iOS - 是否可以缓存CGContextDrawImage?

时间:2012-03-31 11:13:36

标签: ios caching core-animation cgcontextdrawimage

我使用时序配置文件工具来识别95%的时间花在调用CGContextDrawImage函数上。

在我的应用程序中,有很多重复的图像可以从精灵地图中重复切割并绘制到屏幕上。我想知道是否有可能将CGContextDrawImage的输出缓存在NSMutableDictionay中,然后如果再次请求相同的精灵,它可以从缓存中拉出它而不是完成剪切和再次渲染的所有工作。这就是我所拥有的,但我没有成功:

解释

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

 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 可能有一种更好的方式来渲染CGImage,这是我最终的缓存目标,但目前我只是想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();
}

1 个答案:

答案 0 :(得分:3)

是的,可以缓存渲染图像。以下是如何完成的示例:

+ (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。因为在渲染过程中,您拥有上下文,所以您可以自由地执行任何操作。您只需要事先确定输出大小。

生成的图片只是UIImage的一个实例,您可以将其放入NSMutableDictionary以供日后使用。