If I understand what you want to do, the 'bitmap' program from the Slackware 'bitmap' package isn't relevant. It's a really old, really crude tool for creating X cursors and stuff.
You need to work out what your first "SOMEHOW??" actually is. Everything else flows from that.
If you're writing a text-console-mode game, the first "SOMEHOW??" is the setfont command, and the second "SOMEHOW??" is just to write the right ascii character in the right position like you would have done on a VT100. Therefore you want to create a Linux text-console font.
See these pages:
and the man pages for the relevant commands in Slackware's kbd package: setfont, psfaddtable, etc
UPDATE! UPDATE! UPDATE!
(smacks own head)
The dear old VT220 [and therefore, everything that came after it] had the native capability of receiving soft-downloaded graphics characters! Of course! And then you selected and displayed them just like the line-drawing character set that you may already be familiar with. I saw Space Invaders done this way on a text vdu in 1980
I doubt the Linux text console supports enough VT220 emulation to do this, but xterm might well support it. And it may or may not be more difficult than creating a psf font for Linux. But it's another option.