optimized OOB-pixels in _RotateScaleSprite, calcSinCosSMC, and sprite-pointer rotation offsets

Author: ZERICO2005

src/graphx/graphx.asm

@@ -4881,7 +4881,7 @@ gfx_RotatedScaledSprite_NoClip:
 ;  arg4 : Scale factor (64 = 100%)
 ; Returns:
 ;  The size of the sprite after scaling
-	ld	h, $21	; ld hl, *
+	ld	h, $11	; ld de, *
 	db	$FD	; ld h, * --> ld iyh, *
 ;-------------------------------------------------------------------------------
 gfx_RotatedScaledSprite:
@@ -4910,7 +4910,7 @@ gfx_RotatedScaledTransparentSprite_NoClip:
 ;  arg4 : Scale factor (64 = 100%)
 ; Returns:
 ;  The size of the sprite after scaling
-	ld	h, $21	; ld hl, *
+	ld	h, $11	; ld de, *
 	db	$FD	; ld h, * --> ld iyh, *
 ;-------------------------------------------------------------------------------
 gfx_RotatedScaledTransparentSprite:
@@ -4959,8 +4959,7 @@ _RSS_NC:
 	inc	hl
 
 	; or	a, a	; carry already cleared
-	dec	b
-	sbc	hl, bc	; offset the sprite pointer by (size - 1) * 256
+	sbc	hl, bc	; offset the sprite pointer by (size * 256)
 
 	ld	(iy + (.dsrs_sprptr_0A - .dsrs_base_address)), hl	; write smc
 	ld	(iy + (.dsrs_sprptr_0B - .dsrs_base_address)), hl	; write smc
@@ -5031,18 +5030,21 @@ _RSS_NC:
 	ld	b, a	; render height
 	ld	c, a	; render width
 
-	; changes from call * to ld hl, *
+	; changes from call * to ld de, *
 	.dsrs_clip_call := $+0
 	call	_RotatedScaled_ClipAdjust
+	; UHL is zero
 
 	ld	(iy + (.dsrs_size_1 - .dsrs_base_address)), c	; write smc
 
-	or	a, a
-	sbc	hl, hl
-	ld	l, c
-	ld	de, ti.lcdWidth
-	ex	de, hl
-	sbc	hl, de
+	; HL = ti.lcdWidth - C
+	ld	a, $40	; 320 % 256
+	sub	a, c
+	ld	l, a	; low 8 bits
+	sbc	a, a
+	inc	a
+	ld	h, a
+	; HL is [65, 319] since C is [1, 255]
 	ld	(iy + (.line_add - .dsrs_base_address)), hl
 
 	; calculate y-loop offset for IX
@@ -5051,7 +5053,7 @@ _RSS_NC:
 	call	_set_DE_to_HL_mul_C
 	ld	hl, (iy + (.dsrs_sinf_1_plus_offset_ix - .dsrs_base_address))
 	or	a, a
-	sbc.s	hl, de	; make sure UHL is zero
+	sbc	hl, de
 	ld	(iy + (.dsrs_sinf_1_plus_offset_ix - .dsrs_base_address)), hl
 
 	; calculate y-loop offset for HL
@@ -5105,19 +5107,19 @@ _RSS_NC:
 	jr	c, .skip_pixel
 .inner_opaque_hijack:
 	; get pixel and draw to buffer
-	push	hl			; xs
+	push	hl			; preserve ys
 	ld	l, a
 	inc	l
+	ld	b, l	; L is a known constant (A + 1) that we can compensate for
 	mlt	hl
-	ld	b, a	; A is a known constant that we can compensate for
 	; result is at most 255 * 255 + 255 or 65279. Make sure UBC is zero
 	add	hl, bc			; y * size + x
 
 	ld	bc, 0
 .dsrs_sprptr_0B := $-3
 	add	hl, bc
 	ldi
-	pop	hl
+	pop	hl			; restore ys
 
 	ld	bc, 0			; smc = -sinf
 .dsrs_sinf_0B := $-3
@@ -5161,12 +5163,12 @@ _RSS_NC:
 	jr	c, .skip_pixel
 	; get pixel and draw to buffer
 	; SMC: push hl \ ld l, a --> jr inner_opaque_hijack
-	push	hl			; xs
+	push	hl			; preserve ys
 	ld	l, a
 .dsrs_jump_2 := $-1
 	inc	l
+	ld	b, l	; L is a known constant (A + 1) that we can compensate for
 	mlt	hl
-	ld	b, a	; A is a known constant that we can compensate for
 	; result is at most 255 * 255 + 255 or 65279. Make sure UBC is zero
 	add	hl, bc			; y * size + x
 
@@ -5181,7 +5183,7 @@ smcByte _TransparentColor
 	ld	(de), a
 .transparent_pixel:
 	ld	a, b	; restore A
-	pop	hl			; ys
+	pop	hl			; restore ys
 .skip_pixel:
 	inc	de			; x++s
 	ld	bc, 0			; smc = -sinf
@@ -5207,10 +5209,9 @@ smcByte _TransparentColor
 ;-------------------------------------------------------------------------------
 _rss_not_culled:
 	; offscreen
-	ld	a, iyl	; sprite out size (iyl/width should remain untouched)
 	ld	sp, ix
-	pop	ix
-	ret
+	jr	_RSS_NC.finish
+
 _RotatedScaled_ClipAdjust:
 ; modified version of _ClipCoordinates
 	push	iy
@@ -5346,7 +5347,7 @@ smcWord _XMin
 	; DE = HL * B(height)
 	call	_set_DE_to_HL_mul_C
 	pop	hl
-	add.s	hl, de	; make sure UHL is zero
+	add.s	hl, de	; make sure UHL is zero when returning from this function
 	; ld	(iy + (_RSS_NC.dsrs_size128_0_plus_dyc_0 - _RSS_NC.dsrs_base_address)), hl
 	ld	(ix - 12), hl	; dsrs_size128_0_plus_dyc_0
 
@@ -5401,8 +5402,7 @@ gfx_RotateScaleSprite:
 	inc	hl
 
 	or	a, a
-	dec	b
-	sbc	hl, bc	; offset the sprite pointer by (size - 1) * 256
+	sbc	hl, bc	; offset the sprite pointer by (size * 256)
 
 	ld	(iy + (_smc_dsrs_sprptr_0 - _smc_dsrs_base_address)), hl ; write smc
 
@@ -5441,7 +5441,7 @@ gfx_RotateScaleSprite:
 	sbc	hl, hl
 	ld	h, b
 	; BC = size * scale
-	mlt	bc
+	mlt	bc	; UBC cleared
 	; HL = size / 2
 	srl	h
 	; rr	l
@@ -5517,6 +5517,27 @@ gfx_RotateScaleSprite:
 	jr	drawSpriteRotateScale_Begin
 
 ;-------------------------------------------------------------------------------
+
+drawSpriteRotateScale_SkipPixel:
+	ex	de, hl
+	ld	(hl), TRASPARENT_COLOR	; write pixel
+smcByte _TransparentColor
+	ex	de, hl
+	inc	de			; x++s
+
+	ld	bc, 0			; smc = -sinf
+_smc_dsrs_sinf_0B := $-3
+	add	hl, bc			; ys += -sinf
+
+	ld	bc, 0			; smc = cosf
+_smc_dsrs_cosf_0B := $-3
+	add	ix, bc			; xs += cosf
+
+	dec	iyl
+	jr	nz, _xloop		; x loop
+	; We are here because the right edge of the sprite was transparent.
+	dec	iyh
+	jr	z, drawSpriteRotateScale_Finish
 _yloop:
 	ld	bc, $000000		; smc = cosf
 _smc_dsrs_cosf_1_plus_offset_hl := $-3
@@ -5537,11 +5558,11 @@ _xloop:
 	cp	a, c
 	jr	c, drawSpriteRotateScale_SkipPixel
 	; get pixel and draw to buffer
-	push	hl			; xs
+	push	hl			; preserve ys
 	ld	l, a
 	inc	l
+	ld	b, l	; L is a known constant (A + 1) that we can compensate for
 	mlt	hl
-	ld	b, a	; A is a known constant that we can compensate for
 	; result is at most 255 * 255 + 255 or 65279. Make sure UBC is zero
 	add	hl, bc			; y * size + x
 
@@ -5553,7 +5574,7 @@ _smc_dsrs_sprptr_0 := $-3
 	; inc	de			; x++s
 	ldi
 
-	pop	hl			; ys
+	pop	hl			; restore ys
 	ld	bc, $000000		; smc = -sinf
 _smc_dsrs_sinf_0A := $-3
 	add	hl, bc			; ys += -sinf
@@ -5567,31 +5588,7 @@ _smc_dsrs_cosf_0A := $-3
 
 	dec	iyh
 	jr	nz, _yloop		; y loop
-	pop	hl			; sprite out ptr
-	pop	ix
-	ret
-
-drawSpriteRotateScale_SkipPixel:
-	ld	b, a	; preserve A
-	ld	a,TRASPARENT_COLOR
-smcByte _TransparentColor
-	ld	(de), a			; write pixel
-	inc	de			; x++s
-	ld	a, b	; restore A
-
-	ld	bc, 0			; smc = -sinf
-_smc_dsrs_sinf_0B := $-3
-	add	hl, bc			; ys += -sinf
-
-	ld	bc, 0			; smc = cosf
-_smc_dsrs_cosf_0B := $-3
-	add	ix, bc			; xs += cosf
-
-	dec	iyl
-	jr	nz, _xloop		; x loop
-	; We are here because the right edge of the sprite was transparent.
-	dec	iyh
-	jr	nz, _yloop		; y loop
+drawSpriteRotateScale_Finish:
 	pop	hl			; sprite out ptr
 	pop	ix
 	ret
@@ -5602,36 +5599,32 @@ calcSinCosSMC_loadCosine:
 	ld	a, 64
 	add	a, (ix + 15)
 calcSinCosSMC:
-	ld	e, (ix + 18)
 ; inputs:
 ; A = angle
-; E = scale
 ; outputs:
 ; HL = 16bit quotient
 ; UHL = 0
 	; getSinCos:
 	; returns a = sin/cos(a) * 128
-	ld	bc, $80
+	ld	bc, $107F	; b = 16, c = $7F
 	ld	d, a
-	bit	7, a
-	jr	z, .bit7
-	sub	a, c	; sub a, 128
-.bit7:
 	bit	6, a
 	jr	z, .bit6
-	;	A = 128 - A
-	neg
-	add	a, c	; add a, 128
+	cpl
+	inc	a
 .bit6:
+	and	a, c	; and a, $7F
+	; A is [0, 64]
 	ld	c, a
-	ld	hl, _SineTable
+	ld	hl, _SineTable - $1000	; since BC is offset by $1000
 	add	hl, bc
 	ld	h, (hl)
-	ld	l, b	; ld l, 0
-	; hl = _SineTable[angle + 64] * 128
+	xor	a, a
+	ld	l, a	; ld l, 0
+	; hl = _SineTable[angle] * 128
 	; H is [0, 127]
 	; HL <<= 7
-	add.s	hl, hl
+	add.s	hl, hl	; also clears UHL
 	add	hl, hl
 	add	hl, hl
 	add	hl, hl
@@ -5640,10 +5633,10 @@ calcSinCosSMC:
 	add	hl, hl
 
 	; _16Div8Signed:
-	; hl = _SineTable[angle + 64] * 128 / scale (cos)
-	ld	b, 16
-	xor	a, a
-.div:
+	; hl = _SineTable[angle] * 128 / scale (sin)
+	ld	e, (ix + 18)	; scale
+	; 16 iterations
+.div_loop:
 	add	hl, hl
 	rla
 	jr	c, .overflow	; this path is only used when E >= 128
@@ -5653,7 +5646,7 @@ calcSinCosSMC:
 	sub	a, e
 	inc	l
 .check:
-	djnz	.div
+	djnz	.div_loop
 	bit	7, d
 	; UHL is zero here
 	ret	z
@@ -5692,6 +5685,7 @@ _CalcDXS:
 	ld	b, a			; -(size * scale / 128)
 	ld	(iy + 0), bc		; smc base address
 _16Mul16SignedNeg:
+	; same as __smulu_fast
 	; outputs to HL
 	; UHL = 0
 	ld	d, b