Archive

Archive for June, 2016

计算机底层是如何访问显卡的?

June 17th, 2016 No comments

以前 DOS下做游戏,操作系统除了磁盘和文件管理外基本不管事情,所有游戏都是直接操作显卡和声卡的,用不了什么驱动。

虽然没有驱动,但是硬件标准还是放在那里,VGA, SVGA, VESA, VESA2.0 之类的硬件标准,最起码,你只做320x200x256c的游戏,或者 ModeX 下 320x240x256c 的游戏的话,需要用到VGA和部分 SVGA标准,而要做真彩高彩,更高分辨率的游戏的话,就必须掌握 VESA的各项规范了。

翻几段以前写的代码演示下:

例子1: 初始化 VGA/VESA 显示模式

基本是参考 VGA的编程手册来做:

INT 10,0 - Set Video Mode
    AH = 00
    AL = 00  40x25 B/W text (CGA,EGA,MCGA,VGA)
       = 01  40x25 16 color text (CGA,EGA,MCGA,VGA)
       = 02  80x25 16 shades of gray text (CGA,EGA,MCGA,VGA)
       = 03  80x25 16 color text (CGA,EGA,MCGA,VGA)
       = 04  320x200 4 color graphics (CGA,EGA,MCGA,VGA)
       = 05  320x200 4 color graphics (CGA,EGA,MCGA,VGA)
       = 06  640x200 B/W graphics (CGA,EGA,MCGA,VGA)
       = 07  80x25 Monochrome text (MDA,HERC,EGA,VGA)
       = 08  160x200 16 color graphics (PCjr)
       = 09  320x200 16 color graphics (PCjr)
       = 0A  640x200 4 color graphics (PCjr)
       = 0B  Reserved (EGA BIOS function 11)
       = 0C  Reserved (EGA BIOS function 11)
       = 0D  320x200 16 color graphics (EGA,VGA)
       = 0E  640x200 16 color graphics (EGA,VGA)
       = 0F  640x350 Monochrome graphics (EGA,VGA)
       = 10  640x350 16 color graphics (EGA or VGA with 128K)
         640x350 4 color graphics (64K EGA)
       = 11  640x480 B/W graphics (MCGA,VGA)
       = 12  640x480 16 color graphics (VGA)
       = 13  320x200 256 color graphics (MCGA,VGA)
       = 8x  EGA, MCGA or VGA ignore bit 7, see below
       = 9x  EGA, MCGA or VGA ignore bit 7, see below

    - if AL bit 7=1, prevents EGA,MCGA & VGA from clearing display
    - function updates byte at 40:49;  bit 7 of byte 40:87
      (EGA/VGA Display Data Area) is set to the value of AL bit 7

转换成代码的话,类似这样:

// enter standard graphic mode
int display_enter_graph(int mode)
{ 
    short hr = 0;
    union REGS r;
    memset(&r, 0, sizeof(r));
    if (mode < 0x100) { 
        r.w.ax = (short)mode;
        int386(0x10, &r, &r);
        r.h.ah = 0xf;
        int386(0x10, &r, &r);
        if (r.h.al != mode) hr = -1;
    }   
    else { 
        r.w.ax = 0x4f02;
        r.w.bx = (short)mode;
        int386(0x10, &r, &r);
        if (r.w.ax != 0x004f) hr = -1;
    }
    return hr;
}

Read more…

Categories: 图形编程 Tags: ,