From 6ef407f525324393600a9eb6a39ad7cf21a814a3 Mon Sep 17 00:00:00 2001
From: Miquel Sabaté Solà <mssola@mssola.com>
Date: Sun, 15 Mar 2026 22:50:12 +0100
Subject: Update the shuttle as fuel is getting in
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Just like in the original, the shuttle turns purple for each fuel
tank. That being said, due to the restriction from the NES/Famicom on
updating background tile attributes, a "half-filled" strategy is being
used here to convey the same idea for a total of 6 fuel tanks to be
delivered.

Signed-off-by: Miquel Sabaté Solà <mssola@mssola.com>
---
 src/items.s | 88 ++++++++++++++++++++++++++++++++++++++++++++++++++++++-------
 1 file changed, 79 insertions(+), 9 deletions(-)

(limited to 'src/items.s')

diff --git a/src/items.s b/src/items.s
index dc5b018..1490174 100644
--- a/src/items.s
+++ b/src/items.s
@@ -816,21 +816,91 @@
     ;;
     ;; NOTE: this has to be called with the PPU disabled.
     .proc update_shuttle
-        lda Globals::zp_level_kind
-        bne @fuel
+        lda Items::zp_collected
+        cmp #9
+        bne @high_middle
+        bit PPU::m_status
+        lda #$2B
+        sta PPU::m_address
+        lda #$E5
+        sta PPU::m_address
+        lda #%10100000
+        sta PPU::m_data
+        jmp @end
+
+    @high_middle:
+        lda Items::zp_collected
+        cmp #8
+        bcc @half_high_middle
+        bit PPU::m_status
+        lda #$2B
+        sta PPU::m_address
+        lda #$ED
+        sta PPU::m_address
+        lda #%10101010
+        sta PPU::m_data
+        bne @end
+
+    @half_high_middle:
+        lda Items::zp_collected
+        cmp #7
+        bcc @low_middle
+        bit PPU::m_status
+        lda #$2B
+        sta PPU::m_address
+        lda #$ED
+        sta PPU::m_address
+        lda #%10100010
+        sta PPU::m_data
+        bne @end
 
-        ;; Update the shuttle.
+    @low_middle:
         lda Items::zp_collected
+        cmp #6
+        bcc @half_low_middle
+        bit PPU::m_status
+        lda #$2B
+        sta PPU::m_address
+        lda #$ED
+        sta PPU::m_address
+        lda #%10100000
+        sta PPU::m_data
+        bne @end
+
+    @half_low_middle:
+        lda Items::zp_collected
+        cmp #5
+        bcc @low
+        bit PPU::m_status
+        lda #$2B
+        sta PPU::m_address
+        lda #$ED
+        sta PPU::m_address
+        lda #%00100000
+        sta PPU::m_data
+        bne @end
+
+    @low:
+        lda Items::zp_collected
+        cmp #4
+        bcc @just_top
+        bit PPU::m_status
+        lda #$2B
+        sta PPU::m_address
+        lda #$F5
+        sta PPU::m_address
+        lda #%10101010
+        sta PPU::m_data
+
+    @just_top:
         cmp #3
-        bne @mid_shuttle
+        bcc @just_middle
         jsr draw_high_part_shuttle
-    @mid_shuttle:
-        jsr draw_middle_part_shuttle
-        rts
 
-    @fuel:
-        ;; TODO
+    @just_middle:
+        jsr draw_middle_part_shuttle
 
+    @end:
         rts
     .endproc
 
-- 
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