android - `drawTextOnPath()` 硬件加速的奇怪行为

Question

在 hardware accelerated 自定义 View 添加到 ScrollView 或 ListView 以下两个代码 fragment 产生相同的结果: (请暂时忽略最佳实践)

@Override
protected void onDraw(Canvas canvas) {
    super.onDraw(canvas); 
    // centering stuff
    float centerX = getWidth() / 2f;
    float centerY = getHeight() / 2f;
    float size = 80;
    float halfSize = size / 2f;
    float left = centerX - halfSize;
    float top = centerY - halfSize;
    
    RectF oval = new RectF(left, top, left + size, top + size);
    
    Path path = new Path();
    path.addArc(oval, 160, 359);
    
    Paint paint = new Paint();
    paint.setTextSize(30);
    paint.setStyle(Style.STROKE);
    
    canvas.drawTextOnPath("Hello world", path, 0, 0, paint); //<--- line A
    canvas.drawCircle(centerX, centerY, 10, paint);          //<--- line B
}

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@Override
protected void onDraw(Canvas canvas) {
    super.onDraw(canvas); 
    // centering stuff
    float centerX = getWidth() / 2f;
    float centerY = getHeight() / 2f;
    float size = 80;
    float halfSize = size / 2f;
    float left = centerX - halfSize;
    float top = centerY - halfSize;
    
    RectF oval = new RectF(left, top, left + size, top + size);
    
    Path path = new Path();
    path.addArc(oval, 160, 359);
    
    Paint paint = new Paint();
    paint.setTextSize(30);
    paint.setStyle(Style.STROKE);
    
    canvas.drawCircle(centerX, centerY, 10, paint);          //<--- line B
    canvas.drawTextOnPath("Hello world", path, 0, 0, paint); //<--- line A
}

相同的结果:

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但是对于后面的代码 fragment ，只要你滚动 ScrollView (我在下面有不可见的虚拟 View 所以我可以滚动) 和helloworld 触摸 ActionBar，发生了一些非常有趣的事情，你看到了 intelligent humankind used to see in old Windows OS 的东西.

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我知道硬件加速模式不支持 drawTextOnPath()，但为什么先调用它就可以工作？

Answer 1

drawTextOnPath() Android 4.1后支持硬件加速这在此处正式提到:https://code.google.com/p/android/issues/detail?id=37925但下一条评论似乎在某种程度上表明了你的问题，所以可能是一个错误。

当然，对于 4.1 之前的版本，只是不要让它使用 HW accel - 通过调用 View.setLayerType(View.LAYER_TYPE_SOFTWARE, null) 在您的 View 上设置软件层类型，并尝试权衡性能与错误