问Core Plot 1.0视网膜图像显示不正确

EN

{
    //first annotation
    NSValue *value = [self.myData objectAtIndex:index];
    CGPoint point = [value CGPointValue];
    NSString *number1 = [NSString stringWithFormat:@"(%.2f, ", point.x];
    NSString *number2 = [NSString stringWithFormat:@"%.2f)", point.y];
    NSNumber *x = [NSNumber numberWithFloat:point.x];
    NSNumber *y = [NSNumber numberWithFloat:point.y];    
    NSArray *anchorPoint = [NSArray arrayWithObjects: x, y, nil];
    NSString *final = [number1 stringByAppendingString:number2];

    //second annotation        
    UIImage *bubble = [UIImage imageNamed:@"Bubble.png"];
    CPTImage *fillimage = [CPTImage imageWithCGImage:bubble.CGImage];
    CPTBorderedLayer *imageLayer = [[CPTBorderedLayer alloc] init];
    //imageLayer.contentsScale = [[UIScreen mainScreen] scale]; //tried this
    imageLayer.frame = CGRectMake(0, 0, 150, 80);
    //imageLayer.contentsScale = 2.0f;  //and this

    imageLayer.fill = [CPTFill fillWithImage:fillimage];

    CPTTextLayer *textLayer = [[CPTTextLayer alloc] initWithText:final style:annotationTextStyle];
    _annotation = [[CPTPlotSpaceAnnotation alloc] initWithPlotSpace:graph.defaultPlotSpace anchorPlotPoint:anchorPoint];        
    _annotation.contentLayer = textLayer;        
    _annotation.displacement = CGPointMake(90.0f, 5.0f);
    _annotation.rotation = M_PI * .03f;

    _picAnnotation = [[CPTPlotSpaceAnnotation alloc] initWithPlotSpace:graph.defaultPlotSpace anchorPlotPoint:anchorPoint];
    _picAnnotation.contentLayer = imageLayer;
    _picAnnotation.displacement = CGPointMake(75.0f, 5.0f);

}