Flipping a bitmap in android help?

问题

I want to save up memory for my game and I wanted to ask you because I couldn't find anything and last time that I asked something here I got a good answer. Can i flip the bitmap inside eclipse so i could save on memory for sprites? All the tutorials that i found were about rotating and not flipping. The tutorials for flipping a bitmap were only for open Gl or something like that. Please help me. I've been looking up for tutorials in google but i gave up at page 5. Can anyone help me? Does anyone have a good tutorial? By the way I am using a canvas. Thanks!

I get a force close everytime I try to run it... can u figure it out? here is my code:

       Matrix flipHorizontalMatrix = new Matrix();
       flipHorizontalMatrix.setScale(-1,1);
       flipHorizontalMatrix.postTranslate(0, canvas.getHeight()-arrowL.getHeight());
       canvas.drawBitmap(arrowL, flipHorizontalMatrix, null);

I want the arrow to be at the bottom right corner.

回答1:

Since you're using Canvas, why not try the drawBitmap (Bitmap bitmap, Matrix matrix, Paint paint) method. Use a Matrix that flips the x coordinates.

You can do something like this:

Matrix flipHorizontalMatrix = new Matrix();
flipHorizontalMatrix.setScale(-1,1);
flipHorizontalMatrix.postTranslate(myBitmap.getWidth(),0);

canvas.drawBitmap(myBitmap, flipHorizontalMatrix, myPaint);

回答2:

Thanks,check out this code it may be useful for you to rotate an Bitmap image.. Here i have a taken a aquarium fish example,it should be moved from left to right and flipped and continue moving from right to left and viceversa.. here is the code for you..

           protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN,
            WindowManager.LayoutParams.FLAG_FULLSCREEN);
    requestWindowFeature(Window.FEATURE_NO_TITLE);
    fish = BitmapFactory.decodeResource(getResources(), R.drawable.fish);
            v = new OurView(this); 

public class OurView extends SurfaceView implements Runnable {

    Thread t = null;
    SurfaceHolder holder;
    boolean isitOK = false;
    String Flag = "right";
    Bitmap rotatedBitmap=null;
    Matrix rotateRight = new Matrix();
    Matrix rotateLeft = new Matrix();
    Bitmap rSprite=null;
    Bitmap lSprite=null;
    public OurView(Context context) {
        super(context);
        holder = getHolder();
        rotateLeft.setScale(-1, 1);


         rSprite = Bitmap.createBitmap(fish, 0, 0,
                fish.getWidth(), fish.getHeight(), rotateRight, true);
         lSprite = Bitmap.createBitmap(fish, 0, 0,
                fish.getWidth(), fish.getHeight(), rotateLeft, true);
    }

    @Override
    public void run() {
        // TODO Auto-generated method stub

        while (isitOK == true) {
            if (!holder.getSurface().isValid()) {
                continue;
            }
            Canvas canvas = holder.lockCanvas();

            canvas.drawBitmap(bg, 0, 0, null);
            if(Flag == "right")
            canvas.drawBitmap(lSprite, x, y, null);

            if(Flag == "left")
            canvas.drawBitmap(fish, x, y, null);    

                if (Flag == "right" && x <= 60) {

                    x++;
                    if (x == 60) {

                        Flag = "left";
                    //  canvas.drawBitmap(rSprite, 0, fish.getWidth(), null);
                        canvas.drawBitmap(fish, x, y, null);    
                    }
                }               
                if (Flag == "left" && x >= 0) {
                    x--;
                    if (x == 0) {
                    Flag = "right";

                    canvas.drawBitmap(fish, x, y, null);
                    }
                }




            holder.unlockCanvasAndPost(canvas);



        }
    }

来源：https://stackoverflow.com/questions/7774618/flipping-a-bitmap-in-android-help