MKOverlay View is blurred

问题

I'm trying to add a png image as a custom map using MKOverlayView. I'm almost there - I am able to get the image lined up in the right place, and I know that the -drawMapRect: method in the subclass of MKOverlayView is being called periodically; I just can't seem to get the image to render properly. It's totally blurry, almost beyond recognition. I also know the image is large enough (it is 1936 × 2967). Here is my code for -drawMapRect:

- (void)drawMapRect:(MKMapRect)mapRect zoomScale:(MKZoomScale)zoomScale inContext:(CGContextRef)context{


    // Load image from applicaiton bundle
    NSString* imageFileName = [[[NSBundle mainBundle] resourcePath] stringByAppendingPathComponent:@"map.jpg"];
    CGDataProviderRef provider = CGDataProviderCreateWithFilename([imageFileName UTF8String]);
    CGImageRef image = CGImageCreateWithJPEGDataProvider(provider, NULL, true, kCGRenderingIntentDefault);
    CGDataProviderRelease(provider);

    // save context before screwing with it
    CGContextSaveGState(context);
    CGContextScaleCTM(context, 1.0, -1.0);
    CGContextSetAlpha(context, 1.0);

    // get the overlay bounds
    MKMapRect theMapRect = [self.overlay boundingMapRect];
    CGRect theRect = [self rectForMapRect:theMapRect];

    // Draw image
    CGContextDrawImage(context, theRect, image);
    CGImageRelease(image);
    CGContextRestoreGState(context);

Does anyone have a clue what's going on?

Thanks! -Matt

回答1:

I've had a similar problem. The problem was that my boundingMapRect was defined incorrectly. The full image is rendered scaled down when the scale is small on a tile. Then the map is zoomed and not all the image tiles are in the boundingMapRect tiles so they are not redrawn in the correct scale and the scaled down version is zoomed. At least that's what I think happens.

Hope this helps.

回答2:

Get rid of CGContextScaleCTM(context, 1.0, -1.0); and do a vertical flip on your image in preview instead. the mapkit seems to use the context information to determine which part of the image to render more clearly. Know it's been a while, but hope it helps!

回答3:

Thanks Rob, you made my day. My blur overlay image got sharpen when I replaced

CGContextScaleCTM(context, 1.0, -1.0);

with

CGAffineTransform flipVertical = CGAffineTransformMake(1, 0, 0, -1, 0, theRect.size.height);
CGContextConcatCTM(context, flipVertical);

来源：https://stackoverflow.com/questions/4117182/mkoverlay-view-is-blurred

标签

iphone

core-graphics

mkmapview

overlay

cgimage