From 122654c1ef9d99af8210ce95dee4eb4d1bc04b67 Mon Sep 17 00:00:00 2001
From: Miquel Sabaté Solà <mikisabate@gmail.com>
Date: Thu, 15 May 2025 16:27:36 +0200
Subject: Define the notion of a level
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This is for now just a variable that will be set during initialization,
and that it can be influenced through the `LEVEL` make variable. Both
the level and the level "kind" notions are used tracking, at least,
which kind of enemy wave we have to send.

Signed-off-by: Miquel Sabaté Solà <mikisabate@gmail.com>
---
 Makefile          |  7 +++++++
 include/globals.s |  8 ++++++++
 src/jetpac.s      | 13 +++++++++++++
 3 files changed, 28 insertions(+)

diff --git a/Makefile b/Makefile
index a00dc6b..91bd0dd 100644
--- a/Makefile
+++ b/Makefile
@@ -24,6 +24,10 @@ endif
 RUBY ?= ruby
 HAS_RUBY := $(shell command -v $(RUBY) >/dev/null 2>&1 && echo true || echo false)
 
+##
+# Variables for building the game.
+LEVEL ?= 0
+
 .PHONY: all
 all: clean deps build
 
@@ -54,6 +58,7 @@ build: gen-values build-full build-partial build-pal
 build-full:
 	$(Q) rm -f config/generated.s
 	$(Q) echo "HZ = 60" >> config/generated.s
+	$(Q) echo "LEVEL = $(LEVEL)" >> config/generated.s
 
 	$(E) "	CC	 jetpac (NTSC)"
 	$(Q) $(CC65) $(CCOPTS) src/jetpac.s -C config/nrom.cfg -o "out/Jetpac (NTSC).nes"
@@ -63,6 +68,7 @@ build-partial:
 	$(Q) rm -f config/generated.s
 	$(Q) echo "PARTIAL = 1"  >> config/generated.s
 	$(Q) echo "HZ = 60" >> config/generated.s
+	$(Q) echo "LEVEL = $(LEVEL)" >> config/generated.s
 
 	$(E) "	CC	 jetpac (partial)"
 	$(Q) $(CC65) $(CCOPTS) src/jetpac.s -C config/nrom.cfg -o "out/Jetpac (DEV).nes"
@@ -72,6 +78,7 @@ build-pal:
 	$(Q) rm -f config/generated.s
 	$(Q) echo "PAL = 1"  >> config/generated.s
 	$(Q) echo "HZ = 50" >> config/generated.s
+	$(Q) echo "LEVEL = $(LEVEL)" >> config/generated.s
 
 	$(E) "	CC	 jetpac (PAL)"
 	$(Q) $(CC65) $(CCOPTS) src/jetpac.s -C config/nrom.cfg -o "out/Jetpac (PAL).nes"
diff --git a/include/globals.s b/include/globals.s
index 395df61..531c812 100644
--- a/include/globals.s
+++ b/include/globals.s
@@ -34,4 +34,12 @@
     ;; |   2 | title over | We are transitioning from title to game                     |
     ;; | 1-0 | game       | 0: title; 1: game; 2: game over, 3: game over (coin)        |
     zp_flags = $20
+
+    ;; Current level of the game.
+    zp_level = $24
+
+    ;; The level "kind". Note that `zp_level` can go on forever, but the level
+    ;; "kind" repeats every 8 waves. Hence, this is just a cached version of
+    ;; masking `zp_level`.
+    zp_level_kind = $25
 .endscope
diff --git a/src/jetpac.s b/src/jetpac.s
index 0c75bf4..ada5d1f 100644
--- a/src/jetpac.s
+++ b/src/jetpac.s
@@ -58,6 +58,19 @@
     sta Joypad::zp_buttons1
     sta Joypad::zp_buttons2
 
+    ;; Initialize the level. We allow the build system to pass its own value for
+    ;; this in `LEVEL`, just in case we want to debug the enemy of a specific
+    ;; level.
+    .ifdef LEVEL
+        lda #LEVEL
+        sta Globals::zp_level
+        and #%00000111
+        sta Globals::zp_level_kind
+    .else
+        sta Globals::zp_level
+        sta Globals::zp_level_kind
+    .endif
+
     ;; Initialize the assets for the game.
     jsr Assets::init
 
-- 
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