YYKit探究之YYImage（一）
1.读取图片数据
+ (nullable YYImage *)imageNamed:(NSString *)name; // no cache! + (nullable YYImage *)imageWithContentsOfFile:(NSString *)path; + (nullable YYImage *)imageWithData:(NSData *)data; + (nullable YYImage *)imageWithData:(NSData *)data scale:(CGFloat)scale;
这4种类方法用于获取图片数据/路径。前三种方法的实现最后都归结为 imageWithData:(NSData *)data scale:(CGFloat)scale 这个方法。让我们看看imageWithData:(NSData *)data scale:(CGFloat)scale 这个方法的实现逻辑。
2.由实例方法演变而来。
+ (YYImage *)imageWithData:(NSData *)data scale:(CGFloat)scale { return [[self alloc] initWithData:data scale:scale]; }
具体看实例方法的逻辑。
- (instancetype)initWithData:(NSData *)data scale:(CGFloat)scale { if (data.length == 0) return nil;
//获取屏幕分辨率，传入解码decoder if (scale <= 0) scale = [UIScreen mainScreen].scale;
//创建信号量，参数：信号量的初值，如果小于0则会返回NULL，crate的value表示，最多几个资源可访问 _preloadedLock = dispatch_semaphore_create(1); @autoreleasepool {
// 解析图片数据，见2 YYImageDecoder *decoder = [YYImageDecoder decoderWithData:data scale:scale];
//对当前的图片进行解码操作，见3 YYImageFrame *frame = [decoder frameAtIndex:0 decodeForDisplay:YES];
//获取图片第一帧 UIImage *image = frame.image; if (!image) return nil;
//Image初始化 self = [self initWithCGImage:image.CGImage scale:decoder.scale orientation:image.imageOrientation]; if (!self) return nil; _animatedImageType = decoder.type;
// 动图的处理方法 if (decoder.frameCount > 1) { _decoder = decoder; _bytesPerFrame = CGImageGetBytesPerRow(image.CGImage) * CGImageGetHeight(image.CGImage); _animatedImageMemorySize = _bytesPerFrame * decoder.frameCount; } self.isDecodedForDisplay = YES; } return self; }
2.1，解析图片数据
+ (instancetype)decoderWithData:(NSData *)data scale:(CGFloat)scale { if (!data) return nil; YYImageDecoder *decoder = [[YYImageDecoder alloc] initWithScale:scale]; [decoder updateData:data final:YES]; if (decoder.frameCount == 0) return nil; return decoder; }
这一步主要看updateData里面做了什么
- (BOOL)updateData:(NSData *)data final:(BOOL)final { BOOL result = NO; //对线程上锁，此时其他线程阻塞等待该线程释放锁 pthread_mutex_lock(&_lock); //这里先判断图片格式YYImageDetectType((__bridge CFDataRef)data)，再根据格式获取图片帧 result = [self _updateData:data final:final]; // //执行完后释放锁 pthread_mutex_unlock(&_lock); return result; }
2.2.获取图片帧数据
updateData里面除了判断图片格式，是否是动图，还要更新源（可以是data，也可以是路径），下面以updataSourceAPNG为例，剖析实现过程
[self _updateSourceImageIO]; // decode first frame if (_frameCount == 0) return; // png decode failed if (!_finalized) return; // ignore multi-frame before finalized //_data.bytes 提供存储apng的内存对应的指针，获取动图的数据信息 yy_png_info *apng = yy_png_info_create(_data.bytes, (uint32_t)_data.length); if (!apng) return; // apng decode failed if (apng->apng_frame_num == 0 || (apng->apng_frame_num == 1 && apng->apng_first_frame_is_cover)) { yy_png_info_release(apng); return; // no animation } if (_source) { // apng decode succeed, no longer need image souce CFRelease(_source); _source = NULL; }
其中_data.bytes 提供存储apng的内存对应的指针，获取动图的数据信息，接下来就是对动图各个帧数据处理
uint32_t canvasWidth = apng->header.width; uint32_t canvasHeight = apng->header.height; NSMutableArray *frames = [NSMutableArray new]; BOOL needBlend = NO; uint32_t lastBlendIndex = 0;
//PNG动画的逐帧信息返回到Frames数组中 for (uint32_t i = 0; i < apng->apng_frame_num; i++) { _YYImageDecoderFrame *frame = [_YYImageDecoderFrame new]; [frames addObject:frame]; yy_png_frame_info *fi = apng->apng_frames + i; frame.index = i; frame.duration = yy_png_delay_to_seconds(fi->frame_control.delay_num, fi->frame_control.delay_den); frame.hasAlpha = YES; frame.width = fi->frame_control.width; frame.height = fi->frame_control.height; frame.offsetX = fi->frame_control.x_offset; frame.offsetY = canvasHeight - fi->frame_control.y_offset - fi->frame_control.height; BOOL sizeEqualsToCanvas = (frame.width == canvasWidth && frame.height == canvasHeight); BOOL offsetIsZero = (fi->frame_control.x_offset == 0 && fi->frame_control.y_offset == 0); frame.isFullSize = (sizeEqualsToCanvas && offsetIsZero); switch (fi->frame_control.dispose_op) { case YY_PNG_DISPOSE_OP_BACKGROUND: { frame.dispose = YYImageDisposeBackground; } break; case YY_PNG_DISPOSE_OP_PREVIOUS: { frame.dispose = YYImageDisposePrevious; } break; default: { frame.dispose = YYImageDisposeNone; } break; } switch (fi->frame_control.blend_op) { case YY_PNG_BLEND_OP_OVER: { frame.blend = YYImageBlendOver; } break; default: { frame.blend = YYImageBlendNone; } break; } if (frame.blend == YYImageBlendNone && frame.isFullSize) { frame.blendFromIndex = i; if (frame.dispose != YYImageDisposePrevious) lastBlendIndex = i; } else { if (frame.dispose == YYImageDisposeBackground && frame.isFullSize) { frame.blendFromIndex = lastBlendIndex; lastBlendIndex = i + 1; } else { frame.blendFromIndex = lastBlendIndex; } } if (frame.index != frame.blendFromIndex) needBlend = YES; } _width = canvasWidth; _height = canvasHeight; _frameCount = frames.count; _loopCount = apng->apng_loop_num; _needBlend = needBlend; _apngSource = apng; dispatch_semaphore_wait(_framesLock, DISPATCH_TIME_FOREVER); _frames = frames; dispatch_semaphore_signal(_framesLock); }
3.各个帧数据进行解码和显示，获取imageRef的步骤如3.1所示
//解码，从GPU中拿到imageRef CGImageRef imageRef = [self _newUnblendedImageAtIndex:index extendToCanvas:extendToCanvas decoded:&decoded]; if (!imageRef) return nil; if (decodeForDisplay && !decoded) { CGImageRef imageRefDecoded = YYCGImageCreateDecodedCopy(imageRef, YES); if (imageRefDecoded) { CFRelease(imageRef); imageRef = imageRefDecoded; decoded = YES; } }
//获取当前帧 UIImage *image = [UIImage imageWithCGImage:imageRef scale:_scale orientation:_orientation]; CFRelease(imageRef); if (!image) return nil; image.isDecodedForDisplay = decoded; frame.image = image; return frame;
3.1，获取imageRef
//开始解码 CGImageRef imageRef = CGImageSourceCreateImageAtIndex(_source, index, (CFDictionaryRef)@{(id)kCGImageSourceShouldCache:@(YES)}); if (imageRef && extendToCanvas) { size_t width = CGImageGetWidth(imageRef); size_t height = CGImageGetHeight(imageRef); if (width == _width && height == _height) { CGImageRef imageRefExtended = YYCGImageCreateDecodedCopy(imageRef, YES); if (imageRefExtended) { CFRelease(imageRef); imageRef = imageRefExtended; if (decoded) *decoded = YES; } } else { //没有就绘制 CGContextRef context = CGBitmapContextCreate(NULL, _width, _height, 8, 0, YYCGColorSpaceGetDeviceRGB(), kCGBitmapByteOrder32Host | kCGImageAlphaPremultipliedFirst); if (context) { //获取像素信息 CGContextDrawImage(context, CGRectMake(0, _height - height, width, height), imageRef); CGImageRef imageRefExtended = CGBitmapContextCreateImage(context); CFRelease(context); if (imageRefExtended) { CFRelease(imageRef); imageRef = imageRefExtended; if (decoded) *decoded = YES; } } } } return imageRef;
YYImage处理图片流程
1.用imageWithData:(NSData *)data scale:(CGFloat)scale获取图片源数据。
2.解析图片数据，分为两步，判断图片格式（如果是动图，就开启loop），以及返回当前帧的信息yy_png_info_create(_data.bytes, (uint32_t)_data.length)。
3.根据帧信息开始解码CGImageSourceCreateImageAtIndex，并展示出来。
