From:	"Henri Ossi" <henri DOT ossi AT mail DOT htk DOT fi>
Newsgroups:	comp.os.msdos.djgpp
Subject:	Blitting chars
Date:	Sun, 17 May 1998 14:06:00 +0300
Organization:	Telecom Finland News Service
Lines:	141
Message-ID:	<6jmgi6$imc$1@hiisi.inet.fi>
NNTP-Posting-Host:	pc2022.public.htk.fi
To:	djgpp AT delorie DOT com
DJ-Gateway:	from newsgroup comp.os.msdos.djgpp

God, I hate outlook Express, sorry if this message already came.....


Hi.

I've been trying to make a char drawer in asm (using NASM)
But i'm still quite confused about some things:

1) if I use a double buffer, it is sized 320x200, so its 64k, right?
    so my program crashes, if i use .com files
2) i have no idea, how to make .exe files ( well, i've read about it from
the tutorials, but still...)
3) i dont know, which registers i can globber and which i cant (beginners
problem =)
4) can i even do this kind of stuff to a com file?
5) my program doesnt work at all

But, heres the code in C (djgpp) and in asm, look for stupid things that
I've made in the asm version.
( like the fact that if it works, it still doesn't draw a visible character
to the screen...)

void char_blt(int x, int y, int color, unsigned char c)
{
        int offset, x2, y2;
        char *work_char;
unsigned char bit_mask = 0x80;

        rom_char_set=(char*)ROM_START_POINT+__djgpp_conventional_base;
        work_char = rom_char_set + c * CHAR_HEIGHT;

        offset = (y*320) + x;

        for(y2=0; y2<CHAR_HEIGHT; y2++) {
  bit_mask = 0x80;
                for(x2=0; x2<CHAR_WIDTH; x2++) {
   if((*work_char & bit_mask))
                                dblbuf[offset+x2] = color;
                        else dblbuf[offset+x2] = 0;
   bit_mask = (bit_mask >> 1);
  }
  offset += 320;
  work_char++;
}
}



---------------

          BITS 16
          ORG 0x100

screen_ram  EQU 0A000h
CHAR_WIDTH  EQU 8
CHAR_HEIGHT EQU 8
CHAR_START1 EQU 0xf000
CHAR_START2 EQU 0xfa6e


;==============
Mainprogram:
;==============

CALL SetVGAMode
CALL FillScreen_black
CALL DrawChar
CALL WaitForKey
CALL EndProgram


;==============
DrawChar:
;==============
PUSH AX ;counting
PUSH BX ;bitmask
PUSH CX ;CH xcount, CL ycount

PUSH ES ;screen ram
PUSH DI ;offset

PUSH DS ;char rom
PUSH SI ;work_char

        ;es:di is screen ram
        MOV AX, screen_ram
        MOV ES,AX
        XOR DI,DI

        ;ds:si is the char rom
        MOV AX, CHAR_START1
        MOV DS,AX
        MOV SI, CHAR_START2

.YLOOP  MOV CL, 0h

MOV BL, 80h ;bitmask reset

.XLOOP  MOV CH, 0h

        MOV AL, [DS:SI]
        AND AL,BL        ;mask
        MOV [ES:DI], byte al ;write to screen

        SHR BX,1         ;move mask

CMP CH,CHAR_WIDTH
JNZ .XLOOP

        ADD DI, 320 ;offset+=320
        ADD SI, 1   ;work_Char++

CMP CL,CHAR_HEIGHT
JNZ .YLOOP


POP SI
POP DS
POP DI
POP ES
POP CX
POP BX
POP AX

RET



-----------



If you have any source code about anything like this, please send it to me.
I'd really appreciate it.

Thanks for your time

-Henri Ossi

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