iOS:长图切割并转为动画gif——精灵表单sprite Sheet的转化
iOS:长图切割并转为动画gif——精灵表单sprite Sheet的转化
通常的,iOS显示gif可以将文件转为NSData
后再对其进行解析,通过CADisplayLink
逐帧进行提取、播放,判断NSData
是否为gif图的方法如下:
-(void)isGifData:(NSData *)data {
BOOL hasData = ([data length] > 0);
if (!hasData) {
return NO;
}
CGImageSourceRef imageSource = CGImageSourceCreateWithData((__bridge CFDataRef)data,
(__bridge CFDictionaryRef)@{(NSString *)kCGImageSourceShouldCache: @NO});
// Early return on failure!
if (!imageSource) {
return NO;
}
// Early return if not GIF!
//关键未知
CFStringRef imageSourceContainerType = CGImageSourceGetType(imageSource);
BOOL isGIFData = UTTypeConformsTo(imageSourceContainerType, kUTTypeGIF);
return isGIFData;
}
///参考第三方库FLAnimatedImage中FLAniamtedImage.m
///- (instancetype)initWithAnimatedGIFData:(NSData *)data optimalFrameCacheSize:(NSUInteger)optimalFrameCacheSize predrawingEnabled:(BOOL)isPredrawingEnabled
(此方法稍微改造一下还可以同时识别PNG/JPEG)
而精灵表单的本质上是一张大的图片,是将所有帧的图像堆到同一张图片里,只需要在一定间隔内读取指定小区域的照片,利用人眼视觉残留的特性,即可呈现动画效果,本文将探讨如何将此类图转为gif。
//相关参数,根据实际情况自行赋值,省略
CGFloat frameDurations;//帧间隔,单位为秒
NSMutableArray <NSValue *>* frameRects;//每一帧在大图中的区域
NSURL *savePathURL;//保存gif图片地址
UIImage *image;//sprite sheet大图
//gif图的参数
NSDictionary *fileSetting = @{
(__bridge id)kCGImagePropertyGIFDictionary: @{
(__bridge id)kCGImagePropertyGIFLoopCount: @0, // 0 means loop forever
}
};
NSDictionary *frameSetting = @{
(__bridge id)kCGImagePropertyGIFDictionary: @{
(__bridge id)kCGImagePropertyGIFDelayTime: @(frameDurations), // a float (not double!) in seconds, rounded to centiseconds in the GIF data
}
};
CGImageDestinationRef destination = CGImageDestinationCreateWithURL((__bridge CFURLRef)savePathURL, kUTTypeGIF, frameRects.count, NULL);
CGImageDestinationSetProperties(destination, (__bridge CFDictionaryRef)fileSetting);
//开始处理
for (int i = 0; i < frameRects.count; i ++) {
CGRect rect = contentRects[i].CGRectValue;
@autoreleasepool {
//及时释放循环中累计的内存
CGImageRef subImageRef = CGImageCreateWithImageInRect(image.CGImage, rect);
CGImageDestinationAddImage(destination, subImageRef, (__bridge CFDictionaryRef)frameSetting);
CGImageRelease(subImageRef);
}
}
//善后
if (!CGImageDestinationFinalize(destination)) {
NSLog(@"failed to finalize image destination");
}
CFRelease(destination);
//生成gif
NSData *fileData = [[NSData alloc] initWithContentsOfURL:savePathURL];
//根据情况是否删除缓存文件
此段代码参考从视频中截取缩略图生成gif图片
还可以改进的地方:文中实现了图片->gif类型data的转换,需要将整个动画生成后才能对其做下一步的操作(比如显示动画),但实际上我们还可以通过CADisplayLink实时显示截取对应帧数的区域.
本文来自博客园,作者:MrYu4,转载请注明原文链接:https://www.cnblogs.com/MrYU4/p/15778871.html