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Re: Graphos: works on Cocoa not on GNUstep

From: Wolfgang Lux
Subject: Re: Graphos: works on Cocoa not on GNUstep
Date: Sun, 9 Sep 2012 14:47:25 +0200

Riccardo Mottola wrote:


I did a file-frmat change in Graphos: colors are nov saved, represented and copy&pasted using RGB and not CMYK as it was using as a "GDraw derivative".
Everything appears to work on Mac.

I have problems with copy&paste with Graphos on GNUstep when copy&pasting text objects. All other objects do work, TextObjects are not that different (except for some information which did NOT change. copy&paste did work before...). At the first copy&paste nothing happens... afterwards the program may become unstable and crash.

Can you help figuring out+ I thought about exceptions, but non is raised. I don't say it is a GS bug, it could be an error in Graphos about which Mac is more lenient...

It is certainly not a GS bug. Running Graphos with GNUstep under OS X I got a nice crash report when attempting to paste a text object:

Thread 0 Crashed:
0   libobjc-gnu.3.dylib                 0x0007cf2c objc_msg_lookup + 76
1 libgnustep-base.1.24.dylib 0x00f14310 GSIMapAddPair + 360 (GSIMap.h:1087) 2 libgnustep-base.1.24.dylib 0x00f15418 -[GSDictionary initWithObjects:forKeys:count:] + 912 (GSDictionary.m:220) 3 libgnustep-base.1.24.dylib 0x0103dbc0 +[NSDictionary dictionaryWithObjectsAndKeys:] + 980 (NSDictionary.m:539) 4 Graphos 0x000219c4 -[GRText draw] + 1108 (GRText.m:465) 5 Graphos 0x00018a08 -[GRDocView drawRect:] + 1736 (GRDocView.m:1662)

Given that Graphos crashes in a function like GSIMapAddPair, the most likely cause is a memory corruption. Looking at the code in GRText I see three objects passed to -dictionaryWithObjectsAndKeys:. Two of them, temp and style, are assigned locally in the -draw method and third is the attribute strokeColor. Now looking at the code of - initFromData:inView:zoomFactor:, which is the initializer used for pasted objects, I see that the strokeColor attribute is assigned an autoreleased color object. Retaining this object will avoid the crash (and FWIW, the same error is present for the fillColor attribute).

This code works on OS X either because Cocoa is returning a preallocated color (you might try whether copying a text object with some non-standard color works) or because Cocoa uses a cache of color objects.


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