secondOffset = 0f;
// Called when the user taps on the watch face
private void startChronograph() {
isChronographRunning = true;
secondOffset = mCalendar.get(Calendar.SECOND) + mCalendar.get(Calendar.MILLISECOND) / 1000f;
}
// Called from your draw loop if(isChronographRunning)
private float getChronographRotation() {
float currentSecond = mCalendar.get(Calendar.SECOND) + mCalendar.get(Calendar.MILLISECOND) / 1000f;
float chronographSecond = currentSecond - secondOffset;
return chronographSecond * 6f;
}