The render_7segment() function

I won't go into great detail on the render_7segment() function, except to describe in broad terms how it works.

Here's the prototype for render_7segment():

render_7segment (char *digits,
                 unsigned char *r,
                 int xsize,
                 int ysize);

The parameters are:

This is the ASCII string to render into the raw bitmap. Currently, the render_7seg() function understands the numbers 0 through 9, a blank, and the digits A through F (upper and lower case).
This is the raw graphics bitmap, allocated by the caller. It is stored as one byte per pixel, left to right, top to bottom (i.e., r [7] is X-coordinate 7, Y-coordinate 0).
xsize, ysize
This defines the size of the graphical bitmap. To write to an arbitrary (X, Y) location, add the X value to the product of the Y value and the xsize parameter.

As an exercise for the reader, you can extend the character set accepted by the render_7segment() function. You'll want to pay particular attention to the seg7 array, because it contains the individual segment encodings for each character.