; Copyright (c) 1999 Greg Haerr <greg@censoft.com>
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; Copyright (c) 1999 Greg Haerr <greg@censoft.com>
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; Copyright (c) 1991 David I. Bell
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; Copyright (c) 1991 David I. Bell
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; Permission is granted to use, distribute, or modify this source,
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; Permission is granted to use, distribute, or modify this source,
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; provided that this copyright notice remains intact.
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; provided that this copyright notice remains intact.
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;
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;
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; EGA/VGA Screen Driver 16 color 4 planes, higher speed MASM version
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; EGA/VGA Screen Driver 16 color 4 planes, higher speed MASM version
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;
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;
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; Note: this file is a replacement for vgaplan4.c, when raw
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; Note: this file is a replacement for vgaplan4.c, when raw
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; speed rather than portability is desired
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; speed rather than portability is desired
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;
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;
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; The algorithms for some of these routines are taken from the book:
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; The algorithms for some of these routines are taken from the book:
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; Programmer's Guide to PC and PS/2 Video Systems by Richard Wilton.
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; Programmer's Guide to PC and PS/2 Video Systems by Richard Wilton.
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;
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;
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; Routines to draw pixels and lines for EGA/VGA resolutions.
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; Routines to draw pixels and lines for EGA/VGA resolutions.
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; The drawing mode in the data/rotate register is not changed in this
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; The drawing mode in the data/rotate register is not changed in this
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; module, and must be changed as necessary by the callers.
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; module, and must be changed as necessary by the callers.
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;
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;
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PIXBYTES = 80 ; number of bytes in scan line
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PIXBYTES = 80 ; number of bytes in scan line
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MSC = 1
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MSC = 1
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;__MEDIUM__ = 1
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;__MEDIUM__ = 1
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include asm.h
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include asm.h
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.header
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.header
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|
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.cextrn gr_mode,word ; temp kluge devdraw.c graphics draw mode
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.cextrn gr_mode,word ; temp kluge devdraw.c graphics draw mode
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.dseg
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.dseg
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mode_table:
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mode_table:
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db 00h,18h,10h,08h ; vga draw modes
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db 00h,18h,10h,08h ; vga draw modes
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|
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.cseg
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.cseg
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;
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;
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; int ega_init(PSD psd)
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; int ega_init(PSD psd)
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;
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;
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.cproc ega_init
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.cproc ega_init
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mov ax,1 ; success
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mov ax,1 ; success
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ret
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ret
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.cendp ega_init
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.cendp ega_init
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|
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;
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;
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; Routine to draw a horizontal line.
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; Routine to draw a horizontal line.
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; Called from C:
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; Called from C:
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; ega_drawhine(x1, x2, y, color);
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; ega_drawhine(x1, x2, y, color);
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;
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;
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; works in the following EGA and VGA modes:
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; works in the following EGA and VGA modes:
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; 200 line 16 colors modes
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; 200 line 16 colors modes
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; 350 line modes
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; 350 line modes
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; 640x480 16 color
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; 640x480 16 color
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; argument offsets from bp
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; argument offsets from bp
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x1 = arg1 ; first X coordinate
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x1 = arg1 ; first X coordinate
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x2 = arg1 + 2 ; second X coordinate
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x2 = arg1 + 2 ; second X coordinate
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y = arg1 + 4 ; second Y coordinate
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y = arg1 + 4 ; second Y coordinate
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color = arg1 + 6 ; pixel value
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color = arg1 + 6 ; pixel value
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|
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.cproc ega_drawhline
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.cproc ega_drawhline
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push bp ; setup stack frame and preserve registers
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push bp ; setup stack frame and preserve registers
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mov bp, sp
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mov bp, sp
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push si
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push si
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push di
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push di
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push es
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push es
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|
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; configure the graphics controller
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; configure the graphics controller
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|
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mov dx, 03ceh ; DX := Graphics Controller port address
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mov dx, 03ceh ; DX := Graphics Controller port address
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|
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mov al, #3 ; set data rotate register
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mov al, #3 ; set data rotate register
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lea bx, mode_table
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lea bx, mode_table
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add bx, @gr_mode
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add bx, @gr_mode
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mov ah, [bx]
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mov ah, [bx]
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out dx, ax
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out dx, ax
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|
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mov ah, color[bp] ; pixel value
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mov ah, color[bp] ; pixel value
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xor al, al ; Set/Reset register number (0)
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xor al, al ; Set/Reset register number (0)
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out dx, ax
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out dx, ax
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|
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mov ax, 0f01h ; AH := bit plane mask for Enable Set/Reset
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mov ax, 0f01h ; AH := bit plane mask for Enable Set/Reset
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out dx, ax ; AL := Enable Set/Reset register number
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out dx, ax ; AL := Enable Set/Reset register number
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|
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push ds ; preserve DS
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push ds ; preserve DS
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|
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mov ax, y[bp]
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mov ax, y[bp]
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mov bx, x1[bp]
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mov bx, x1[bp]
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|
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; compute pixel address
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; compute pixel address
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mov dx, offset PIXBYTES ; AX := [row * PIXBYTES]
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mov dx, offset PIXBYTES ; AX := [row * PIXBYTES]
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mul dx
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mul dx
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mov cl, bl ; save low order column bits
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mov cl, bl ; save low order column bits
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shr bx, 1 ; BX := [col / 8]
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shr bx, 1 ; BX := [col / 8]
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shr bx, 1
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shr bx, 1
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shr bx, 1
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shr bx, 1
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add bx, ax ; BX := [row * PIXBYTES] + [col / 8]
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add bx, ax ; BX := [row * PIXBYTES] + [col / 8]
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and cl, 07h ; CL := [col % 8]
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and cl, 07h ; CL := [col % 8]
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xor cl, 07h ; CL := 7 - [col % 8]
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xor cl, 07h ; CL := 7 - [col % 8]
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mov ah, 01h ; AH := 1 << [7 - [col % 8]] [mask]
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mov ah, 01h ; AH := 1 << [7 - [col % 8]] [mask]
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mov dx, 0a000h ; ES := EGA buffer segment address
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mov dx, 0a000h ; ES := EGA buffer segment address
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mov es, dx
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mov es, dx
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; AH := bit mask
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; AH := bit mask
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; ES:BX -> video buffer
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; ES:BX -> video buffer
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; CL := number bits to shift left
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; CL := number bits to shift left
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mov di, bx ; ES:DI -> buffer
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mov di, bx ; ES:DI -> buffer
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mov dh, ah ; DH := unshifted bit mask for left byte
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mov dh, ah ; DH := unshifted bit mask for left byte
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|
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not dh
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not dh
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shl dh, cl ; DH := reverse bit mask for first byte
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shl dh, cl ; DH := reverse bit mask for first byte
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not dh ; DH := bit mask for first byte
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not dh ; DH := bit mask for first byte
|
|
|
mov cx, x2[bp]
|
mov cx, x2[bp]
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and cl, 7
|
and cl, 7
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xor cl, 7 ; CL := number of bits to shift left
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xor cl, 7 ; CL := number of bits to shift left
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mov dl, 0ffh ; DL := unshifted bit mask for right byte
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mov dl, 0ffh ; DL := unshifted bit mask for right byte
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shl dl, cl ; DL := bit mask for last byte
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shl dl, cl ; DL := bit mask for last byte
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|
|
; determine byte offset of first and last pixel in the line
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; determine byte offset of first and last pixel in the line
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|
|
mov ax, x2[bp] ; AX := x2
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mov ax, x2[bp] ; AX := x2
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mov bx, x1[bp] ; BX := x1
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mov bx, x1[bp] ; BX := x1
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|
|
mov cl, 3 ; bits to convert pixels to bytes
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mov cl, 3 ; bits to convert pixels to bytes
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|
|
shr ax, cl ; AX := byte offset of X2
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shr ax, cl ; AX := byte offset of X2
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shr bx, cl ; BX := byte offset of X1
|
shr bx, cl ; BX := byte offset of X1
|
mov cx, ax
|
mov cx, ax
|
sub cx, bx ; CX := [number of bytes in line] - 1
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sub cx, bx ; CX := [number of bytes in line] - 1
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|
|
; get Graphics Controller port address into DX
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; get Graphics Controller port address into DX
|
|
|
mov bx, dx ; BH := bit mask for first byte
|
mov bx, dx ; BH := bit mask for first byte
|
; BL := bit mask for last byte
|
; BL := bit mask for last byte
|
mov dx, 03ceh ; DX := Graphics Controller port
|
mov dx, 03ceh ; DX := Graphics Controller port
|
mov al, 8 ; AL := Bit mask Register number
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mov al, 8 ; AL := Bit mask Register number
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|
|
; make video buffer addressable through DS:SI
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; make video buffer addressable through DS:SI
|
|
|
push es
|
push es
|
pop ds
|
pop ds
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mov si, di ; DS:SI -> video buffer
|
mov si, di ; DS:SI -> video buffer
|
|
|
; set pixels in leftmost byte of the line
|
; set pixels in leftmost byte of the line
|
|
|
or bh, bh
|
or bh, bh
|
js L43 ; jump if byte-aligned [x1 is leftmost]
|
js L43 ; jump if byte-aligned [x1 is leftmost]
|
|
|
or cx, cx
|
or cx, cx
|
jnz L42 ; jump if more than one byte in the line
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jnz L42 ; jump if more than one byte in the line
|
|
|
and bl, bh ; BL := bit mask for the line
|
and bl, bh ; BL := bit mask for the line
|
jmp short L44
|
jmp short L44
|
|
|
L42: mov ah, bh ; AH := bit mask for first byte
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L42: mov ah, bh ; AH := bit mask for first byte
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out dx, ax ; update graphics controller
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out dx, ax ; update graphics controller
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|
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movsb ; update bit planes
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movsb ; update bit planes
|
dec cx
|
dec cx
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|
|
; use a fast 8086 machine instruction to draw the remainder of the line
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; use a fast 8086 machine instruction to draw the remainder of the line
|
|
|
L43: mov ah, 0ffh ; AH := bit mask
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L43: mov ah, 0ffh ; AH := bit mask
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out dx, ax ; update Bit Mask register
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out dx, ax ; update Bit Mask register
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rep movsb ; update all pixels in the line
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rep movsb ; update all pixels in the line
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|
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; set pixels in the rightmost byte of the line
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; set pixels in the rightmost byte of the line
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|
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L44: mov ah, bl ; AH := bit mask for last byte
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L44: mov ah, bl ; AH := bit mask for last byte
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out dx, ax ; update Graphics Controller
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out dx, ax ; update Graphics Controller
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movsb ; update bit planes
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movsb ; update bit planes
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|
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pop ds ; restore ds
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pop ds ; restore ds
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|
|
|
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; restore default Graphics Controller state and return to caller
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; restore default Graphics Controller state and return to caller
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;;xor ax, ax ; AH := 0, AL := 0
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;;xor ax, ax ; AH := 0, AL := 0
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;;out dx, ax ; restore Set/Reset register
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;;out dx, ax ; restore Set/Reset register
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;;inc ax ; AH := 0, AL := 1
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;;inc ax ; AH := 0, AL := 1
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;;out dx, ax ; restore Enable Set/Reset register
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;;out dx, ax ; restore Enable Set/Reset register
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;;mov ax, 0ff08h ; AH := 0xff, AL := 0
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;;mov ax, 0ff08h ; AH := 0xff, AL := 0
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;;out dx, ax ; restore Bit Mask register
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;;out dx, ax ; restore Bit Mask register
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|
|
pop es
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pop es
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pop di
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pop di
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pop si
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pop si
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pop bp
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pop bp
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ret
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ret
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.cendp ega_drawhline
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.cendp ega_drawhline
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|
|
|
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;
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;
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; Routine to draw a vertical line.
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; Routine to draw a vertical line.
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; Called from C:
|
; Called from C:
|
; ega_drawvline(x, y1, y2, color);
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; ega_drawvline(x, y1, y2, color);
|
;
|
;
|
; works in the following EGA and VGA modes:
|
; works in the following EGA and VGA modes:
|
; 200 line 16 colors modes
|
; 200 line 16 colors modes
|
; 350 line modes
|
; 350 line modes
|
; 640x480 16 color
|
; 640x480 16 color
|
|
|
; argument offsets from bp
|
; argument offsets from bp
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x = arg1 ; first X coordinate
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x = arg1 ; first X coordinate
|
y1 = arg1 + 2 ; first Y coordinate
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y1 = arg1 + 2 ; first Y coordinate
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y2 = arg1 + 4 ; second Y coordinate
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y2 = arg1 + 4 ; second Y coordinate
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color = arg1 + 6 ; pixel value
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color = arg1 + 6 ; pixel value
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|
|
.cproc ega_drawvline
|
.cproc ega_drawvline
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push bp ; setup stack frame and preserve registers
|
push bp ; setup stack frame and preserve registers
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mov bp, sp
|
mov bp, sp
|
push ds
|
push ds
|
|
|
; configure the graphics controller
|
; configure the graphics controller
|
|
|
mov dx, 03ceh ; DX := Graphics Controller port address
|
mov dx, 03ceh ; DX := Graphics Controller port address
|
|
|
mov al, #3 ; set data rotate register
|
mov al, #3 ; set data rotate register
|
lea bx, mode_table
|
lea bx, mode_table
|
add bx, @gr_mode
|
add bx, @gr_mode
|
mov ah, [bx]
|
mov ah, [bx]
|
out dx, ax
|
out dx, ax
|
|
|
mov ah, color[bp] ; pixel value
|
mov ah, color[bp] ; pixel value
|
xor al, al ; Set/Reset register number (0)
|
xor al, al ; Set/Reset register number (0)
|
out dx, ax
|
out dx, ax
|
|
|
mov ax, 0f01h ; AH := bit plane mask for Enable Set/Reset
|
mov ax, 0f01h ; AH := bit plane mask for Enable Set/Reset
|
out dx, ax ; AL := Enable Set/Reset register number
|
out dx, ax ; AL := Enable Set/Reset register number
|
|
|
; prepare to draw vertical line
|
; prepare to draw vertical line
|
|
|
mov ax, y1[bp] ; AX := y1
|
mov ax, y1[bp] ; AX := y1
|
mov cx, y2[bp] ; BX := y2
|
mov cx, y2[bp] ; BX := y2
|
;;mov cx, bx
|
;;mov cx, bx
|
sub cx, ax ; CX := dy
|
sub cx, ax ; CX := dy
|
;;jge L311 ; jump if dy >= 0
|
;;jge L311 ; jump if dy >= 0
|
;;neg cx ; force dy >= 0
|
;;neg cx ; force dy >= 0
|
;;mov ax, bx ; AX := y2
|
;;mov ax, bx ; AX := y2
|
|
|
L311: inc cx ; CX := number of pixels to draw
|
L311: inc cx ; CX := number of pixels to draw
|
mov bx, x[bp] ; BX := x
|
mov bx, x[bp] ; BX := x
|
push cx ; save register
|
push cx ; save register
|
|
|
; compute pixel address
|
; compute pixel address
|
push dx
|
push dx
|
mov dx, offset PIXBYTES ; AX := [row * PIXBYTES]
|
mov dx, offset PIXBYTES ; AX := [row * PIXBYTES]
|
mul dx
|
mul dx
|
mov cl, bl ; save low order column bits
|
mov cl, bl ; save low order column bits
|
shr bx, 1 ; BX := [col / 8]
|
shr bx, 1 ; BX := [col / 8]
|
shr bx, 1
|
shr bx, 1
|
shr bx, 1
|
shr bx, 1
|
add bx, ax ; BX := [row * PIXBYTES] + [col / 8]
|
add bx, ax ; BX := [row * PIXBYTES] + [col / 8]
|
and cl, 07h ; CL := [col % 8]
|
and cl, 07h ; CL := [col % 8]
|
xor cl, 07h ; CL := 7 - [col % 8]
|
xor cl, 07h ; CL := 7 - [col % 8]
|
mov ah, 01h ; AH := 1 << [7 - [col % 8]] [mask]
|
mov ah, 01h ; AH := 1 << [7 - [col % 8]] [mask]
|
mov dx, 0a000h ; DS := EGA buffer segment address
|
mov dx, 0a000h ; DS := EGA buffer segment address
|
mov ds, dx
|
mov ds, dx
|
pop dx
|
pop dx
|
; AH := bit mask
|
; AH := bit mask
|
; DS:BX -> video buffer
|
; DS:BX -> video buffer
|
; CL := number bits to shift left
|
; CL := number bits to shift left
|
|
|
; set up Graphics controller
|
; set up Graphics controller
|
|
|
shl ah, cl ; AH := bit mask in proper position
|
shl ah, cl ; AH := bit mask in proper position
|
mov al, 08h ; AL := Bit Mask register number
|
mov al, 08h ; AL := Bit Mask register number
|
out dx, ax
|
out dx, ax
|
|
|
pop cx ; restore register
|
pop cx ; restore register
|
|
|
; draw the line
|
; draw the line
|
|
|
mov dx, offset PIXBYTES ; increment for video buffer
|
mov dx, offset PIXBYTES ; increment for video buffer
|
L1111: or [bx], al ; set pixel
|
L1111: or [bx], al ; set pixel
|
add bx, dx ; increment to next line
|
add bx, dx ; increment to next line
|
loop L1111
|
loop L1111
|
|
|
; restore default Graphics Controller state and return to caller
|
; restore default Graphics Controller state and return to caller
|
;;xor ax, ax ; AH := 0, AL := 0
|
;;xor ax, ax ; AH := 0, AL := 0
|
;;out dx, ax ; restore Set/Reset register
|
;;out dx, ax ; restore Set/Reset register
|
;;inc ax ; AH := 0, AL := 1
|
;;inc ax ; AH := 0, AL := 1
|
;;out dx, ax ; restore Enable Set/Reset register
|
;;out dx, ax ; restore Enable Set/Reset register
|
;;mov ax, 0ff08h ; AH := 0xff, AL := 0
|
;;mov ax, 0ff08h ; AH := 0xff, AL := 0
|
;;out dx, ax ; restore Bit Mask register
|
;;out dx, ax ; restore Bit Mask register
|
|
|
pop ds
|
pop ds
|
pop bp
|
pop bp
|
ret
|
ret
|
.cendp ega_drawvline
|
.cendp ega_drawvline
|
|
|
|
|
;
|
;
|
; Routine to set an individual pixel value.
|
; Routine to set an individual pixel value.
|
; Called from C like:
|
; Called from C like:
|
; ega_drawpixel(x, y, color);
|
; ega_drawpixel(x, y, color);
|
;
|
;
|
|
|
; argument offsets from bp
|
; argument offsets from bp
|
x = arg1 ; X coordinate
|
x = arg1 ; X coordinate
|
y = arg1+2 ; Y coordinate
|
y = arg1+2 ; Y coordinate
|
color = arg1+4 ; pixel value
|
color = arg1+4 ; pixel value
|
|
|
.cproc ega_drawpixel
|
.cproc ega_drawpixel
|
push bp
|
push bp
|
mov bp, sp
|
mov bp, sp
|
|
|
mov dx, 03ceh ; graphics controller port address
|
mov dx, 03ceh ; graphics controller port address
|
mov al, #3 ; set data rotate register
|
mov al, #3 ; set data rotate register
|
lea bx, mode_table
|
lea bx, mode_table
|
add bx, @gr_mode
|
add bx, @gr_mode
|
mov ah, [bx]
|
mov ah, [bx]
|
out dx, ax
|
out dx, ax
|
|
|
mov cx, x[bp] ; ECX := x
|
mov cx, x[bp] ; ECX := x
|
mov ax, y[bp] ; EAX := y
|
mov ax, y[bp] ; EAX := y
|
|
|
mov dx, offset PIXBYTES ; AX := [y * PIXBYTES]
|
mov dx, offset PIXBYTES ; AX := [y * PIXBYTES]
|
mul dx
|
mul dx
|
|
|
mov bx, cx ; BX := [x / 8]
|
mov bx, cx ; BX := [x / 8]
|
shr bx, 1
|
shr bx, 1
|
shr bx, 1
|
shr bx, 1
|
shr bx, 1
|
shr bx, 1
|
|
|
add bx, ax ; BX := [y * PIXBYTES] + [x / 8]
|
add bx, ax ; BX := [y * PIXBYTES] + [x / 8]
|
|
|
and cl, 07h ; CL := [x % 8]
|
and cl, 07h ; CL := [x % 8]
|
xor cl, 07h ; CL := 7 - [x % 8]
|
xor cl, 07h ; CL := 7 - [x % 8]
|
mov ch, 01h ; CH := 1 << [7 - [x % 8]] [mask]
|
mov ch, 01h ; CH := 1 << [7 - [x % 8]] [mask]
|
shl ch, cl
|
shl ch, cl
|
|
|
mov dx, 03ceh ; graphics controller port address
|
mov dx, 03ceh ; graphics controller port address
|
|
|
;;required for old code
|
;;required for old code
|
;;mov ax, 0205h ; select write mode 2
|
;;mov ax, 0205h ; select write mode 2
|
;;out dx, ax ; [load value 2 into mode register 5]
|
;;out dx, ax ; [load value 2 into mode register 5]
|
|
|
; new code
|
; new code
|
xor ax,ax ; set color register 0
|
xor ax,ax ; set color register 0
|
mov ah,[bp+8] ; color pixel value
|
mov ah,[bp+8] ; color pixel value
|
out dx,ax
|
out dx,ax
|
|
|
; original code
|
; original code
|
mov al, 08h ; set the bit mask register
|
mov al, 08h ; set the bit mask register
|
mov ah, ch ; [load bit mask into register 8]
|
mov ah, ch ; [load bit mask into register 8]
|
out dx, ax
|
out dx, ax
|
|
|
push ds
|
push ds
|
mov ax, 0a000h ; DS := EGA buffer segment address
|
mov ax, 0a000h ; DS := EGA buffer segment address
|
mov ds, ax
|
mov ds, ax
|
|
|
; new code
|
; new code
|
or [bx],al ; quick rmw to set pixel
|
or [bx],al ; quick rmw to set pixel
|
|
|
;;the following fails under ELKS without cli/sti
|
;;the following fails under ELKS without cli/sti
|
;;using ES works though. Code changed to use single
|
;;using ES works though. Code changed to use single
|
;;rmw above rather than write mode 2, but the
|
;;rmw above rather than write mode 2, but the
|
;;reason for this failure is still unknown...
|
;;reason for this failure is still unknown...
|
;;cli
|
;;cli
|
;;mov al, [bx] ; dummy read to latch bit planes
|
;;mov al, [bx] ; dummy read to latch bit planes
|
;;mov al, color[bp] ; pixel value
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;;mov al, color[bp] ; pixel value
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;;mov [bx], al ; write pixel back to bit planes
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;;mov [bx], al ; write pixel back to bit planes
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;;sti
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;;sti
|
|
|
pop ds ; restore registers and return
|
pop ds ; restore registers and return
|
|
|
mov ax, 0005h ; restore default write mode 0
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mov ax, 0005h ; restore default write mode 0
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out dx, ax ; [load value 0 into mode register 5]
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out dx, ax ; [load value 0 into mode register 5]
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;;mov ax, 0ff08h ; restore default bit mask
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;;mov ax, 0ff08h ; restore default bit mask
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;;out dx, ax ; [load value ff into register 8]
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;;out dx, ax ; [load value ff into register 8]
|
|
|
pop bp
|
pop bp
|
ret
|
ret
|
.cendp ega_drawpixel
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.cendp ega_drawpixel
|
|
|
;
|
;
|
; Routine to read the value of an individual pixel.
|
; Routine to read the value of an individual pixel.
|
; Called from C like:
|
; Called from C like:
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; color = ega_readpixel(x, y);
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; color = ega_readpixel(x, y);
|
;
|
;
|
|
|
; argument offsets from bp
|
; argument offsets from bp
|
x = arg1 ; X coordinate
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x = arg1 ; X coordinate
|
y = arg1+2 ; Y coordinate
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y = arg1+2 ; Y coordinate
|
|
|
.cproc ega_readpixel
|
.cproc ega_readpixel
|
push bp
|
push bp
|
mov bp, sp
|
mov bp, sp
|
push si
|
push si
|
push ds
|
push ds
|
|
|
mov ax, y[bp] ; EAX := y
|
mov ax, y[bp] ; EAX := y
|
mov bx, x[bp] ; EBX := x
|
mov bx, x[bp] ; EBX := x
|
mov dx, offset PIXBYTES ; AX := [y * PIXBYTES]
|
mov dx, offset PIXBYTES ; AX := [y * PIXBYTES]
|
mul dx
|
mul dx
|
|
|
mov cl, bl ; save low order column bits
|
mov cl, bl ; save low order column bits
|
shr bx, 1 ; BX := [x / 8]
|
shr bx, 1 ; BX := [x / 8]
|
shr bx, 1
|
shr bx, 1
|
shr bx, 1
|
shr bx, 1
|
|
|
add bx, ax ; BX := [y * PIXBYTES] + [x / 8]
|
add bx, ax ; BX := [y * PIXBYTES] + [x / 8]
|
|
|
and cl, 07h ; CL := [x % 8]
|
and cl, 07h ; CL := [x % 8]
|
xor cl, 07h ; CL := 7 - [x % 8]
|
xor cl, 07h ; CL := 7 - [x % 8]
|
|
|
mov dx, 0a000h ; DS := EGA buffer segment address
|
mov dx, 0a000h ; DS := EGA buffer segment address
|
mov ds, dx
|
mov ds, dx
|
|
|
mov ch, 01h ; CH := 1 << [7 - [col % 8]] [mask]
|
mov ch, 01h ; CH := 1 << [7 - [col % 8]] [mask]
|
shl ch, cl ; CH := bit mask in proper position
|
shl ch, cl ; CH := bit mask in proper position
|
|
|
mov si, bx ; DS:SI -> region buffer byte
|
mov si, bx ; DS:SI -> region buffer byte
|
xor bl, bl ; BL is used to accumulate the pixel value
|
xor bl, bl ; BL is used to accumulate the pixel value
|
|
|
mov dx, 03ceh ; DX := Graphics Controller port
|
mov dx, 03ceh ; DX := Graphics Controller port
|
mov ax, 0304h ; AH := initial bit plane number
|
mov ax, 0304h ; AH := initial bit plane number
|
; AL := Read Map Select register number
|
; AL := Read Map Select register number
|
|
|
L112: out dx, ax ; select bit plane
|
L112: out dx, ax ; select bit plane
|
mov bh, [si] ; BH := byte from current bit plane
|
mov bh, [si] ; BH := byte from current bit plane
|
and bh, ch ; mask one bit
|
and bh, ch ; mask one bit
|
neg bh ; bit 7 of BH := 1 if masked bit = 1
|
neg bh ; bit 7 of BH := 1 if masked bit = 1
|
; bit 7 of BH := 0 if masked bit = 0
|
; bit 7 of BH := 0 if masked bit = 0
|
rol bx, 1 ; bit 0 of BL := next bit from pixel value
|
rol bx, 1 ; bit 0 of BL := next bit from pixel value
|
dec ah ; AH := next bit plane number
|
dec ah ; AH := next bit plane number
|
jge L112
|
jge L112
|
|
|
xor ax, ax ; AL := pixel value
|
xor ax, ax ; AL := pixel value
|
mov al, bl
|
mov al, bl
|
|
|
pop ds
|
pop ds
|
pop si
|
pop si
|
pop bp
|
pop bp
|
ret
|
ret
|
.cendp ega_readpixel
|
.cendp ega_readpixel
|
|
|
.cend
|
.cend
|
end
|
end
|
|
|
