Add support for the SUSE coin

This is a coin that appears after going through a first cycle of levels
and that allows the player to get a different game over screen than
usual.

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

8 files changed, 152 insertions, 36 deletions

diff --git a/.nasm/segments.txt b/.nasm/segments.txt
index 403b691..ffbe519 100644
--- a/.nasm/segments.txt
+++ b/.nasm/segments.txt
@@ -1,4 +1,4 @@
 - HEADER: 16/16 (100%)
-- ROM0: 8066/32762 (24.62%)
+- ROM0: 8238/32762 (25.14%)
 - ROMV: 6/6 (100%)
 - ROM2: 8192/8192 (100%)
diff --git a/CHANGELOG.md b/CHANGELOG.md
index f0fbde8..11057c3 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -24,7 +24,7 @@ adapted to the reality of the NES/Famicom. This means:
   hard to do and probably not worth it. In the end: different machine, different
   rules. Hence, bullets are handled in a similar way as other games for the
   NES/Famicom, even if it's not particularly close to the original.
-- As an homage to Donkey Kong 64, you can **collect a coin** after completing 16
+- As an homage to Donkey Kong 64, you can **collect a coin** after completing 8
   stages. This coin features a chameleon as a reference to SUSE, since I
   originally bootstrapped this project during [Hackweek
   23](https://hackweek.opensuse.org/projects/port-the-jetpac-game-to-the-nes).
diff --git a/include/asm.s b/include/asm.s
index e44aedf..09229f9 100644
--- a/include/asm.s
+++ b/include/asm.s
@@ -1,8 +1,3 @@
-;; Sanity check for the 'LEVEL' build parameter.
-.if !(LEVEL >= 0 && LEVEL < 8)
-    .error "You have defined a bad 'LEVEL' value, it should be between 0 and 7 (both included)"
-.endif
-
 ;; Jump And Link: jump to subroutine but use the return address that the caller
 ;; had whenever the given subroutine runs `rts`. In other words, "link" the
 ;; return address from the caller to the callee.
diff --git a/src/assets.s b/src/assets.s
index cfcddbf..26f6546 100644
--- a/src/assets.s
+++ b/src/assets.s
@@ -180,7 +180,7 @@
         ;; 2: enemy 2, fuel & bonuses
         .byte $0F, $16, $24, $28
         ;; 3: SUSE easter egg
-        .byte $0F, $16, $10, $2B
+        .byte $0F, $16, $1B, $2B
     .endproc
 
     ;; Having 2KB for screen data is quite wasteful, but since it's such a
diff --git a/src/driver.s b/src/driver.s
index e1c2eb7..bfa6294 100644
--- a/src/driver.s
+++ b/src/driver.s
@@ -323,12 +323,16 @@
         and #%00000110
         bne @reset_timer
 
-        ;; No! Toggle the game over bit.
-        ;; TODO: missing the coin game over.
+        ;; No! Set the game over bit (with or without coin).
         lda Globals::zp_flags
         ora #%00000010
         sta Globals::zp_flags
+        lda Items::zp_state
+        and #$04
+        beq @invalidate_items
+        inc Globals::zp_flags
 
+    @invalidate_items:
         ;; Invalidate items, which were skipped on move_sprites_out() on purpose
         ;; to keep them after each death. But since we are about to go to the
         ;; title screen, now they are no longer useful.
diff --git a/src/items.s b/src/items.s
index 731756d..de0a28e 100644
--- a/src/items.s
+++ b/src/items.s
@@ -44,7 +44,7 @@
     ;;   |- F: falling.
     ;;   |- D: dropping: together with 'falling', but the player cannot re-grab it.
     ;;   |- C: 1: collectable (i.e. disappears on collision); 0: part (i.e. follows the player)
-    ;;   |- K: object kind (00: high shuttle; 01: mid shuttle; 10: fuel; 11: regular item; 100: coin)
+    ;;   |- K: object kind (000: high shuttle; 001: mid shuttle; 010: fuel; 011: regular item; 100: coin)
     ;;
     ;; 2. Y coordinate.
     ;; 3. X coordinate.
@@ -72,11 +72,12 @@
     ;; Bitmap which holds different boolean values for the state of items in
     ;; general.
     ;;
-    ;; |GNS- --FF|
+    ;; |GNS- -CFF|
     ;; |
     ;; |- G: the player is Grabbing an item
     ;; |- N: a fuel tank is Needed.
     ;; |- S: there is a fuel tank on Screen.
+    ;; |- C: SUSE's Coin has been collected.
     ;; |- F: number of Falling items.
     zp_state = $CA
 
@@ -128,7 +129,9 @@
         lda Globals::zp_level_kind
         bne @other_screens
 
-        lda #0
+        ;; Zero out the state except for the 'C' bit.
+        lda Items::zp_state
+        and #$04
         sta Items::zp_state
 
         ;; We haven't collected anything yet, but it's convenient for us to mock
@@ -179,13 +182,16 @@
 
         ;; Palettes.
         lda #0
-        sta Items::zp_current_tiles + 6, x
+        sta Items::zp_current_tiles + 5, x
 
-        beq @invalidate_third
+        beq @coin_or_invalidate_third
 
     @other_screens:
-        ;; Fuel tanks are needed, that's all.
-        lda #%01000000
+        ;; Zero out the state except for the 'C' bit. The 'N' bit needs to be
+        ;; set always.
+        lda Items::zp_state
+        and #$04
+        ora #$40
         sta Items::zp_state
 
         ;; Shuttle parts are counted as "collected". This makes the
@@ -197,6 +203,46 @@
         lda #$FF
         sta Items::zp_pool_base, x
         sta Items::zp_pool_base + 3, x
+        bne @invalidate_third
+
+    @coin_or_invalidate_third:
+        ;; If we have finished the game once, and we have not collected the
+        ;; SUSE's coin yet, let it be.
+        lda Globals::zp_level
+        cmp #8
+        bne @invalidate_third
+        lda Items::zp_state
+        and #$04
+        bne @invalidate_third
+
+        ;; SUSE's coin will fall from the sky. Hence, compute this new item as a
+        ;; falling one.
+        inc Items::zp_state
+
+        ;; SUSE's coin can be Collected, is identified by the '100' kind, and is
+        ;; in a Falling state.
+        lda #%01001100
+        sta Items::zp_pool_base + 6, x
+
+        ;; Falling from the sky at the right platform.
+        lda #Background::UPPER_MARGIN_Y_COORD
+        sta Items::zp_pool_base + 7, x
+        lsr
+        lsr
+        lsr
+        sta Items::zp_current_tiles + 6, x
+        lda #$D0
+        sta Items::zp_pool_base + 8, x
+        lsr
+        lsr
+        lsr
+        sta Items::zp_current_tiles + 7, x
+
+        ;; Default palette, the tile ID is simply ignored.
+        lda #0
+        sta Items::zp_current_tiles + 8, x
+
+        rts
 
     @invalidate_third:
         ;; Always invalidate the third item.
@@ -248,26 +294,23 @@
         cmp #$01
         bne @do_fuel_or_regular
         lda #$06
-        bne @no_attributes
+        beq @do_fuel_or_regular
+
+    @no_attributes:
+        sta Globals::zp_arg0
+        lda #0
+        sta Globals::zp_arg1
+        JAL allocate_metasprite_x_y
 
     @do_fuel_or_regular:
-        ;; Is it a fuel tank?
+        ;; Switch statement for the kind of item (regular, fuel, coin).
         lda Items::zp_pool_base, x
-        and #$03
+        and #$07
         cmp #2
-        bne @regular
+        beq @fuel
         cmp #4
         beq @coin
 
-        ;; Then just pick the tile from the fuel tank and pick the right
-        ;; palette.
-        lda #$0C
-        sta Globals::zp_arg0
-        lda #2
-        sta Globals::zp_arg1
-        JAL allocate_metasprite_x_y
-
-    @regular:
         ;; This is a regular item
         lda Items::zp_current_tiles + 2, x
         lsr
@@ -284,12 +327,19 @@
         sta Globals::zp_arg0
         JAL allocate_metasprite_x_y
 
+    @fuel:
+        ;; Then just pick the tile from the fuel tank and pick the right
+        ;; palette.
+        lda #$0C
+        sta Globals::zp_arg0
+        lda #2
+        sta Globals::zp_arg1
+        JAL allocate_metasprite_x_y
+
     @coin:
         lda #$0A
-
-    @no_attributes:
         sta Globals::zp_arg0
-        lda #0
+        lda #3
         sta Globals::zp_arg1
         JAL allocate_metasprite_x_y
 
@@ -709,8 +759,6 @@
 
         ;; We start by generating a new state. If the state is asking for a fuel
         ;; tank, let it be. Otherwise it will be a regular item.
-        ;;
-        ;; TODO: coin support.
         lda Items::zp_state
         and #$40
         beq @regular
@@ -862,6 +910,18 @@
     .proc collect
         ldx Items::zp_pool_index
 
+        ;; Are we collecting the one and only SUSE coin?!
+        lda Items::zp_pool_base, x
+        and #$07
+        cmp #4
+        bne @check_fall
+
+        ;; Hell, yeah!
+        lda Items::zp_state
+        ora #$04
+        sta Items::zp_state
+
+    @check_fall:
         ;; If the collected item was actually falling down, decrease the number
         ;; of falling items.
         lda Items::zp_pool_base, x
diff --git a/src/jetpac.s b/src/jetpac.s
index 2d397ac..f6a53a9 100644
--- a/src/jetpac.s
+++ b/src/jetpac.s
@@ -129,6 +129,7 @@
     sta Joypad::zp_buttons
     sta Joypad::zp_prev
     sta Player::zp_state
+    sta Items::zp_state
 
     ;; 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
diff --git a/src/over.s b/src/over.s
index cb59ef8..cca59ae 100644
--- a/src/over.s
+++ b/src/over.s
@@ -67,9 +67,16 @@
 
     @do_render:
         jsr Over::clear_out_screen
-        ;; TODO: coin game over.
+        lda Globals::zp_flags
+        and #$03
+        cmp #2
+        beq @regular
+        jsr Over::render_coin_game_over
+        jmp @next
+    @regular:
         jsr Over::render_regular_game_over
 
+    @next:
         ;; Enable back the PPU (only background).
         lda #%00001110
         sta PPU::zp_mask
@@ -234,4 +241,53 @@
         ;; "OVER"
         .byte $29, $30, $1F, $2C, $FF
     .endproc
+
+    ;; Render the "Game over" in the case the player has collected SUSE's coin.
+    ;; TODO: see how much it can be merged
+    ;; TODO: not centered nor fully realized.
+    .proc render_coin_game_over
+        ;; Set the position.
+        bit PPU::m_status
+        ldx #$29
+        stx PPU::m_address
+        ldx #$6C
+        stx PPU::m_address
+
+        ;; And just iterate over the "message" until we reach the end of string
+        ;; $FF character.
+        ldx #0
+    @message_loop:
+        lda message, x
+        cmp #$FF
+        beq @out
+        sta PPU::m_data
+        inx
+        bne @message_loop
+
+    @out:
+        ;; Reset attributes for the end of the message.
+        bit PPU::m_status
+        ldx #$2B
+        stx PPU::m_address
+        ldx #$D5
+        stx PPU::m_address
+        lda #0
+        sta PPU::m_data
+        sta PPU::m_data
+        sta PPU::m_data
+
+        rts
+
+    message:
+        ;; "YOU "
+        .byte $33, $29, $2F, $00
+        ;; "ARE "
+        .byte $1B, $2C, $1F, $00
+        ;; "A "
+        .byte $1B, $00
+        ;; "SUPER "
+        .byte $2D, $2F, $2A, $1F, $2C, $00
+        ;; "PLAYER!" TODO
+        .byte $2A, $26, $1B, $33, $1F, $2C, $FF
+    .endproc
 .endscope