objective-c - CABasicAnimation - 设置起始笔画位置

Question

我正在为基本圆的绘图制作动画。这工作正常，除了动画开始绘制在 3 点钟的位置。有谁知道我怎样才能让它在 12 点开始？

self.circle = [CAShapeLayer layer];
self.circle.fillColor = nil;
self.circle.lineWidth = 7;
self.circle.strokeColor = [UIColor blackColor].CGColor;
self.circle.bounds = CGRectMake(0, 0, 200, 200);
self.circle.path = [UIBezierPath bezierPathWithOvalInRect:self.circle.bounds].CGPath;
[self.view.layer addSublayer:self.circle];

CABasicAnimation *drawAnimation = [CABasicAnimation animationWithKeyPath:@"strokeEnd"];
drawAnimation.duration            = 5.0;
drawAnimation.repeatCount         = 1.0;
drawAnimation.removedOnCompletion = NO;
drawAnimation.fromValue = [NSNumber numberWithFloat:0.0f];
drawAnimation.toValue   = [NSNumber numberWithFloat:1.0f];
drawAnimation.timingFunction = [CAMediaTimingFunction functionWithName:kCAMediaTimingFunctionEaseIn];
[self.circle addAnimation:drawAnimation forKey:@"drawCircleAnimation"];

Answer 1

您可以使用 bezierPathWithArcCenter 而不是 bezierPathWithOvalInRect，因为这样可以指定开始和结束角度:

CGFloat radius = self.circle.bounds.size.width/2; // Assuming that width == height
self.circle.path = [UIBezierPath bezierPathWithArcCenter:CGPointMake(radius, radius)
                                                  radius:radius
                                              startAngle:(-M_PI/2)
                                                endAngle:(3*M_PI/2)
                                               clockwise:YES].CGPath;

参见 bezierPathWithArcCenter角度含义的文档。