android - 如何在启用抗锯齿的情况下旋转可绘制对象

Question

我需要将 ImageView 旋转几度。我通过子类化 ImageView 和重载 onDraw()

来做到这一点

@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();
}

问题是生成的图像显示出一堆锯齿。

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

如何对需要旋转以消除锯齿的 ImageView 进行抗锯齿处理？有更好的方法吗？

Answer 1

如果您知道您的 Drawable 是一个 BitmapDrawable，您可以在位图的 Paint 中使用抗锯齿来执行如下操作:

/**
 * 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();
    }
}