setting graphics mode in ASM

I don''t think that''s possible with a standard VGA display. The best you''ll get is 640x480 at 16 colors. Are you absolutely sure Bochs has no SVGA capability at all?



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Bart

Set AX to 13 and use int 10.

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Original post by trzy
I don''t think that''s possible with a standard VGA display. The best you''ll get is 640x480 at 16 colors. Are you absolutely sure Bochs has no SVGA capability at all
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Bart

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Bochs has SVGA capability, I just cant use interrupts (VESA) to set the video mode. I''m tired of the low resolution mode 13h, So I want to know how to use the i/o ports to set a higher resolution

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Original post by trzy
I don''t think that''s possible with a standard VGA display. The best you''ll get is 640x480 at 16 colors. Are you absolutely sure Bochs has no SVGA capability at all?

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That would be correct, standard VGA only has 256KB of memory. The highest resolution you can get with VGA is 640x480x4 (16 colors) and the most colors you can get is 320x200x8 (256 colors). In order to use SVGA ''modes'' you need to either 1) Hard code your own drivers for every possible graphics card out there or 2) Have VESA drivers or VESA bios extensions installed.

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Original post by Andrew Nguyen
Set AX to 13 and use int 10.

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You need to set AX to 19 (13h) and call interrupt 16 (10h). That will give you 320x200x8. To get 640x480x4 set AX to 18 (12h).

CLOSE ENOUGH!

Once one has set the video mode, how does one get and modify the graphics? If I remember right, a char (byte) pointer to 1000h will do, but a protected-mode compiler won''t like that, will it?

You want higher-res?

*thinks*

Use DirectDraw, and lock the backbuffer to get a pointer to its image data. I''ve got code for that somewhere around here...

Oo! It''s also in the DirectX8.1 SDK... they included samples for DirectDraw, and one of them is called "direct surface write". Look at that.

I don''t mean to flame here, but:

There''s more to writting an operating system than just knowing how to write in assembly language. So learn about the computer first, then write an OS. I suggest starting at

http://developer.intel.com

and downloading the old 386 doucmentation. It''s a great place to start.

--Andrew

If you want to set the video mode using i/o ports, good luck! The only standard relating to i/o ports on video cards is VGA, which you state you don''t want, so unless you only want your program to run on one type of video card only, i''d steer away from i/o ports. You could possibly hack up something to use windows drivers, supplying the driver with any emulated win32 API calls it might want, it would be a mission but could work, allowing your program to use any video card with win drivers (i am assuming ur program isn''t already running in windows).

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Bochs has SVGA capability, I just cant use interrupts (VESA) to set the video mode. I''m tired of the low resolution mode 13h, So I want to know how to use the i/o ports to set a higher resolution

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AFAIK, there is no such thing as a true SVGA standard. Doesn''t Bochs provide a method to use VESA? Perhaps a VESA BIOS of its own?

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Once one has set the video mode, how does one get and modify the graphics? If I remember right, a char (byte) pointer to 1000h will do, but a protected-mode compiler won''t like that, will it?

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Assuming you are developing under DOS, it depends on the protected mode environment your extender provides.

Under DJGPP, you have to use a selector called _dos_ds to access the VRAM at 0xA0000. You can set FS to this selector by doing: _farsetsel(_dos_ds);

Then, you can peek/poke using the _farnspeek*() and _farnspoke*() functions. There are also the _farpeek*()/_farpoke*() functions which require you to pass the selector each time.

Once you use _farsetsel(), the FS register is set to the selector you passed so in assembly language, you can use FS segment overrides or move FS to DS or ES when necessary (for example, to blit using MOVS, you can set ES to FS to access VRAM and use DS to access your buffer.)

See the go32.h and sys/farptr.h header files DJGPP provides.

With Watcom and DOS4GW things are much easier. Just set a pointer to 0xa0000 and you''re set DOS4GW''s default data selector allows you to access all memory.


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Bart