Develop Reference

Android SurfaceView with drawBitmap(Matrix) leaves blinking ghost image

To preface, I'm probably going to work with Views instead of SurfaceView given this weird interaction, but my curiosity is getting the better of me and I want to know what's going on.
So I have a matrix class variable. I run matrix.setTranslate() once, and every other frame I say matrix.setTranslate(). After this I call canvas.drawBitmap(, matrix, null). After 100 frames, I stop drawing the bitmap.
Here's the code:
public void onDraw(Canvas canvas) {
super.onDraw(canvas);
// matrix = new Matrix(); //Doesn't matter if I add this.
// matrix.reset(); //This doesn't matter either.
if (!once) {
matrix.setTranslate(100, 100);
} else {
matrix.setTranslate(800,800);
}
once = true;
if (++timer < 100) {
canvas.drawBitmap(ball, matrix, null);
}
}
What I expect to happen: Three possibilities.
Only the bottom right bitmap is visible since the entire screen was invalidated
Both bitmaps are visible because SurfaceView was smart with the dirty rectangle
Nothing is shown because nothing was drawn.
What actually happens: The top left bitmap blinks, bottom right bitmap displays solidly.
I'm pretty sure I have all of my bases covered:
All class variables are properly set in the constructor.
SurfaceView.onDraw() is called every 33 millis in its own thread.
Thread calls lockCanvas, then onDraw, then unlockCanvasAndPost
So, what's going on here? And bonus question, do these ghost images consume any extra resources and how can I clear them?
Rest of the code, mostly boilerplate:
public class FullscreenActivity extends Activity {
GameSurface ball;
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
ball = new GameSurface(this);
setContentView(ball);
}
}
class GameSurface extends SurfaceView implements SurfaceHolder.Callback {
GameThread thread;
boolean once = false;
Bitmap ball;
Matrix matrix;
int timer = 0;
public GameSurface(Context context) {
super(context);
ball = BitmapFactory.decodeResource(getResources(),R.drawable.football);
matrix = new Matrix();
getHolder().addCallback(this);
setFocusable(true);
}
#Override
public void onDraw(Canvas canvas) {
super.onDraw(canvas);
// matrix = new Matrix(); //Doesn't matter if I add this.
// matrix.reset(); //This doesn't matter either.
if (!once) {
matrix.setTranslate(100, 100);
} else {
matrix.setTranslate(800,800);
}
//matrix.postRotate(timer); //For even more weirdness...
once = true;
if (++timer < 100) {
canvas.drawBitmap(ball, matrix, null);
}
}
#Override
public void surfaceChanged(SurfaceHolder holder, int format, int width, int height) {
}
#Override
public void surfaceCreated(SurfaceHolder holder) {
thread = new GameThread(getHolder(), this);
thread.setRunning(true);
thread.start();
}
#Override
public void surfaceDestroyed(SurfaceHolder holder) {
}
class GameThread extends Thread {
private SurfaceHolder surfaceHolder;
private GameSurface gameView;
private boolean run = false;
public GameThread(SurfaceHolder surfaceHolder, GameSurface gameView) {
this.surfaceHolder = surfaceHolder;
this.gameView = gameView;
}
public void setRunning(boolean run) {
this.run = run;
}
#Override
public void run() {
Canvas c;
while (run) {
c = null;
try {
Thread.sleep(33);
}
catch(InterruptedException e) {}
try {
c = surfaceHolder.lockCanvas();
synchronized (surfaceHolder) {
gameView.onDraw(c);
}
} finally {
if (c != null) {
surfaceHolder.unlockCanvasAndPost(c);
}
}
}
}
}
}

Partial redrawing bitmaps in Android

I am coding a snake game in Android, and I am blocked by the fact that i can't draw a wall using a loop inside onDraw method, the wall just don't show up.
Is there a way i can draw the wall so that the onDraw will keep it intact and keep on redrawing others things (snake and objects) ?
GameView:
public void surfaceCreated(SurfaceHolder holder) {
gameLoopThread.setRunning(true);
gameLoopThread.start();
}
#Override
protected void onDraw(final Canvas canvas) {
canvas.drawColor(Color.WHITE);
if(drawWall) {
int i = 0;
while(i < getWidth()) {
canvas.drawBitmap(wall.getImage(), i, 0, null);
i += 17;
}
drawWall = false;
}
x += dx;
y += dy;
}
GameLoop:
public class GameLoopThread extends Thread {
private GameView view;
private boolean running = false;
public GameLoopThread(GameView view) {
this.view = view;
}
public void setRunning(boolean run) {
running = run;
}
#Override
public void run() {
while (running) {
Canvas c = null;
try {
c = view.getHolder().lockCanvas();
synchronized (view.getHolder()) {
view.onDraw(c);
}
} finally {
if (c != null) {
view.getHolder().unlockCanvasAndPost(c);
}
}
}
}
}

I don't know what your view hierarchy is, however, why not make your life easier and just have an ImageView behind your SurfaceView with your walls on it? Or have a FrameLayout contain your SurfaceView and have the walls as a background image for the FrameLayout?The collision with the walls is going to be handled in the code and the graphical representation of the walls is really just for the users benefit.
Put the images of the walls in the background and let Android worry about it, in your SurfaceView just concentrate of redrawing the snake and the dots.
That being said, looks like you're drawing in a background thread. You can't actually do that on Android and you should be drawing in the main thread.

Android SurfaceView canvas drawing with a thread

I am experimenting with drawing on a canvas using a thread to create a simple game engine but I'm having some weird issues I cannot explain.
The purpose of this "game" is to draw a circle every second on the canvas.
This works, but not the way I want it to work, it seems the app is switching between two canvasses and adding a circle to each canvas so you get a switch between two canvasses every second with the same number of circles but in a different place on the canvas.
I don't know what I'm doing wrong, but I'm not that familiar with Treadding, has it something to do with how many cores my android device has or something like that?
My code is shown below, so I just use a launchthread which uses a layoutfile that links to the animationthread which starts a thread and draws a circle on the canvas every second.
(You can ignore the touchevent, it isn't uses yet).
The project exists out of a main launchthread:
public class MainActivity extends Activity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
}
}
which uses this layout file:
<?xml version="1.0" encoding="utf-8"?>
<FrameLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="fill_parent">
<com.androidtesting.AnimationView
android:id="#+id/aview"
android:layout_width="fill_parent"
android:layout_height="fill_parent"/>
</FrameLayout>
And my Surfaceview class with an inner Thread class:
class AnimationView extends SurfaceView implements SurfaceHolder.Callback {
private boolean touched = false;
private float touched_x, touched_y = 0;
private Paint paint;
private Canvas c;
private Random random;
private AnimationThread thread;
public AnimationView(Context context, AttributeSet attrs) {
super(context, attrs);
SurfaceHolder holder = getHolder();
holder.addCallback(this);
thread = new AnimationThread(holder);
}
class AnimationThread extends Thread {
private boolean mRun;
private SurfaceHolder mSurfaceHolder;
public AnimationThread(SurfaceHolder surfaceHolder) {
mSurfaceHolder = surfaceHolder;
paint = new Paint();
paint.setARGB(255,255,255,255);
paint.setTextSize(32);
}
#Override
public void run() {
while (mRun) {
c = null;
try {
c = mSurfaceHolder.lockCanvas(null);
synchronized (mSurfaceHolder) {
doDraw(c);
sleep(1000);
}
} catch (Exception e) {
e.printStackTrace();
}finally {
if (c != null) {
mSurfaceHolder.unlockCanvasAndPost(c);
}
}
}
}
private void doDraw(Canvas canvas) {
//clear the canvas
//canvas.drawColor(Color.BLACK);
random = new Random();
int w = canvas.getWidth();
int h = canvas.getHeight();
int x = random.nextInt(w-50);
int y = random.nextInt(h-50);
int r = random.nextInt(255);
int g = random.nextInt(255);
int b = random.nextInt(255);
int size = 20;
canvas.drawCircle(x,y,size,paint);
canvas.restore();
}
public void setRunning(boolean b) {
mRun = b;
}
}
public void surfaceChanged(SurfaceHolder holder, int format, int width, int height) {
}
#Override
public boolean onTouchEvent(MotionEvent event) {
touched_x = event.getX();
touched_y = event.getY();
int action = event.getAction();
switch(action){
case MotionEvent.ACTION_DOWN:
touched = true;
break;
case MotionEvent.ACTION_MOVE:
touched = true;
break;
default:
touched = false;
break;
}
return true;
}
public void surfaceCreated(SurfaceHolder holder) {
thread.setRunning(true);
thread.start();
}
public void surfaceDestroyed(SurfaceHolder holder) {
boolean retry = true;
thread.setRunning(false);
while (retry) {
try {
thread.join();
retry = false;
} catch (InterruptedException e) {
}
}
}
}

it seems the app is switching between two canvasses
Yes, this is how it works. It is called double buffering and you need to redraw all the frame each time:
The content of the Surface is never preserved between unlockCanvas() and lockCanvas(), for this reason, every pixel within the Surface area must be written.
So you need this line canvas.drawColor(Color.BLACK) to be uncommented in your code.
And you shouldn't call Thread.sleep(1000) while canvas is locked, it will cause starvation issue.

It sounds like you have this working, but I did just notice a small error that I should point out.
You called canvas.restore() without calling canvas.save() beforehand.
From the Android developer reference for Canvas: "It is an error to call restore() more times than save() was called."
I don't see any reason for you to call canvas.save() in your case, therefore you should remove the call to canvas.restore().

Multi-threading in the same Canvas

Well, I'll try to explain exactly what I pretend:
I want to draw a bitmap in a canvas in random positions according to the coordinates of the screen on touch, and I want a message(text) to be displayed everytime the user touches the screen.
So, if a draw the text in the same thread than I do for the bitmap, it will appear and dissapear right after, and I want it to stay in the screen for a few seconds and the dissapear. My first idea was to use Thread.sleep(), but for that I have to create a thread only for the text, or I will mess with the Bitmap too.
I've been trying to use multithreading in the same canvas, but I don't know how. Can someone please explain to me...
That's some of the code i've got so far:
private void init() {
// CREATE SURFACEHOLDER AND ADD THIS CLASS AS HIS CALLBACK
enemyHolder = getHolder();
enemyHolder.addCallback(this);
scoreHolder = getHolder();
scoreHolder.addCallback(this);
hasSurface = false;
}
public void resume() {
if (surfaceViewThread == null) {
surfaceViewThread = new SurfaceViewThread(); // CREATE A NEW
// THREAD
if (hasSurface)
surfaceViewThread.start(); // START OUR THREAD
}
if (secondThread == null) {
secondThread = new SecondThread();
if (hasSurface)
secondThread.start();
}
}
public void surfaceCreated(SurfaceHolder holder) {
hasSurface = true;
if (surfaceViewThread != null)
surfaceViewThread.start();
if (scoreShow == 1) {
if (secondThread != null)
secondThread.start();
}
}
// THREAD
private final class SurfaceViewThread extends Thread {
private boolean done;
SurfaceViewThread() {
super();
done = false;
}
#Override
public void run() {
// TODO Auto-generated method stub
super.run();
SurfaceHolder surfaceHolder = enemyHolder;
while (!done) {
Canvas canvas = surfaceHolder.lockCanvas();
canvas.drawColor(Color.WHITE);
canvas.drawBitmap(enemy1, enemy1X, enemy1Y, null); // DRAW
// FIRST
// ENEMY
// SECOND THREAD
private final class SecondThread extends Thread {
private boolean done;
SecondThread() {
super();
done = false;
}
#Override
public void run() {
// TODO Auto-generated method stub
super.run();
SurfaceHolder surfaceHolder = scoreHolder;
while (!done) {
Canvas canvas = surfaceHolder.lockCanvas();
Paint paint = new Paint();
paint.setColor(Color.BLACK);
canvas.drawText("xD", 50, 50, paint);
surfaceHolder.unlockCanvasAndPost(canvas);
try {
Thread.sleep(1000);
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
scoreShow = 0;
}
}

Do you need to use a SurfaceView? It seems like a hard work way of doing things.
I've just done something similar by creating a custom view class and overriding the onDraw method. Then use canvas.save() and canvas.restore(). Here's the relevant bits of my onDraw.
#Override
public void onDraw(Canvas canvas) {
canvas.save();
// scale the canvas
canvas.scale(scaleFactor, scaleFactor); //, mid.x, mid.y);
// and translate...
canvas.translate(translateX / scaleFactor, translateY / scaleFactor);
super.onDraw(canvas);
// draw the lights
for(Light light:lights){
if (light.isOn){
canvas.drawCircle(light.getX(),light.getY(), light.getDiameter() / scaleFactor,light.paint);
}
}
canvas.restore();
}
The lights are turned on and off by a separate thread back in the activity which has inflated the view. They stay on screen as long as they are on.
Cheers

Here's some incomplete pseudo code to do what you've described. There are plenty of good examples around for each of these elements to help you fill in the blanks.
public class MyCustomView extends View {
int touchPointX;
int touchPointY;
private String mText;
public MyCustomView(Context context) {
// do initialisation stuff
}
public setText(String text){
mText = text;
this.invalidate();
}
#Override
public void onDraw(Canvas canvas) {
canvas.save();
super.onDraw(canvas);
canvas.drawBitmap(touchPointX, touchPointY, bitmap)
if (!mText.equals(""){
canvas.drawText(touchPointX, touchPointY + 10, mText)
}
canvas.restore();
}
}
public class MyActivity extends Activity implements OnTouchListener{
private Handler mHandler = new Handler();
private MyCustomView mCustomView;
#Override
protected void onCreate(Bundle savedInstanceState) {
mCustomView = (MyCustomView) findViewById(r.id.myCustomView);
}
#Override
public boolean onTouch(View v, MotionEvent rawEvent) {
// get x and y of touch
mCustomview.touchPointX = x;
mCustomview.touchPointY = y;
mCustomView.setText("Screen touched");
// clear the text after 5 seconds
mHandler.postDelayed(clearText, 5000);
// redraw the view
mCustomView.invalidate();
}
private void clearText(){mCustomView.setText("");}
}

Android: Background on SurfaceView?

I have a surface view, and whenever I touch the screen, an image comes up in the spot I touch. It's great, but I cannot figure out how to put a background on the SurfaceView. I have tried using the OnDraw to draw a background right away (Without having to touch it), and that only works some of the time. It force closes most of the time.
Would anyone want to look at my code and see if it's possible to get a background image on the Surface view? Thanks in advance.
class MyView extends SurfaceView implements SurfaceHolder.Callback {
private Thready _thread;
private ArrayList _graphicsz = new ArrayList();
private GraphicObject _currentGraphic = null;
public MyView(Context context) {
super(context);
getHolder().addCallback(this);
_thread = new Thready(getHolder(), this);
setFocusable(true);
}
#Override
public boolean onTouchEvent(MotionEvent event) {
synchronized (_thread.getSurfaceHolder()) {
GraphicObject graphic = null;
if (event.getAction() == MotionEvent.ACTION_DOWN) {
graphic = new GraphicObject(BitmapFactory.decodeResource(getResources(), R.drawable.cat1small));
graphic.getCoordinates().setX((int) event.getX() - graphic.getGraphic().getWidth() / 2);
graphic.getCoordinates().setY((int) event.getY() - graphic.getGraphic().getHeight() / 2);
_currentGraphic = graphic;
} else if (event.getAction() == MotionEvent.ACTION_MOVE) {
_currentGraphic.getCoordinates().setX((int) event.getX() - _currentGraphic.getGraphic().getWidth() / 2);
_currentGraphic.getCoordinates().setY((int) event.getY() - _currentGraphic.getGraphic().getHeight() / 2);
} else if (event.getAction() == MotionEvent.ACTION_UP) {
_graphicsz.add(_currentGraphic);
_currentGraphic = null;
}
return true;
}
}
#Override
public void onDraw(Canvas canvas) {
canvas.drawColor(Color.BLACK);
Bitmap bitmap1;
GraphicObject.Coordinates coords1;
for (GraphicObject graphic : _graphicsz) {
bitmap1 = graphic.getGraphic();
coords1 = graphic.getCoordinates();
canvas.drawBitmap(bitmap1, coords1.getX(), coords1.getY(), null);
}
// draw current graphic at last...
if (_currentGraphic != null) {
bitmap1 = _currentGraphic.getGraphic();
coords1 = _currentGraphic.getCoordinates();
canvas.drawBitmap(bitmap1, coords1.getX(), coords1.getY(), null);
}
}
public void surfaceChanged(SurfaceHolder holder, int format, int width, int height) {
// TODO Auto-generated method stub
}
public void surfaceCreated(SurfaceHolder holder) {
_thread.setRunning(true);
_thread.start();
}
public void surfaceDestroyed(SurfaceHolder holder) {
// simply copied from sample application LunarLander:
// we have to tell thread to shut down & wait for it to finish, or else
// it might touch the Surface after we return and explode
boolean retry = true;
_thread.setRunning(false);
while (retry) {
try {
_thread.join();
retry = false;
} catch (InterruptedException e) {
// we will try it again and again...
}
}
}
}
class Thready extends Thread {
private SurfaceHolder _surfaceHolder;
private MyView _panel;
private boolean _run = false;
public Thready(SurfaceHolder surfaceHolder, MyView panel) {
_surfaceHolder = surfaceHolder;
_panel = panel;
}
public void setRunning(boolean run) {
_run = run;
}
public SurfaceHolder getSurfaceHolder() {
return _surfaceHolder;
}
#Override
public void run() {
Canvas c;
while (_run) {
c = null;
try {
c = _surfaceHolder.lockCanvas(null);
synchronized (_surfaceHolder) {
_panel.onDraw(c);
}
} finally {
// do this in a finally so that if an exception is thrown
// during the above, we don't leave the Surface in an
// inconsistent state
if (c != null) {
_surfaceHolder.unlockCanvasAndPost(c);
}
}
}
}
}
class GraphicObject {
/**
* Contains the coordinates of the graphic.
*/
public class Coordinates {
private int _x = 100;
private int _y = 0;
public int getX() {
return _x + _bitmap.getWidth() / 2;
}
public void setX(int value) {
_x = value - _bitmap.getWidth() / 2;
}
public int getY() {
return _y + _bitmap.getHeight() / 2;
}
public void setY(int value) {
_y = value - _bitmap.getHeight() / 2;
}
public String toString() {
return "Coordinates: (" + _x + "/" + _y + ")";
}
}
private Bitmap _bitmap;
private Coordinates _coordinates;
public GraphicObject(Bitmap bitmap) {
_bitmap = bitmap;
_coordinates = new Coordinates();
}
public Bitmap getGraphic() {
return _bitmap;
}
public Coordinates getCoordinates() {
return _coordinates;
}
}

Well, what strikes me first off all (and what could be causing a lot of problem) is this:
you're creating new bitmap way too often
Every time you get a touch event, you're loading in your bitmaps ... and you can get 80 to 100 touchevents every second!
So to start with, define global bitmaps (private Bitmap bmp1; etc), load them somewhere else and THEN use them in your touch event.
Also, remove the bmp loading/creation from onDraw and move it to somewhere else.
After you've done that, see what happens; you might have more problems (a REALY quick scan of your code seemed fine), but not creating and loading bitmaps 80 times a second will definitely help out :)