Add twoplayer-garbage convenience IPS

Makefile

@@ -1,7 +1,7 @@
-all: tetris taus screens custom handicap twoplayer playerid build/game_palette.pal build/menu_palette.pal build/game_nametable.nam build/level_menu_nametable.nam
+all: tetris taus screens custom handicap twoplayer twoplayer-garbage playerid build/game_palette.pal build/menu_palette.pal build/game_nametable.nam build/level_menu_nametable.nam
 test: build/tetris-test build/taus-test.test build/chart-test.test build/twoplayer-test.test
 # These are simply aliases
-.PHONY: all dis tetris taus screens custom handicap twoplayer playerid
+.PHONY: all dis tetris taus screens custom handicap twoplayer twoplayer-garbage playerid
 
 dis: build/tetris-PRG.s
 
@@ -92,6 +92,17 @@ build/twoplayer-test.test: twoplayer-test.lua build/twoplayer.nes
 build/twoplayer-pal.nes.cfg: twoplayer.nes.cfg ntsc2pal.awk | build
 	awk -f ntsc2pal.awk $< > $@
 
+twoplayer-garbage: build/twoplayer-garbage.nes
+# For .o files, manually list prerequisites that are generated. Non-generated
+# files will automatically be computed
+build/twoplayer-garbage.o: build/tetris.inc
+# Detect IPS hunks. These .o files used ips_segments in their .s
+build/twoplayer-garbage.ips.cfg: build/twoplayer-garbage.o
+# Linker dependencies. There is a corresponding .cfg file
+build/twoplayer-garbage.ips: build/twoplayer-garbage.o build/ips.o
+# IPS base file. There is a corresponding .ips file
+build/twoplayer-garbage.nes: build/twoplayer.nes
+
 custom: build/custom.nes
 build/custom.nes: build/taus.ips build/highscores.ips build/playerid.ips
 build/custom.nes: build/tetris.nes

README.md

@@ -78,7 +78,8 @@ of lines.
 [![Next on top](media/twoplayer-top.thumb.png)](media/twoplayer-top.aspect.png)
 
 The twoplayer mod allows two simultaneous players to play while receiving the
-same pieces. Garbage is not sent between players.
+same pieces. Garbage is not sent between players by default. The GameGenie code
+KUTPUX or the twoplayer-garbage IPS enables garbage.
 
 There are two variations of the mod. One shows the next piece on the side,
 which makes it easier to see with peripheral vision. The other shows it on top,

twoplayer-garbage.s

@@ -0,0 +1,13 @@
+;
+; Mod that enables garbage for twoplayer mod
+;
+
+.include "ips.inc"
+.include "build/tetris.inc"
+
+.segment "ADD_GARBAGE"
+        ips_segment     "ADD_GARBAGE",$9AE2
+
+        ; The twoplayer mod disables garbage by throwing away the garbage here.
+        ; This reverts the change.
+        sta     pendingGarbageInactivePlayer