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VGA 640x480 Pixel Write....400 points!!!

Hello Everyone...
OK, so I can write to the VGA memory and get something on the screen, I get the write color and beginning position, but when I try to write only one pixel, I get what seems to be 4 pixels in a row. I have an idea of what it is, but I can seem to come up with a solution for it. Anyone care to help? I need to be able to write to one pixel, with a specified color.

Thanks,
Ernie

BeyondWu

In which Mode? 16 colors or 256 colors? pls post some of your code.

regards,
Wu

fastawdtsi

ASKER

648x480 16 colors...

Thanks

ASKER CERTIFIED SOLUTION

MrT-RSI

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BeyondWu

fastawdtsi,

Sorry for my late response, I'm on the vacation..
Here is the code, although it's not a pure asm code, but it really can work, it works well in my windows WDM driver(both CRT and LCD)...
I think it's easy for you to convert it into assemble languange, if not, please tell me, I hope I can convert it for you.

void outportb(short port, BYTE val)
{
      __asm
      {
            mov dx, port
            mov al, val
            out dx, al
      }
}

gramMem is your VGA memory pointer. A000:0000
// x,y--> coordinates
// val--> color
// odd--> see WriteLine function, FIXME, this parameter could be optimized
void drawpixel16(int x, int y, BYTE val, BYTE odd)
{
      BYTE i = 3 - x % 4;
      BYTE temp;

      /*0 - means copy, 0x8 - AND, 0x10 - OR, 0x18 - XOR*/
      outportb(0x3ce, 0x03);
      outportb(0x3cf, 0x0);

      outportb(0x3ce, 0x05);
      outportb(0x3cf, 0x02);

      outportb(0x3C4, 2);
      outportb(0x3C5, 0xFF);

      /*ditermine which bit we want to change*/
      /*Bit Mask Register, enable/disable the bit modify with 0/1*/
      outportb(0x3ce, 0x08);
      if(x%8 < 4)
            outportb(0x3Cf, 1<<(i+4));
      else
            outportb(0x3Cf, 1<<(i+0));

      temp = gramMem[y*80 + x/8]; // need to read it again! otherwise in you can't show anything, it's crazy!

      if(x%2 == 0)
            gramMem[y*80 + x/8] = val>>(odd?0:4);
      else
            gramMem[y*80 + x/8] = val>>(odd?4:0);
}

// how to draw a line
void WriteLine(int x, int y, BYTE* buffer, int nlen, int bitcount)
{
      switch(bitcount)
      {
      case 4:
            {
                  int i=0;
                  BYTE odd = x % 2;

                  while(i < nlen)
                  {
                        drawpixel16(x, y, *buffer, odd);
                        if(i%2)
                              buffer++;
                        i++;
                        x++;
                  }
            }
            break;
      }
}

regards,
Wu