bug#69992: Minor improvement to image map transformation logic

[David Ponce via "Bug reports for GNU Emacs, the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>]

On 30/03/2024 09:10, Eli Zaretskii wrote:
>> Date: Fri, 29 Mar 2024 11:19:11 +0100
>> From: David Ponce <da_vid@orange.fr>
>> Cc: Eli Zaretskii <eliz@gnu.org>, Joseph Turner <joseph@breatheoutbreathe.in>
>>
>>> The attached new patch fixes the logic to be consistent with Emacs
>>> internal implementation, plus some other tweaks to check if a
>>> transformation apply before to call the transformation function.
>>> I also updated some tests according to functions changes.
>>> Here is a possible change log:
>>>
>>> 2024-03-28  David Ponce  <da_vid@orange.fr>
>>>
>>>       * lisp/image.el (image--compute-scaling)
>>>       (image--compute-rotation): New functions.
>>>       (image--compute-map, image--compute-original-map): Use them.
>>>       Ensure all transformations are applied or undone according to what
>>>       Emacs does internally.  Call a transformation function only when
>>>       needed.  Fix doc string.
>>>       (image--scale-map): Assume effective scale argument.
>>>       (image--rotate-map): Assume effective rotation argument.
>>>       (image--rotate-coord): Improve doc string.
>>>       (image--flip-map): Remove no more used flip argument.
>>>
>>>       * test/lisp/image-tests.el (image-create-image-with-map): Use a
>>>       valid SVG image otherwise `image-size' will not return a valid
>>>       value and calculation of scale could fail.
>>>       (image-transform-map): Update according to changed signature of
>>>       image--flip-map.
>> [...]
>>
>> Hello,
>>
>> Please find attached a new patch with an additional small fix I forgot to
>> include.  Sorry.
> 
> Thanks.  Please resend with the updated commit log message, and I will
> install it.

Hello Eli,

The change log is the same.  The last patch include a slightly modified
version of the new function `image--compute-rotation' to return 0 by default
when no rotation is specified, instead of nil.

Please let me know if you need anything else.
Thanks!