Develop Reference

Andengine swipe navigation

I am new to andengine and want to know that how I can switch between two BaseGameActivities. And also when switching from first activity to second, there is no black screen transition in between switching. Is there any possible way to do it.
Please help me out.

A BaseGameActivity can be used as any other Android Activity, too:
Intent intent = new Intent(this, MyOtherBaseGameActivity.class);
startActivity(intent);
So if you want to change from your program to another app (maybe by opening the browser…) you can do that as with any other Android App, too. However if both Activities are part of your own App, there is rarely a case where this is recommendable (It is like starting a second program). Although it is possible to exchange data between the activities as described in this post.
But maybe you are only looking for a way to switch between Views in AndEngine. If that's the case you can switch between Scenes without any transition necessary.
MyOtherScene secondScene = new MyOtherScene();
mEngine.setScene(secondScene);
That way you can switch between what is being displayed, without needing to load every image again.
EDIT:
Since you can't use AndEngine to switch between Activities, nor is a smooth switching between scenes possible. Here a quick example on how to switch between two screens (e.g. menus). In this example the screens are actually 2 different images (as big as the display … maybe some background images). Note: there is no such thing as 'screens' in AndEngine, it is simply a self made class that extends Entity.
Your Screen
public MyScreen extends Entity{
private float firstX;
public MyScreen(Sprite niceBackgroundImage1, Sprite niceBackgroundImage2){
this.attachChild(niceBackgroundImage1); // attach something to the screen, so you can see it (preferably an image that is as big as your camera)
this.attachChild(niceBackgroundImage2);
this.firstY=-1; // this is a variable to remember the first x coordinate touched
}
#Override
public boolean onAreaTouched(TouchEvent sceneTouchEvent, float touchAreaLocalX, float touchAreaLocalY) {
if(sceneTouchEvent.getAction()==TouchEvent.ACTION_DOWN){
this.firstY=touchAreaLocalX; // remember the x, on the first touch
}
if(sceneTouchEvent.getAction()==TouchEvent.ACTION_MOVE){
if(touchAreaLocalX>firstY+20){
// user swiped from left to right (at least 20 pixels)
niceBackgroundImage1.registerEntityModifier(new MoveModifier(3f, 0, niceBackgroundImage1.getWidth(), 0, 0, EaseBounceOut.getInstance()));
// the last line actualy moves the nice..image1 from left to right (in 3 seconds) and lets it bounce a little bit before it is completely out of the screen
return true;
}
}
return false;
}
...
}
Your Activity
private HUD hud; // create a HUD
...
#Override
protected void onCreateResources() {
this.hud = new HUD(); // init the HUD
this.myScreen = new MyScreen(image1, image2) // init the screen
this.hud.attachChild(myScreen); // attach the screen to the hud
mEngine.getCamera().setHud(hud); // attach your HUD to the camera
}
#Override
protected Scene onCreateScene() {
Scene myScene = new Scene();
myScene.registerTouchArea(myScreen); // you have to register the touch area of your Screen Class to the scene.
mEngine.setScene(myScene);
}
And this is how it works:
you create yourself a own screen class that extends Entity. An Entity can be everything visible in AndEngine (like a Sprite, Rectangle or even a whole scene). Put something in your screen class to make it look nice, preferably a big image that fills the whole display. That image will be responsible to register the touch afterwards. If the image is too small and the user misses the image, then no touch will be registered.
In this case I attach the instance of MyScreen to the cameras HUD. That way it will be at a fixed position on the display and it will have a fixed size (just in case you want to make the scene scrollable or zoomable).
Now when the app starts the HUD will be created and attached to the camera and with it your MyScreen class. Then the scene will be created and the screen's area will be registered as touch area to the scene. When a swipe movement on a horizontal axis gets noticed by the screen class, the first image will move outside the screen (in the same direction as the swipe).
But be careful, this is just an example. There is nothing defined on how the touch has to act when the first image was moved outside the screen or how big the screen actually is etc...
I know this is quite a long example, maybe it won't even work the first time and it is definitely not the only way on how switching between different screens can be done. But it shows you how to override the onAreaTouched() method and register the entity modifier to make the image move. Hopefully it will lead you in the right direction, to accomplish what you want to do.

Using view's drawingCache on VIew.onDraw() for smooth scrolling

I would like to implement a custom View with smooth scrolling feature. I have read Android View.onDraw() always has a clean Canvas. By building an off-screen bitmap, it even take some more time to draw the off-screen bitmap. Therefore, I have think of using the view drawing cache.
#Override
public void onDraw(Canvas canvas){
long start = System.nanoTime();
if(redrawAll){
drawFullScreen(canvas);
handler.post(new Runnable(){
#Override
public void run() {
cachedBitmap = SampleView4.this.getDrawingCache();
}
});
}
else{
if(cachedBitmap != null && !cachedBitmap.isRecycled()){
canvas.drawBitmap(cachedBitmap ,scrollByX, scrollByY, p);
drawPartOfScreen(canvas, scrollByX, scrollByY);
}
handler.post(new Runnable(){
#Override
public void run() {
cachedBitmap = SampleView4.this.getDrawingCache();
}
});
}
Log.d(TAG, "drawTiles take: "+(System.nanoTime() - start) + " ns");
}
It probably work but have strange behaviour. Sometime, the cached Bitmap do no change after onDraw() and thus look very weird.
And, the main problem is the performance do not have not much different with just call drawFullScreen(canvas); each time the view scrolls.
Am I on the right track? I have develop on Android 4 so I turn on the hardware acceleration. But the docs say the view has cached in hardware-texture. Do I really need drawing cache in hardware acceleration environment?

I think you can't rely on drawing cache when hardware acceleration is ON. According the doc about View.setDrawingCacheEnabled() :
"Enabling the drawing cache is similar to setting a layer when hardware acceleration is turned off. When hardware acceleration is turned on, enabling the drawing cache has no effect on rendering because the system uses a different mechanism for acceleration which ignores the flag. If you want to use a Bitmap for the view, even when hardware acceleration is enabled, see setLayerType(int, android.graphics.Paint) for information on how to enable software and hardware layers."

Window already focused, ignoring focus gain of For raising height of sprite the preferences

I know this has been asked before and I went through all the answers and nope this ain't that, and yes I have the activity named in the manifest so it's not that.
Here's my problem:
I have a sprite moving across the screen and when in the window where you choose the livewallpaper, I have a preference that lets the user choose the height (so they can move the sprite up or down) the only problem is the sprite is constantly moving so when they use the seekbar to move the sprite up or down I get the old 'Window already focused, ignoring focus gain of" Now if I go out and come back in again of course this stop and restarts it and the new preference hight is already in their so it moves to the new height then but not in the live preview.
Here is the sprite code:
private void addShipOne() {
int heightPosition = (screenSized / 2) - (screenSized / /*this.bigShipHeight*/gettheFreakingHeight());
int widthPosition = 0;
Point startPoint = new Point(widthPosition, heightPosition);
this._shipone.add(new SpaceShipOne(this._context, this, startPoint, 125));
(sorry about the method name I was using to test a quick version I was a bit frustrated at that point) lol
It then goes into an OnDraw method then into the render to render it all.
public void render(){
Canvas canvas = null;
try{
canvas = this._surfaceHolder.lockCanvas(null);
synchronized (this._surfaceHolder) {
this.onDraw(canvas);
}
}finally{
if(canvas != null){
this._surfaceHolder.unlockCanvasAndPost(canvas);
}
}
}
I have another preference that allows the user to choose the frequency of the ships appearing it works fine but it goes from left to right and changes ships then so it updates the frequency then, but the height one doesn't work, I tested the log to make sure the height int goes through and it does so its not that, the only thing I can come up with is the maybe add this when the ship turns left or right, but it does not work while its moving by the looks of it.
this.bigShipHeight is where the new height value goes into ( I was just testing it another way with the gettheFreakingHeight() (I used an if else statement for that method that used the frquency preference instead which does work nicely.
Just to add the full code part.
In the onDraw(Canvas canvas)
I render the _shipone as such
for (Renderable renderable : this._shipone) {
renderable.render(canvas);
}
Any help would be appreciated.
Thanks in advance
Sam

Ok I should of looked into the my sprite class first, sorry about this I answered my own question once again and it was too obvious, that's what I get for looking at the code way to long, I should walk away then come back it always is clearer then.
Just in case others run into this issue I'll put the answer.
In my sprite class which SpaceShipOne runs from I just added this
this.getSprite().setYPos(this._blimp.gettheFreakingHeight());
This updates right away with no window already focused.
I don't know why I didn't see this last night because it is the only place it can be added and be updated right away, all I had to do was set the Y position to the preference instead.
It works like a charm.
Hope this helps someone else out
Sam

Preventing "flickering" when calling Drawable.draw()

I have a little experimentation app (essentially a very cut-down version of the LunarLander demo in the Android SDK), with a single SurfaceView. I have a Drawable "sprite" which I periodically draw into the SurfaceView's Canvas object in different locations, without attempting to erase the previous image. Thus:
private class MyThread extends Thread {
SurfaceHolder holder; // Initialised in ctor (acquired via getHolder())
Drawable sprite; // Initialised in ctor
Rect bounds; // Initialised in ctor
...
#Override
public void run() {
while (true) {
Canvas c = holder.lockCanvas();
synchronized (bounds) {
sprite.setBounds(bounds);
}
sprite.draw(c);
holder.unlockCanvasAndPost(c);
}
}
/**
* Periodically called from activity thread
*/
public void updatePos(int dx, int dy) {
synchronized (bounds) {
bounds.offset(dx, dy);
}
}
}
Running in the emulator, what I'm seeing is that after a few updates have occurred, several old "copies" of the image begin to flicker, i.e. appearing and disappearing. I initially assumed that perhaps I was misunderstanding the semantics of a Canvas, and that it somehow maintains "layers", and that I was thrashing it to death. However, I then discovered that I only get this effect if I try to update faster than roughly every 200 ms. So my next best theory is that this is perhaps an artifact of the emulator not being able to keep up, and tearing the display. (I don't have a physical device to test on, yet.)
Is either of these theories correct?
Note: I don't actually want to do this in practice (i.e. draw hundreds of overlaid copies of the same thing). However, I would like to understand why this is happening.
Environment:
Eclipse 3.6.1 (Helios) on Windows 7
JDK 6
Android SDK Tools r9
App is targetting Android 2.3.1
Tangential question:
My run() method is essentially a stripped-down version of how the LunarLander example works (with all the excess logic removed). I don't quite understand why this isn't going to saturate the CPU, as there seems to be nothing to prevent it running at full pelt. Can anyone clarify this?

Ok, I've butchered Lunar Lander in a similar way to you, and having seen the flickering I can tell you that what you are seeing is a simple artefact of the double-buffering mechanism that every Surface has.
When you draw anything on a Canvas attached to a Surface, you are drawing to the 'back' buffer (the invisible one). And when you unlockCanvasAndPost() you are swapping the buffers over... what you drew suddenly becomes visible as the "back" buffer becomes the "front", and vice versa. And so your next frame of drawing is done to the old "front" buffer...
The point is that you always draw to seperate buffers on alternate frames. I guess there's an implicit assumption in graphics architecture that you're always going to be writing every pixel.
Having understood this, I think the real question is why doesn't it flicker on hardware? Having worked on graphics drivers in years gone by, I can guess at the reasons but hesitate to speculate too far. Hopefully the above will be sufficient to satisfy your curiousity about this rendering artefact. :-)

You need to clear the previous position of the sprite, as well as the new position. This is what the View system does automatically. However, if you use a Surface directly and do not redraw every pixel (either with an opaque color or using a SRC blending mode) you must clear the content of the buffer yourself. Note that you can pass a dirty rectangle to lockCanvas() and it will do the union for you of the previous dirty rectangle and the one you are passing (this is the mechanism used by the UI toolkit.) It will also set the clip rect of the Canvas to be the union of these two rectangles.
As for your second question, unlockAndPost() will do a vsync, so you will never draw at more than ~60fps (most devices that I've seen have a display refresh rate set around 55Hz.)

Android game scrolling background

I'm just trying to figure out the best approach for running a scolling background on an android device. The method I have so far.... its pretty laggy. I use threads, which I believe is not the best bet for android platforms
#Override
public void run() {
// Game Loop
while(runningThread){
//Scroll background down
bgY += 1;
try {
this.postInvalidate();
t.sleep(10);
} catch (Exception e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
where postinvalidate in the onDraw function simply pushings the background image down
canvas.drawBitmap(backgroundImage, bgX, bgY, null);
Thanks in advance
UPDATE
I've identified the problem. And it is the fact that my player updates the same rate as the background scrolls (making it look choppy). from top to bottom. This is because both get drawn in the same function. I'm not really sure how to tackle this and would be grateful for any help. i.e so that player movement is handled separately from the map scrolling
Also how can I control the speed at which onDraw(canvas) get called?
Thanks in advance.
However, I have patched together a different run loop for anyone having the same problem. This is partially from the jetboy example on google.
Below is my inner class in my surfaceview
class MapThread extends Thread{
private Map map;
private SurfaceHolder holder;
private boolean run = false;
public MapThread(Map map, SurfaceHolder holder){
this.holder = holder;
this.map = map;
setRunning(true);
}
public void setRunning(boolean run){
this.run = run;
}
#Override
public void run(){
while(run){
try{
Canvas c = null;
try {
c = holder.lockCanvas(null);
synchronized (holder) {
map.onDraw(c);
}
} finally {
if (c != null) {
holder.unlockCanvasAndPost(c);
}
}
}
}
}
SOLUTION
https://gamedev.stackexchange.com/questions/8127/android-game-scrolling-background

Use the SurfaceView implementation draw on the screen. It allows you more control of what to draw and when.
The SurfaceView is a special subclass of View that offers a dedicated drawing surface within the View hierarchy. The aim is to offer this drawing surface to an application's secondary thread, so that the application isn't required to wait until the system's View hierarchy is ready to draw.
The basic design is to have a surfaceview that draws continuously in a while loop. Then add an if-statement whose condition is to be true if a timer thread tells you its time to draw. Say, every 30ms, draw the bitmap. This will give you about 33 fps.
Now you may also have another timer thread that tells you when to update the the bgX or bgY values. Say at every 60ms, it will set a boolean updateFlag = true; Then in your main thread, you have an if-statement check this flag, set it to false, and update your bgX and bgY values. By accurately controlling the timer and the bgX/bgY increments, you should be able to produce smooth animations.
It would be a good idea to look at the LunarLander source code provided by Google.

One thing to keep in mind is that sleep is very inaccurate. To work around this, you can keep track of exactly how much time passed during the sleep and update how much you move things accordingly.
Its not clear from you code, but you need to make sure that all of your UI updates happen in the UI thread.
You do need to do your timing outside of the UI thread, because otherwise the UI will never update. There are other methods of timing, like using a Handler that can be a little bit cleaner, but I think the overhead on them might be a bit much for what you are trying to do. I think a simple thread has the least amount of overhead.

I am using this method on the second level of my SpaceQuestAlpha game. This makes a seemless scroll.
I used the 2 lines below to set original position.
moony=0;
moon2y=-(heighty);
Then these lines increment both versions of the background image. One starts at 0 and one starts at negative screen height. Every time one of the images goes below the bottom of the screen it is moved up twice the height to move it back into position. I am using surface view with no latency issues.
moony+=5;
moon2y+=5;
if(moon2y>=heighty) {moon2y=moon2y-(heighty*2);}
canvas.drawBitmap(lavabackground, 0, moon2y, null);
if(moony>=heighty){moony=moony-(heighty*2);}
canvas.drawBitmap(lavabackground, 0, moony, null);