如何在启用抗锯齿的情况下旋转可绘制对象

How to rotate a drawable with anti-aliasing enabled(如何在启用抗锯齿的情况下旋转可绘制对象)

问题描述

我需要将 ImageView 旋转几度.我通过继承 ImageView 和重载 onDraw()

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();
}

问题是生成的图像显示了一堆锯齿.

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

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

如何对需要旋转的 ImageView 进行抗锯齿处理以消除锯齿?有没有更好的方法来做到这一点?

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

推荐答案

如果您知道您的 Drawable 是 BitmapDrawable，您可以在位图的 Paint 中使用抗锯齿来执行以下操作:

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();
    }
}

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