Function vesa_SetWindow

sys/msdos/vidvesa.c:272–313

Set the memory window and return the offset */

/* Set the memory window and return the offset */
static unsigned long
vesa_SetWindow(int window, unsigned long offset)
{
    /* If the desired offset is already within the window, leave the window
       as it is and return the address based on the current window position.
       This minimizes the use of the window switch function.

       On the first call to the function, vesa_win_pos[window] == 0xFFFFFFFF,
       the offset will always be less than this, and the BIOS will always be
       called. */

    unsigned long pos = vesa_win_pos[window];
    if (offset < pos || pos + vesa_win_size <= offset) {
        __dpmi_regs regs;

        memset(&regs, 0, sizeof(regs));
        regs.x.ax = 0x4F05;
        regs.h.bh = 0x00;
        regs.h.bl = window;
        regs.x.dx = offset / vesa_win_gran;
        pos = regs.x.dx * vesa_win_gran;

        if (vesa_win_func != 0) {
            regs.x.cs = vesa_win_func >> 16;
            regs.x.ip = vesa_win_func & 0xFFFF;
            (void) __dpmi_simulate_real_mode_procedure_retf(&regs);
        } else {
            (void) __dpmi_int(VIDEO_BIOS, &regs);
        }
        vesa_win_pos[window] = pos;
    }

    offset = offset - vesa_win_pos[window] + vesa_win_addr[window];
    /* Keep from crashing the system if some malfunction gives us a bad
       offset */
    if (offset < 0xA0000 || offset > 0xBFFFF) {
        vesa_SwitchMode(MODETEXT);
        fprintf(stderr, "Abort: offset=%08lX\n", offset);
        exit(1);
    }
    return offset;
}

static unsigned long
vesa_ReadPixel32(unsigned x, unsigned y)