iPhone：当从应用程序文档中的文件加载图像时，创建Texture2D的速度要慢得多，为什么？

Question

比什么慢？比从应用程序包加载的图像创建相同的纹理慢。 慢了多少？ iPhone 上慢 80 倍，Mac 上的比率相似（但总体更快）。

我下面的示例显示使用 imageNamed: 加载图像：从第一张图像创建纹理；将图像保存到应用程序文档目录中的文件中；从该文件加载图像；从第二张图像创建纹理。

图像为 640x640 png，每种情况下创建 100 个 64x64 纹理。 创建时间为 0.51 秒 vs. 41.3 秒。

谁能解释一下这种巨大的差异，并指出我加快第二种情况的方法和方法，使其与第一种情况一样快（如果可能的话）？

鲁迪夫

#import "Texture2D.h"

#define START_TIMER NSTimeInterval start = [NSDate timeIntervalSinceReferenceDate];
#define END_TIMER NSTimeInterval stop = [NSDate timeIntervalSinceReferenceDate]; NSLog(@"Time = %f", stop-start); 


@interface UIImage (CS_Extensions)
-(UIImage *) imageAtRect:(CGRect)rect;
+(NSString *) documentsDirectory;
+(void) saveImage:(UIImage *)image toDocumentsFile:(NSString *)filename;
+(UIImage *) imageFromDocumentsFile:(NSString *)filename;
+(BOOL) documentsFileExists:(NSString *)filename;
+(void) createTexturesFromImage:(UIImage *)image640x640 texture:(Texture2D **)texture;

@end;

@implementation UIImage (MiscExt)

-(UIImage *)imageAtRect:(CGRect)rect {
    CGImageRef imageRef = CGImageCreateWithImageInRect([self CGImage], rect);
    UIImage* subImage = [UIImage imageWithCGImage: imageRef];
    CGImageRelease(imageRef);
    return subImage;
}

+(NSString *) documentsDirectory {
    NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
    NSString *documentsDirectory = [paths objectAtIndex:0];
    return documentsDirectory;
}

+(UIImage *) imageFromDocumentsFile:(NSString *)filename {
    //  NSString *documentsDirectory = [NSHomeDirectory() stringByAppendingPathComponent:@"Documents"];
    NSString *documentsDirectory = [self documentsDirectory];
    NSString *path = [NSString stringWithFormat:@"%@/%@", documentsDirectory, filename];
    NSLog(@"%s : path %@", __FUNCTION__, path);
    NSData *data = [[NSData alloc] initWithContentsOfFile:path];
    UIImage *image = [[UIImage alloc] initWithData:data];
    return image;
}

+(void) saveImage:(UIImage *)image toDocumentsFile:(NSString *)filename {
    if (image != nil) {     // save to local file
        //      NSString *documentsDirectory = [NSHomeDirectory() stringByAppendingPathComponent:@"Documents"];
        NSString *documentsDirectory = [self documentsDirectory];
        NSString *path = [NSString stringWithFormat:@"%@/%@", documentsDirectory, filename];
        NSLog(@"%s : path %@", __FUNCTION__, path);
        //You can write an NSData to the fs w/ a method on NSData.
        //If you have a UIImage, you can do UIImageJPEGRepresentation() or UIImagePNGRepresentation to get data.
        NSData *data = UIImagePNGRepresentation(image);
        [data writeToFile:path atomically:YES];
        // Check if file exists
        NSFileManager *fileManager = [NSFileManager defaultManager];
        BOOL ok = [fileManager fileExistsAtPath:path];
        if (ok) {
            NSLog(@"%s : written file %@", __FUNCTION__, path);
        }
        else {
            NSLog(@"%s : failed to write file %@", __FUNCTION__, path);
        }
    }
}

+(BOOL) documentsFileExists:(NSString *)filename {
    NSString *documentsDirectory = [self documentsDirectory];
    NSString *path = [documentsDirectory stringByAppendingPathComponent:filename];
    NSLog(@"%s : path %@", __FUNCTION__, path);
    BOOL exists = [[NSFileManager defaultManager] fileExistsAtPath:path];
    return exists;
}

+(void) createTexturesFromImage:(UIImage *)image640x640 texture:(Texture2D **)texture {
    NSLog(@"%s -> ", __FUNCTION__);
    START_TIMER;
    for (int x = 0; x < 9; ++x) {
        for (int y = 0; y < 9; ++y) {
            UIImage *ulCorner = [image640x640 imageAtRect:CGRectMake(x*64,y*64,64,64)];
            texture[y*10+x] = [[Texture2D alloc] initWithImage:ulCorner];
        }
    }
    END_TIMER;
    NSLog(@"%s <- ", __FUNCTION__);
}

@end


-(void) test {

    Texture2D *texture1[100];
    Texture2D *texture2[100];

    // compare texture creation from a bundled file vs Documents file
    {
        UIImage *imageBundled = [UIImage imageNamed:@"bivio-640x640.png"];
        [UIImage createTexturesFromImage:imageBundled texture:texture1];

        [UIImage saveImage:imageBundled toDocumentsFile:@"docfile.png"];
        BOOL ok = [UIImage documentsFileExists:@"docfile.png"];

        UIImage *imageFromFile = [UIImage imageFromDocumentsFile:@"docfile.png"];
        [UIImage createTexturesFromImage:imageFromFile texture:texture2];
    }
}

Answer 1

当您构建项目时，XCode 会优化您放入资源中的 PNG。

本文详细解释了它： http://iphonedevelopment.blogspot.com /2008/10/iphone-optimized-pngs.html