YYImage源码浅析
2019-11-07 本文已影响0人
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简介
YYImage是与UIImage完全兼容的子类,YYImage扩展了UIImage使其支持WebP,GIF,APNG图片数据的解码.它也支持NSCoding协议来进行归解档.
YYImage的接口
@interface YYImage : UIImage <YYAnimatedImage>
//使用图片名称加载图片,此方法不会缓存图片
+ (nullable YYImage *)imageNamed:(NSString *)name;
//使用图片路径加载图片
+ (nullable YYImage *)imageWithContentsOfFile:(NSString *)path;
//使用NSData加载图片
+ (nullable YYImage *)imageWithData:(NSData *)data;
//使用NSData和图片缩放加载图片
+ (nullable YYImage *)imageWithData:(NSData *)data scale:(CGFloat)scale;
//图片的类型
@property (nonatomic, readonly) YYImageType animatedImageType;
//原始带动画的图片的数据
@property (nullable, nonatomic, readonly) NSData *animatedImageData;
//多帧图片数据所占用的内存,如果不是由多帧图片数据创建则返回0
@property (nonatomic, readonly) NSUInteger animatedImageMemorySize;
//是否预加载所有的帧
@property (nonatomic) BOOL preloadAllAnimatedImageFrames;
@end
创建方法
- (instancetype)initWithData:(NSData *)data scale:(CGFloat)scale {
//数据合理性检查
if (data.length == 0) return nil;
if (scale <= 0) scale = [UIScreen mainScreen].scale;
//加锁
_preloadedLock = dispatch_semaphore_create(1);
@autoreleasepool {
//创建图片解码器
YYImageDecoder *decoder = [YYImageDecoder decoderWithData:data scale:scale];
//解码出图片数据
YYImageFrame *frame = [decoder frameAtIndex:0 decodeForDisplay:YES];
UIImage *image = frame.image;
if (!image) return nil;
// 实例化自身
self = [self initWithCGImage:image.CGImage scale:decoder.scale orientation:image.imageOrientation];
if (!self) return nil;
//存储图片类型信息
_animatedImageType = decoder.type;
if (decoder.frameCount > 1) {
//当有多帧时复用解码器
_decoder = decoder;
//每帧大小
_bytesPerFrame = CGImageGetBytesPerRow(image.CGImage) * CGImageGetHeight(image.CGImage);
//多帧图片的总大小
_animatedImageMemorySize = _bytesPerFrame * decoder.frameCount;
}
//标记解码成功
self.isDecodedForDisplay = YES;
}
return self;
}
从源码可知,YYImage主要调用YYImageDecoder来获取图片相关信息.
YYImageDecoder
YYImageDecoder是线程安全的图片解码器,支持的格式有PNG, JPG, JP2, BMP, TIFF, PIC, ICNS 和ICO.可以用来解码完整的图片数据也可以用来增量地解码数据.
YYImageDecoder接口:
@interface YYImageDecoder : NSObject
//图片二进制数据
@property (nullable, nonatomic, readonly) NSData *data;
//图片类型.png,jpeg,webP,gif...
@property (nonatomic, readonly) YYImageType type;
//图片缩放比率
@property (nonatomic, readonly) CGFloat scale;
//图片帧数
@property (nonatomic, readonly) NSUInteger frameCount;
//图片循环数,0是无限循环
@property (nonatomic, readonly) NSUInteger loopCount;
//图片宽度
@property (nonatomic, readonly) NSUInteger width;
//图片高度
@property (nonatomic, readonly) NSUInteger height;
//是否解码完成
@property (nonatomic, readonly, getter=isFinalized) BOOL finalized;
//使用图片缩放比率初始化
- (instancetype)initWithScale:(CGFloat)scale;
//使用累计数据更新图片
- (BOOL)updateData:(nullable NSData *)data final:(BOOL)final;
//使用图片数据和缩放比率初始化
+ (nullable instancetype)decoderWithData:(NSData *)data scale:(CGFloat)scale;
//解码一帧图片,decodeForDisplay 为YES时会解码为bitmap以供显示
- (nullable YYImageFrame *)frameAtIndex:(NSUInteger)index decodeForDisplay:(BOOL)decodeForDisplay;
//获取某一帧的持续时长
- (NSTimeInterval)frameDurationAtIndex:(NSUInteger)index;
//获取图片的属性
- (nullable NSDictionary *)imageProperties;
@end
初始化
- (instancetype)initWithScale:(CGFloat)scale {
self = [super init];
if (scale <= 0) scale = 1;
//保存缩放比例
_scale = scale;
//创建两个锁
_framesLock = dispatch_semaphore_create(1);
pthread_mutex_init_recursive(&_lock, true);
return self;
}
+ (instancetype)decoderWithData:(NSData *)data scale:(CGFloat)scale {
if (!data) return nil;
//调用实例初始化方法
YYImageDecoder *decoder = [[YYImageDecoder alloc] initWithScale:scale];
//添加待解码数据
[decoder updateData:data final:YES];
if (decoder.frameCount == 0) return nil;
return decoder;
}
添加数据及解码
//更新待解码数据
- (BOOL)updateData:(NSData *)data final:(BOOL)final {
BOOL result = NO;
//加锁
pthread_mutex_lock(&_lock);
//调用私有实现方法
result = [self _updateData:data final:final];
pthread_mutex_unlock(&_lock);
return result;
}
//私有更新待解码数据
- (BOOL)_updateData:(NSData *)data final:(BOOL)final {
//如果已经结束则直接返回
if (_finalized) return NO;
//不是增量解码,直接返回
if (data.length < _data.length) return NO;
_finalized = final;
_data = data;
//获取图片类型
YYImageType type = YYImageDetectType((__bridge CFDataRef)data);
//如果已经解析过图片类型
if (_sourceTypeDetected) {
if (_type != type) {
//与之前解析出来图片类型不一致,直接返回失败
return NO;
} else {
//调用私有更新资源方法
[self _updateSource];
}
} else {
//图片数据长度大于16的情况下才能解析出图片类型
if (_data.length > 16) {
_type = type;
//已经解析过图片类型
_sourceTypeDetected = YES;
//调用私有更新资源方法
[self _updateSource];
}
}
return YES;
}
//私有更新资源方法
- (void)_updateSource {
//解析不同的图片类型,调用私有特定类型的更新数据方法
switch (_type) {
case YYImageTypeWebP: {
//更新WebP资源
[self _updateSourceWebP];
} break;
case YYImageTypePNG: {
//更新PNG资源
[self _updateSourceAPNG];
} break;
default: {
//更新其他类型
[self _updateSourceImageIO];
} break;
}
}
//更新WebP资源
- (void)_updateSourceWebP {
#if YYIMAGE_WEBP_ENABLED
//初始化数据
_width = 0;
_height = 0;
_loopCount = 0;
//清除之前解码过得webp数据
if (_webpSource) WebPDemuxDelete(_webpSource);
_webpSource = NULL;
//清除解码过的帧
dispatch_semaphore_wait(_framesLock, DISPATCH_TIME_FOREVER);
_frames = nil;
dispatch_semaphore_signal(_framesLock);
// 以WebP开头的都是goole WebP.framework中的数据结构和方法
//构造WebP类型数据
WebPData webPData = {0};
webPData.bytes = _data.bytes;
webPData.size = _data.length;
//解析WebP数据解码器
WebPDemuxer *demuxer = WebPDemux(&webPData);
//解析失败直接return
if (!demuxer) return;
//获取帧数信息
uint32_t webpFrameCount = WebPDemuxGetI(demuxer, WEBP_FF_FRAME_COUNT);
//获取循环次数信息
uint32_t webpLoopCount = WebPDemuxGetI(demuxer, WEBP_FF_LOOP_COUNT);
//获取图片宽度
uint32_t canvasWidth = WebPDemuxGetI(demuxer, WEBP_FF_CANVAS_WIDTH);
//获取图片高度
uint32_t canvasHeight = WebPDemuxGetI(demuxer, WEBP_FF_CANVAS_HEIGHT);
//图片信息合理性判断
if (webpFrameCount == 0 || canvasWidth < 1 || canvasHeight < 1) {
//释放内存
WebPDemuxDelete(demuxer);
return;
}
//创建帧数组
NSMutableArray *frames = [NSMutableArray new];
BOOL needBlend = NO;
uint32_t iterIndex = 0;
uint32_t lastBlendIndex = 0;
//创建迭代器
WebPIterator iter = {0};
//获取第一帧成功
if (WebPDemuxGetFrame(demuxer, 1, &iter)) { // one-based index...
do {
//创建YY帧对象
_YYImageDecoderFrame *frame = [_YYImageDecoderFrame new];
//添加到帧数组中
[frames addObject:frame];
//设置帧的绘制方式
if (iter.dispose_method == WEBP_MUX_DISPOSE_BACKGROUND) {
frame.dispose = YYImageDisposeBackground;
}
//设置混合模式
if (iter.blend_method == WEBP_MUX_BLEND) {
frame.blend = YYImageBlendOver;
}
//获取画布宽度
int canvasWidth = WebPDemuxGetI(demuxer, WEBP_FF_CANVAS_WIDTH);
//获取画布高度
int canvasHeight = WebPDemuxGetI(demuxer, WEBP_FF_CANVAS_HEIGHT);
//把获取到的帧数据赋值给_YYImageDecoderFrame
frame.index = iterIndex;
frame.duration = iter.duration / 1000.0;
frame.width = iter.width;
frame.height = iter.height;
frame.hasAlpha = iter.has_alpha;
frame.blend = iter.blend_method == WEBP_MUX_BLEND;
frame.offsetX = iter.x_offset;
frame.offsetY = canvasHeight - iter.y_offset - iter.height;
BOOL sizeEqualsToCanvas = (iter.width == canvasWidth && iter.height == canvasHeight);
//判断偏移
BOOL offsetIsZero = (iter.x_offset == 0 && iter.y_offset == 0);
//判断是否尺寸读取完毕
frame.isFullSize = (sizeEqualsToCanvas && offsetIsZero);
if ((!frame.blend || !frame.hasAlpha) && frame.isFullSize) {
frame.blendFromIndex = lastBlendIndex = iterIndex;
} else {
if (frame.dispose && frame.isFullSize) {
//设置要混合的帧的索引
frame.blendFromIndex = lastBlendIndex;
lastBlendIndex = iterIndex + 1;
} else {
frame.blendFromIndex = lastBlendIndex;
}
}
if (frame.index != frame.blendFromIndex) needBlend = YES;
iterIndex++;
} while (WebPDemuxNextFrame(&iter));
//帧获取完毕释放迭代器
WebPDemuxReleaseIterator(&iter);
}
if (frames.count != webpFrameCount) {
//帧数解析不一只则直接返回
WebPDemuxDelete(demuxer);
return;
}
//更新数据
_width = canvasWidth;
_height = canvasHeight;
_frameCount = frames.count;
_loopCount = webpLoopCount;
_needBlend = needBlend;
//保存WebP解码器
_webpSource = demuxer;
//加锁
dispatch_semaphore_wait(_framesLock, DISPATCH_TIME_FOREVER);
//引用解码出的所有帧数据
_frames = frames;
dispatch_semaphore_signal(_framesLock);
#else
static const char *func = __FUNCTION__;
static const int line = __LINE__;
static dispatch_once_t onceToken;
dispatch_once(&onceToken, ^{
NSLog(@"[%s: %d] WebP is not available, check the documentation to see how to install WebP component: https://github.com/ibireme/YYImage#installation", func, line);
});
#endif
}
//解析支持动画的APNG图片
- (void)_updateSourceAPNG {
//释放之前的png数据
yy_png_info_release(_apngSource);
_apngSource = nil;
//解码第一帧
[self _updateSourceImageIO];
//解码失败返回
if (_frameCount == 0) return;
if (!_finalized) return; // ignore multi-frame before finalized
//解码PNG数据
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);
//没有动画直接返回
return;
}
if (_source) { // apng decode succeed, no longer need image souce
CFRelease(_source);
_source = NULL;
}
//获取画布宽度
uint32_t canvasWidth = apng->header.width;
//获取画布高度
uint32_t canvasHeight = apng->header.height;
//创建帧数组
NSMutableArray *frames = [NSMutableArray new];
BOOL needBlend = NO;
uint32_t lastBlendIndex = 0;
//遍历APNG的每一帧
for (uint32_t i = 0; i < apng->apng_frame_num; i++) {
//创建_YYImageDecoderFrame对象并添加到帧数组
_YYImageDecoderFrame *frame = [_YYImageDecoderFrame new];
[frames addObject:frame];
//取出一帧数据
yy_png_frame_info *fi = apng->apng_frames + i;
//为_YYImageDecoderFrame 对象设置信息
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);
//设置帧的绘制方式
switch (fi->frame_control.dispose_op) {
case YY_PNG_DISPOSE_OP_BACKGROUND: {
//绘制下一帧前,清空画布
frame.dispose = YYImageDisposeBackground;
} break;
case YY_PNG_DISPOSE_OP_PREVIOUS: {
//绘制下一帧前,保存画布之前的状态
frame.dispose = YYImageDisposePrevious;
} break;
default: {
//绘制下一帧前,does nothing
frame.dispose = YYImageDisposeNone;
} break;
}
//设置混合方式
switch (fi->frame_control.blend_op) {
case YY_PNG_BLEND_OP_OVER: {
//基于alpha混合
frame.blend = YYImageBlendOver;
} break;
default: {
//覆盖
frame.blend = YYImageBlendNone;
} break;
}
if (frame.blend == YYImageBlendNone && frame.isFullSize) {
frame.blendFromIndex = i;
if (frame.dispose != YYImageDisposePrevious) lastBlendIndex = i;
} else {
//设置要混合的帧索引
if (frame.dispose == YYImageDisposeBackground && frame.isFullSize) {
frame.blendFromIndex = lastBlendIndex;
lastBlendIndex = i + 1;
} else {
frame.blendFromIndex = lastBlendIndex;
}
}
//是否需要混合
if (frame.index != frame.blendFromIndex) needBlend = YES;
}
//保存信息
_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);
}
//使用ImageIO解码
- (void)_updateSourceImageIO {
//清空之前的信息
_width = 0;
_height = 0;
_orientation = UIImageOrientationUp;
_loopCount = 0;
dispatch_semaphore_wait(_framesLock, DISPATCH_TIME_FOREVER);
_frames = nil;
dispatch_semaphore_signal(_framesLock);
//当_sourcesource不存在时创建_source对象
if (!_source) {
if (_finalized) {
//创建CGImageSourceRef 对象
_source = CGImageSourceCreateWithData((__bridge CFDataRef)_data, NULL);
} else {
//创建CGImageSourceRef 对象for 增量渲染
_source = CGImageSourceCreateIncremental(NULL);
if (_source) CGImageSourceUpdateData(_source, (__bridge CFDataRef)_data, false);
}
} else {
//_source存在直接更新数据
CGImageSourceUpdateData(_source, (__bridge CFDataRef)_data, _finalized);
}
//_source创建失败直接返回
if (!_source) return;
//获取图片帧数
_frameCount = CGImageSourceGetCount(_source);
if (_frameCount == 0) return;
//处理需要忽略多帧的情况
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
CFDictionaryRef properties = CGImageSourceCopyProperties(_source, NULL);
if (properties) {
//获取GIF图片信息
CFDictionaryRef gif = CFDictionaryGetValue(properties, kCGImagePropertyGIFDictionary);
if (gif) {
CFTypeRef loop = CFDictionaryGetValue(gif, kCGImagePropertyGIFLoopCount);
//获取GIF图片循环次数
if (loop) CFNumberGetValue(loop, kCFNumberNSIntegerType, &_loopCount);
}
//释放资源
CFRelease(properties);
}
}
}
/*
ICO, GIF, APNG may contains multi-frame.
*/
//创建帧数组
NSMutableArray *frames = [NSMutableArray new];
//遍历每一帧
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];
//获取图片信息
CFDictionaryRef properties = CGImageSourceCopyPropertiesAtIndex(_source, i, NULL);
if (properties) {
NSTimeInterval duration = 0;
NSInteger orientationValue = 0, width = 0, height = 0;
CFTypeRef value = NULL;
//获取像素宽度
value = CFDictionaryGetValue(properties, kCGImagePropertyPixelWidth);
if (value) CFNumberGetValue(value, kCFNumberNSIntegerType, &width);
//获取像素高度
value = CFDictionaryGetValue(properties, kCGImagePropertyPixelHeight);
if (value) CFNumberGetValue(value, kCFNumberNSIntegerType, &height);
//当图片类型是GIF时
if (_type == YYImageTypeGIF) {
//获取gif图片相关的信息
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);
}
//设置duration
if (value) CFNumberGetValue(value, kCFNumberDoubleType, &duration);
}
}
//_YYImageDecoderFrame中设置数据
frame.width = width;
frame.height = height;
frame.duration = duration;
//第一帧图片时
if (i == 0 && _width + _height == 0) { // init first frame
//保存宽高信息
_width = width;
_height = height;
value = CFDictionaryGetValue(properties, kCGImagePropertyOrientation);
if (value) {
//获取图片方向信息
CFNumberGetValue(value, kCFNumberNSIntegerType, &orientationValue);
_orientation = YYUIImageOrientationFromEXIFValue(orientationValue);
}
}
//清除资源
CFRelease(properties);
}
}
//保存帧数组
dispatch_semaphore_wait(_framesLock, DISPATCH_TIME_FOREVER);
_frames = frames;
dispatch_semaphore_signal(_framesLock);
}
获取帧图片
//获取一帧的图片
- (YYImageFrame *)frameAtIndex:(NSUInteger)index decodeForDisplay:(BOOL)decodeForDisplay {
YYImageFrame *result = nil;
pthread_mutex_lock(&_lock);
//调用私有获取方法
result = [self _frameAtIndex:index decodeForDisplay:decodeForDisplay];
pthread_mutex_unlock(&_lock);
return result;
}
//私有获取图片帧方法
- (YYImageFrame *)_frameAtIndex:(NSUInteger)index decodeForDisplay:(BOOL)decodeForDisplay {
if (index >= _frames.count) return 0;
//取出 _YYImageDecoderFrame对象
_YYImageDecoderFrame *frame = [(_YYImageDecoderFrame *)_frames[index] copy];
BOOL decoded = NO;
BOOL extendToCanvas = NO;
//处理ICO图片
if (_type != YYImageTypeICO && decodeForDisplay) { // ICO contains multi-size frame and should not extend to canvas.
extendToCanvas = YES;
}
//当不需要混合时
if (!_needBlend) {
//获取不需要混合的图片数据,此时还没有解码
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);
//解码为CGImageRef
imageRef = imageRefDecoded;
decoded = YES;
}
}
//转换为UIImage
UIImage *image = [UIImage imageWithCGImage:imageRef scale:_scale orientation:_orientation];
CFRelease(imageRef);
if (!image) return nil;
image.isDecodedForDisplay = decoded;
//赋值给_YYImageDecoderFrame
frame.image = image;
return frame;
}
// 需要混合的情况
//创建混合上下文
if (![self _createBlendContextIfNeeded]) return nil;
CGImageRef imageRef = NULL;
if (_blendFrameIndex + 1 == frame.index) {
//创建混合过后的CGImage
imageRef = [self _newBlendedImageWithFrame:frame];
_blendFrameIndex = index;
} else { // should draw canvas from previous frame
_blendFrameIndex = NSNotFound;
//清空CGContext
CGContextClearRect(_blendCanvas, CGRectMake(0, 0, _width, _height));
if (frame.blendFromIndex == frame.index) {
//创建要混合的前一帧图片
CGImageRef unblendedImage = [self _newUnblendedImageAtIndex:index extendToCanvas:NO decoded:NULL];
if (unblendedImage) {
//绘制到CGContext
CGContextDrawImage(_blendCanvas, CGRectMake(frame.offsetX, frame.offsetY, frame.width, frame.height), unblendedImage);
CFRelease(unblendedImage);
}
//解码获取图片
imageRef = CGBitmapContextCreateImage(_blendCanvas);
//如果需要清空
if (frame.dispose == YYImageDisposeBackground) {
//清空对应位置的CGContext
CGContextClearRect(_blendCanvas, CGRectMake(frame.offsetX, frame.offsetY, frame.width, frame.height));
}
_blendFrameIndex = index;
} else { // canvas is not ready
for (uint32_t i = (uint32_t)frame.blendFromIndex; i <= (uint32_t)frame.index; i++) {
if (i == frame.index) {
if (!imageRef) imageRef = [self _newBlendedImageWithFrame:frame];
} else {
[self _blendImageWithFrame:_frames[i]];
}
}
_blendFrameIndex = index;
}
}
if (!imageRef) return nil;
//创建UIImage
UIImage *image = [UIImage imageWithCGImage:imageRef scale:_scale orientation:_orientation];
CFRelease(imageRef);
if (!image) return nil;
image.isDecodedForDisplay = YES;
//赋值给帧对象
frame.image = image;
//是否和画布对齐
if (extendToCanvas) {
frame.width = _width;
frame.height = _height;
frame.offsetX = 0;
frame.offsetY = 0;
frame.dispose = YYImageDisposeNone;
frame.blend = YYImageBlendNone;
}
return frame;
}
混合相关的方法
//创建图片混合上下文
- (BOOL)_createBlendContextIfNeeded {
if (!_blendCanvas) {
//清空缓存索引
_blendFrameIndex = NSNotFound;
//创建位图上下文
_blendCanvas = CGBitmapContextCreate(NULL, _width, _height, 8, 0, YYCGColorSpaceGetDeviceRGB(), kCGBitmapByteOrder32Host | kCGImageAlphaPremultipliedFirst);
}
//返回成功与否
BOOL suc = _blendCanvas != NULL;
return suc;
}
//创建混合图片
- (CGImageRef)_newBlendedImageWithFrame:(_YYImageDecoderFrame *)frame CF_RETURNS_RETAINED{
CGImageRef imageRef = NULL;
//如果画布上的帧区域在绘制之前应该保持之前的状态
if (frame.dispose == YYImageDisposePrevious) {
//帧是基于其alpha合成到输出缓冲区上
if (frame.blend == YYImageBlendOver) {
//获取混合画布上之前的内容
CGImageRef previousImage = CGBitmapContextCreateImage(_blendCanvas);
//使用当前帧生成一张图片
CGImageRef unblendImage = [self _newUnblendedImageAtIndex:frame.index extendToCanvas:NO decoded:NULL];
if (unblendImage) {
//将当前帧图片绘制在混合画布上
CGContextDrawImage(_blendCanvas, CGRectMake(frame.offsetX, frame.offsetY, frame.width, frame.height), unblendImage);
CFRelease(unblendImage);
}
//从混合画布上获取当前图片
imageRef = CGBitmapContextCreateImage(_blendCanvas);
//清空画布
CGContextClearRect(_blendCanvas, CGRectMake(0, 0, _width, _height));
if (previousImage) {
//将之前的状态重新绘制在混合画布上
CGContextDrawImage(_blendCanvas, CGRectMake(0, 0, _width, _height), previousImage);
CFRelease(previousImage);
}
} else { //覆盖当前的区域使用帧的所有颜色分量
//保存混合画布的当前状态
CGImageRef previousImage = CGBitmapContextCreateImage(_blendCanvas);
//使用当前帧生成图片
CGImageRef unblendImage = [self _newUnblendedImageAtIndex:frame.index extendToCanvas:NO decoded:NULL];
if (unblendImage) {
//清空画布
CGContextClearRect(_blendCanvas, CGRectMake(frame.offsetX, frame.offsetY, frame.width, frame.height));
//绘制当前帧
CGContextDrawImage(_blendCanvas, CGRectMake(frame.offsetX, frame.offsetY, frame.width, frame.height), unblendImage);
CFRelease(unblendImage);
}
//从混合画布中取出解码后的当前帧
imageRef = CGBitmapContextCreateImage(_blendCanvas);
//清空画布
CGContextClearRect(_blendCanvas, CGRectMake(0, 0, _width, _height));
if (previousImage) {
//在画布上保存之前的状态
CGContextDrawImage(_blendCanvas, CGRectMake(0, 0, _width, _height), previousImage);
CFRelease(previousImage);
}
}
} else if (frame.dispose == YYImageDisposeBackground) { //画布的帧区域在绘制下一帧之前要被清除为完全透明的黑色
//帧是基于其alpha合成到输出缓冲区上
if (frame.blend == YYImageBlendOver) {
//使用当前帧获取图片
CGImageRef unblendImage = [self _newUnblendedImageAtIndex:frame.index extendToCanvas:NO decoded:NULL];
if (unblendImage) {
//把当前帧图片绘制在画布上
CGContextDrawImage(_blendCanvas, CGRectMake(frame.offsetX, frame.offsetY, frame.width, frame.height), unblendImage);
CFRelease(unblendImage);
}
//从画布中取出当前帧
imageRef = CGBitmapContextCreateImage(_blendCanvas);
//清空画布
CGContextClearRect(_blendCanvas, CGRectMake(frame.offsetX, frame.offsetY, frame.width, frame.height));
} else { //覆盖当前的区域使用帧的所有颜色分量
//使用当前帧获取图片
CGImageRef unblendImage = [self _newUnblendedImageAtIndex:frame.index extendToCanvas:NO decoded:NULL];
if (unblendImage) {
//清空画布
CGContextClearRect(_blendCanvas, CGRectMake(frame.offsetX, frame.offsetY, frame.width, frame.height));
//绘制当前帧
CGContextDrawImage(_blendCanvas, CGRectMake(frame.offsetX, frame.offsetY, frame.width, frame.height), unblendImage);
CFRelease(unblendImage);
}
//从画布中取出当前帧
imageRef = CGBitmapContextCreateImage(_blendCanvas);
//清空画布
CGContextClearRect(_blendCanvas, CGRectMake(frame.offsetX, frame.offsetY, frame.width, frame.height));
}
} else { // no dispose
//在绘制下一帧前,不会对画布进行任何操作,保持原样
//基于alpha混合
if (frame.blend == YYImageBlendOver) {
//使用当前帧创建图片
CGImageRef unblendImage = [self _newUnblendedImageAtIndex:frame.index extendToCanvas:NO decoded:NULL];
if (unblendImage) {
//直接把当前帧绘制到画布上
CGContextDrawImage(_blendCanvas, CGRectMake(frame.offsetX, frame.offsetY, frame.width, frame.height), unblendImage);
CFRelease(unblendImage);
}
//从画布中取出图片
imageRef = CGBitmapContextCreateImage(_blendCanvas);
} else { //覆盖当前的区域使用帧的所有颜色分量
//使用当前帧创建图片
CGImageRef unblendImage = [self _newUnblendedImageAtIndex:frame.index extendToCanvas:NO decoded:NULL];
if (unblendImage) {
//清空画布
CGContextClearRect(_blendCanvas, CGRectMake(frame.offsetX, frame.offsetY, frame.width, frame.height));
//绘制当前帧
CGContextDrawImage(_blendCanvas, CGRectMake(frame.offsetX, frame.offsetY, frame.width, frame.height), unblendImage);
CFRelease(unblendImage);
}
//从当前帧获取图片
imageRef = CGBitmapContextCreateImage(_blendCanvas);
}
}
return imageRef;
}
//将帧绘制到画布上并返回混合后的帧
- (CGImageRef)_newUnblendedImageAtIndex:(NSUInteger)index
extendToCanvas:(BOOL)extendToCanvas
decoded:(BOOL *)decoded CF_RETURNS_RETAINED {
//已经结束直接返回
if (!_finalized && index > 0) return NULL;
//帧索引越界直接失败
if (_frames.count <= index) return NULL;
_YYImageDecoderFrame *frame = _frames[index];
//png,jpeg,ico...
if (_source) {
//从CGImageSourceRef 中获取图片
CGImageRef imageRef = CGImageSourceCreateImageAtIndex(_source, index, (CFDictionaryRef)@{(id)kCGImageSourceShouldCache:@(YES)});
//当需要扩展到画布大小时
if (imageRef && extendToCanvas) {
size_t width = CGImageGetWidth(imageRef);
size_t height = CGImageGetHeight(imageRef);
//与当前大小相等
if (width == _width && height == _height) {
//直接解码图片
CGImageRef imageRefExtended = YYCGImageCreateDecodedCopy(imageRef, YES);
if (imageRefExtended) {
CFRelease(imageRef);
imageRef = imageRefExtended;
if (decoded) *decoded = YES;
}
} else { //与当前大小不相等
//创建画布
CGContextRef context = CGBitmapContextCreate(NULL, _width, _height, 8, 0, YYCGColorSpaceGetDeviceRGB(), kCGBitmapByteOrder32Host | kCGImageAlphaPremultipliedFirst);
if (context) {
//绘制竖直方向上的差异部分
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;
}
//是图片格式是apng
if (_apngSource) {
uint32_t size = 0;
//获取一帧数据
uint8_t *bytes = yy_png_copy_frame_data_at_index(_data.bytes, _apngSource, (uint32_t)index, &size);
if (!bytes) return NULL;
//把帧数据传递给 CGDataProviderRef
CGDataProviderRef provider = CGDataProviderCreateWithData(bytes, bytes, size, YYCGDataProviderReleaseDataCallback);
if (!provider) {
free(bytes);
return NULL;
}
bytes = NULL; // hold by provider
//使用CGDataProviderRef 创建 CGImageSourceRef
CGImageSourceRef source = CGImageSourceCreateWithDataProvider(provider, NULL);
if (!source) {
CFRelease(provider);
return NULL;
}
CFRelease(provider);
//图片帧数小于1,数据错误返回失败
if(CGImageSourceGetCount(source) < 1) {
CFRelease(source);
return NULL;
}
//获取 CGImageRef
CGImageRef imageRef = CGImageSourceCreateImageAtIndex(source, 0, (CFDictionaryRef)@{(id)kCGImageSourceShouldCache:@(YES)});
CFRelease(source);
if (!imageRef) return NULL;
//需要扩展到画布大小
if (extendToCanvas) {
//创建画布
CGContextRef context = CGBitmapContextCreate(NULL, _width, _height, 8, 0, YYCGColorSpaceGetDeviceRGB(), kCGBitmapByteOrder32Host | kCGImageAlphaPremultipliedFirst); //bgrA
if (context) {
//解码当前帧
CGContextDrawImage(context, CGRectMake(frame.offsetX, frame.offsetY, frame.width, frame.height), imageRef);
CFRelease(imageRef);
//从画布中获取解码过后的图片
imageRef = CGBitmapContextCreateImage(context);
CFRelease(context);
if (decoded) *decoded = YES;
}
}
return imageRef;
}
#if YYIMAGE_WEBP_ENABLED
//图片格式是webp
if (_webpSource) {
WebPIterator iter;
//获取webp迭代器
if (!WebPDemuxGetFrame(_webpSource, (int)(index + 1), &iter)) return NULL; // demux webp frame data
// frame numbers are one-based in webp -----------^
//获取图片大小
int frameWidth = iter.width;
int frameHeight = iter.height;
if (frameWidth < 1 || frameHeight < 1) return NULL;
int width = extendToCanvas ? (int)_width : frameWidth;
int height = extendToCanvas ? (int)_height : frameHeight;
if (width > _width || height > _height) return NULL;
//获取数据内存地址
const uint8_t *payload = iter.fragment.bytes;
//获取数据大小
size_t payloadSize = iter.fragment.size;
//创建WebP解码器配置
WebPDecoderConfig config;
if (!WebPInitDecoderConfig(&config)) {
//配置获取失败释放迭代器
WebPDemuxReleaseIterator(&iter);
return NULL;
}
//验证webp帧数据
if (WebPGetFeatures(payload , payloadSize, &config.input) != VP8_STATUS_OK) {
WebPDemuxReleaseIterator(&iter);
return NULL;
}
size_t bitsPerComponent = 8;
size_t bitsPerPixel = 32;
//字节对齐,最近的大于第一个参数的32的整数倍
size_t bytesPerRow = YYImageByteAlign(bitsPerPixel / 8 * width, 32);
//图片数据大小
size_t length = bytesPerRow * height;
CGBitmapInfo bitmapInfo = kCGBitmapByteOrder32Host | kCGImageAlphaPremultipliedFirst; //bgrA
//分配图片内存
void *pixels = calloc(1, length);
if (!pixels) {
WebPDemuxReleaseIterator(&iter);
return NULL;
}
//设置webp颜色空间为RGBA
config.output.colorspace = MODE_bgrA;
//使用外部内存
config.output.is_external_memory = 1;
//关联图片内存
config.output.u.RGBA.rgba = pixels;
//设置bytesPerRow
config.output.u.RGBA.stride = (int)bytesPerRow;
//设置图片大小
config.output.u.RGBA.size = length;
//解码webp数据
VP8StatusCode result = WebPDecode(payload, payloadSize, &config); // decode
//解码不成功释放资源返回失败
if ((result != VP8_STATUS_OK) && (result != VP8_STATUS_NOT_ENOUGH_DATA)) {
WebPDemuxReleaseIterator(&iter);
free(pixels);
return NULL;
}
WebPDemuxReleaseIterator(&iter);
//是否需要扩展到画布大小
if (extendToCanvas && (iter.x_offset != 0 || iter.y_offset != 0)) {
void *tmp = calloc(1, length);
if (tmp) {
//构造vImage_Buffer
vImage_Buffer src = {pixels, height, width, bytesPerRow};
//buffer 2
vImage_Buffer dest = {tmp, height, width, bytesPerRow};
//构造矩阵
vImage_CGAffineTransform transform = {1, 0, 0, 1, iter.x_offset, -iter.y_offset};
uint8_t backColor[4] = {0};
vImage_Error error = vImageAffineWarpCG_ARGB8888(&src, &dest, NULL, &transform, backColor, kvImageBackgroundColorFill);
if (error == kvImageNoError) {
//将变换后的矩阵拷贝到pixels中
memcpy(pixels, tmp, length);
}
free(tmp);
}
}
//创建CGDataProvider
CGDataProviderRef provider = CGDataProviderCreateWithData(pixels, pixels, length, YYCGDataProviderReleaseDataCallback);
if (!provider) {
free(pixels);
return NULL;
}
pixels = NULL; // hold by provider
//创建CGImageRef
CGImageRef image = CGImageCreate(width, height, bitsPerComponent, bitsPerPixel, bytesPerRow, YYCGColorSpaceGetDeviceRGB(), bitmapInfo, provider, NULL, false, kCGRenderingIntentDefault);
CFRelease(provider);
if (decoded) *decoded = YES;
return image;
}
#endif
return NULL;
}
//根据dispose将帧绘制到混合画布上
- (void)_blendImageWithFrame:(_YYImageDecoderFrame *)frame {
//如果混合之前保持之前的状态则什么也不用做
if (frame.dispose == YYImageDisposePrevious) {
// nothing
} else if (frame.dispose == YYImageDisposeBackground) {
//如果在绘制之前要要清空,则清空混合画布
CGContextClearRect(_blendCanvas, CGRectMake(frame.offsetX, frame.offsetY, frame.width, frame.height));
} else { // no dispose
//YYImageDisposeNone 解析混合模式
if (frame.blend == YYImageBlendOver) { //基于alpha 混合
//获取一帧图片
CGImageRef unblendImage = [self _newUnblendedImageAtIndex:frame.index extendToCanvas:NO decoded:NULL];
if (unblendImage) {
//获取到画布上
CGContextDrawImage(_blendCanvas, CGRectMake(frame.offsetX, frame.offsetY, frame.width, frame.height), unblendImage);
CFRelease(unblendImage);
}
} else {
//清空画布
CGContextClearRect(_blendCanvas, CGRectMake(frame.offsetX, frame.offsetY, frame.width, frame.height));
//获取一帧图片
CGImageRef unblendImage = [self _newUnblendedImageAtIndex:frame.index extendToCanvas:NO decoded:NULL];
if (unblendImage) {
//绘制到画布上
CGContextDrawImage(_blendCanvas, CGRectMake(frame.offsetX, frame.offsetY, frame.width, frame.height), unblendImage);
CFRelease(unblendImage);
}
}
}
}
