title: Core Plot CPTextLayer: alignment of text with background image as background color
body: <p>I have write following code to show bar plot annotation. Annotations are shown but with unexpected alignment/position. Text of CPTextLayer is showing at top-left corner of the frame. I am trying to show it at center. I have used a background image of the CPTextLayer as background color. Please have a look through the code- (symbolTextAnnotation is a CPLayerAnnotation object decleared in the interface)</p>
  
  <pre><code>-(void)barPlot:(CPBarPlot *)plot barWasSelectedAtRecordIndex:(NSUInteger)index
  {
      CPXYGraph* graph = (CPXYGraph*)plot.graph;
      NSNumber *value = [self numberForPlot:plot field:CPBarPlotFieldBarTip recordIndex:index];
  
      if ( symbolTextAnnotation ) {
          [graph.plotAreaFrame.plotArea removeAnnotation:symbolTextAnnotation];
          symbolTextAnnotation = nil;
      }
  
      // Setup a style for the annotation
      CPMutableTextStyle *hitAnnotationTextStyle = [CPMutableTextStyle textStyle];
      hitAnnotationTextStyle.color = [CPColor whiteColor];
      hitAnnotationTextStyle.fontSize = 9.0f;
      hitAnnotationTextStyle.fontName = @"Helvetica-Bold";
  
  
      // Determine point of symbol in plot coordinates
      NSNumber *x = [NSNumber numberWithInt:index+1];
      NSNumber *y = [NSNumber numberWithInt:0];
  
      NSArray *anchorPoint = [NSArray arrayWithObjects:y, x, nil];
  
      // Add annotation
      // First make a string for the y value
      NSNumberFormatter *formatter = [[[NSNumberFormatter alloc] init] autorelease];
      [formatter setMaximumFractionDigits:2];
      NSString *yString = [formatter stringFromNumber:value];
  
      // Now add the annotation to the plot area
      UIImage *annotationBG = [UIImage imageNamed:@"annotation-bg.png"]; 
      CPTextLayer *textLayer = [[[CPTextLayer alloc] initWithText:yString style:hitAnnotationTextStyle] autorelease];
  
      textLayer.backgroundColor = [UIColor colorWithPatternImage:annotationBG].CGColor;
      textLayer.frame = CGRectMake(0, 0, annotationBG.size.width, annotationBG.size.height);
  
  
      symbolTextAnnotation = [[CPPlotSpaceAnnotation alloc] initWithPlotSpace:plot.plotSpace anchorPlotPoint:anchorPoint];
      symbolTextAnnotation.contentLayer = textLayer;
      symbolTextAnnotation.displacement = CGPointMake(-18.0f, 3.0f);
  
      [graph.plotAreaFrame.plotArea addAnnotation:symbolTextAnnotation];    
  }
  </code></pre>