Rotating Image on A canvas in android

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心在旅途
心在旅途 2020-11-27 13:33

I want to Rotate Image according to a specific angle in android ,some thing like a compass...

I have this code...it works on drawPath() but i want to replace the pat

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  • 2020-11-27 14:09

    You can either rotate your bitmap when you draw it by using a matrix:

    Matrix matrix = new Matrix();
    matrix.setRotate(angle, imageCenterX, imageCenterY);
    yourCanvas.drawBitmap(yourBitmap, matrix, null);
    

    You can also do it by rotating the canvas before drawing:

    yourCanvas.save(Canvas.MATRIX_SAVE_FLAG); //Saving the canvas and later restoring it so only this image will be rotated.
    yourCanvas.rotate(-angle);
    yourCanvas.drawBitmap(yourBitmap, left, top, null);
    yourCanvas.restore();
    

    Pick the one that suits you the best.

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  • 2020-11-27 14:11

    You have to rotate the canvas first and then draw whatever you want. Then the object drawn will be appeared as rotated on screen.

    canvas.rotate(45); // degrees to rotate
    

    try this its good way.

    Check this tutorial you will get information about how to draw bitmap and how to rotate canvas

    Check complete tutorial

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  • 2020-11-27 14:17

    Use following code. it worked for me

    float rotation = 30.0f;

         Bitmap bitmap = your bitmap
         Rect rect = new Rect(100,100,bitmap.width, bitmap.height);
         Matrix matrix = new Matrix();
         float px = rect.exactCenterX();
         float py = rect.exactCenterY();
         matrix.postTranslate(-bitmap.getWidth()/2, -bitmap.getHeight()/2);
         matrix.postRotate(rotation);
         matrix.postTranslate(px, py);
         canvas.drawBitmap(bitmap, matrix, null);
         matrix.reset();
         invalidate();
    
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  • 2020-11-27 14:25

    This is the only one that worked for me with no problem.

        private Bitmap rotateBitmap(Bitmap bitmap, int rotationAngleDegree){
    
            int w = bitmap.getWidth();
            int h = bitmap.getHeight();
    
            int
    
     newW=w, newH=h;
        if (rotationAngleDegree==90 || rotationAngleDegree==270){
            newW = h;
            newH = w;
        }
        Bitmap rotatedBitmap = Bitmap.createBitmap(newW,newH, bitmap.getConfig());
        Canvas canvas = new Canvas(rotatedBitmap);
    
        Rect rect = new Rect(0,0,newW, newH);
        Matrix matrix = new Matrix();
        float px = rect.exactCenterX();
        float py = rect.exactCenterY();
        matrix.postTranslate(-bitmap.getWidth()/2, -bitmap.getHeight()/2);
        matrix.postRotate(rotationAngleDegree);
        matrix.postTranslate(px, py);
        canvas.drawBitmap(bitmap, matrix, new Paint( Paint.ANTI_ALIAS_FLAG | Paint.DITHER_FLAG | Paint.FILTER_BITMAP_FLAG ));
        matrix.reset();
    
        return rotatedBitmap;
    }
    
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  • 2020-11-27 14:25

    Based on @Sakthi 's code, but add scaling :)

            Rect rect = new Rect(0,0,canvas.getWidth(), canvas.getHeight());
            Matrix matrix = new Matrix();
            matrix.postTranslate(-bitmap.getWidth()/2, -bitmap.getHeight()/2);
            matrix.postScale(
                    ((float)rect.width()) / bitmap.getWidth(),
                    ((float)rect.height()) / bitmap.getHeight());
            matrix.postRotate(180);
            matrix.postTranslate(rect.exactCenterX(), rect.exactCenterY());
            canvas.drawBitmap(bitmap, matrix, null);
    
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  • 2020-11-27 14:29

    @Reham: Look at this example code below,

    public class bitmaptest extends Activity {
    @Override
    public void onCreate(Bundle icicle) {
        super.onCreate(icicle);
        LinearLayout linLayout = new LinearLayout(this);
    
        // load the origial BitMap (500 x 500 px)
        Bitmap bitmapOrg = BitmapFactory.decodeResource(getResources(),
               R.drawable.android);
    
        int width = bitmapOrg.width();
        int height = bitmapOrg.height();
        int newWidth = 200;
        int newHeight = 200;
    
        // calculate the scale - in this case = 0.4f
        float scaleWidth = ((float) newWidth) / width;
        float scaleHeight = ((float) newHeight) / height;
    
        // createa matrix for the manipulation
        Matrix matrix = new Matrix();
        // resize the bit map
        matrix.postScale(scaleWidth, scaleHeight);
        // rotate the Bitmap
        matrix.postRotate(45);
    
        // recreate the new Bitmap
        Bitmap resizedBitmap = Bitmap.createBitmap(bitmapOrg, 0, 0,
                          width, height, matrix, true);
    
        // make a Drawable from Bitmap to allow to set the BitMap
        // to the ImageView, ImageButton or what ever
        BitmapDrawable bmd = new BitmapDrawable(resizedBitmap);
    
        ImageView imageView = new ImageView(this);
    
        // set the Drawable on the ImageView
        imageView.setImageDrawable(bmd);
    
        // center the Image
        imageView.setScaleType(ScaleType.CENTER);
    
        // add ImageView to the Layout
        linLayout.addView(imageView,
                new LinearLayout.LayoutParams(
                      LayoutParams.FILL_PARENT, LayoutParams.FILL_PARENT
                )
        );
    
        // set LinearLayout as ContentView
        setContentView(linLayout);
    }
    }
    

    you have to use the matrix to rotate image look the lines

    matrix.postRotate(45); -
    

    this will rotate the image to 45 degrees

    Hope this help you ...thx

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