Canvas的save和restore

在onDraw方法里，我们经常会看到调用save和restore方法，它们到底是干什么用的呢？

int px = getMeasuredWidth();
int py = getMeasuredWidth();

// Draw background
canvas.drawRect(0, 0, px, py, backgroundPaint);

canvas.save();
canvas.rotate(90, px/2, py/2);                

// Draw up arrow
canvas.drawLine(px / 2, 0, 0, py / 2, linePaint);
canvas.drawLine(px / 2, 0, px, py / 2, linePaint);
canvas.drawLine(px / 2, 0, px / 2, py, linePaint);

canvas.restore();

// Draw circle
canvas.drawCircle(px - 10, py - 10, 10, linePaint);

如果我们不调用save和restore会是什么样子呢？