Useful tricks

Making demonstration videos

When making a video with DOSBox, use the CTRL+F5 key to record. Make sure to properly end the recording before closing the emulator to ensure the AVI gets written correctly. OSX users might want to set up a different key because the F-keys are reserved.

To get good quality on Youtube and other places, it's necessary to upscale the content. To keep the pixel art crisp, use nearest neighbor upscaling.

I use the following ffmpeg command to upscale a video for Youtube:

ffmpeg -i in.avi -vf scale=iw*8:ih*8 out.mp4

This creates a 4x upscaled video using nearest neighbor.

Generating assembly code

When optimizing for speed, it's usually helpful to look at generated assembly code. To do so with DJGPP, use something like the following command:

gcc -c -g -Wa,-a,-ad file.c > file.lst

Other GCC options can be added before the file arguments. This will create a file.lst output file that contains the assembly and the original C code for inspection. See DJGPP's FAQ page for more information.

Creating Allegro datafiles

Datafiles are used to easily and safely load and unload assets. The Makefile contains custom definitions for every datafile we make, which are created using the dat utility. See the Allegro manual on using dat for details on how to use it. The Allegro datafile library documentation contains information on how to use these files in C.