Wolf.ppc

;
; Assembly language functions for wolf 3-D PPC version
; Written by Bill Heineman
; 9-12-94 (Rev for removing scalers and using direct code)
;

;
; Bullshit to make the PPC Mac environment know I'm here
;

 	import VideoWidth		; global variable from C program
	import MacViewHeight
	import ArtData
	import VideoPointer
	import ScaleDiv
	
	toc	
	tc	VideoWidth[TC],VideoWidth
	tc	MacViewHeight[TC],MacViewHeight
	tc	ArtData[TC],ArtData
	tc	VideoPointer[TC],VideoPointer
	tc	ScaleDiv[TC],ScaleDiv
	
	export IO_ScaleWallColumn[DS]
	export .IO_ScaleWallColumn[PR]
	export SpriteGlue[DS]
	export .SpriteGlue[PR]

	toc				;Table of contents for the subroutines
	tc IO_ScaleWallColumn[TC], IO_ScaleWallColumn[DS]
	tc SpriteGlue[TC], SpriteGlue[DS]

	csect	IO_ScaleWallColumn[DS]
	dc.l	.IO_ScaleWallColumn[PR]
	dc.l	TOC[tc0]
	
	csect	SpriteGlue[DS]
	dc.l	.SpriteGlue[PR]
	dc.l	TOC[tc0]

;
; This routine will draw a scaled wall column.
;
; void IO_ScaleWallColumn(Word x,Word scale,LongWord column)
;
	
WALLHEIGHT EQU 128+1

; Passed from "C"
X 		equ R3		;X coord
Scale	equ	R4		;Scale factor 
Tile	equ	R5		;Tile to draw 
Column	equ	R6		;Packed wall column #
; Locals
ArtStart EQU R7		;Pointer to wall art
ScreenPtr EQU R8	;Pointer to screen memory column
Frac	EQU	R9		;Fractional scaler
Integer	EQU	R10		;Fractional integer
VWidth	EQU	R11		;Video of the video screen in bytes
Delta	EQU	R6		;Delta factor and temp
VHeight EQU R12		;Height of mac screen
Temp	EQU	R3		;Temp (Use AFTER X is added)

	csect	.IO_ScaleWallColumn[PR]

	CMPLWI	Scale,0		;Is the scale factor zero?
	BEQLR				;Exit NOW!
	LWZ		ScreenPtr,VideoPointer[TC](RTOC)	;Get handle to video
	LWZ		ArtStart,ArtData[TC](RTOC)			;Get handle to art data list
	LWZ		VWidth,VideoWidth[TC](RTOC)			;Get handle to video width
	LWZ		Frac,ScaleDiv[TC](RTOC)
	LWZ		VHeight,MacViewHeight[TC](RTOC)	;Get pointer to view height
	LWZ		ScreenPtr,0(ScreenPtr)				;I have the base pointer 
	LWZ		VWidth,0(VWidth)					;Init video width
	LWZ		VHeight,0(VHeight)		;Get the number of lines visible

	SLWI	Scale,Scale,1			;Mul scale by 2 (Get true pixel value	
	ADD		ScreenPtr,ScreenPtr,X	;Add the X coord (Frees Temp)
	SLWI	Temp,Scale,1			;Get low word index
	SLWI	Tile,Tile,2			;Get the wall shape pointer
	LWZX	Frac,Frac,Temp			;Get the scale factor
	SLWI	Column,Column,7			;Mul by 128 pixels
	LWZX	ArtStart,ArtStart,Tile	;Get pointer to the shape 
	ADD		ArtStart,ArtStart,Column	;I have the shape ptr
	CMPLW	Scale,VHeight			;Too big?
	BGE		ClipTop				;Clip the top

; 
; No clipping needed!
; Adjust the dest screen for the starting Y coord
;

	MTCTR	Scale				;Init counter
	SUB		Temp,VHeight,Scale	;How many lines to jump down?
	LI		Delta,0				;Init the delta factor
	SRWI	Temp,Temp,1			;Divide by to center vertically
	SRWI	Integer,Frac,24		;Isolate the integer
	MULLW	Temp,VWidth,Temp	;Adjust the Y coord
	SLWI	Frac,Frac,8			;Isolate the fraction
	ADD		ScreenPtr,ScreenPtr,Temp	;Create the dest screen pointer

;
; Tight loop
; Grab byte, adjust fractional scaler values and store to screen
;

More:
	LBZ		R0,0(ArtStart)		;Fetch a shape byte
	ADDC.	Delta,Delta,Frac	;Add the scaler fractional
	STB		R0,0(ScreenPtr)		;Store on the screen
	ADDE	ArtStart,ArtStart,Integer	;Add the constant
	ADD		ScreenPtr,ScreenPtr,VWidth	;Go down a line 
	BDNZ	More		;All lines done?
	BLR					;Exit routine

;
; Clip the top and bottom
; Calc the number of lost lines by clipping and "Fake" 
; the numbers as if I processed those missing lines
;

ClipTop:
	MTCTR	VHeight				;I will draw a screen line full
	SUB		Temp,Scale,VHeight	;How many lines to jump down?
	SRWI	Integer,Frac,24		;Isolate the integer
	SRWI	Temp,Temp,1			;Divide by to center vertically
	MULLW	Temp,Frac,Temp		;Adjust the scaler by lost lines
	SRWI	Delta,Temp,24		;How many bytes are lost?
	ADD		ArtStart,ArtStart,Delta	;Create the SOURCE art pointer
	SLWI	Frac,Frac,8			;Isolate the fraction
	SLWI	Delta,Temp,8		;Init the adjusted delta
	B		More				;Jump to the code
	
;
; Call the compiled scaler to draw a run of the line
;


	csect	.SpriteGlue[PR]

SGArtStart	EQU	R3		;Pointer to the 6 byte run structure
SGFrac	EQU	R4		;Pointer to the scaler
SGInteger	EQU R5		;Pointer to the video
SGScreenPtr	EQU	R6		;Pointer to the run base address
SGCount	EQU R7
SGDelta	EQU	R8
SGVWidth	EQU	R9

	LWZ		SGVWidth,VideoWidth[TC](RTOC)
	LWZ		SGVWidth,0(SGVWidth)
	MTCTR	SGCount
	
SMore:
	LBZ		R0,0(SGArtStart)		;Fetch a shape byte
	ADDC.	SGDelta,SGDelta,SGFrac	;Add the scaler fractional
	STB		R0,0(SGScreenPtr)		;Store on the screen
	ADDE	SGArtStart,SGArtStart,SGInteger	;Add the constant
	ADD		SGScreenPtr,SGScreenPtr,SGVWidth	;Go down a line 
	BDNZ	SMore		;All lines done?
	BLR					;Exit routine