Develop Reference

Flash when changing the screen with fading out effect

I am trying to achieve a simple fadeIn and fadeOut effect when transitioning between screens. I have set a stage but when designing my app I did not use any actors. Therefore, I have put it a black screen as an actor and then I set the alpha to 0 on show(). When fading out what I do is I fade in the black image using
stage.addAction(Actions.sequence(Actions.fadeIn(1), Actions.run(new Runnable() {
#Override
public void run() {
game.setScreen(new gameScreen(game));
This works, however there is a small problem, right at the end of the fade there is a small flash for a millisecond which shows the previous screen before it switches so the transition is not smooth, the black image is removed before switching screens. How can I fix this?

your problem is that stage.clear() and stage.dispose() is being called before rest of your app is being rendered last time.
The solution is to override dispose() Screen method and manually set some flag shouldBeRendered to false and then dispose your stage.
boolean shouldBeRendered = true;
...
public void render(float delta)
{
Gdx.gl.glClearColor(0, 0, 0, 1);
Gdx.gl.glClear(GL20.GL_COLOR_BUFFER_BIT);
if(shouldBeRendered)
{
//here you render all
}
...
}
...
#Override
public void dispose()
{
shouldBeRendered = false;
stage.clear();
stage.dispose();
}
You can add some System.out.println() to both render and dispose methods to see the flow of Screen circle of life

Android moving a shape faster on Canvas

I have a class which is extended from ImageView (lets call it 'surface'). On onDraw method, a little dot is drawing on canvas. When I click a button I try to move this dot to another location. You can consider like manual version of translate animation. It works but now I try to figured out speed of this moving. I mean I want dot moving faster.
Relevant part of surface :
private float actual_x=100,actual_y=100; // Dot is drawn on 100,100 at beginning
private float increase_x,increase_y;
private boolean isMovingResume=false;
private int moving_counter;
public void changeLocation(float x,float y){
isMovingResume=true;
moving_counter=0;
increase_x=(x-actual_x)/50;
increase_y=(y-actual_y)/50;
invalidate(); // This trigger onDraw method
}
protected void onDraw(Canvas canvas) {
super.onDraw(canvas);
canvas.drawCircle(actual_x,actual_y,15,fill_paint);
if(isMovingResume){
actual_x=actual_x+increase_x;
actual_y=actual_y+increase_y;
if(moving_counter==49){ // Moving will end after 50 redraw
isMovingResume=false;
}
else{
moving_counter++;
}
invalidate(); //redraw
}
}
And my button click :
button.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
surface.changeLocation(200,200);
}
});
Like I said, it works but I want it more faster. For example, in this case moving time is 2 second, How can I make it 0,5 second ?
Thanks for all replies.

You need to switch to surfaceview or even faster textureview, both use a canvas as well, and have better performance. Textureview especially as it is hardware accelerated and I also feel it behaves better than surfaceview. That or even consider going to GLSurfaceView.
You can see some example code of surfaceview and textureview: Here

Animate sprites using drawableAnmiation

I have a design question so I don't start off on the wrong way. I am planning to have a sprite where it animates moving and I want to move this sprite around (changing position once every second).
I noticed that some tutorial talk about having a game loop,, onDraw on Canvas, bitmap ..etc
However, I am thinking of using drawableAnimation where I specify the set of images to load in xml and call start on it. Then I can just draw at the position required every second ( no loop, it is more like listener that gets called every sec from different process).
Do you forsee an issue? Any problem with above method
Thank you

Drawable Animation requires a fixed frame animation. Think of it like a flip book. The drawable would have to be the entire size of your canvas and your sprite would have to be prerendered on top of some transparent background to achieve your affect. It also would require a large amount of texture memory depending on the size and number of frames.
The "game loop" as you stated is sort of what Android already provides in a way. Inside of the standard canvas setup you have your "main Thread". So with an entity like a Handler you could tick frames if you like.
i.e.
Handler handler;
public void onCreate(Bundle bundle) {
super.onCreate(bundle);
handler = new Handler();
handler.post(new Runnable() {
public void run() {
boolean isLastFrame = drawFrame();
if (!isLastFrame) {
handler.postDelayed(this, ONE_SECOND_MILLIS);
}
}
});
This is not the greatest really either.
You could also encapsulate your sprite inside a View or own custom Drawable and inside your onDraw() method, you would update your canvas.
public void onDraw(Canvas canvas) {
// clear canvas
mPaint.setColor(Color.WHITE);
canvas.drawPaint(mPaint);
// Draw current
mPaint.setColor(Color.BLACK);
canvas.drawRect(rect, mPaint);
}
public void moveSprite() {
rect.offset(3, 3);
invalidate();
}
You could also, if using a View, use an ObjectAnimator to translate the View from position (x1, y1) to (x2, y2).
public void moveTo() {
if (!moveNeeded) {
return;
}
View view = getMyView();
view.animate().x(1).y(1).setListener(new Animator.AnimatorListener() {
public void onAnimationCancel(Animator a) { }
public void onAnimationStart(Animator a) {
}
public void onAnimationEnd(Animator a) {
moveTo();
}
public void onAnimationRepeat(Animator a) {
}
});
}

invalidate() on custom View does not cause onDraw(Canvas c) to be called

For my activity i use 3 custom views stacked.
the lower one is a SurfaceView fullscreen, the middle one is derived from GridView and overrides onDraw to add custom graphic.
The top one is derived directly from View, sits in a corner of the screen and act as a knob to control the others two views (this is the problematic view).
to add a custom animation to this view, i used this pattern:
public class StubKnobView extends View{
private Drawable knob;
private Point knobPos;
private float rotation;
private boolean needsToMove;
public void moveKnob(){
/* ...various calculations... */
this.needsToMove=true;
invalidate(); //to notify the intention to start animation
}
private void updateAnimation(){
/* ........... */
this.needsToMove= !animationComplete;
invalidate();
}
#Override
protected void onDraw(Canvas canvas) {
int saveCount=canvas.getSaveCount();
canvas.save();
canvas.rotate(this.rotation, this.knobPos.x, this.knobPos.y );
this.knob.draw(canvas);
canvas.restoreToCount(saveCount);
if(this.needsToMove){
updateAnimation();
}
}
}
ideally, if there is an animation pending, after each drawing cycle the view should auto invalidate.
right now this doesn't work, to force the animation i have to touch the screen to cause a onDraw cycle.
Using "show screen updates" of Dev tools I see that no screen invalidate/update cycle happen , apart when i click the screen.
specifying the dirty rect also ha no effect.
So, any idea where to look to know why this invalidate/draw cycle does not work the way is intended?

I encontered this situation, and also doubted that invalidate() doesn't make onDraw() called again.
After simplified the business codes, it's turn out that there is a dead loop - exactly too much iterations, which blocks the UI thread.
So, my advice is that make sure the UI thread going smoothly first.

Try something like this with a private class in your View. The idea is not to call invalidate() from within onDraw(). Instead, post it on the running queue. Instantiate the private class in your View constructor and then just call animateKnob.start() when you want the animation. The onDraw() can then just focus on drawing.
public void moveKnob(){
// update the state to draw... KnobPos, rotation
invalidate()
}
private class AnimateKnob{
public void start(){
// Do some calculations if necessary
// Start the animation
MyView.this.post( new Runnable() {
stepAnimation()
});
}
public void stepAnimation(){
// update the animation, maybe use an interpolator.
// Here you could also determine if the animation is complete or not
MyView.this.moveKnob();
if( !animationComplete ){
// Call it again
MyView.this.post( new Runnable() {
stepAnimation()
});
}
}
}

Growing Line Android Effect

I am developing an android app and I should draw a line from the Point A to the Point B but I would like to show this line be drawing "progressively" from one point to other. How can I do it?
Thanks a lot!

You can use a Thread to progressively increase the size of your line, by increasing its ending x position, as an example, and then call View.postInvalidate() from your thread.
This way, if x is the ending of your line and view the View that draws a line ending at x you would have this thread:
class LineThread extends Thread {
public void run() {
while (x < some_limit) {
x += some_value;
view.postInvalidate();
try {
sleep(some_time);
}
catch(InterruptedException e) {
log.e(getClass.getName(), "sleep() was interrupted", e);
}
}
}
}
and in your view:
#Override
protected void onDraw(Canvas canvas) {
super.onDraw(canvas);
canvas.drawLine(left, top, right + x, bottom, paint);
}
Making LineThread a subclass of your View class would make it easy as they could share x.

You could have a look at linear interpolation, but I'm not sure if it'll be too time consuming just for this - should be fine if you're only doing it for a few lines at a time!
Since you have the start_point and your end_point, you can lerp to find the current_point for each timeframe and then use drawLine between start_point and current_point.