Loooong time viewer, finally getting round to signing up here at StackOverflow!
After a very long time searching for a way to do a scrolling background of a ViewGroup in Android, I've developed the following:
public class SlidingDrawable extends Drawable implements Drawable.Callback {
private static final String TAG = "SlidingDraw";
private static float STEP_SIZE = 1.0f;
private BitmapDrawable mBitmap;
private Context mContext;
private float mPosX;
private int mBitmapWidth;
private Runnable mInvalidater;
private Handler mHandler;
public SlidingDrawable(Context c){
mContext = c;
// use this as the callback as we're implementing the interface
setCallback(this);
mHandler = new Handler();
mInvalidater = new Runnable(){
@Override
public void run(){
// decrement the drawables step size
mPosX -= SlidingDrawable.STEP_SIZE;
/*
* Check to see if the current position is at point where it should
* loop. If so, reset back to 0 to restart
*/
if(Math.abs(mPosX) >= mBitmapWidth) mPosX = 0;
// redraw
invalidateDrawable(null);
}
};
}
public static void setStepSize(float newSize){
SlidingDrawable.STEP_SIZE = newSize;
}
public void createBitmap(String path, ViewGroup parent){
// height of the parent container
int height = parent.getHeight();
/* Initialize local variables
* bgBitmap - the resulting bitmap to send into SlidingDrawable instance
* imageStream - raw bitmap data to be decoded into bgBitmap
*/
WindowManager wMgr = (WindowManager)mContext.getSystemService(Context.WINDOW_SERVICE);
int mScreenWidth = wMgr.getDefaultDisplay().getWidth();
InputStream imageStream;
Matrix imgMatrix = new Matrix();
Bitmap bitmap = null;
try {
imageStream = mContext.getAssets().open(path);
// create a temporary bitmap object for basic data
Bitmap temp = BitmapFactory.decodeStream(imageStream);
int width = temp.getWidth();
// find the width difference as a percentage to apply to the
// transformation matrix
float widthDifference = ((float)mScreenWidth) / (float)(width / 2);
imgMatrix.postScale(widthDifference, 0, 0f, 0f);
// create a copy of the bitmap, scaled correctly to maintain loop
bitmap = Bitmap.createScaledBitmap(temp, (int)(width * widthDifference), height, true);
// recycle the temp bitmap
temp.recycle();
} catch (IOException e) {
e.printStackTrace();
}
mBitmap = new BitmapDrawable(bitmap);
// required
mBitmapWidth = getIntrinsicWidth() / 2;
Rect bounds = new Rect(0, 0, getIntrinsicWidth(), getIntrinsicHeight());
setBounds(bounds);
}
@Override
public void draw(Canvas canvas) {
canvas.drawBitmap(mBitmap.getBitmap(), mPosX, 0f, null);
scheduleDrawable(this, mInvalidater, SystemClock.uptimeMillis());
}
@Override
public int getOpacity() {
return PixelFormat.OPAQUE;
}
@Override
public void scheduleDrawable(Drawable who, Runnable what, long when) {
mHandler.postAtTime(what, who, when);
}
@Override
public void unscheduleDrawable(Drawable who, Runnable what) {
mHandler.removeCallbacks(what, who);
}
@Override
public void invalidateDrawable(Drawable who) {
invalidateSelf();
}
/*
* Methods not directly used or called omitted
*
*/
}
It is used in the Activity like so:
@Override
public void onWindowFocusChanged(boolean focus){
// set the background of the root view of main.xml
SlidingDrawable drawable = new SlidingDrawable(getApplicationContext());
drawable.createBitmap("bgimg/basebg.jpg", mRoot);
mRoot.setBackgroundDrawable(drawable);
}
Long story short, the basebg.jpg image is a tileable image roughly 1600x480. The constructor for SlidingDrawable scales and moves and yaddah yaddah. It works.
Now, the problem is, it seems really inefficient to do it like this. I can't seem to find much information on this sort of implementation, so I'm in the dark on where I can cut CPU cycles, or even if I'm using the method calls correctly.
My questions include:
- Is it better to drawBitmap as opposed to using setTranslate() or postTranslate and draw the bitmap using a Matrix?
- Is it better to use drawBitmap, or the canvas functions such as translate(), save(), and restore()?
- What rate does the draw() method get called at, and is there a way to limit it to, say, 24 FPS o limit redraws?
- What the heck is the "when" parameter of these sorts of things? Passing in SystemClock.uptimeMillis() is the only one that worked, and trying to delay it by adding a " + 100" or something to fire every 100ms just made it stutter.
I've researched this as much as I can... I'm leaving it to StackOverflow now :)
