149 lines
5.2 KiB
NASM
149 lines
5.2 KiB
NASM
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; Command & Conquer Red Alert(tm)
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; Copyright 2025 Electronic Arts Inc.
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;
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; This program is free software: you can redistribute it and/or modify
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; it under the terms of the GNU General Public License as published by
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; the Free Software Foundation, either version 3 of the License, or
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; (at your option) any later version.
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;
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; This program is distributed in the hope that it will be useful,
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; but WITHOUT ANY WARRANTY; without even the implied warranty of
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; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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; GNU General Public License for more details.
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;
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; You should have received a copy of the GNU General Public License
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; along with this program. If not, see <http://www.gnu.org/licenses/>.
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;
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; $Header: g:/library/source/rcs/./facing16.asm 1.10 1994/05/20 15:32:36 joe_bostic Exp $
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;***************************************************************************
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;** C O N F I D E N T I A L --- W E S T W O O D A S S O C I A T E S **
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;***************************************************************************
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;* *
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;* Project Name : Support Library *
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;* *
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;* File Name : FACING16.ASM *
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;* *
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;* Programmer : Joe L. Bostic *
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;* *
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;* Start Date : May 8, 1991 *
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;* *
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;* Last Update : February 6, 1995 [BWG] *
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;* *
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;*-------------------------------------------------------------------------*
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;* Functions: *
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;* Desired_Facing16 -- Converts coordinates into a facing number. *
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;* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - *
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IDEAL
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P386
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MODEL USE32 FLAT
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GLOBAL Desired_Facing16 :NEAR
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; INCLUDE "wwlib.i"
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DATASEG
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; 16 direction desired facing lookup table. Build the index according
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; to the following bits:
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;
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; bit 4 = Is y2 < y1?
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; bit 3 = Is x2 < x1?
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; bit 2 = Is the ABS(x2-x1) < ABS(y2-y1)?
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; bit 1 = Is the lesser absolute difference very close to zero?
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; bit 0 = Is the lesser absolute difference very close to the greater dist?
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NewFacing16 DB 3, 2, 4,-1, 1, 2,0,-1
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DB 13,14,12,-1,15,14,0,-1
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DB 5, 6, 4,-1, 7, 6,8,-1
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DB 11,10,12,-1, 9,10,8,-1
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CODESEG
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;***************************************************************************
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;* DESIRED_FACING16 -- Converts coordinates into a facing number. *
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;* *
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;* This converts coordinates into a desired facing number that ranges *
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;* from 0 to 15 (0 equals North and going clockwise). *
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;* *
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;* INPUT: x1,y1 -- Position of origin point. *
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;* *
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;* x2,y2 -- Position of target. *
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;* *
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;* OUTPUT: Returns desired facing as a number from 0 to 255 but *
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;* accurate to 22.5 degree increments. *
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;* *
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;* WARNINGS: If the two coordinates are the same, then -1 will be *
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;* returned. It is up to you to handle this case. *
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;* *
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;* HISTORY: *
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;* 08/14/1991 JLB : Created. *
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;*=========================================================================*
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; long Desired_Facing16(long x1, long y1, long x2, long y2);
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PROC Desired_Facing16 C near
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USES ebx, ecx, edx
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ARG x1:DWORD
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ARG y1:DWORD
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ARG x2:DWORD
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ARG y2:DWORD
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xor ebx,ebx ; Index byte (built).
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; Determine Y axis difference.
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mov edx,[y1]
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mov ecx,[y2]
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sub edx,ecx ; DX = Y axis (signed).
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jns short ??absy
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inc ebx ; Set the signed bit.
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neg edx ; ABS(y)
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??absy:
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; Determine X axis difference.
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shl ebx,1
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mov eax,[x1]
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mov ecx,[x2]
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sub ecx,eax ; CX = X axis (signed).
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jns short ??absx
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inc ebx ; Set the signed bit.
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neg ecx ; ABS(x)
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??absx:
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; Determine the greater axis.
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cmp ecx,edx
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jb short ??dxisbig
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xchg ecx,edx
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??dxisbig:
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rcl ebx,1 ; Y > X flag bit.
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; Determine the closeness or farness of lesser axis.
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mov eax,edx
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inc eax ; Round up.
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shr eax,1
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inc eax ; Round up.
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shr eax,1 ; 1/4 of greater axis.
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cmp ecx,eax
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rcl ebx,1 ; Very close to major axis bit.
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sub edx,eax
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cmp edx,ecx
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rcl ebx,1 ; Very far from major axis bit.
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xor eax,eax
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mov al,[NewFacing16+ebx]
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; Normalize to 0..FF range.
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shl eax,4
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ret
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ENDP Desired_Facing16
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END
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