Button click to execute a code repeatedly in Libgdx - button

Question

I've developed an Android application using Libgdx in 3D space to render some buildings with interaction buttons to help user navigating in the environment. For example, left and right buttons to move the camera in left and right direction. While pushing a button causes to execute the code once, I've used this trick to keep executing the code as the user holding the button down.
private void createStage() {
stage = new Stage();
intervalTime = 15L;
buttonLeft = new TextButton("", leftStyle);
buttonLeft.addListener(new InputListener() {
// repeat an action with ScheduledExecutorService
final Runnable leftRunnable = new Runnable() {
#Override
public void run() {
Vector3 dir = new Vector3();
dir.fromString(cam.direction.toString()).scl(0.5f);
cam.position.add(dir.z, 0, -dir.x); // camera moves to left
cam.update();
}
};
// add on thread to object
final ScheduledExecutorService executor = Executors.newScheduledThreadPool(1);
ScheduledFuture<?> future; // future schedule to run and stop task
#Override
public boolean touchDown(InputEvent event, float x, float y, int pointer, int button) {
future = executor.scheduleAtFixedRate(leftRunnable, 0L, intervalTime, TimeUnit.MILLISECONDS);
return true;
}
#Override
public void touchUp(InputEvent event, float x, float y, int pointer, int button) {
super.touchUp(event, x, y, pointer, button);
//leftFlag = false;
if (future != null) {
future.cancel(true);
}
}
});
This method is invoked in the create() function of AndroidListener and the stage will be drawn in render() function as well. There are about 12 buttons which use the same approach but it gives me some lagging in rendering process while the user holds the buttons down for seconds or pushing two buttons simultaneously. Is there something wrong with the approach or is it an appropriate structure for executing a code frequently?

Answer 1

Camera is not a thread-safe class, so you would need to use synchronization if modifying it from your background thread.
That said, updating a camera is a trivial operation, so multi-threading is adding a lot of needless complexity. You're generating a fair amount of garbage, although I don't know if that's the only reason you're seeing some lagging.
Here's how I'd do it more simply.
stage = new Stage();
float camSpeed = 0.5f / 15; // Units per ms
float camDisp = camSpeed * Gdx.graphics.getDeltaTime();
buttonLeft = new TextButton("", leftStyle){
public void act(float delta){
super.act(delta);
if (isPressed()){
camera.position.add(camera.direction.z * camDisp,
0,
-camera.direction.x * camDisp);
camera.update();
}
}
}
Not quite sure what you're doing with the camera direction, but I tried to copy the same behavior. If I just wanted to pan the camera to the left, I'd do it like this. The temp variable is to avoid instantiating objects and triggering GC.
private static final Vector3 TMP = new Vector3();
//...
TMP.set(camera.direction).crs(camera.up); // right vector of camera
camera.position.add(TMP.scl(-camDisp));