流程图

屏幕快照 2017-05-10 17.10.38.png

- (void)_updateSource {
    switch (_type) {
        case YYImageTypeWebP: {
            [self _updateSourceWebP];
        } break;
            
        case YYImageTypePNG: {
            [self _updateSourceAPNG];
        } break;
            
        default: {
            [self _updateSourceImageIO];
        } break;
    }
}

一、 研究一下_updateSourceImageIO

- (void)_updateSourceImageIO {
    _width = 0;
    _height = 0;
    _orientation = UIImageOrientationUp;
    _loopCount = 0;
    dispatch_semaphore_wait(_framesLock, DISPATCH_TIME_FOREVER);
    _frames = nil;
    dispatch_semaphore_signal(_framesLock);
    /*
     * 加载动态图资源
     * CGImageSourceCreateWithData 需传入data
     * CGImageSourceCreateIncremental 不需要先传入data 创建后可以使用
       CGImageSourceUpdateData 更新
     */
    if (!_source) {
        if (_finalized) {
            _source = CGImageSourceCreateWithData((__bridge CFDataRef)_data, NULL);
        } else {
            _source = CGImageSourceCreateIncremental(NULL);
            if (_source) CGImageSourceUpdateData(_source, (__bridge CFDataRef)_data, false);
        }
    } else {
        CGImageSourceUpdateData(_source, (__bridge CFDataRef)_data, _finalized);
    }
    if (!_source) return;
    /* 
     * CGImageSourceGetCount获取动图图中资源个数
     */
    _frameCount = CGImageSourceGetCount(_source);
    if (_frameCount == 0) return;
    
    if (!_finalized) { // ignore multi-frame before finalized
        _frameCount = 1;
    } else {
        if (_type == YYImageTypePNG) { // use custom apng decoder and ignore multi-frame
            _frameCount = 1;
        }
        if (_type == YYImageTypeGIF) { // get gif loop count
        /*
         * CGImageSourceCopyProperties 返回图片资源的属性列表
         * CFDictionaryGetValue 找到对应key的value
         */
            CFDictionaryRef properties = CGImageSourceCopyProperties(_source, NULL);
            if (properties) {
                CFDictionaryRef gif = CFDictionaryGetValue(properties, kCGImagePropertyGIFDictionary);
                if (gif) {
                    CFTypeRef loop = CFDictionaryGetValue(gif, kCGImagePropertyGIFLoopCount);
                    if (loop) CFNumberGetValue(loop, kCFNumberNSIntegerType, &_loopCount);
                }
                CFRelease(properties);
            }
        }
    }
    
    /*
     ICO, GIF, APNG may contains multi-frame.
     */
    NSMutableArray *frames = [NSMutableArray new];
    for (NSUInteger i = 0; i < _frameCount; i++) {
        _YYImageDecoderFrame *frame = [_YYImageDecoderFrame new];
        frame.index = i;
        frame.blendFromIndex = i;
        frame.hasAlpha = YES;
        frame.isFullSize = YES;
        [frames addObject:frame];
        
        CFDictionaryRef properties = CGImageSourceCopyPropertiesAtIndex(_source, i, NULL);
        if (properties) {
            NSTimeInterval duration = 0;
            NSInteger orientationValue = 0, width = 0, height = 0;
            CFTypeRef value = NULL;
            
            value = CFDictionaryGetValue(properties, kCGImagePropertyPixelWidth);
            if (value) CFNumberGetValue(value, kCFNumberNSIntegerType, &width);
            value = CFDictionaryGetValue(properties, kCGImagePropertyPixelHeight);
            if (value) CFNumberGetValue(value, kCFNumberNSIntegerType, &height);
            if (_type == YYImageTypeGIF) {
                CFDictionaryRef gif = CFDictionaryGetValue(properties, kCGImagePropertyGIFDictionary);
                if (gif) {
                    // Use the unclamped frame delay if it exists.
                    value = CFDictionaryGetValue(gif, kCGImagePropertyGIFUnclampedDelayTime);
                    if (!value) {
                        // Fall back to the clamped frame delay if the unclamped frame delay does not exist.
                        value = CFDictionaryGetValue(gif, kCGImagePropertyGIFDelayTime);
                    }
                    if (value) CFNumberGetValue(value, kCFNumberDoubleType, &duration);
                }
            }
            
            frame.width = width;
            frame.height = height;
            frame.duration = duration;
            
            if (i == 0 && _width + _height == 0) { // init first frame
                _width = width;
                _height = height;
                value = CFDictionaryGetValue(properties, kCGImagePropertyOrientation);
                if (value) {
                    CFNumberGetValue(value, kCFNumberNSIntegerType, &orientationValue);
                    _orientation = YYUIImageOrientationFromEXIFValue(orientationValue);
                }
            }
            CFRelease(properties);
        }
    }
    dispatch_semaphore_wait(_framesLock, DISPATCH_TIME_FOREVER);
    _frames = frames;
    dispatch_semaphore_signal(_framesLock);
}

二、Image传入ImageView
1、 imageChanged

- (void)imageChanged {
    YYAnimatedImageType newType = [self currentImageType];
    /*
     * 获取当前YYImage
     * 找到所有帧数
     * 初始化参数
     */
    id newVisibleImage = [self imageForType:newType];
    NSUInteger newImageFrameCount = 0;
    BOOL hasContentsRect = NO;
    if ([newVisibleImage isKindOfClass:[UIImage class]] &&
        [newVisibleImage conformsToProtocol:@protocol(YYAnimatedImage)]) {
        newImageFrameCount = ((UIImage<YYAnimatedImage> *) newVisibleImage).animatedImageFrameCount;
        if (newImageFrameCount > 1) {
            hasContentsRect = [((UIImage<YYAnimatedImage> *) newVisibleImage) respondsToSelector:@selector(animatedImageContentsRectAtIndex:)];
        }
    }
    if (!hasContentsRect && _curImageHasContentsRect) {
        if (!CGRectEqualToRect(self.layer.contentsRect, CGRectMake(0, 0, 1, 1)) ) {
            [CATransaction begin];
            [CATransaction setDisableActions:YES];
            self.layer.contentsRect = CGRectMake(0, 0, 1, 1);
            [CATransaction commit];
        }
    }
    _curImageHasContentsRect = hasContentsRect;
    if (hasContentsRect) {
        CGRect rect = [((UIImage<YYAnimatedImage> *) newVisibleImage) animatedImageContentsRectAtIndex:0];
        [self setContentsRect:rect forImage:newVisibleImage];
    }
    
    if (newImageFrameCount > 1) {
        [self resetAnimated];
        _curAnimatedImage = newVisibleImage;
        _curFrame = newVisibleImage;
        _totalLoop = _curAnimatedImage.animatedImageLoopCount;
        _totalFrameCount = _curAnimatedImage.animatedImageFrameCount;
        //计算内存
        [self calcMaxBufferCount];
    }
    [self setNeedsDisplay];
    [self didMoved];
}

2、 resetAnimated

// init the animated params.
/*
 * 初始化动画
 */
- (void)resetAnimated {
    dispatch_once(&_onceToken, ^{
        _lock = dispatch_semaphore_create(1);
        _buffer = [NSMutableDictionary new];
        _requestQueue = [[NSOperationQueue alloc] init];
        _requestQueue.maxConcurrentOperationCount = 1;
        _link = [CADisplayLink displayLinkWithTarget:[YYWeakProxy proxyWithTarget:self] selector:@selector(step:)];
        if (_runloopMode) {
            [_link addToRunLoop:[NSRunLoop mainRunLoop] forMode:_runloopMode];
        }
        _link.paused = YES;
        
        [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(didReceiveMemoryWarning:) name:UIApplicationDidReceiveMemoryWarningNotification object:nil];
        [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(didEnterBackground:) name:UIApplicationDidEnterBackgroundNotification object:nil];
    });
    
    [_requestQueue cancelAllOperations];
    LOCK(
         if (_buffer.count) {
             NSMutableDictionary *holder = _buffer;
             _buffer = [NSMutableDictionary new];
             dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_LOW, 0), ^{
                 // Capture the dictionary to global queue,
                 // release these images in background to avoid blocking UI thread.
                 [holder class];
             });
         }
    );
    _link.paused = YES;
    _time = 0;
    if (_curIndex != 0) {
        [self willChangeValueForKey:@"currentAnimatedImageIndex"];
        _curIndex = 0;
        [self didChangeValueForKey:@"currentAnimatedImageIndex"];
    }
    _curAnimatedImage = nil;
    _curFrame = nil;
    _curLoop = 0;
    _totalLoop = 0;
    _totalFrameCount = 1;
    _loopEnd = NO;
    _bufferMiss = NO;
    _incrBufferCount = 0;
}

3、 step 核心方法

- (void)step:(CADisplayLink *)link {
    //当前image
    UIImage <YYAnimatedImage> *image = _curAnimatedImage;
    //存储的是{@(index):image}每一帧的索引以及对应image
    NSMutableDictionary *buffer = _buffer;
    UIImage *bufferedImage = nil;
    NSUInteger nextIndex = (_curIndex + 1) % _totalFrameCount;
    BOOL bufferIsFull = NO;
    
    if (!image) return;
    if (_loopEnd) { // view will keep in last frame
        [self stopAnimating];
        return;
    }
    
    NSTimeInterval delay = 0;
    if (!_bufferMiss) {
    //对于每次切换帧的控制
        _time += link.duration;
        delay = [image animatedImageDurationAtIndex:_curIndex];
        if (_time < delay) return;
        _time -= delay;
        if (nextIndex == 0) {
            _curLoop++;
            if (_curLoop >= _totalLoop && _totalLoop != 0) {
                _loopEnd = YES;
                [self stopAnimating];
                [self.layer setNeedsDisplay]; // let system call `displayLayer:` before runloop sleep
                return; // stop at last frame
            }
        }
        delay = [image animatedImageDurationAtIndex:nextIndex];
        if (_time > delay) _time = delay; // do not jump over frame
    }
    LOCK(
         bufferedImage = buffer[@(nextIndex)];
         if (bufferedImage) {
             if ((int)_incrBufferCount < _totalFrameCount) {
                 [buffer removeObjectForKey:@(nextIndex)];
             }
             [self willChangeValueForKey:@"currentAnimatedImageIndex"];
             _curIndex = nextIndex;
             [self didChangeValueForKey:@"currentAnimatedImageIndex"];
             _curFrame = bufferedImage == (id)[NSNull null] ? nil : bufferedImage;
             if (_curImageHasContentsRect) {
                 _curContentsRect = [image animatedImageContentsRectAtIndex:_curIndex];
                 [self setContentsRect:_curContentsRect forImage:_curFrame];
             }
             nextIndex = (_curIndex + 1) % _totalFrameCount;
             _bufferMiss = NO;
             if (buffer.count == _totalFrameCount) {
                 bufferIsFull = YES;
             }
         } else {
             _bufferMiss = YES;
         }
    )//LOCK
    
    if (!_bufferMiss) {
        [self.layer setNeedsDisplay]; // let system call `displayLayer:` before runloop sleep
    }
    
    if (!bufferIsFull && _requestQueue.operationCount == 0) { // if some work not finished, wait for next opportunity
    //获取buffer数据
        _YYAnimatedImageViewFetchOperation *operation = [_YYAnimatedImageViewFetchOperation new];
        operation.view = self;
        operation.nextIndex = nextIndex;
        operation.curImage = image;
        [_requestQueue addOperation:operation];
    }
}