iphone－CoreGraphics切割图片

 - (UIImage*)imageByCropping:(UIImage *)imageToCrop toRect:(CGRect)rect

{

   //create a context to do our clipping in

   UIGraphicsBeginImageContext(rect.size);

   CGContextRef currentContext = UIGraphicsGetCurrentContext();

   //create a rect with the size we want to crop the image to

   //the X and Y here are zero so we start at the beginning of our

   //newly created context

   CGRect clippedRect = CGRectMake(0, 0, rect.size.width, rect.size.height);

   CGContextClipToRect( currentContext, 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(rect.origin.x * -1,

                                rect.origin.y * -1,

                                imageToCrop.size.width,

                                imageToCrop.size.height);

   //draw the image to our clipped context using our offset rect

   CGContextDrawImage(currentContext, drawRect, imageToCrop.CGImage);

   //pull the image from our cropped context

   UIImage *cropped = UIGraphicsGetImageFromCurrentImageContext();

   //pop the context to get back to the default

   UIGraphicsEndImageContext();

   //Note: this is autoreleased

   return cropped;

}

 

Then call the code with something like:

- (void)drawRect:(CGRect)rect

{

   //draw the whole lights off image

   //the on images will be drawn overtop

   [lightsOffImage drawInRect:rect];

   //if we don't have any lights on... no point in continuing

   if( numberOfLightsOn < 1 )

     return;

   //figure out the dimensions of numberOfLights on bulbs

   CGSize croppedSize = CGSizeMake(LIGHT_WIDTH * numberOfLightsOn, LIGHT_HEIGHT);

   CGRect clippedRect = CGRectMake(0, 0, croppedSize.width, croppedSize.height);

   //get the "on" bulbs by cropping the image

   UIImage *cropped = [self imageByCropping:lightsOnImage toRect:clippedRect];

   //create a rect to draw the newly cropped on images to

   CGRect lightsOnRect = CGRectMake(LIGHT_BULB_OFFSET_X,

                                    LIGHT_BULB_OFFSET_Y,

                                    croppedSize.width,

                                    croppedSize.height);

   //draw the "on" lights

   [cropped drawInRect:lightsOnRect];

   //cropped is autoreleased so no need to worry about cleanup

}