From f5d1aa9ee6ccb6a851b9d279e63a18adb1b7b883 Mon Sep 17 00:00:00 2001
From: Jeremy Rand <jeremy@rand-family.com>
Date: Sun, 6 Sep 2020 02:05:33 -0400
Subject: [PATCH] Improve the performance of the centipede segment draw
 function.

---
 BuGS/gameSegments.s  | 52 +++++++++++++++-----------------------------
 BuGS/global.macros   |  8 +++----
 BuGS/make/config.txt |  2 +-
 3 files changed, 23 insertions(+), 39 deletions(-)

diff --git a/BuGS/gameSegments.s b/BuGS/gameSegments.s
index daab9c1..261177b 100644
--- a/BuGS/gameSegments.s
+++ b/BuGS/gameSegments.s
@@ -35,10 +35,8 @@ drawSegments entry
         ldx #SEGMENT_MAX_OFFSET
 drawSegments_nextSegment anop
         lda segmentStates,x
-        bne drawSegments_cont
-        jmp drawSegments_skipSegment
+        beq drawSegments_skipSegment
 
-drawSegments_cont anop
         lda segmentFacing,x
         clc
         adc segmentSpriteOffset
@@ -54,23 +52,16 @@ drawSegments_head anop
         jsl segmentHeadJump
         
 drawSegments_handleTiles anop
-        phx
-        txa
-        asl a
-        asl a
-        tay
-        
-        _dirtyGameTileWithY segmentTileOffsets
-        _dirtyGameTileWithY segmentTileOffsets+2
-        _dirtyGameTileWithY segmentTileOffsets+4
-        _dirtyGameTileWithY segmentTileOffsets+6
-        plx
+        _dirtyGameTileWithX segmentTileOffsetsUL
+        _dirtyGameTileWithX segmentTileOffsetsUR
+        _dirtyGameTileWithX segmentTileOffsetsLL
+        _dirtyGameTileWithX segmentTileOffsetsLR
         
 drawSegments_skipSegment anop
         dex
         dex
         bmi drawSegments_done
-        jmp drawSegments_nextSegment
+        bra drawSegments_nextSegment
         
 drawSegments_done anop
         rtl
@@ -169,15 +160,10 @@ addBodySegment entry
         stz segmentScreenShifts,x
 
         txa
-        asl a
-        asl a
-        tay
-
-        txa
-        sta segmentTileOffsets,y
-        sta segmentTileOffsets+2,y
-        sta segmentTileOffsets+4,y
-        sta segmentTileOffsets+6,y
+        sta segmentTileOffsetsUL,x
+        sta segmentTileOffsetsUR,x
+        sta segmentTileOffsetsLL,x
+        sta segmentTileOffsetsLR,x
         
         inc numSegments
 
@@ -206,15 +192,10 @@ addHeadSegment entry
         stz segmentScreenShifts,x
         
         txa
-        asl a
-        asl a
-        tay
-        
-        txa
-        sta segmentTileOffsets,y
-        sta segmentTileOffsets+2,y
-        sta segmentTileOffsets+4,y
-        sta segmentTileOffsets+6,y
+        sta segmentTileOffsetsUL,x
+        sta segmentTileOffsetsUR,x
+        sta segmentTileOffsetsLL,x
+        sta segmentTileOffsetsLR,x
         
         inc numSegments
         
@@ -233,7 +214,10 @@ segmentDirections       dc 12i2'SEGMENT_DIR_RIGHT'
 segmentFacing           dc 12i2'SEGMENT_FACING_DOWN'
 segmentScreenOffsets    dc 12i2'0'
 segmentScreenShifts     dc 12i2'0'
-segmentTileOffsets      dc 48i2'0'
+segmentTileOffsetsUL    dc 12i2'0'
+segmentTileOffsetsUR    dc 12i2'0'
+segmentTileOffsetsLL    dc 12i2'0'
+segmentTileOffsetsLR    dc 12i2'0'
 
 SEGMENT_SPRITE_LAST_OFFSET  gequ 7*4
 segmentSpriteOffset dc i2'SEGMENT_SPRITE_LAST_OFFSET'
diff --git a/BuGS/global.macros b/BuGS/global.macros
index 5a11c3c..c635171 100644
--- a/BuGS/global.macros
+++ b/BuGS/global.macros
@@ -66,13 +66,13 @@ _drawDirtyGameRow_skip&tileOffset anop
         
         mend
 
-; This macro uses the Y register as an index into the tile offsets.  This is
+; This macro uses the X register as an index into the tile offsets.  This is
 ; needed for segments because each segment has their own dirty tile offsets.
         macro
-        _dirtyGameTileWithY &tileOffset
-        ldx &tileOffset,y
+        _dirtyGameTileWithX &tileOffset
+        ldy &tileOffset,x
         lda #TILE_STATE_DIRTY
-        sta tileDirty,x
+        sta tileDirty,y
         mend
         
         
diff --git a/BuGS/make/config.txt b/BuGS/make/config.txt
index 6e02df5..4cf9182 100644
--- a/BuGS/make/config.txt
+++ b/BuGS/make/config.txt
@@ -8,7 +8,7 @@ s6d2 =
 
 s7d1 = /Users/jrand/Library/Developer/Xcode/DerivedData/BuGS-bffpexoblaghkzcbtjtzxeulnuto/Build/Products/Debug/BuGS.2mg
 
-g_limit_speed = 0
+g_limit_speed = 3
 
 
 bram1[00] = 00 00 00 01 00 00 0d 06 02 01 01 00 01 00 00 00