Re: Correcting NSAffineTransform

[Adam Fedor]

On Thursday, January 15, 2004, at 05:54 PM, Fred Kiefer wrote:

> Ken Ferry just send me testing results from Cocoa that seem to prove, 
> that the GNUstep implementation of prependTransform: and 
> appendTransform: are the wrong way around. This is due to the fact, 
> that the documentation from Apple is rather confusing, but, as I 
> convinced myself after hard thinking, is mathematically correct.
>
> We will need to exchange the code of this two methods and also inspect 
> all their usages. There are, for example, the GNUstep extension 
> methods concatenateWith: and concatenateWithMatrix:. I am not sure, if 
> these also need correcting or if the former could just be changed to 
> use prependTransform, wheras the later could be left unchanged?
>
> In GUI appenTransform: also gets used in NSView and NSPrintOperation. 
> And both methods get used in the backends. Here a simple exchange of 
> the calls should do.
>
> As this is a dangerous process I would like to hear a few comments 
> before I start it.

Well, I haven't looked at what things change, but I imagine it should 
be fairly obvious if something is not working after the change - 
perhaps some of the drawing tests that Alex wrote would help or just 
running some common applications. If you can't find any obvious 
failures then any remaining bugs are probably not important enough to 
not commit the change.