i_vtexta.asm

;
; Copyright (C) 2024 Frenkel Smeijers
;
; This program is free software; you can redistribute it and/or
; modify it under the terms of the GNU General Public License
; as published by the Free Software Foundation; either version 2
; of the License, or (at your option) any later version.
;
; This program is distributed in the hope that it will be useful,
; but WITHOUT ANY WARRANTY; without even the implied warranty of
; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
; GNU General Public License for more details.
;
; You should have received a copy of the GNU General Public License
; along with this program. If not, see <https://www.gnu.org/licenses/>.
;

bits 16

extern source
extern colormap
extern dest

last_pixel_jump_table:
%assign i 0
%rep VIEWWINDOWHEIGHT+1
	dw last_pixel%+i,
%assign i i+1
%endrep


;
; input:
;   ax = fracstep
;   dx = frac
;   cx = count		1 <= count <= VIEWWINDOWHEIGHT	=>	ch = 0
;

global R_DrawColumn2
R_DrawColumn2:
	push si
	push di
	push es
	push bp

	xchg bp, ax						; bp = fracstep

	mov bx, cx						; bx = count

	mov cx, [colormap]

	les di, [dest]					; es:di = dest
	lds si, [source]				; ds:si = source

	shl bl, 1
	cs jmp last_pixel_jump_table[bx]


%assign i VIEWWINDOWHEIGHT
%rep VIEWWINDOWHEIGHT-1
last_pixel%+i:
	mov al, dh						; al = hi byte of frac
	shr al, 1						; 0 <= al <= 127
	mov bx, si						; bx = source
	xlat							; al = source[al]
	mov bx, cx						; bx = colormap
	ss xlat							; al = colormap[al]
	stosb							; write pixel
	add di, PLANEWIDTH-1			; point to next line
	add dx, bp						; frac += fracstep
%assign i i-1
%endrep


last_pixel1:
	mov al, dh
	shr al, 1
	mov bx, si
	xlat
	mov bx, cx
	mov dx, ss
	mov ds, dx
	xlat
	stosb

last_pixel0:	; count > 0, so the code never jumps to this label
	pop bp
	pop es
	pop di
	pop si
	retf