Re: [MACTCL] Partial PNG transparency not working in Cocoa Tk

[Linus N. <li...@fa...>]

Hi and thank both of you for replying.

I can confirm that the same thing works fine on Mac OS X Lion.
Unfortunately, Mavericks is not going away any time soon, and it’s a little scary that we appear to be the only ones trying to show transparent icons on the latest Mac OS X.

I now managed to download and compile the sources for Tcl/Tk 8.6.1 and using printf:s around the code I managed to track down the problem:
- The way Tk composits photo images with alpha by creating an image of the background window and manually blending that image with the transparent image (see TkImgPhotoDisplay() in tkImgPhInstance.c).
- When it fails to create the image of the background image, it simply draws the image without alpha (see TkImgPhotoDisplay() @ “We failed to get the image so draw without blending alpha. It's the best we can do”).
- The problem is in case is that exactly that fails.
- The reason for the failure is inside XCopyArea() in tkMacOSXDraw.c. There we can find this code:
	NSView *view = TkMacOSXDrawableView(srcDraw); 
	NSWindow *w = [view window];
	NSInteger gs = [w windowNumber] > 0 ? [w gState] : 0;

… and gs becomes 0, which makes the method return prematurely.
When googling for NSWindow gState, I found this:
https://developer.apple.com/library/mac/releasenotes/AppKit/RN-AppKit/#//apple_ref/doc/uid/TP30000741-CH2-SW51
where it states:
> Beginning in Mac OS X 10.9 -[NSView allocateGState] and -[NSView releaseGState] are no ops. These methods were seldom used. Additionally, methods that relied on the side effects of these methods, specifically -[NSView gState] and -[NSWindow gState] will now always return 0.


That would explain it, I think… But I don’t know what “gState” is and I don’t know how to solve it.
Any ideas??

Best regards,

Linus

On 3 dec 2013, at 15:40, Kevin Walzer <kw...@co...> wrote:

> On 11/29/13, 3:58 AM, Wojciech Kocjan wrote:
>> - happens on OS X 10.9 only - does not happen on 10.8 and below (also,
>> transparency works fine on all other systems and all other OS X
>> versions, so I suspect this is a change in OS X 10.9 that broke it)
>> 
>> - happens with latest Tcl/Tk from fossil, latest ActiveTcl
>> 
>> - happens with both tkpng and Img
>> 
>> - I can also confirm it only happens with Cocoa, not Carbon
>> 
>> So this is definitely an issue with Tk.
> 
> I'm not certain where to start with this. I've seen reports in Apple's 
> dev forums about wonky color calibration in Mavericks (sRGB is no longer 
> accurately rendered in many contexts, which is causing headaches for 
> graphics shops), yet Linus reports that images created with the 
> tk::mac::IconBitmap command (which is just a thin wrapper around various 
> NSImage methods) work just fine. NSImage is itself an opaque wrapper 
> around many, many different things.
> 
> If the issues with alpha channel rendering are based in the system 
> changes in Mavericks, I am not optimistic about fixing them...it does 
> not seem like a good idea to try to special-case image code in the Img, 
> TkPNG, and 8.6 core, I would think. (Nor would I even know where to 
> start here.)
> 
> --Kevin
> 
> -- 
> Kevin Walzer
> Code by Kevin/Mobile Code by Kevin
> http://www.codebykevin.com
> http://www.wtmobilesoftware.com
> 
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