From 78306033203afad237d1d548270d9d5b3e64e141 Mon Sep 17 00:00:00 2001
From: Bobbi Webber-Manners <bobbi.manners@gmail.com>
Date: Mon, 19 Sep 2022 13:21:07 -0400
Subject: [PATCH] Reverse scrolling now works in MODE1 / HGR.

---
 auxmem.gfx.s  | 12 ++++++++++++
 auxmem.vdu.s  | 15 +++++++++++----
 mainmem.gfx.s | 35 +++++++++++++++++++++++++++++++++++
 3 files changed, 58 insertions(+), 4 deletions(-)

diff --git a/auxmem.gfx.s b/auxmem.gfx.s
index 9a36b1f..1f55c08 100644
--- a/auxmem.gfx.s
+++ b/auxmem.gfx.s
@@ -35,6 +35,7 @@ PRCHRSOFT    CMP   #$A0              ; Convert to screen code
 PUTCHRET     >>>   ENTAUX
              RTS
 
+* Forwards scroll one line
 HSCR1LINE    >>>   WRTMAIN
              LDX   TXTWINLFT
              STX   MTXTWINLFT
@@ -45,6 +46,17 @@ HSCR1LINE    >>>   WRTMAIN
 HSCR1RET     >>>   ENTAUX
              RTS
 
+* Reverse scroll one line
+HRSCR1LINE   >>>   WRTMAIN
+             LDX   TXTWINLFT
+             STX   MTXTWINLFT
+             LDX   TXTWINRGT
+             STX   MTXTWINRGT
+             >>>   WRTAUX
+             >>>   XF2MAIN,HGRRSCR1L
+HRSCR1RET    >>>   ENTAUX
+             RTS
+
 HSCRCLREOL   LDA   VDUTEXTY
              ASL
              TAX
diff --git a/auxmem.vdu.s b/auxmem.vdu.s
index 0ae5f38..17ed92f 100644
--- a/auxmem.vdu.s
+++ b/auxmem.vdu.s
@@ -727,7 +727,10 @@ CLREOLGS      BIT   $C01F
 SCROLLER      LDA   TXTWINTOP
 :L1           PHA
               JSR   SCR1LINE
-              PLA
+              BIT   VDUSCREEN
+              BPL   :S0
+              JSR   SCR1SOFT               ; Scroll graphics screen
+:S0           PLA
               INC
               CMP   TXTWINBOT
               BNE   :L1
@@ -745,7 +748,10 @@ RSCROLLER     DEC   TXTWINTOP
               DEC   A
 :L1           PHA
               JSR   RSCR1LINE
-              PLA
+              BIT   VDUSCREEN
+              BPL   :S0
+              JSR   RSCR1SOFT              ; Scroll graphics screen
+:S0           PLA
               DEC   A
               CMP   TXTWINTOP
               BNE   :L1
@@ -827,8 +833,6 @@ DOSCR1LINE    INC   TXTWINRGT
               BMI   :L2
 SCR1LNDONE    DEC   TXTWINRGT
               PLA
-              BIT   VDUSCREEN
-              BMI   SCR1SOFT               ; Scroll graphics screen
               RTS
 SCR1LINEGS    LDX   TXTWINLFT
               BIT   $C01F
@@ -867,6 +871,9 @@ SCR1LINEGS    LDX   TXTWINLFT
 * Copy text line A+1 to line A for HGR bitmap gfx mode
 SCR1SOFT      JMP   HSCR1LINE
 
+* Copy text line A to line A+1 for HGR bitmap gfx mode
+RSCR1SOFT      JMP   HRSCR1LINE
+
 * VDU 16 - CLG, clear graphics window
 VDU16         JMP   HSCRCLEAR
 
diff --git a/mainmem.gfx.s b/mainmem.gfx.s
index a7bd5ab..4645a21 100644
--- a/mainmem.gfx.s
+++ b/mainmem.gfx.s
@@ -178,6 +178,41 @@ HGRSCR1L    >>>   ENTMAIN
             BNE   :L1
             >>>   XF2AUX,HSCR1RET
 
+* Copy text line A to line A+1
+HGRRSCR1L   >>>   ENTMAIN
+            INC   MTXTWINRGT
+            ASL                     ; Source addr->A1L,A1H
+            TAX
+            LDA   MHGRTAB,X
+            STA   A1L
+            LDA   MHGRTAB+1,X
+            STA   A1H
+            INX                     ; Dest addr->A4L,A4H
+            INX
+            LDA   MHGRTAB,X
+            STA   A4L
+            LDA   MHGRTAB+1,X
+            STA   A4H
+            LDX   #$00
+:L1         LDY   MTXTWINLFT
+:L2         LDA   (A1L),Y
+            STA   (A4L),Y
+            INY
+            CPY   MTXTWINRGT
+            BNE   :L2
+            INC   A1H               ; Advance source 1024 bytes
+            INC   A1H
+            INC   A1H
+            INC   A1H
+            INC   A4H               ; Advance dest 1024 bytes
+            INC   A4H
+            INC   A4H
+            INC   A4H
+            INX
+            CPX   #8                ; 8 pixel rows in character
+            BNE   :L1
+            >>>   XF2AUX,HRSCR1RET
+
 * Clear one text line on HGR screen,
 * from current cursor col to text window right limit
 HCLREOL     >>>   ENTMAIN