Add support for adding scores

Signed-off-by: Miquel Sabaté Solà <mssola@mssola.com>

2 files changed, 172 insertions, 1 deletions

diff --git a/src/jetpac.s b/src/jetpac.s
index 3cf8f0a..b356192 100644
--- a/src/jetpac.s
+++ b/src/jetpac.s
@@ -42,6 +42,7 @@
 .include "background.s"
 .include "prng.s"
 .include "explosions.s"
+.include "score.s"
 .include "items.s"
 .include "player.s"
 .include "enemies.s"
@@ -112,7 +113,14 @@
 .endproc
 
 .proc main
-    ;; TODO: high score initialization has to happen here.
+    ;; Initialize the high score.
+    lda #0
+    sta Score::m_hi
+    sta Score::m_hi + 1
+    sta Score::m_hi + 2
+    sta Score::m_hi + 3
+    sta Score::m_hi + 4
+    sta Score::m_hi + 5
 
 @init:
     ;; Disable the PPU and zero out variables which shadow PPU registers.
@@ -156,6 +164,10 @@
     ;; Initialize some variables from the "Game Over" side of the game.
     jsr Over::init
 
+    ;; Initialize the score for both players. Note that initializing the high
+    ;; score is the first thing we do in main().
+    jsr Score::init_players_scores
+
     ;; Initialize variables from the game's driver that need to be set before
     ;; NMIs start ticking.
     jsr Driver::init_before_nmi
diff --git a/src/score.s b/src/score.s
new file mode 100644
index 0000000..ed36283
--- /dev/null
+++ b/src/score.s
@@ -0,0 +1,159 @@
+;; Clear the carry and add ADDR to the indexed digit on 'Score::m_players'. If
+;; the result is larger or equal than 10, then 0 is stored and the carry flag is
+;; set. Otherwise the carry flag is cleared.
+.macro BCD_ADD ADDR
+    lda Score::m_players, x
+    clc
+    adc ADDR
+    cmp #10
+    bcc :+
+    sec
+    lda #0
+:
+    sta Score::m_players, x
+.endmacro
+
+;; Add ADDR to the indexed digit on 'Score::m_players' _with_ carry. If the
+;; result is larger or equal than 10, then 0 is stored and the carry flag is
+;; set. Otherwise the carry flag is cleared.
+.macro BCD_ADDC ADDR
+    lda Score::m_players, x
+    adc ADDR
+    clc
+    cmp #10
+    bcc :+
+    sec
+    lda #0
+:
+    sta Score::m_players, x
+.endmacro
+
+;; Only add the carry to the indexed digit on 'Score::m_players' _with_
+;; carry. If the result is larger or equal than 10, then 0 is stored and the
+;; carry flag is set. Otherwise the carry flag is cleared.
+.macro BCD_JUST_CARRY
+    lda Score::m_players, x
+    adc #0
+    clc
+    cmp #10
+    bne :+
+    sec
+    lda #0
+:
+    sta Score::m_players, x
+.endmacro
+
+;; A score is a 6-digit number where each digit is stored on a byte of its
+;; own. This makes adding numbers and representing them into the screen dead
+;; easy.
+;;
+;; This is indeed rather wasteful, but we have a lot of RAM to spare and the
+;; ease of use is quite convenient.
+.scope Score
+    ;; Scores for both players are stored in a single buffer. Even indeces
+    ;; contain digits for the first player, and odd indeces contain digits for
+    ;; the second player. Digits are stored in little-endian format.
+    ;;
+    ;; Interweaving digits this way might seem weird, but it actually makes
+    ;; indexing things super easy: the 'active' bit from
+    ;; 'Globals::zp_multiplayer' can be used to index the first item, and then
+    ;; it's a matter of advancing the 'x' register twice in order to get the
+    ;; next digit.
+    PLAYERS_BUFF_SIZE = $0C
+    m_players = $300     ; asan:reserve PLAYERS_BUFF_SIZE
+
+    ;; The high score for this session.
+    m_hi = $30C           ; asan:reserve $06
+
+    ;; Initialize the scores for both players.
+    .proc init_players_scores
+        lda #0
+        ldx #0
+
+    @loop:
+        sta m_players, x
+        inx
+        cpx #PLAYERS_BUFF_SIZE
+        bne @loop
+
+        rts
+    .endproc
+
+    ;; Add to the current player's score the number stored in
+    ;; 'Globals::zp_tmp{0,1,2}', where 'Globals::zp_tmp0' has the least
+    ;; significant number.
+    .proc add_to_player
+        ;; See 'Score::m_players' on why this is the way to select the current
+        ;; player's score.
+        lda Globals::zp_multiplayer
+        and #$01
+        tax
+
+        ;;;
+        ;; The first three digits are the product of adding the contents of
+        ;; 'Globals::zp_tmp{0,1,2}'.
+
+        BCD_ADD Globals::zp_tmp0
+        inx
+        inx
+
+        BCD_ADDC Globals::zp_tmp1
+        inx
+        inx
+
+        BCD_ADDC Globals::zp_tmp2
+        inx
+        inx
+
+        ;;;
+        ;; The rest are just a matter of adding the carry.
+
+        BCD_JUST_CARRY
+        inx
+        inx
+
+        BCD_JUST_CARRY
+        inx
+        inx
+
+        BCD_JUST_CARRY
+
+        ;; TODO: set a flag about updating the score on the HUD.
+
+        rts
+    .endproc
+.endscope
+
+;; Add the score for a dead enemy to the current player's score.
+.macro ADD_ENEMY_SCORE
+    lda #5
+    sta Globals::zp_tmp0
+    lda #2
+    sta Globals::zp_tmp1
+    lda #0
+    sta Globals::zp_tmp2
+    jsr Score::add_to_player
+.endmacro
+
+;; Add the score for grabbing a shuttle part / fuel tank to the current player's
+;; score.
+.macro ADD_PART_FUEL_SCORE
+    lda #0
+    sta Globals::zp_tmp0
+    lda #0
+    sta Globals::zp_tmp1
+    lda #1
+    sta Globals::zp_tmp2
+    jsr Score::add_to_player
+.endmacro
+
+;; Add the score for grabbing an item to the current player's score.
+.macro ADD_ITEM_SCORE
+    lda #0
+    sta Globals::zp_tmp0
+    lda #5
+    sta Globals::zp_tmp1
+    lda #2
+    sta Globals::zp_tmp2
+    jsr Score::add_to_player
+.endmacro