How to make a bitmap font having only a PNG file?

Question

Is there a way to "convert" an existing PNG file with the characters' images into a bitmap font? Basically, I want to create a FNT file using an image like this...

_{(source: opengameart.org)}

...without the access to a TTF file of the image's characters or any other typical font formats.

Answer 1

The characters in such a monospace font are ordered in increasing ASCII codepoint row-major order.

This means that you can derive the cell offset by simple arithmetic. Given the codepoint base of the top left character, the cell index col,row of a codepoint ch is:

col= (ch-base) % columns
row= (ch-base) / columns

You can then compute X and Y of the rectangle by multiplying the cell index by the width/height of a cell.

Given the computed extents of each character, you can then emit a FNT file based on the FNT specification, or try to find a FNT generator that you can provide with input regions and a bitmap.