canvas.clipRect

clipRect(float left, float top, float right, float bottom)
Intersect the current clip with the specified rectangle, which is expressed in local coordinates.

只有在这个区域内的才显示，其他所有内容好像被裁剪掉了一样，不显示。

public void onDraw(Canvas canvas)
{
super.onDraw(canvas);
/* 设置画布的颜色 */
canvas.drawColor(Color.BLACK);
/* 设置取消锯齿效果 */
mPaint.setAntiAlias(true);
//mPaint.setStyle(Paint.Style.STROKE);
mPaint.setColor(Color.RED);
//canvas.save();
// 设置裁剪区域
//canvas.drawRect(new Rect(1, 1, 320, 400),mPaint);
canvas.clipRect(40, 40, 280, 260);
canvas.drawColor(Color.GRAY);
/* 线锁定画布 */
canvas.save();
/* 旋转画布,顺时针旋转“画布”，以左上角为圆心 */
canvas.rotate(45.0f);
//canvas.drawRect(new Rect(40, 40, 280, 260),mPaint);
/* 设置颜色及绘制矩形 */
mPaint.setColor(Color.RED);
canvas.drawRect(new Rect(45,45,140,100), mPaint);
/* 解除画布的锁定 */
canvas.restore();
/* 设置颜色及绘制另一个矩形 */
mPaint.setColor(Color.GREEN);
canvas.drawRect(new Rect(150,75,260,120), mPaint);
}

public void onDraw(Canvas canvas)
{
    super.onDraw(canvas);

    /* 设置画布的颜色 */
    canvas.drawColor(Color.BLACK);

    /* 设置取消锯齿效果 */
    mPaint.setAntiAlias(true);
    mPaint.setStyle(Paint.Style.STROKE);//空心，不填充
    mPaint.setColor(Color.RED);
    /* 线锁定画布 */
    canvas.save();
    //整个屏幕加个边框
    canvas.drawRect(new Rect(1, 1, 320, 400),mPaint);
    //这里不用clipRect，而改为drawRect，仅模拟裁剪的区域，而不真正裁剪
    canvas.drawRect(new Rect(40, 40, 280, 260),mPaint);

    /* 旋转画布 */
    canvas.rotate(45.0f);
    //旋转后的屏幕边框
    canvas.drawRect(new Rect(1, 1, 320, 400),mPaint);
    //裁剪框旋转后的weizhi
    canvas.drawRect(new Rect(40, 40, 280, 260),mPaint);

    /* 设置颜色及绘制矩形 */
    mPaint.setColor(Color.RED);
    canvas.drawRect(new Rect(45,45,140,100), mPaint);

    /* 解除画布的锁定 */
    canvas.restore();

    /* 设置颜色及绘制另一个矩形 */
    mPaint.setColor(Color.GREEN);
    canvas.drawRect(new Rect(150,75,260,120), mPaint);
}