159 lines
7.2 KiB
NASM
159 lines
7.2 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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;***************************************************************************
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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 : Draw Shape Routines for library. *
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;* *
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;* File Name : DS_LSRS.ASM *
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;* *
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;* Programmer : Scott K. Bowen *
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;* *
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;* Start Date : August 24, 1993 *
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;* *
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;* Last Update : June 2, 1994 [BR] *
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;* *
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;*-------------------------------------------------------------------------*
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;* Functions: *
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;* Left_Scale_Reverse_Skip -- Skips past a scaled row of pixels *
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;* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - *
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;********************* Model & Processor Directives ************************
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IDEAL
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P386
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MODEL USE32 FLAT
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;******************************** Includes *********************************
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INCLUDE "shape.inc"
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;********************************* Code ************************************
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CODESEG
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;***************************************************************************
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;* Left_Scale_Reverse_Skip -- Skips past a scaled row of pixels *
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;* *
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;* INPUT: *
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;* ECX = number of uncompressed bytes to skip *
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;* ESI = shape (source) buffer data address *
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;* EDI = viewport (destination) address *
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;* [WidthCount] = shape's width *
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;* *
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;* OUTPUT: *
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;* ECX - negative # pixels (not bytes) overrun, or 0 *
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;* EDX - XTotal initializer value *
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;* ESI - updated to the current location in the shape data *
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;* EDI - decremented by # pixels (not bytes) overrun *
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;* [WidthCount] - decremented by # bytes skipped *
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;* *
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;* The value returned in EDX reflects what XTotal's accumulated value *
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;* should be at the new pixel location. If no bytes are overrun, this *
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;* will be whatever is stored in [XTotalInit] (which will be 0 if no *
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;* pixels are left-clipped). *
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;* *
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;* WARNINGS: none *
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;* *
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;* HISTORY: *
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;* 04/20/1992 PWG : Created. *
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;* 08/19/1993 SKB : Split drawshp.asm into several modules. *
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;* 06/02/1994 BR : Converted to 32-bit *
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;*=========================================================================*
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PROC Left_Scale_Reverse_Skip NOLANGUAGE NEAR
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sub [WidthCount],ecx ; we process ECX bytes of real width
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;--------------------------------------------------------------------
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; Put shape data address in EDI so we can do a scasb on it
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;--------------------------------------------------------------------
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xchg esi,edi ; xchange ESI and EDI
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jcxz ??getrem ; exit if no bytes to skip
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;--------------------------------------------------------------------
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; Search through the string and count down the info we have handled.
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; If we find a run (0 followed by a count byte), then handle it.
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;--------------------------------------------------------------------
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??cliptop:
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mov eax,0 ; set al to 0 (we're scanning for 0)
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repne scasb ; scan through source data
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jz short ??on_run ; if it is a run then deal with it
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;--------------------------------------------------------------------
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; Default exit point: store default x-scale bits & exit
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;--------------------------------------------------------------------
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??getrem:
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mov edx,[XTotalInit] ; store out the remainder
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jmp short ??out ; we're done, get outta here
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;--------------------------------------------------------------------
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; If we have a run then get the next byte which is the length.
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;--------------------------------------------------------------------
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??on_run:
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mov al,[BYTE PTR edi] ; get the count of zeros to run
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inc edi ; advance past the count
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inc ecx ; the 0 found doesn't count
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sub ecx,eax ; subtract the count from remaining
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jg ??cliptop ; if more bytes left, scan again
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jz ??getrem ; exactly enough bytes; exit
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;--------------------------------------------------------------------
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; Overrun exit point: ECX is negative by the # of bytes overrun.
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; - adjust [WidthCount] by # of overrun bytes
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; - compute the remainder at the new location (EDX)
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; - compute the number of destination pixels to skip (ECX)
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; - adjust EDI by # of overrun bytes
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;--------------------------------------------------------------------
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;
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;............... adjust [WidthCount] by overrun bytes ...............
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;
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add [WidthCount],ecx ; adjust overrun in bytes
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;
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;................. put x-scale roundoff bits in EDX .................
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;
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mov eax,ecx ; get the number of bytes we overran
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neg eax ; negate it since overun is negative
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add eax,[LeftClipBytes] ; add the number of bytes we leftclip
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mul [ScaleX] ; convert to pixels plus roundoff bits
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mov edx,0 ; clear EDX
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mov dl,al ; DL = x-scaling roundoff bits
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;
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;................ put negative overrun pixels in ECX ................
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;
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shr eax,8 ; EAX = total # left pixels
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sub eax,[LeftClipPixels] ; EAX = # pixels overrun
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mov ecx,eax ; store # overrun pixels
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neg ecx ; make it negative
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;
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;................ adjust dest ptr by overrun pixels .................
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;
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sub esi,eax ; decrement ESI (EDI) by overrun pixels
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;--------------------------------------------------------------------
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; Put shape address back into ESI, adjust EDI
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;--------------------------------------------------------------------
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??out:
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xchg esi,edi ; xchange ESI and EDI
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ret ; return back to the real function
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ENDP Left_Scale_Reverse_Skip
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END
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;**************************** End of ds_lsrs.asm ****************************
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