void zero_open(char *device, int *w, int *h, int *d, int s, int *line);
int  zero_update(void *fb, void *pal);
void zero_close(void);

Since the terminal framebuffer has a fixed resolution (the whole screen), parameters to zero_open are of output type: instead of asking for a specific resolution, the function returns current terminal framebuffer resolution and depth.

It adds an extra output parameter line, which is the number of bytes you have to jump from one row to the next one (width * depth doesn't work here). See the rgb as an example of this.