iphonecgcontextcatiledlayer

Using NSString's drawAtPoint method in place of CGContextShowGlyphsAtPoint problems

In my app I'm trying to render text along a path; this is fine for most characters but not for Japanese (or anything non mac-Roman). I've been advised to use [NSString drawAtPoint] which displays the correct characters in my CATiledLayer; however, they dissapear after approximately 5 seconds. In this time I can zoom the layer and they scale properly, but they don't seem to get committed to the CATiledLayer like the rest of the text usually is.

Before I render, I check the string and decide whether any of them will not be renderable. If I'm going to have issues, I use drawAtpoint instead:

if (!isFullyDisplayable)
 {
  CGContextShowGlyphsAtPoint(context, pt.x, pt.y, realGlyph, 1);
 }
 else {
  // fall back on less flexible font rendering for difficult characters

  NSString *b = [gv text];
  NSString *c = [b substringWithRange:NSMakeRange(j,1)];

  [c drawAtPoint:pt withFont:[UIFont fontWithName:@"Helvetica-Bold" size:16.0]];


 }

Does anyone have any pointers as to why the text disappears?

As soon as the drawAtPoint is used my debug output gets flooded with:

<Error>: CGContextGetShouldSmoothFonts: invalid context
<Error>: CGContextSetFont: invalid context
<Error>: CGContextSetTextMatrix: invalid context
<Error>: CGContextSetFontSize: invalid context
<Error>: CGContextSetTextPosition: invalid context
<Error>: CGContextShowGlyphsWithAdvances: invalid context

So I'm guessing it is something to do with my context management, but I assumed that if this is in the same place as I use CGContextShowGlyphsAtPoint it should have the correct context already?

Solution

  • Answering my own question:

    NSString drawAtPoint:withFont: makes use of the context stack, and from where I was calling this method the stack was empty. Wrapping the call with 

    UIGraphicsPushContext(context); and UIGraphicsPopContext();

    did the trick.