alpnm - Portable aNyMap addon for Allegro

Version 1.2

Introduction

alpnm is an addon library for Allegro to allow it to load from and save to the various PNM and PAM file formats. These file formats are very limited and are quite inefficient, but you never know when you may need a loader for them.

Download

alpnm is available for download here or here.

Using alpnm

MinGW users can link to the libalpng.a library supplied in the alpnm archive. The .a file can be built by GCC through the following commands:

gcc -c *.c
ar -rcs libalpnm.a *.o

Alternatively, you can just include the alpnm source files in your project.

There is an included .bat file for MinGW users to copy the library to you MinGW directory.

API - Standard Functions

alpnm uses a straightforward API as similar to Allegro's image IO routines as possible. One point of difference is that the PNM format does not store any palette information, so no palettes are specified when loading or saving PNM files.

load_pnm

BITMAP *load_pnm(const char *filename);

load_pnm() will read the file to determine what PNM format it is. It returns the created bitmap on sucess, and NULL on failure.

save_pnm

int save_pnm(BITMAP *bmp, const char *filename, int mode, const char *comment);

save_pnm() will save to the PNM format specified by mode. This must be one of the following: PBM_ASCII, PBM_BINARY, PGM_ASCII, PGM_BINARY, PPM_ASCII, PPM_BINARY. Returns 0 on success, 1 on failure.

load_pam

BITMAP *load_pam(const char *filename);

Reads and loads a PAM file, sets alpha channel if found. It returns the created bitmap on sucess, and NULL on failure.

save_pam

int save_pam(BITMAP *bmp, const char *filename, pam_mode mode, const char *comment);

Saves to a PAM file. The mode must be one of the following: PAM_BLACKANDWHITE, PAM_BLACKANDWHITE_ALPHA, PAM_GRAYSCALE, PAM_GRAYSCALE_ALPHA, PAM_RGB, PAM_RGB_ALPHA.

get_alpnm_error

char *get_alpnm_error();

A function for generating a string containing a message detailing the last error encountered by alpnm.

API - Background Functions

These are used internally by alpng to load/save the various formats, but you can use them if you want. The loading functions do not check that the file is of the specified type, so using them incorrectly can cause erratic behaviour.

BITMAP *load_pbm(const char *filename);
int save_pbm(BITMAP *bmp, const char *filename, const char *comment);
BITMAP *load_pbm_b(const char *filename);
int save_pbm_b(BITMAP *bmp, const char *filename, const char *comment);


BITMAP *load_pgm(const char *filename);
int save_pgm(BITMAP *bmp, const char *filename, const char *comment);
BITMAP *load_pgm_b(const char *filename);
int save_pgm_b(BITMAP *bmp, const char *filename, const char *comment);


BITMAP *load_ppm(const char *filename);
int save_ppm(BITMAP *bmp, const char *filename, const char *comment);
BITMAP *load_ppm_b(const char *filename);
int save_ppm_b(BITMAP *bmp, const char *filename, const char *comment);

Technical Notes

The PNM format has undergone several changes since its inception, and there is no backwards compatability. alpnm can load all PNM formats, but with files containing more than one image, only the first image will be loaded.

The alpnm save functions use a simple version of the original specification so that the files it creates can be used by any PNM application. Because of this, any comments longer than 68 characters will be truncated. This does not apply to PAM files.

When saving an image to .pbm (monochrome) format, all non-white pixels will be ocnverted to black, with no dithering. When saving an image to .pgm (greyscale) format, coloured pixels are converted to greyscale using the following formula: grey = red * 0.30 + green * 0.59 + blue * 0.11

Version History

Version 1.0

Released 08/05/09

Initial release.

Version 1.1

Released 09/05/09

Added error codes and the get_alpnm_error() function for better error handling.

Version 1.2

Released 12/05/09

Added support for the PAM file format.

Licence

alpnm is licenced under the Lesser GNU Public Licence (LGPL)

GNU LESSER GENERAL PUBLIC LICENSE

Version 3, 29 June 2007

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