比什么慢？比从应用程序包加载的图像创建相同的纹理要慢。慢多少？在 iPhone 上慢 80 倍，在 Mac 上类似（但总体上更快）。
我下面的示例显示了使用 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的 Documents 目录中的文件；从该文件加载图像；从第二个图像创建纹理。
图像为 640x640 png，每种情况下创建 100 个 64x64 纹理。创建时间为 0.51 秒与 41.3 秒。
谁能解释这个巨大的差异，并指出加快第二种情况的方法和方法，如果可能的话，使其与第一种情况一样快？
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];
}
}