static void cga_scroll(int delta)
{
int new_backscroll = max(min(crtsave_backscroll - delta, (int) crtsave_size), 0);
if (new_backscroll == crtsave_backscroll)
return;
if (crtsave_backscroll == 0)
// save current screen
cga_savebuf_copy(crtsave_pos + crtsave_size, 0);
crtsave_backscroll = new_backscroll;
cga_savebuf_copy(crtsave_pos + crtsave_size - crtsave_backscroll, 1);
}
static void
cga_putc(int c)
{
#if CRT_SAVEROWS > 0
// unscroll if necessary
if (crtsave_backscroll > 0) {
cga_savebuf_copy(crtsave_pos + crtsave_size, 1);
crtsave_backscroll = 0;
}
#endif
// if no attribute given, then use light gray on black
if (!(c & ~0xFF))
c |= 0x0700;
switch (c & 0xff) {
case '\b':
if (crt_pos > 0) {
crt_pos--;
crt_buf[crt_pos] = (c & ~0xff) | ' ';
}
break;
case '\n':
crt_pos += CRT_COLS;
/* fallthru */
case '\r':
crt_pos -= (crt_pos % CRT_COLS);
break;
case '\t':
cons_putc(' ');
cons_putc(' ');
cons_putc(' ');
cons_putc(' ');
cons_putc(' ');
break;
default:
crt_buf[crt_pos++] = c; /* write the character */
break;
}
// What is the purpose of this?
if (crt_pos >= CRT_SIZE) {
int i;
#if CRT_SAVEROWS > 0
// Save the scrolled-back row
if (crtsave_size == CRT_SAVEROWS - CRT_ROWS)
crtsave_pos = (crtsave_pos + 1) % CRT_SAVEROWS;
else
crtsave_size++;
memcpy(crtsave_buf + ((crtsave_pos + crtsave_size - 1) % CRT_SAVEROWS) * CRT_COLS, crt_buf, CRT_COLS * sizeof(uint16_t));
#endif
memcpy(crt_buf, crt_buf + CRT_COLS, (CRT_SIZE - CRT_COLS) * sizeof(uint16_t));
for (i = CRT_SIZE - CRT_COLS; i < CRT_SIZE; i++)
crt_buf[i] = 0x0700 | ' ';
crt_pos -= CRT_COLS;
}
/* move that little blinky thing */
outb(addr_6845, 14);
outb(addr_6845 + 1, crt_pos >> 8);
outb(addr_6845, 15);
outb(addr_6845 + 1, crt_pos);
}