iOS:GIF图片的预览以及生成
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需求
需要在ios平台上实现GIF图片的展示以及生成
展示需求
通过调研发现有两种方式来实现
1. 根据gif的格式来自己解析出图片，或者使用ImageMagick这个库来做 2. 使用sdk当中自带的ImageIO来做，但是需要iOS系统版本4.0以上（这个基本上木有问题了，因为现在xcode默认是4.3以上了）
解决
这里使用了ImageIO来做，基本上很简单，直接上代码:
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NSData* data = [NSData dataWithContentOfFile:@"some.gif"];CGImageSourceRef source = CGImageSourceCreateWithData((CFDataRef)data, NULL);size_t count = CGImageSourceGetCount(source);NSMutableArray* tmpArray = [NSMutableArray array];for (size_t i = 0; i < count; i++){ CGImageRef image = CGImageSourceCreateImageAtIndex(source, i, NULL); image = [UIImage imageWithCGImage:image scale:[UIScreen mainScreen].scale orientation:UIImageOrientationUp]; NSDictionary* frameProperties = [(NSDictionary*)CGImageSourceCopyPropertiesAtIndex(source, i, NULL) autorelease]; duration = [[[frameProperties objectForKey:(NSString*)kCGImagePropertyGIFDictionary] objectForKey:(NSString*)kCGImagePropertyGIFDelayTime] doubleValue]; duration = MAX(duration, 0.01); [tmpArray addObject:image]; CGImageRelease(image);}CFRelease(source);self.imageFrameArray = nil;if (tmpArray.count > 1){ self.imageFrameArray = tmpArray;}
生成GIF
基本上方法也是和展示差不多就是ImageIO,或者是使用ImageMagick,这里我都做了测试，先上代码
使用ImageIO来生成
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#import "MagickWand.h"// Commented out starts hereNSMutableData* imgData = [NSMutableData data];CGImageDestinationRef destination = CGImageDestinationCreateWithData((__bridge CFMutableDataRef)imgData, kUTTypeGIF, imgs.count, NULL);NSString* path = [[[DataCenter sharedDataCenter] getLibraryPath] stringByAppendingPathComponent:@"test.gif"];CFURLRef url = CFURLCreateWithFileSystemPath ( kCFAllocatorDefault, (CFStringRef)path, kCFURLPOSIXPathStyle, false);destination = CGImageDestinationCreateWithURL(url, kUTTypeGIF, imgs.count, NULL);NSDictionary *frameProperties = [NSDictionary dictionaryWithObject:[NSMutableDictionary dictionaryWithObjectsAndKeys:[NSNumber numberWithFloat:duration], (NSString *)kCGImagePropertyGIFDelayTime, nil] forKey:(NSString *)kCGImagePropertyGIFDictionary];NSMutableDictionary *dict = [NSMutableDictionary dictionaryWithCapacity:2];[dict setObject:[NSNumber numberWithBool:YES] forKey:(NSString*)kCGImagePropertyGIFHasGlobalColorMap];[dict setObject:(NSString *)kCGImagePropertyColorModelRGB forKey:(NSString *)kCGImagePropertyColorModel];[dict setObject:[NSNumber numberWithInt:8] forKey:(NSString*)kCGImagePropertyDepth];[dict setObject:[NSNumber numberWithInt:0] forKey:(NSString *)kCGImagePropertyGIFLoopCount];NSDictionary *gifProperties = [NSDictionary dictionaryWithObject:dict forKey:(NSString *)kCGImagePropertyGIFDictionary];for (UIImage* dImg in imgs){ UIGraphicsBeginImageContextWithOptions(CGSizeMake(size.width, size.height), FALSE, 1); UIView* gifBgView = [[UIView alloc] initWithFrame:CGRectMake(0, 0, size.width, size.height)]; gifBgView.backgroundColor = [UIColor clearColor]; UIImageView* imgView = [[UIImageView alloc] initWithFrame:CGRectMake(0, 0, size.width, size.height)]; [imgView setBackgroundColor:[UIColor clearColor]]; [imgView setContentMode:UIViewContentModeScaleAspectFill]; [imgView setImage:self.image]; imgView.center = gifBgView.center; [gifBgView addSubview:imgView]; UIImageView* dImgView = [[UIImageView alloc] initWithFrame:CGRectMake(0, 0, size.width, size.height)]; dImgView.center = imgView.center; [dImgView setBackgroundColor:[UIColor clearColor]]; [dImgView setImage:dImg]; [dImgView setContentMode:UIViewContentModeScaleAspectFill]; [gifBgView addSubview:dImgView]; [[gifBgView layer] renderInContext:UIGraphicsGetCurrentContext()]; UIImage* img = UIGraphicsGetImageFromCurrentImageContext(); UIGraphicsEndImageContext(); CGImageDestinationAddImage(destination, img.CGImage, (__bridge CFDictionaryRef)frameProperties);}CGImageDestinationSetProperties(destination, (__bridge CFDictionaryRef)gifProperties);CGImageDestinationFinalize(destination);CFRelease(destination);imgData = [NSData dataWithContentsOfFile:[[[DataCenter sharedDataCenter] getLibraryPath] stringByAppendingPathComponent:@"test.gif"]];return imgData;
使用ImageMagick来生成
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MagickWandGenesis();MagickWand* mw = NewMagickWand();MagickSetImageFormat(mw, "gif");for (UIImage* dImg in imgs){ UIGraphicsBeginImageContextWithOptions(CGSizeMake(size.width, size.height), FALSE, 1); UIView* gifBgView = [[UIView alloc] initWithFrame:CGRectMake(0, 0, size.width, size.height)]; gifBgView.backgroundColor = [UIColor clearColor]; UIImageView* imgView = [[UIImageView alloc] initWithFrame:CGRectMake(0, 0, size.width, size.height)]; [imgView setBackgroundColor:[UIColor clearColor]]; [imgView setContentMode:UIViewContentModeScaleAspectFill]; [imgView setImage:self.image]; imgView.center = gifBgView.center; [gifBgView addSubview:imgView]; UIImageView* dImgView = [[UIImageView alloc] initWithFrame:CGRectMake(0, 0, size.width, size.height)]; dImgView.center = imgView.center; [dImgView setBackgroundColor:[UIColor clearColor]]; [dImgView setImage:dImg]; [dImgView setContentMode:UIViewContentModeScaleAspectFill]; [gifBgView addSubview:dImgView]; [[gifBgView layer] renderInContext:UIGraphicsGetCurrentContext()]; UIImage* img = UIGraphicsGetImageFromCurrentImageContext(); UIGraphicsEndImageContext(); MagickWand* tempMW = NewMagickWand(); NSData* data = UIImageJPEGRepresentation(img, 1.0); MagickReadImageBlob(tempMW, [data bytes], [data length]); MagickSetImageDelay(tempMW, duration*100); MagickAddImage(mw, tempMW); tempMW = DestroyMagickWand(tempMW);}MagickWriteImages(mw, [[[[DataCenter sharedDataCenter] getLibraryPath] stringByAppendingPathComponent:@"test.gif"] cStringUsingEncoding:NSUTF8StringEncoding], MagickTrue);mw = DestroyMagickWand(mw);MagickWandTerminus();NSData* imgData = [NSData dataWithContentsOfFile:[[[DataCenter sharedDataCenter] getLibraryPath] stringByAppendingPathComponent:@"test.gif"]];return imgData;
对比
这两个方法都能生成GIF图片，但是ImageIO的生成速度要比ImageMagick快上不少,不过测试上来看用ImageIO容易造成内存的warrning，还有就是使用ImageIO的话如果使用默认的color table那么生成的图片有的像素比较低，严重的会丢颜色。这也是为什么ImageIO要快的原因把。相比如果项目假设用户的等待时间不是很限制的话，个人推荐使用ImageMagick来做。
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