VESA Video Modes: Difference between revisions

;INT 0x10, AX=0x4F00

: Get Controller Info. This is the one that returns the array of all supported video modes.

struct VbeInfoBlock {

char VbeSignature[4]; // == "VESA"

v86_bios(0x10, {ax:0x4f00, es:SEG(vib), di:OFF(vib)}, &out);

if (out.ax!=0x004f) die("Something wrong with VBE get info");

 

In assembly(nasm):

struc VesaInfoBlock ; VesaInfoBlock_size = 512 bytes

.Signature resb 4 ; must be 'VESA'

times 508 db 0

iend

 

'''INT 0x10, AX=0x4F01, CX=mode, ES:DI=256 byte buffer'''

: Get Mode Info. Call this for each member of the mode array to find out the details of that mode. The 256 byte buffer will be filled by the mode info block.

 

struct vbe_mode_info_structure {

uint16_t attributes; // deprecated, only bit 7 should be of interest to you, and it indicates the mode supports a linear frame buffer.

uint8_t reserved1[206];

} __attribute__ ((packed));

 

In assembly(nasm):

struc VesaModeInfoBlock ; VesaModeInfoBlock_size = 256 bytes

.ModeAttributes resw 1

times VesaModeInfoBlock_size db 0

iend

 

'''INT 0x10, AX=0x4F02, BX=mode, ES:DI=CRTCInfoBlock'''

Here's a sample code, assuming you have a VirtualMonitor already ... Basically, you will scan the 'modes list' referenced by the VbeInfoBlock.videomodes[] and then call 'get mode info' for each mode. You can then compare width, height and colordepth of each mode with the desired one.

 

uint16_t findMode(int x, int y, int d)

{

return best;

}

 

== Common Mistakes ==