fb_set_par()可以透過計算fb_info->var.yres_virtual的大小(相較fb_info->var.yres)得知
(SDL 1.2.15)src/video/fbcon/SDL_fbvideo.c +1040
if ( (vinfo.xres != width) || (vinfo.yres != height) || (vinfo.bits_per_pixel != bpp) || (flags & SDL_DOUBLEBUF) ) { vinfo.activate = FB_ACTIVATE_NOW; vinfo.accel_flags = 0; vinfo.bits_per_pixel = bpp; vinfo.xres = width; vinfo.xres_virtual = width; vinfo.yres = height; if ( flags & SDL_DOUBLEBUF ) { vinfo.yres_virtual = height*2; } else { vinfo.yres_virtual = height; }