Re: [Pyobjc-dev] Call for help

[Nico W. <nic...@gm...>]

Hi,

I sent this a few days before this list became more active again, so I  
dare to repost my question (sorry). I found the question "How do I  
handle an FSRef in pyobjc?" in several other places of the web, so I  
guess other people would benefit from an answer too.

Nico

On 31.01.2009, at 20:00, Nico Weber wrote:

> Hi,
>
> I want to load a font from a ttf file and then draw some text using  
> this font, and I want to do that in Python using the PyObjC bridge.  
> My program already does some drawing; it uses NSBitmapImageReps and  
> NSGraphicsContext for that. The font I'm trying to load is http://damieng.com/blog/2008/05/26/envy-code-r-preview-7-coding-font-released 
>  .
>
> If someone has an idea how I could get this to work, please speak up.
>
> Here's what I tried so far:
>
>
> 1.) Activate the font through ATS, then load it through NSFont  
> through its postscript name.
>
> This is what most programs written in ObjC do – they call  
> ATSFontActivateFromFileReference to load a ttf file and then can use  
> NSFont to load the font given its postscript name. The problem is  
> that there seems to be no built-in python binding for ATS. This fails:
>
>    import ATS
>
> Now, ATS.framework is a subframework in the ApplicationServices  
> framework, but this fails as well:
>
>    import ApplicationServices
>
> Fair enough. The pyobjc documentation shows how to write your own  
> wrapper:
>
>    import objc
>    b =  objc.loadBundle("ApplicationServices", globals(),
>    bundle_path=objc.pathForFramework(u'/System/Library/Frameworks/ 
> ApplicationServices.framework/'))
>
> For reasons I don't quite understand, this doesn't load the ATS  
> subframework methods, though (might be related that there is no  
> ATS.bridgesupport in /System/Library/Frameworks/ 
> ApplicationServices.framework/Versions/A/Frameworks/ATS.framework/ 
> Versions/A/Resources/BridgeSupport). I tried to create the  
> bridgesupport file on my own, using
>
>    gen_bridge_metadata -f /System/Library/Frameworks/ 
> ApplicationServices.framework/Frameworks/ATS.framework -o  
> ATS.bridgesupport
>
> This gave some linking errors, and didn't work. `man  
> gen_bridge_metadata` even says that there might be problems if you  
> want to create bridgesupport files for subframeworks of umbrella  
> frameworks, but doesn't really say how to work around them. I tried  
> explicitly setting special compiler flags with
>
>    gen_bridge_metadata -f /System/Library/Frameworks/ 
> ApplicationServices.framework/Frameworks/ATS.framework -o  
> ATS.bridgesupport -c ' -F /System/Library/Frameworks/ 
> ApplicationServices.framework/Frameworks/ATS.framework -framework  
> ApplicationServices'
>
> , but in vain.
>
> Now, pyobjc has a `loadBundleFunctions` function that can be used to  
> load functions from a bundle. One of the examples in /Developer/ 
> Examples/Python/PyObjC/Cocoa/AppKit/PyObjCLauncher/LaunchServices.py  
> does use this function to load a specific function from a bundle. So  
> I tried loading ATSFontActivateFromFileReference thusly (in its own  
> file `myfile.py`):
>
>    import objc
>
>    __bundle__ = objc.loadBundle("ApplicationServices", globals(),
>        bundle_path=objc.pathForFramework(u'/System/Library/ 
> Frameworks/ApplicationServices.framework/'))
>    functions = [( u'ATSFontActivateFromFileReference',  
> 's^{FSRef=[80C]}II^vIo^I' )]
>    objc.loadBundleFunctions(__bundle__, globals(), functions)
>
> (See http://developer.apple.com/documentation/Cocoa/Conceptual/ObjCRuntimeGuide/Articles/chapter_7_section_1.html 
>  for how the type encodings work; you can use `NSLog(@"FSRef*: %s",  
> @encode(FSRef*));` to let gcc show you the type encoding for a given  
> type).
>
> To some extent, this even worked. After `import myfile`, I can call  
> ATSFontActivateFromFileReference on the `myfile` module. Cool. Now I  
> need an FSRef of my font to pass it to the function. I tried:
>
>    from Cocoa import *
>    from CoreFoundation import *
>    import myfile
>
>    url = NSURL.fileURLWithPath_(u'Envy Code R Bold.ttf')
>    status, fsref = CFURLGetFSRef(url, None)
>
>    kATSFontContextLocal = 2
>    kATSFontFormatUnspecified = 0
>    kATSOptionFlagsDefault = 0
>    print myfile.ATSFontActivateFromFileReference(fsref,
>       kATSFontContextLocal, kATSFontFormatUnspecified, None,
>       kATSOptionFlagsDefault, None)
>
> However, this fails with the error message "# ValueError:  
> depythonifying 'pointer', got 'Carbon.File.FSRef'". The problem is  
> that I claimed that ATSFontActivate... takes a  
> '^{FSRef=[80C]}' ("pointer to a struct FSRef which is 80 bytes"),  
> but CFURLGetFSRef returns a Carbon.File.FSRef object instead (which,  
> as far as I understand, is something from the days before pyobjc).  
> Now, this object has a `.data()` function that returns the raw 80  
> bytes that make up the FSRef as a str, but there seems to be no way  
> to pass raw data to a function that was loaded through  
> loadBundleFunctions – so I have a reference to the function and all  
> data I need to call it, but I can't get my data through the bridge.
>
> Looks like a dead end (and http://osdir.com/ml/python.pyobjc.devel/2006-12/msg00024.html 
>  seems to agree. Then again, that is a pre-Leopard post).
>
>
> 2.) Load the font through CoreGraphics, then convert it to a  
> CoreText CTFont, which is toll-free bridged to NSFont, and use that  
> for drawing.
>
> CoreGraphics provides a function to load a font from a file, which I  
> can then convert to a CTFont, which is toll-free bridged to an  
> NSFont. So I should be able to load a font this way and then use  
> Cocoa's normal drawInRect_withAttributes_ function to draw it. I  
> tried:
>
>    from CoreGraphics import *
>    from CoreText import *
>
>    fontDataProvider = CGDataProviderCreateWithFilename('Envy Code  
> R.ttf')
>    customFont = CGFontCreateWithDataProvider(fontDataProvider)
>    print customFont  # looks good so far!
>
>    ctFont = CTFontCreateWithGraphicsFont(customFont, 12.0, None, None)
>    print CTFontCopyPostScriptName(ctFont)  # looks still good
>    print ctFont
>
> However, printing the ctFont or using it as an NSFont gives the  
> error message "<Error>: can't find font object for font id  
> 13828539." – and after that, even printing the postscript name  
> returns "(null)". This does also happen when I call the same  
> functions in an Objective-C program, so this is a limitation of the  
> Cocoa runtime. Another dead end.
>
>
> 3.) Load the font through CoreGraphics, and also draw the text  
> through CoreGraphics
>
> It's possible to get a CoreGraphics context from an  
> NSGraphicsContext. Then I can set the current font of the cg context  
> to the font I loaded from the ttf file. The first few steps even work:
>
>    from CoreGraphics import *
>    from CoreText import *  # contains CGContextSetFont for some reason
>
>    fontDataProvider = CGDataProviderCreateWithFilename('Envy Code  
> R.ttf')
>    customFont = CGFontCreateWithDataProvider(fontDataProvider)
>
>    cgContext = NSGraphicsContext.currentContext().graphicsPort()
>    CGContextSetFont(cgContext, customFont)
>
> Now, CG has a function CGContextShowTextAtPoint that draws a given  
> string (char*) at a given position into a cg context. Sounds great,  
> but as it turns out this function doesn't work for fonts loaded from  
> a file – it only works for activated system fonts loaded through  
> CGContextSelectFont (source: http://developer.apple.com/documentation/GraphicsImaging/Conceptual/drawingwithquartz2d/dq_text/chapter_18_section_4.html 
>  ). There is a function CGContextShowGlyphsAtPoint that works, but  
> it takes a list of glyphs (indices into the font's glyph table –  
> which glyph corresponds to which character is font-dependent!).  
> There is no official function that converts a string to a list of  
> glyphs for a given font, however. But there is an undocumented  
> function: CGFontGetGlyphsForUnichars. As this function is  
> undocumented, we have to load it ourselves again:
>
>    # CoreGraphics is part of the ApplicationServices umbrella  
> framework
>    functions = [
>       # bool CGFontGetGlyphsForUnichars(CGFontRef, unichar[],  
> CGGlyph[], size_t);
>       ( u'CGFontGetGlyphsForUnichars', 'B^{CGFont=}^So^SI'),
>    ]
>
>    # This gives a bus error btw:
>    #import CoreGraphics
>    #objc.loadBundleFunctions(CoreGraphics, globals(), functions)
>
>    AppServices = objc.loadBundle("ApplicationServices", globals(),
>        bundle_path=objc.pathForFramework(u'/System/Library/ 
> Frameworks/ApplicationServices.framework/'))
>    objc.loadBundleFunctions(AppServices, globals(), functions)
>
> Now, let's try to call it:
>
>    print CGFontGetGlyphsForUnichars(customFont, 'py', None, 2)
>
> This gives "ValueError: depythonifying 'pointer', got 'str'" as  
> error. I couldn't figure out how to pass python text to a function  
> that takes `unichar*`. This is probably possible somehow, but since  
> this needs undocumented functions anyways, I'm not too happy with  
> this approach anyway.
>
>
> 4.) Give up, write a small C-based module that calls  
> ATSFontActivateFromFileReference given an string, call that from  
> Python, and call it a day
>
> That's what I ended up doing. It works, but it is strange that this  
> seems necessary for such mundane a task.
>
>
> Thanks,
> Nico