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android – How to rotate a drawable with anti-aliasing enabled

Posted by: admin June 15, 2020 Leave a comment

Questions:

I need to rotate an ImageView by a few degrees. I’m doing this by subclassing ImageView and overloading onDraw()

@Override
protected void onDraw(Canvas canvas) {
    canvas.save();
    canvas.scale(0.92f,0.92f);
    canvas.translate(14, 0);
    canvas.rotate(1,0,0);
    super.onDraw(canvas);
    canvas.restore();
}

The problem is that the image that results shows a bunch of jaggies.

http://img.skitch.com/20100608-gmdy4sexsm1c71di9rgiktdjhu.png

How can I antialias an ImageView that I need to rotate in order to eliminate jaggies? Is there a better way to do this?

How to&Answers:

If you know that your Drawable is a BitmapDrawable, you can use anti-aliasing in the bitmap’s Paint to do something like the following:

/**
 * Not as full featured as ImageView.onDraw().  Does not handle 
 * drawables other than BitmapDrawable, crop to padding, or other adjustments.
 */
@Override
protected void onDraw(Canvas canvas) {
    final Drawable d = getDrawable();

    if( d!=null && d instanceof BitmapDrawable && ((BitmapDrawable)d).getBitmap()!=null ) {
        final Paint p = new Paint(Paint.ANTI_ALIAS_FLAG);
        final int paddingLeft = getPaddingLeft();
        final int paddingTop = getPaddingTop();

        canvas.save();

        // do my rotation and other adjustments
        canvas.scale(0.92f,0.92f);
        canvas.rotate(1,0,0);

        if( paddingLeft!=0 )
            canvas.translate(paddingLeft,0);

        if( paddingTop!=0 )
            canvas.translate(0,paddingTop);

        canvas.drawBitmap( ((BitmapDrawable)d).getBitmap(),0,0,p );
        canvas.restore();
    }
}

Answer:

Set antialias and filterBitmap to the paint that draw’s the bitmap.
I had a similar problem and this worked for me:

Paint bitmapPaint = new Paint();
bitmapPaint.setAntiAlias(true);
bitmapPaint.setFilterBitmap(true);

Answer:

I did the following to get it to work:

In AndroidManifest.xml I enabled hardware-acceleration <application android:hardwareAccelerated="true">.

Instead of using a custom draw-method, I changed the layer-type of the parent-view to hardware-accelerated with anti-aliasing enabled and added my subviews as follows:

Paint layerPaint =  new Paint();
layerPaint.setAntiAlias(true);
layerPaint.setFilterBitmap(true);
layerPaint.setDither(true);

RelativeLayout parentLayout = (RelativeLayout) LayoutInflater.from(context).inflate(R.layout.myLayout, null);
parentLayout.setLayerType(View.LAYER_TYPE_HARDWARE, layerPaint);

parentLayout.addView(myChildView);

I have to add that clipping cannot be disabled when using this approach.

Answer:

This rotation solves just one part of problem – jagged edges, but the image instead became wierd.

ifound only one solution yet:
in ondraw or dispatch draw method

        Bitmap bmp = ((BitmapDrawable)image.getDrawable()).getBitmap();
    double scale = (0.0+bmp.getWidth()+40.0)/getWidth();
    if (scale > 1){
        bmp = Bitmap.createScaledBitmap(bmp, getWidth()-40, (int) (bmp.getHeight()/scale), true);
    }

    canvas.drawColor(Color.TRANSPARENT); 
    canvas.save();

    canvas.translate(20, yShift);

    int left = borderSize;
    int top = borderSize;
    int right = bmp.getWidth() - borderSize;
    int bottom = bmp.getHeight() - borderSize;

    if(showText){
        mPaint.setColor(Color.WHITE);
        canvas.rotate(getAngel());
        canvas.drawRect(left, top, right, bottom, mPaint);

        canvas.translate(0,0);
        textFrame.draw(canvas);
    }else{
        // rotaed bitmap 
        mMatrix.setRotate(getAngel());

        // draw bitmap after creation of new rotated bitmap from rotated matrix
        canvas.drawBitmap(Bitmap.createBitmap(bmp, 0, 0, bmp.getWidth(), bmp.getHeight(), mMatrix, true)
                   , 0, 0, mPaint);
    }
    canvas.restore();       

Answer:

@Primoz990’s solution worked for me 🙂 I also enabled Dithering, so my final code which removes the jagged edges on rotation is this:

Paint bitmapPaint =  new Paint();
bitmapPaint.setAntiAlias(true);
bitmapPaint.setFilterBitmap(true);
bitmapPaint.setDither(true);