What is the simplest way to get a higher resolution Graphics Mode?-CodePudding

I'm working on a little operating system, and I've decided that I've grown tired of VGA's 320x200 8-bit color limitations. I really don't want to refactor all my code, so my goal is implementing the simplest way to get 720p and 16-bit colors. Here's some of my code (and a link to my GitHub):

boot.asm:

[org 0x7c00]                        
KERNEL_LOCATION equ 0x1000
                                    

mov [BOOT_DISK], dl                 

                                    
xor ax, ax                          
mov es, ax
mov ds, ax
mov bp, 0x8000
mov sp, bp

mov bx, KERNEL_LOCATION
mov dh, 32

mov ah, 0x02
mov al, dh 
mov ch, 0x00
mov dh, 0x00
mov cl, 0x02
mov dl, [BOOT_DISK]
int 0x13

                                    
mov ah, 0x00
mov al, 0x13
int 0x10                ; text mode


CODE_SEG equ GDT_code - GDT_start
DATA_SEG equ GDT_data - GDT_start

cli
lgdt [GDT_descriptor]
mov eax, cr0
or eax, 1
mov cr0, eax
jmp CODE_SEG:start_protected_mode

jmp $
                                    
BOOT_DISK: db 0

GDT_start:
    GDT_null:
        dd 0x0
        dd 0x0

    GDT_code:
        dw 0xffff
        dw 0x0
        db 0x0
        db 0b10011010
        db 0b11001111
        db 0x0

    GDT_data:
        dw 0xffff
        dw 0x0
        db 0x0
        db 0b10010010
        db 0b11001111
        db 0x0

GDT_end:

GDT_descriptor:
    dw GDT_end - GDT_start - 1
    dd GDT_start


[bits 32]
start_protected_mode:
    mov ax, DATA_SEG
    mov ds, ax
    mov ss, ax
    mov es, ax
    mov fs, ax
    mov gs, ax
    
    mov ebp, 0x90000        ; 32 bit stack base pointer
    mov esp, ebp

    jmp KERNEL_LOCATION

                                     
 
times 510-($-$$) db 0              
dw 0xaa55

kernel.cpp:

typedef unsigned char uint8_t;
typedef unsigned char u8;
typedef unsigned short uint16_t;
typedef unsigned int u32;
typedef u32 size_t;
#define SCREEN_WIDTH 320
#define SCREEN_HEIGHT 200
#define SCREEN_SIZE (SCREEN_WIDTH * SCREEN_HEIGHT)
#define FPS 30
#define PIT_HERTZ 1193131.666
#define CLOCK_HIT (int)(PIT_HERTZ/FPS)
#define KEY_LEFT 0x4B
#define KEY_UP 0x48
#define KEY_RIGHT 0x4D
#define KEY_DOWN 0x50

static uint8_t *BUFFER = (uint8_t *) 0xA0000;

// double buffers
uint8_t _sbuffers[2][SCREEN_SIZE];
uint8_t _sback = 0;

#define CURRENT (_sbuffers[_sback])
#define SWAP() (_sback = 1 - _sback)

#define screen_buffer() (_sbuffers[_sback])

#define screen_set(_p, _x, _y)\
    (_sbuffers[_sback][((_y) * SCREEN_WIDTH   (_x))]=(_p))

static inline void outb(uint16_t port, uint8_t val)
{
    asm volatile ( "outb %0, %1" : : "a"(val), "Nd"(port) );
}

static inline uint8_t inb(uint16_t port)
{
    uint8_t ret;
    asm volatile ( "inb %1, %0"
                   : "=a"(ret)
                   : "Nd"(port) );
    return ret;
}

const unsigned char font[128-32][8] = {
    { 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00},   // U 0020 (space)
           /*deleted to aid in shorter code...*/
    { 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00}    // U 007F
};

static inline void *memcpy(void *dst, const void *src, size_t n)
{
    u8 *d = (u8*)dst;
    const u8 *s = (const u8*)src;

    while (n-- > 0) {
        *d   = *s  ;
    }

    return d;
}

void screen_swap() {
    memcpy(BUFFER, CURRENT, SCREEN_SIZE);
    SWAP();
}

unsigned read_pit(void) {
    unsigned count = 0;
 
    // al = channel in bits 6 and 7, remaining bits clear
    outb(0x43,0b0000000);
 
    count = inb(0x40);          // Low byte
    count |= inb(0x40)<<8;      // High byte
 
    return count;
}
 
void draw_char(char c, int x, int y, unsigned char color)
{
    const unsigned char *glyph = font[(int)c-32];
 
    for(int cy=0;cy<8;cy  ){
        for(int cx=0;cx<8;cx  ){
            if(((int)glyph[cy]&(1<<cx))==(1<<cx)){
                screen_set(color,x cx,y cy);
            }
        } 
    }
}

void draw_string(const char * s, int x, int y, unsigned char color) {
    int i = 0;
    while(s[i] != false) {
        draw_char(s[i],x (i*8),y,color);
        i  ;
    }
}

void draw_rect(int pos_x, int pos_y, int w, int h, unsigned char color) {
    for(int y = 0; y<h; y  ) {
        for(int x = 0; x<w; x  ) {
            screen_set(color,x pos_x,y pos_y);
        }
    }
}

CodePudding user response：

Since you're targetting 16-bit color, suggesting to use the higher VGA 640x480 resolution isn't going to cut it for you!
What you need is switching to a VESA video mode. The "VESA BIOS EXTENSION (VBE) Core Function Standard v3" from https://vesa.org/ is the document that you should read.

Unrelated to your graphics question, but nonetheless important are the errors in your bootloader code. And because I see that you keep re-posting these errors, I find it is urgent that you address these...

Your mov [BOOT_DISK], dl instruction already depends on a correct DS segment register. You must store DL after setting up the segment registers.
If you change (E)SP, then also change SS and do it in the instruction directly above it.

xor ax, ax
mov ds, ax
mov es, ax
mov ss, ax      ; \
mov sp, 0x8000  ; /
mov [BOOT_DISK], dl

and

mov ax, DATA_SEG
mov ds, ax
mov es, ax
mov fs, ax
mov gs, ax
mov ss, ax              ; \
mov esp, 0x00090000     ; /  32 bit stack base pointer
mov ebp, esp            ; Only if you need this!

You cannot omit checking the error status after the BIOS.LoadSectors function 02h! Should an error occur, retry the operation a few times, then fail with a suitable message.
Comment your code, and write comments that are true! With mov ah, 0x00 mov al, 0x13 int 0x10 ; text mode, you are setting up a graphics mode.