iOS-是否可以缓存CGContextDrawImage？

我使用计时配置文件工具来确定95%的时间都花在调用函数CGContextDrawImage上

在我的应用程序中，有许多重复的图像被从精灵地图上截取并绘制到屏幕上。我想知道是否有可能将CGContextDrawImage的输出缓存在NSMutableDictionary中，然后如果再次请求相同的精灵，则可以将其从缓存中拉出，而不是再次执行所有剪辑和渲染工作。这就是我所得到的，但我没有成功：

定义

if(cache == NULL) cache = [[NSMutableDictionary alloc]init];
//Identifier based on the name of the sprite and location within the sprite.
NSString* identifier = [NSString stringWithFormat:@"%@-%d",filename,frame];

添加到缓存中

 CGRect clippedRect = CGRectMake(0, 0, clipRect.size.width, clipRect.size.height);
    CGContextClipToRect( context, clippedRect);

    //create a rect equivalent to the full size of the image
    //offset the rect by the X and Y we want to start the crop
    //from in order to cut off anything before them
    CGRect drawRect = CGRectMake(clipRect.origin.x * -1,
                                 clipRect.origin.y * -1,
                                 atlas.size.width,
                                 atlas.size.height);

    //draw the image to our clipped context using our offset rect
    CGContextDrawImage(context, drawRect, atlas.CGImage);
    [cache setValue:UIGraphicsGetImageFromCurrentImageContext() forKey:identifier];
    UIGraphicsEndImageContext();

渲染缓存的精灵 可能有更好的方法来渲染CGImage，这是我的最终缓存目标，但目前我只是希望成功渲染缓存的图像，但这并没有成功

 UIImage* cachedImage = [cache objectForKey:identifier];

if(cachedImage){
    NSLog(@"Cached %@",identifier);

    CGRect imageRect =  CGRectMake(0,
                                   0,
                                   cachedImage.size.width,
                                   cachedImage.size.height);

    if (NULL != UIGraphicsBeginImageContextWithOptions)
        UIGraphicsBeginImageContextWithOptions(imageRect.size, NO, 0);
    else
        UIGraphicsBeginImageContext(imageRect.size);

    //Use draw for now just to see if the image renders out ok
    CGContextDrawImage(context, imageRect, cachedImage.CGImage);
     UIGraphicsEndImageContext();
}

---

是的，可以缓存渲染图像。下面是如何完成的示例：

+ (UIImage *)getRenderedImage:(UIImage *)image targetSize:(CGSize)targetSize
{
    CGRect targetRect = CGRectIntegral(CGRectMake(0, 0, targetSize.width, targetSize.height)); // should be used by your drawing code
    CGImageRef imageRef = image.CGImage; // should be used by your drawing code
    UIGraphicsBeginImageContextWithOptions(targetSize, NO, 0);
    CGContextRef context = UIGraphicsGetCurrentContext();
    // TODO: draw and clip your image here onto context
    // CGContextDrawImage CGContextClipToRect calls
    CGImageRef newImageRef = CGBitmapContextCreateImage(context);
    UIImage *newImage = [UIImage imageWithCGImage:newImageRef];
    CGImageRelease(newImageRef);
    UIGraphicsEndImageContext();
    return newImage;
}

这样，您将获得资源图像的渲染副本。因为在渲染期间，您拥有上下文，您可以自由地执行任何您想要的操作。您只需要事先确定输出大小

生成的图像只是

UIImage

的一个实例，您可以将其放入

NSMutableDictionary

中供以后使用