Defer the program termination on error until all files are closed and
(if applicable) all incompletely-written output files are deleted.
In addition, perform the following maintenance tasks:
* Rename and document the internal helpers used by the functions
`png2pnm` and `pnm2png`.
* Unset the executable permission bits for the *.bat test programs.
The pngminus programs use several PNG image transformations:
`png_set_expand`, `png_set_expand_1_2_4_to_8`, etc. (in png2pnm.c);
`png_set_packing`, `png_set_invert_mono`, etc. (in pnm2png.c).
The availability of all of these transformations in libpng is now
required at compile time.
On the topic of transformations, apply an unrelated fix to the use
of `png_set_gamma`.
Improve and modernize png2pnm.c:
* Remove the explicit reading of the input PNG file signature.
Libpng is now able to read it, check it, and issue an appropriate
error message in case of magic number mismatch or file corruption.
(See the function `png_read_sig`.)
* Remove the explicit allocation and dealocation of the image data.
Libpng is now able to manage all the image data automatically.
(See the function `png_read_png`.)
* Specify the needed image transformations without a-priori checking
the image type for applicability.
* Use the `png_set_expand_gray_1_2_4_to_8` transformation.
Since libpng version 1.2.9, this transformation (if needed) must
be enabled separately from `png_set_expand`.
Improve and modernize pnm2png.c:
* Modify the allocation of image data, in order to match libpng's
internal allocation model.
* Transfer the ownership of the image data from the `pnm2png` function
to libpng, which will manage and dealocate it at the right time.
(See the functions `png_set_image_rows` and `png_data_freer`.)
Refactor, clean up, etc.
Improve png2pnm.c:
* Add support for writing 16-bit raw PNM image files.
Fix and improve pnm2png.c:
* Add support for reading 16-bit raw PNM image files.
* Fix the parsing of arbitrarily long numeric strings.
In the parsing of PNM tokens, we can and we should avoid storing
more than one leading '0' in the token buffer. All valid (in-range)
numeric strings must fit in this limited-size buffer, regardless of
their actual length in the input file.
* Refactor the PNM parsing in order to make it more capable to handle
various kinds of input file errors.
* Remove the volatile qualifiers from all variable declarations.
Their original purpose was to appease old (and incorrect) warnings
issued by ancient optimizing compilers.
* Print a note about the program's lack of support for the PAM ("P7")
file format when the input is in this format.
* Add FIXME notes about the need to signal incorrect or incomplete
input files. (For png2pnm, this is done inside libpng.)
Change the license to MIT.
Move the license text from the source files to a LICENSE file.
Move the change log from the source files to a CHANGES file.
Delete the Turbo C makefile and simplify the Linux makefile heavily.
Create explicitly named static and shared executables in the makefile.
Refresh the README file a bit from the twenty year old one.
Signed-off-by: Willem van Schaik <willem@schaik.com>
Signed-off-by: Cosmin Truta <ctruta@gmail.com>
