grub graphics

[haybame]

how do i use grub graphics mode?:

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menuentry "*****" {
        set root='(hd96)'
        set gfxpayload=1024x768x32
        multiboot /boot/kernel.bin
}

[klange]

Try moving the "set gfxpayload=1024x768x32" after the "multiboot" command.

[haybame]

UPDATE
i got the graphics mode to work. but i cant draw a pixel.
how do i draw a pixel?

[pvc]

Multiboot compatible loaders (like GRUB) pass boot information structure pointer to your code in EBX register. It's structure is

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        +-------------------+
0       | flags             |    (required)
        +-------------------+
4       | mem_lower         |    (present if flags[0] is set)
8       | mem_upper         |    (present if flags[0] is set)
        +-------------------+
12      | boot_device       |    (present if flags[1] is set)
        +-------------------+
16      | cmdline           |    (present if flags[2] is set)
        +-------------------+
20      | mods_count        |    (present if flags[3] is set)
24      | mods_addr         |    (present if flags[3] is set)
        +-------------------+
28 - 40 | syms              |    (present if flags[4] or
        |                   |                flags[5] is set)
        +-------------------+
44      | mmap_length       |    (present if flags[6] is set)
48      | mmap_addr         |    (present if flags[6] is set)
        +-------------------+
52      | drives_length     |    (present if flags[7] is set)
56      | drives_addr       |    (present if flags[7] is set)
        +-------------------+
60      | config_table      |    (present if flags[8] is set)
        +-------------------+
64      | boot_loader_name  |    (present if flags[9] is set)
        +-------------------+
68      | apm_table         |    (present if flags[10] is set)
        +-------------------+
72      | vbe_control_info  |    (present if flags[11] is set)
76      | vbe_mode_info     |
80      | vbe_mode          |
82      | vbe_interface_seg |
84      | vbe_interface_off |
86      | vbe_interface_len |
        +-------------------+
88      | framebuffer_addr  |    (present if flags[12] is set)
96      | framebuffer_pitch |
100     | framebuffer_width |
104     | framebuffer_height|
108     | framebuffer_bpp   |
109     | framebuffer_type  |
110-115 | color_info        |
        +-------------------+

You're interested in framebuffer_* fields. framebuffer_addr points to memory location where pixel data is stored. Any writes to this buffer will immediately be visible on screen. How exactly pixel offset is calculated depends on your video mode. To get detailed descriptions of these fields read https://www.gnu.org/software/grub/manua ... iboot.html.

[p34c3]

They have some nice example kernel right there:
https://www.gnu.org/software/grub/manua ... -code.html

[haybame]

how do i compile the code?

[haybame]

can someone please get this code to draw a pixel?
it already sets the mode to 800x600x32 and i am using this: https://wiki.osdev.org/Drawing_In_Protected_Mode

kernel.c

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kmain()
{
        
}

kernel.asm

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bits    32
section .text
   align 4
   
   dd 0x1BADB002
   dd 0x04
   dd -(0x1BADB002 + 0x04)
   
   dd 0 ; skip some flags
   dd 0
   dd 0
   dd 0
   dd 0
   
   dd 0 ; sets it to graphical mode
   dd 800 ; sets the width
   dd 600 ; sets the height
   dd 32 ; sets the bits per pixel
        
push ebx
global start
extern kmain
start:
        cli
        call kmain
        hlt

thanks in advance

[pvc]

Haven't tested it, but should work:

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bits    32
section .text
   align 4
   
   dd 0x1BADB002
   dd 0x04
   dd -(0x1BADB002 + 0x04)
   
   dd 0 ; skip some flags
   dd 0
   dd 0
   dd 0
   dd 0
   
   dd 0 ; sets it to graphical mode
   dd 800 ; sets the width
   dd 600 ; sets the height
   dd 32 ; sets the bits per pixel
       
global start
extern kmain
start:
    mov edi, dword [ebx + 88] ; edi <- framebuffer_addr
    mov dword [edi], 0x00FFFFFF ; white pixel should appear in top left corner
    mov esp, stack.end
    push ebx
    call kmain
    pop ebx
    cli
    hlt

stack: resb 4096
.end:

[haybame]

it works! but is there a way to make a function in C?

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vesa_clear();

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vesa_drawpixel(x,y,colour)

[pvc]

Haven't tested this either. But it should be something along these lines.

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typedef struct
{
    char skip[88];                // there are some interesting fields here but
	                               // we skip them for simplicity

    unsigned framebuffer_addr_lo; // separated these fields to avoid 64 bit
    unsigned framebuffer_addr_hi; // arithmetic (which may need some extra code)
    unsigned framebuffer_pitch;   // this is basically bytes per line
    unsigned framebuffer_width;
    unsigned framebuffer_height;
    unsigned char framebuffer_bpp;
} multiboot_info_t;

multiboot_info_t *mbinfo;

void vesa_drawpixel(unsigned x, unsigned y, unsigned color)
{   // assuming 32bpp
    unsigned *line = (unsigned *)(mbinfo->framebuffer_addr_lo + y * mbinfo->framebuffer_pitch);
    line[x] = color;
}

void vesa_clear(unsigned color)
{   // slow but simple
    for(unsigned y = 0; y < mbinfo->framebuffer_height; ++y)
    {
        for(unsigned x = 0; x < mbinfo->framebuffer_width; ++x)
            vesa_drawpixel(x, y, color);
    } 
}

void kmain(multiboot_info_t *mboot_info)
{
    mbinfo = mboot_info;
    vesa_clear(0x00203040);
    vesa_drawpixel(400, 300, 0x00FFFFFF);
}

For different color depths, you have to change data type of line in vesa_drawpixel. For 16 bit it would be unsigned short and unsigned char for 8 bit.
TBH. These are the basics of the basics. If you want to be able to write something more than 'Hello, World!' for your OS, you really need to be fluent in regular programming as well.

[haybame]

How would i implement a double buffer?

[Love4Boobies]

I think this thread should be locked. It's all "How do I compile, how do I this, how do I that?" Pick up a programming book if you don't know how to do anything.

[haybame]

how do i close a thread?