descent/TEXMAP/TMAP_FLT.ASM

;THE COMPUTER CODE CONTAINED HEREIN IS THE SOLE PROPERTY OF PARALLAX
;SOFTWARE CORPORATION ("PARALLAX").  PARALLAX, IN DISTRIBUTING THE CODE TO
;END-USERS, AND SUBJECT TO ALL OF THE TERMS AND CONDITIONS HEREIN, GRANTS A
;ROYALTY-FREE, PERPETUAL LICENSE TO SUCH END-USERS FOR USE BY SUCH END-USERS
;IN USING, DISPLAYING,  AND CREATING DERIVATIVE WORKS THEREOF, SO LONG AS
;SUCH USE, DISPLAY OR CREATION IS FOR NON-COMMERCIAL, ROYALTY OR REVENUE
;FREE PURPOSES.  IN NO EVENT SHALL THE END-USER USE THE COMPUTER CODE
;CONTAINED HEREIN FOR REVENUE-BEARING PURPOSES.  THE END-USER UNDERSTANDS
;AND AGREES TO THE TERMS HEREIN AND ACCEPTS THE SAME BY USE OF THIS FILE.  
;COPYRIGHT 1993-1998 PARALLAX SOFTWARE CORPORATION.  ALL RIGHTS RESERVED.
;
; $Source: f:/miner/source/texmap/rcs/tmap_flt.asm $
; $Revision: 1.10 $
; $Author: john $
; $Date: 1995/02/20 18:22:53 $
;
; Flat shader derived from texture mapper (kind of slow)
;
; $Log: tmap_flt.asm $
; Revision 1.10  1995/02/20  18:22:53  john
; Put all the externs in the assembly modules into tmap_inc.asm.
; Also, moved all the C versions of the inner loops into a new module, 
; scanline.c.
; 
; Revision 1.9  1995/02/20  17:08:51  john
; Added code so that you can build the tmapper with no assembly!
; 
; Revision 1.8  1994/12/02  23:29:21  mike
; change jb/ja to jl/jg.
; 
; Revision 1.7  1994/11/12  16:39:35  mike
; jae to ja.
; 
; Revision 1.6  1994/08/09  11:27:53  john
; Added cthru mode.
; 
; Revision 1.5  1994/07/08  17:43:11  john
; Added flat-shaded-zbuffered polygon.
; 
; Revision 1.4  1994/04/08  16:25:43  mike
; optimize inner loop of flat shader.
; 
; Revision 1.3  1994/03/31  08:34:20  mike
; Optimized (well, speeded-up) inner loop for tmap-based flat shader.
; 
; Revision 1.2  1993/11/22  10:24:57  mike
; *** empty log message ***
; 
; Revision 1.1  1993/09/08  17:29:46  mike
; Initial revision
; 
;
;

	.386

	public	asm_tmap_scanline_flat_

	include	tmap_inc.asm

_DATA	SEGMENT DWORD PUBLIC USE32 'DATA'


_DATA	ENDS

DGROUP	GROUP	_DATA

_TEXT   SEGMENT DWORD PUBLIC USE32 'CODE'

	ASSUME	DS:_DATA
	ASSUME	CS:_TEXT

; --------------------------------------------------------------------------------------------------
; Enter:
;	_xleft	fixed point left x coordinate
;	_xright	fixed point right x coordinate
;	_y	fixed point y coordinate
;**;	_pixptr	address of source pixel map

;   for (x = (int) xleft; x <= (int) xright; x++) {
;      _setcolor(read_pixel_from_tmap(srcb,((int) (u/z)) & 63,((int) (v/z)) & 63));
;      _setpixel(x,y);
;
;      z += dz_dx;
;   }

asm_tmap_scanline_flat_:
	pusha

; Setup for loop:	_loop_count  iterations = (int) xright - (int) xleft
;**;	esi	source pixel pointer = pixptr
;	edi	initial row pointer = y*320+x

; set esi = pointer to start of texture map data
;**	mov	esi,_pixptr

; set edi = address of first pixel to modify
	mov	edi,_fx_y
	cmp	edi,_window_bottom
	ja	_none_to_do

	imul	edi,_bytes_per_row
	mov	eax,_fx_xleft
	test	eax, eax
	jns	eax_ok
	sub	eax,eax
eax_ok:
	add	edi,eax
	add	edi,write_buffer

; set _loop_count = # of iterations
	mov	eax,_fx_xright

	cmp	eax,_window_right
	jl	eax_ok1
	mov	eax,_window_right
eax_ok1:	cmp	eax,_window_left
	jg	eax_ok2
	mov	eax,_window_left
eax_ok2:

	mov	ebx,_fx_xleft
	sub	eax,ebx
	js	_none_to_do
	cmp	eax,_window_width
	jbe	_ok_to_do
	mov	eax,_window_width
	dec	eax
_ok_to_do:
	mov	ecx,eax

; edi = destination pixel pointer
	cmp	_tmap_flat_cthru_table, 0
	jne	do_flat_cthru

	mov	al,_tmap_flat_color

; word align
	inc	ecx
	test	edi,1
	je	edi_even
	mov	es:[edi],al
	inc	edi
	dec	ecx
	je	_none_to_do
edi_even:	shr	ecx,1
	je	_no_full_words
	mov	ah,al
	rep	stosw
_no_full_words:	adc	ecx,ecx	; if cy set, then write one more pixel (ecx == 0)
	rep	stosb	; write 0 or 1 pixel

_none_to_do:	popa
	ret

do_flat_cthru:
	mov	esi, _tmap_flat_cthru_table
	xor	eax, eax
	cmp	ecx, 0
	je	_none_to_do
	; edi = dest, esi = table, ecx = count

flat_cthru_loop:
	mov	al, es:[edi]	; get already drawn pixel
	mov	al, [eax+esi]	; xlat thru cthru table
	mov	es:[edi],al	; write it
	inc	edi
	dec	ecx
	jnz	flat_cthru_loop
	popa
	ret

_TEXT	ends

	end