📄 drawchar.asm
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;
; DRAWCHAR.ASM
;
; Author: Matt Pritchard
; Released to public domain
;
;Assumes Character set of 128 x 8 Bytes
; Character Set has a 16 byte Scratch Buffer at end....
;
;GPRINTC (CharSet, CharNum, Xpos, Ypos, ColorF, ColorB)
;
; in "C"
;void GPRINTC(far char* SetData, int CharNum, int Xpos,
; int Ypos, int Color_Fg, int Color_Bg)
;
; in "BASIC"
;TYPE CharSET
; BitMaps AS STRING * 1024
; Scratch AS STRING * 16 ;END TYPE
;
;DIM SetData AS CharSET
;
;DECLARE SUB GPRINTC(SEG SetData AS ANY, BYVAL CharNum%, BYVAL Xpos%,_
; BYVAL Ypos%, BYVAL ColorF%, BYVAL ColorB%)
;
;
;Draws Text Character (8x8) in Graphics Mode 13 at Pixel (Xpos,Ypos)
;In Color: COLORF with background of COLORB
;
.MODEL Medium
.CODE
SCRATCH_OFS EQU 1024+2 ;Character Set Working Area Offset
VGA_SEGMENT EQU 0A000H ;Vga Memory Segment
SCREEN_WIDTH EQU 320 ;Width of screen in Pixels/Bytes
GPC_STACK STRUC
DW ? ;DI
DW ? ;SI
DW ? ;DS
DW ? ;BP
DD ? ;Caller
GPC_COLORB DB ?,? ;Background Color
GPC_COLORF DB ?,? ;Forground Color
GPC_YPOS DW ? ;Y position
GPC_XPOS DW ? ;X position
GPC_CHAR_NUM DB ?,? ;Character #
GPC_SET_OFS DW ? ;Offset of Set Data
GPC_SET_SEG DW ? ;Segment of Set Data GPC_STACK
ENDS
PUBLIC GPRINTC
GPRINTC PROC FAR
PUSH BP
PUSH DS ;Save Data Seg
PUSH SI ;BC7 - Save Si,DI, Dir Flag
PUSH DI
MOV BP,SP ;Set to address of bp
;Compute Screen Addr to Write to in ES:DI
MOV AX,[BP].GPC_YPOS ;Get Value of Ypos (mult * 320)
MOV DH,AL ;Save 256*Y
MOV CL,6 ;mult * 2^6 (Y * 64)
SHL AX,CL ;Shift Left
ADD AH,DH ;Add in 256 * Ypos
ADD AX,[BP].GPC_XPOS ;Add X position to addr
MOV DI,AX ;Save in DI
;Get Source ADDR of Character Bit Map in DS:SI
;But first, save colors in lookup table
MOV BX,[BP].GPC_SET_OFS ;Get OFFSET of Character Set
MOV SI,BX ;Save in SI for now..
;Get colors
MOV AX,[BP].GPC_SET_SEG ;Segment of Charset
MOV ES,AX ;Use ES to point to it...
MOV AL,[BP].GPC_COLORB ;Get Backgorund color
MOV ES:[SI+SCRATCH_OFS],AL ;Save in Table at Pos (0)
MOV AL,[BP].GPC_COLORF ;Forground Color (1)
MOV ES:[SI+SCRATCH_OFS+1],AL ;Save in Table
;Get addr of character map
MOV AL,[BP].GPC_CHAR_NUM ;Get Character #
AND AX,007FH ;Valid #'s are 0..127
SHL AX,1 ;* 2
SHL AX,1 ;* 4
SHL AX,1 ;* 8
MOV BX,SI ;BX = Start of Char Set
ADD BX,SCRATCH_OFS ;BX points to lookup table
ADD SI,AX ;Add Start of Character Set
;Get segment of character map
MOV DS,[BP].GPC_SET_SEG ;Get Segment of Character Set
;Cant use DS (DGROUP) anymore
MOV AX,VGA_SEGMENT ;VGA Graphics Segment
MOV ES,AX
CLD ;Forwards....
MOV CX,8 ;8 Bytes to Decode
DECODE_CHAR_BYTE:
LODSB ;Get Byte to decode in DS:SI
MOV DL,AL ;Save in DL
XOR DH,DH ;Clear DH
SHL DX,1 ;Get Bit #1
MOV AL,DH ;Put in AL
XLAT AL ;Translate into DAC value
STOSB ;Write to Video Buffer
XOR DH,DH ;Clear DH
SHL DX,1 ;Get Bit #2
MOV AL,DH ;put in AL
XLAT AL ;Translate into DAC value
STOSB ;Write to Video Buffer
XOR DH,DH ;Clear DH
SHL DX,1 ;Get Bit #3
MOV AL,DH ;put in AL
XLAT AL ;Translate into DAC value
STOSB ;Write to Video Buffer
XOR DH,DH ;Clear DH
SHL DX,1 ;Get Bit #4
MOV AL,DH ;put in AL
XLAT AL ;Translate into DAC value
STOSB ;Write to Video Buffer
XOR DH,DH ;Clear DH
SHL DX,1 ;Get Bit #5
MOV AL,DH ;put in AL
XLAT AL ;Translate into DAC value
STOSB ;Write to Video Buffer
XOR DH,DH ;Clear DH
SHL DX,1 ;Get Bit #6
MOV AL,DH ;put in AL
XLAT AL ;Translate into DAC value
STOSB ;Write to Video Buffer
XOR DH,DH ;Clear DH
SHL DX,1 ;Get Bit #7
MOV AL,DH ;put in AL
XLAT AL ;Translate into DAC value
STOSB ;Write to Video Buffer
XOR DH,DH ;Clear DH
SHL DX,1 ;Get Bit #8
MOV AL,DH ;put in AL
XLAT AL ;Translate into DAC value
STOSB ;Write to Video Buffer
ADD DI,SCREEN_WIDTH-8 ;Point to Next Line
LOOP DECODE_CHAR_BYTE ;Process all Lines
POP DI
POP SI
POP DS ;Restore Data Segment
POP BP ;Restore Bp
RET 14 ;Exit and Clean up Stack
GPRINTC ENDP
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