Fix full-screen tile refreshes; incremental tile drawing crashes

assets/tiled/world_1-1.tmx

@@ -1,5 +1,8 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <map version="1.5" tiledversion="1.7.1" orientation="orthogonal" renderorder="right-down" width="256" height="30" tilewidth="8" tileheight="8" infinite="0" nextlayerid="3" nextobjectid="2">
+ <editorsettings>
+  <export target="world_1-1.json" format="json"/>
+ </editorsettings>
  <tileset firstgid="1" source="Overworld.tsx"/>
  <layer id="1" name="Tile Layer 1" width="256" height="30">
   <data encoding="csv">

src/Actions.s

@@ -30,11 +30,21 @@ MoveRight
 MoveUp
                      clc
                      adc       StartY               ; Increment the virtual Y-position
-                     jsr       SetBG0YPos
+                     pha
 
-                     lda       StartY
+                     lda       #240                 ; virtual play field height
-                     lsr
+                     sec
-                     jsr       SetBG1YPos
+                     sbc       ScreenHeight
+                     tax
+                     cmp       1,s
+                     bcc       *+4
+                     lda       1,s
+                     jsr       SetBG0YPos
+                     pla
+
+;                     lda       StartY
+;                     lsr
+;                     jsr       SetBG1YPos
 
                      jsr       DoFrame
                      rts
@@ -276,3 +286,6 @@ _DoTimers
 
                      pla
                      rts
+
+
+

src/App.Main.s

@@ -118,13 +118,13 @@ NO_MUSIC             equ        1                    ; turn music + tool loading
                      jsr        BlitInit             ; Initialize the memory
                      jsr        GrafInit             ; Initialize the graphics screen
 
-                     ldx        #6                   ; Gameboy Advance size
+                     ldx        #0                   ; Gameboy Advance size
                      jsr        SetScreenMode
 
                      lda        #0                   ; Set the virtual Y-position
                      jsr        SetBG0YPos
 
-                     lda        #15                  ; Set the virtual X-position
+                     lda        #0                   ; Set the virtual X-position
                      jsr        SetBG0XPos
 
                      jsr        _InitBG1             ; Initialize the second background
@@ -140,9 +140,10 @@ NO_MUSIC             equ        1                    ; turn music + tool loading
                      jsr        AllocOneBank2        ; Alloc 64KB for Load/Unpack
                      sta        BankLoad             ; Store "Bank Pointer"
 
-                     ldx        #0
+                     jsr        MovePlayerToOrigin   ; Put the player at the beginning of the map
-                     jsr        SetScreenMode
+                     lda        #$FFFF               ; Force a redraw of all the tiles
-                     jsr        MovePlayerToOrigin
+                     jsr        _UpdateBG0TileMap
+
 
 ;                     jsr        DoTiles
 ;                     jsr        DoLoadBG1
@@ -1292,6 +1293,15 @@ qtRec                adrl       $0000
 
 
 
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src/Render.s

@@ -70,7 +70,6 @@ Render
 ; finally patch out the code field.  Right now, the BRA operand is getting overwritten by tile data.
             jsr   _ApplyBG0XPosPre
 
-            lda   #$FFFF              ; Force a tile refresh
             jsr   _UpdateBG0TileMap
 
             jsr   _ApplyBG0XPos       ; Patch the PEA instructions with exit BRA opcode
@@ -112,3 +111,4 @@ Render
 
 
 
+

src/TileMap.s

@@ -215,19 +215,23 @@ _UpdateBG0TileMap
 
 ; This is a private subroutine that draws in tiles into the code fields using the
 ; data from the tilemap and the local :Top, :Left, :Bottom and :Right parameters.
+;
+; The ranges are [:Left, :Right) and [:Top, :Bottom), so :Right can be, at most, 41
+; if we are drawing all 41 tiles (Index 0 through 40).  The :Bottom value can be
+; at most 26.
+MAX_TILE_X         equ   40
+MAX_TILE_Y         equ   25
 :DrawRectBG0
 
                    lda   :Bottom
                    sec
                    sbc   :Top
-                   inc
+                   sta   :Height            ; Maximum value of 25
-                   sta   :Height
 
                    lda   :Right
                    sec
                    sbc   :Left
-                   inc
+                   sta   :Width             ; Maximum value of 40
-                   sta   :Width
 
 ; Compute the offset into the tile array of the top-left corner
 
@@ -298,7 +302,7 @@ _UpdateBG0TileMap
 
                    lda   :BlkX
                    inc
-                   cmp   #42                ; If we go past the physical block index, wrap around
+                   cmp   #MAX_TILE_X+1      ; If we go past the physical block index, wrap around
                    bcc   *+5
                    lda   #0
                    sta   :BlkX
@@ -319,7 +323,7 @@ _UpdateBG0TileMap
 
                    lda   :BlkY              ; The y lookup has a double0length array, may not need the bounds check
                    inc
-                   cmp   #27
+                   cmp   #MAX_TILE_Y+1
                    bcc   *+5
                    lda   #0
                    sta   :BlkY
@@ -377,6 +381,22 @@ _UpdateBG0TileMap
 
 
 
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