利用预渲染加速iOS设备的图像显示

//  ImageView.h

#import 


@interface ImageView : UIView {
    UIImage *image;
}

@property (retain, nonatomic) UIImage *image;

@end

//  ImageView.m

#include 
#import "ImageView.h"


@implementation ImageView

#define LABEL_TAG 1

static const CGRect imageRect = {{0, 0}, {100, 100}};
static const CGPoint imagePoint = {0, 0};

@synthesize image;

- (void)awakeFromNib {
    if (!self.image) {
        self.image = [UIImage imageNamed:@"random.jpg"];
    }
}

- (void)drawRect:(CGRect)rect {
    if (CGRectEqualToRect(rect, imageRect)) {
        uint64_t start = mach_absolute_time();
        [image drawAtPoint:imagePoint];
        uint64_t drawTime = mach_absolute_time() - start;
        
        NSString *text = [[NSString alloc] initWithFormat:@"%ld", drawTime];
        UILabel *label = (UILabel *)[self viewWithTag:LABEL_TAG];
        label.text = text;
        [text release];
    }
}

- (void)dealloc {
    [super dealloc];
    [image release];
}

@end

static const CGSize imageSize = {100, 100};

- (void)awakeFromNib {
    if (!self.image) {
        self.image = [UIImage imageNamed:@"random.jpg"];
        if (NULL != UIGraphicsBeginImageContextWithOptions)
            UIGraphicsBeginImageContextWithOptions(imageSize, YES, 0);
        else
            UIGraphicsBeginImageContext(imageSize);
        [image drawInRect:imageRect];
        self.image = UIGraphicsGetImageFromCurrentImageContext();
        UIGraphicsEndImageContext();
    }
}

static CGImageRef imageRef;

imageRef = self.image.CGImage;

CGContextRef context = UIGraphicsGetCurrentContext();
CGContextDrawImage(context, imageRect, imageRef);

CGContextRef context = UIGraphicsGetCurrentContext();
CGContextTranslateCTM(context, 0, 100);
CGContextScaleCTM(context, 1, -1);
CGContextDrawImage(context, imageRect, imageRef);