iOS可以通过CADisplayLink实现自定义动画引擎，pop就是基于此实现的，而且比原生Core Animation更强大好用。譬如当ViewController侧滑返回的时候，系统会将Core Animation的动画会停止，而基于CADisplayLink实现的动画则不会停止，因而可以实现类似网易云音乐从播放页侧滑时hold住专辑封面图旋转的效果。
八一八魔性的pop
1、实用的宏
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#define POP_ARRAY_COUNT(x) sizeof(x) / sizeof(x[0])#define FB_PROPERTY_GET(stype, property, ctype) - (ctype)property { return ((stype *)_state)->property; }#define FB_PROPERTY_SET(stype, property, mutator, ctype, ...) - (void)mutator (ctype)value { if (value == ((stype *)_state)->property) return; ((stype *)_state)->property = value; __VA_ARGS__ }#define FB_PROPERTY_SET_OBJ_COPY(stype, property, mutator, ctype, ...) - (void)mutator (ctype)value { if (value == ((stype *)_state)->property) return; ((stype *)_state)->property = [value copy]; __VA_ARGS__ } |
2、判定值的数据类型
pop定义了支持的值的数据类型
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const POPValueType kPOPAnimatableSupportTypes[10] = {kPOPValueInteger, kPOPValueFloat, kPOPValuePoint, kPOPValueSize, kPOPValueRect, kPOPValueEdgeInsets, kPOPValueColor, kPOPValueSCNVector3, kPOPValueSCNVector4}; |
通过@encode指令，将给定类型编码的内部字符串与objcType对比，得到值的数据类型
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static bool FBCompareTypeEncoding(const char *objctype, POPValueType type){ switch (type) { case kPOPValueFloat: return (strcmp(objctype, @encode(float)) == 0 || strcmp(objctype, @encode(double)) == 0 ); case kPOPValuePoint: return (strcmp(objctype, @encode(CGPoint)) == 0#if !TARGET_OS_IPHONE || strcmp(objctype, @encode(NSPoint)) == 0#endif ); case kPOPValueSize: return (strcmp(objctype, @encode(CGSize)) == 0#if !TARGET_OS_IPHONE || strcmp(objctype, @encode(NSSize)) == 0#endif ); case kPOPValueRect: return (strcmp(objctype, @encode(CGRect)) == 0#if !TARGET_OS_IPHONE || strcmp(objctype, @encode(NSRect)) == 0#endif ); case kPOPValueEdgeInsets:#if TARGET_OS_IPHONE return strcmp(objctype, @encode(UIEdgeInsets)) == 0;#else return false;#endif case kPOPValueAffineTransform: return strcmp(objctype, @encode(CGAffineTransform)) == 0; case kPOPValueTransform: return strcmp(objctype, @encode(CATransform3D)) == 0; case kPOPValueRange: return strcmp(objctype, @encode(CFRange)) == 0 || strcmp(objctype, @encode (NSRange)) == 0; case kPOPValueInteger: return (strcmp(objctype, @encode(int)) == 0 || strcmp(objctype, @encode(unsigned int)) == 0 || strcmp(objctype, @encode(short)) == 0 || strcmp(objctype, @encode(unsigned short)) == 0 || strcmp(objctype, @encode(long)) == 0 || strcmp(objctype, @encode(unsigned long)) == 0 || strcmp(objctype, @encode(long long)) == 0 || strcmp(objctype, @encode(unsigned long long)) == 0 ); case kPOPValueSCNVector3:#if SCENEKIT_SDK_AVAILABLE return strcmp(objctype, @encode(SCNVector3)) == 0;#else return false;#endif case kPOPValueSCNVector4:#if SCENEKIT_SDK_AVAILABLE return strcmp(objctype, @encode(SCNVector4)) == 0;#else return false;#endif default: return false; }} |
3、将值的数据类型标准化为Vector
举个CGRect类型的例子：
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case kPOPValueRect: vec = Vector::new_cg_rect([value CGRectValue]); Vector *Vector::new_cg_rect(const CGRect &r) { Vector *v = new Vector(4); v->_values[0] = r.origin.x; v->_values[1] = r.origin.y; v->_values[2] = r.size.width; v->_values[3] = r.size.height; return v; } |
通过Vector的两个参数size_t _count;、CGFloat *_values;将给定的类型抽象出来，实现解耦。此外还有一个好处，当创建属性动画为kPOPLayerBounds，但toValue属性赋值的是一个NSNumber，得益于_values是数组指针，并不会引发数组越界导致的crash，只是动画效果不可预期。
4、基于NSRunLoop的动画更新机制
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- (void)_scheduleProcessPendingList{ // see WebKit for magic numbers, eg http://trac.webkit.org/changeset/166540 static const CFIndex CATransactionCommitRunLoopOrder = 2000000; static const CFIndex POPAnimationApplyRunLoopOrder = CATransactionCommitRunLoopOrder - 1; // lock OSSpinLockLock(&_lock); if (!_pendingListObserver) { __weak POPAnimator *weakSelf = self; _pendingListObserver = CFRunLoopObserverCreateWithHandler(kCFAllocatorDefault, kCFRunLoopBeforeWaiting | kCFRunLoopExit, false, POPAnimationApplyRunLoopOrder, ^(CFRunLoopObserverRef observer, CFRunLoopActivity activity) { [weakSelf _processPendingList]; }); if (_pendingListObserver) { CFRunLoopAddObserver(CFRunLoopGetMain(), _pendingListObserver, kCFRunLoopCommonModes); } } // unlock OSSpinLockUnlock(&_lock);} |
在主线程RunLoop中添加观察者，监听了kCFAllocatorDefault、kCFRunLoopBeforeWaiting、kCFRunLoopExit事件，在收到回调的时候，处理_pendingList里的动画。
5、更新动画的回调数组
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static POPStaticAnimatablePropertyState _staticStates[] ={ /* CALayer */ {kPOPLayerBackgroundColor, ^(CALayer *obj, CGFloat values[]) { POPCGColorGetRGBAComponents(obj.backgroundColor, values); }, ^(CALayer *obj, const CGFloat values[]) { CGColorRef color = POPCGColorRGBACreate(values); [obj setBackgroundColor:color]; CGColorRelease(color); }, kPOPThresholdColor }, {kPOPLayerBounds, ^(CALayer *obj, CGFloat values[]) { values_from_rect(values, [obj bounds]); }, ^(CALayer *obj, const CGFloat values[]) { [obj setBounds:values_to_rect(values)]; }, kPOPThresholdPoint },... |
封装不同的动画行为，实现类似模板模式，只需统一调用，即可更新动画
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// write valuewrite(obj, currentVec->data()); |
6、动画插值的动态实现
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switch (type) { case kPOPAnimationSpring: advanced = advance(time, dt, obj); break; case kPOPAnimationDecay: advanced = advance(time, dt, obj); break; case kPOPAnimationBasic: { advanced = advance(time, dt, obj); computedProgress = true; break; } case kPOPAnimationCustom: { customFinished = [self _advance:obj currentTime:time elapsedTime:dt] ? false : true; advanced = true; break; } default: break; } |
可以看出总共有四种动画插值的算法，以kPOPAnimationBasic为例：
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bool advance(CFTimeInterval time, CFTimeInterval dt, id obj) { // default timing function if (!timingFunction) { ((POPBasicAnimation *)self).timingFunction = [CAMediaTimingFunction functionWithName:kCAMediaTimingFunctionDefault]; } // solve for normalized time, aka progresss [0, 1] CGFloat p = 1.0f; if (duration > 0.0f) { // cap local time to duration CFTimeInterval t = MIN(time - startTime, duration) / duration; p = POPTimingFunctionSolve(timingControlPoints, t, SOLVE_EPS(duration)); timeProgress = t; } else { timeProgress = 1.; } // interpolate and advance interpolate(valueType, valueCount, fromVec->data(), toVec->data(), currentVec->data(), p); progress = p; clampCurrentValue(); return true; } |
依照给定的timingFunction，使用POPTimingFunctionSolve计算贝塞尔曲线的变化率，再通过混合计算#define MIX(a, b, f) ((a) + (f) * ((b) - (a)))，最终得到动画的插值。
小结
pop中还有很多有意思的地方，譬如TransformationMatrix里的矩阵操作，这里就暂且不挖WebCore底层了。简而言之，无论性能(c++混编)、易用、容错，pop都有着作为引擎该有的特性，而它所暴露的和Core Animation相似的接口也让人极易上手！