From ade60127d188feecf85005842edf2bf1230a43aa Mon Sep 17 00:00:00 2001
From: blondie7575 <qd@quinndunki.com>
Date: Mon, 7 Aug 2017 20:47:17 -0700
Subject: [PATCH] Negative XLEFT, almost saves a couple cycles

---
 terrain.s | 61 +++++++++++++++++++++++++++++++------------------------
 1 file changed, 34 insertions(+), 27 deletions(-)

diff --git a/terrain.s b/terrain.s
index 38fa51c..c89ea7d 100644
--- a/terrain.s
+++ b/terrain.s
@@ -52,7 +52,7 @@ renderClippedSpanChain:
 
 	; Prepare our state
 	; = 23 cycles per row + 80 cycles for actual pixels
-	lda #80					; 2
+	lda #-80					; 2
 	sta <XLEFT				; 3
 	lda #$1111				; 2
 	sta <CURRMAPPIXELS		; 3
@@ -75,8 +75,13 @@ renderClippedSpanChainLoop:
 renderClippedSpanChainLoop2:
 	; Now render spans until left edge of screen
 	; = 28 cycles per span rendered
-	cmp <XLEFT			; 3
-	bcs renderClippedSpanChainLastSpan	; 2/3
+	;cmp <XLEFT			; 3
+	tax					; 2
+	clc					; 2
+	adc <XLEFT			; 3
+	bpl renderClippedSpanChainLastSpan	; 2/3
+	sta <XLEFT			; 3
+	txa					; 2   14
 
 	; Render this span
 	ldx spanColors,y	; 4
@@ -86,28 +91,6 @@ renderClippedSpanChainLoop2:
 	tax					; 2
 	jmp (renderSpanJumpTable,x)	; 6   (jmp back = 6)
 
-renderSpanComplete:
-	; This is modified to redirect return from the
-	; unrolled span rendering blocks
-	jmp renderClippedSpanChainRenderNext	; 3
-
-
-renderClippedSpanChainRenderNext:
-	; Track remaining words until left edge
-	; = 26 cycles per span rendered
-	lsr					; 2
-	eor #$ffff			; 2
-	inc					; 2
-	clc					; 2
-	adc <XLEFT			; 3
-	sta <XLEFT			; 3
-	dey					; 2
-	dey					; 2
-
-	; For mid-stream spans, bypass the right-edge clipping code
-	lda spanChain,y		; 5
-	bra renderClippedSpanChainLoop2	; 3
-
 renderClippedSpanChainNextSpan:
 	; Track remaining distance from right edge and
 	; continue searching for visible right edge
@@ -118,13 +101,37 @@ renderClippedSpanChainNextSpan:
 	dey					; 2
 	bra renderClippedSpanChainLoop	; 3
 
+
+renderSpanComplete:
+	; This is modified to redirect return from the
+	; unrolled span rendering blocks
+	jmp renderClippedSpanChainRenderNext	; 3
+
+
+renderClippedSpanChainRenderNext:
+	; Track remaining words until left edge
+	; = 26 cycles per span rendered
+;	lsr					; 2
+;	eor #$ffff			; 2
+;	inc					; 2
+;	clc					; 2
+;	adc <XLEFT			; 3
+;	sta <XLEFT			; 3
+
+	dey					; 2
+	dey					; 2
+
+	; For mid-stream spans, bypass the right-edge clipping code
+	lda spanChain,y		; 5
+	bra renderClippedSpanChainLoop2	; 3
+
 renderClippedSpanChainLastSpan:
 	; Render visible portion of last visible span
 	; = 26 cycles per row
 	ldx spanColors,y	; 4
 	stx <CURRMAPPIXELS	; 3
-
-	lda <XLEFT			; 3
+brk
+;	lda <XLEFT			; 3
 	asl					; 2
 	tax					; 2