Hide objects properly

README.md

@@ -5,4 +5,9 @@ A small NES game, heavily inspired by the chrome dino.
 You can build it with `build.sh`
 To build it and run it directly use `./build_and_run.sh`
 
-Currently it may run a bit too fast on an NTSC NES.
+It is made for PAL but it can also run on NTSC, your region gets detected on
+reset.
+
+Big thanks to Gros Chien, Fiskbit, sylvie, johnybot, TakuikaNinja and other
+people on the Nesdev Discord and forum for helping me to fix bugs, improve it,
+etc.

inc/defs.inc

@@ -60,6 +60,8 @@ PPUOAM  = $4014
 
 .define NTSCSPRITE #$0F
 
+.define VOIDSPRITE #$FF
+
 PLAYERX = $0207
 PLAYERY = $0204
 PLAYERTILE = $0205

src/main.asm

@@ -259,6 +259,8 @@ OBJINITLOOP:
     STA wait, Y
     JSR RAND
     LDX loopx
+    LDA VOIDSPRITE
+    STA OBJECTTILE, X
     CPX BIRDSTART
     BCC SETHEIGHT
     LDA FLOOR
@@ -461,6 +463,12 @@ MOVEOBJLOOP:
     STA wait, Y
     JMP MOVELOOPEND
 MOVE:
+    LDA OBJECTTILE, X
+    CMP VOIDSPRITE
+    BNE UPDATEX
+    LDA #$0C
+    STA OBJECTTILE, X
+UPDATEX:
     LDA OBJECTX, X
     STA oldx
     SEC
@@ -483,6 +491,8 @@ MOVECONTINUE:
     STA wait, Y
     JSR RAND
     LDX loopx
+    LDA VOIDSPRITE
+    STA OBJECTTILE, X
     CPX BIRDSTART
     BCC MOVELOOPEND
     LDA FLOOR
@@ -556,6 +566,8 @@ RESETTICK:
     LDX BIRDSTART
 BIRDLOOP:
     LDY OBJECTTILE, X
+    CPY VOIDSPRITE
+    BEQ CONTINUEBIRDLOOP
     LDA #$11
     STA OBJECTTILE, X
     CPY #$11