I am trying to open some very small .bmp files I made in gimp, and when I try to open them, I get a null pointer.

I thought that there could something wrong with my bmp format, maybe some have alpha channel, maybe some have the wrong color depth.

Is there a way to get any debugging message from allegro?

Else, what is the BMP format that must be respected for true color bitmaps.

Also, probably obvious, but make sure the library is initialized first before calling load_bitmap(); it will return NULL if this isn't the case.

There are a few things that could be happening, but I agree with LennyLen that there's a 99.99% certainty that it isn't your bitmap.

Usual errors are:

- Allegro has not been initialized (`al_init()`)
- The image addon has not been initialized ( al_init_image_addon()).
- Your paths are not aligned... meaning that whatever the path is where you are running your program, it's not able to find the image relative to that. (you might start by putting the image in the same place as the program executable, and run the program from within the same path, and see if that works.)

DANGIT

Thanks for the feedback.

The code is on another computer, so I cannot check it immediately. I am pretty sure I initialized allegro. Maybe it is the path since it's using a path passed in command line argument. Maybe it needs to be modified before using.

I am basically trying to make a tool take takes multiple small bitmaps and converge them into a single bitmap atlas similar to bitmap fonts.

In GIMP, when I file->open, some files are marked as "RGB, 1 layer" while others are marked as "RGB-alpha, 1 layer". The bitmaps with alpha could be posing a problem, but if I remember my test results correctly, all files failed to open.

Well, Yes Allegro has a number of functions that can be used for debugging.

One common method is to use the al_show_native_message_box function, which displays a message box with a specified message, title, and set of buttons. This can be useful for displaying error messages or other debugging information to the user.
Another option is to use the al_trace function, which prints a message to the Allegro log. The log can be viewed using the al_get_allegro_log function and can be useful for debugging when running a program from the command line or in a non-graphical environment.

Hope it will help.
Thanks

Just test your loading code first, then worry about the atlas.

Use an absolute path in your loading code, to test issues with the path. Save in kolourpaint or something else to test different .bmp formats.

Is your Gimp version up to date? Also make sure when saving as a bmp from Gimp you select Advanced Options and check "Do not write colour space information"