[MACTCL] Re: TkPutImage crash on very wide images

[Jim I. <ji...@ap...>]

Daniel,

On Sunday, December 9, 2001, at 11:31  PM, Daniel A. Steffen wrote:

> Dear All,
>
> tkMacDraw.c's TkPutImage crashes in CopyBits when using very wide 
> images.
>
> I have a case here where a Tk app (which is working fine on unix & win) 
> uses an image 4846 pixels wide (and 32 bits deep), which results in a 
> bytes_per_line value of 0x4BB8. However, according to IM, PixMap's 
> maximal value for rowBytes is 0x3FFF (c.f. [1]) and indeed CopyBits 
> crashes on the PixMap constructed by TkPutImage with
> 	pixmap.rowBytes = image->bytes_per_line | 0x8000;
> (rowBytes is a short whose high 2 bits are used as QD flags, thus the 
> 0x3FFF limit)
>
> In practical terms this means that Tk will crash when using any 32bit 
> image wider than 4095 pixels.
>
> Not sure what the best solution is here, I've now added a panic before 
> the CopyBits to at least exit gracefully, a better solution would be to 
> split the image into blocks that are maximally 0x4000 bytes wide and do 
> CopyBits on each block... The question is how common is the use of 
> images this wide, is it worth putting in time to get this to work?
>

This depends on how much free time you have.  Not many screens can 
display an image this big, so I wouldn't imagine this is all that common.

> BTW, this problem almost certainly also exist on TkAqua, as TkPutImage 
> is essentially unchanged in tkMacOSXDraw.c (and Carbon CopyBits still 
> uses Bit 15 as a flag)
>

Yes, but I would solve this problem on X not by breaking the image up, 
as you would have to on 9, but by replacing CopyBits with a CoreGraphics 
problem at some point, since that would also open the possibility of 
compositing with alpha channels as well.  So I don't think this is a 
motivation to do this work on 9 (of course, who knows when I will get 
around to this...)

Jim
--
Jim Ingham                                   ji...@ap...
Developer Tools - gdb
Apple Computer