Added flicker-free planets to Commodore 64 version

src/elite-modify.py

@@ -14,8 +14,17 @@
 # It does the following:
 #
 #   * Decrypt the gma6 file
-#   * Modify the gma6 file to draw flicker-free ships
+#   * Modify the gma6 file to draw flicker-free ships and planets
 #   * Encrypt the gma6 file
+#
+#   * Decrypt the gma5 file
+#   * Modify the gma5 file to draw flicker-free planets
+#   * Encrypt the gma5 file
+#
+#   * Decrypt the gma4 file
+#   * Modify the gma4 file to draw flicker-free planets
+#   * Encrypt the gma4 file
+#
 #   * Modify the gma1 file to remove disk protection
 #
 # Run this script by changing directory to the folder containing the disk files
@@ -86,7 +95,7 @@ print()
 print("Modifying Commodore 64 Elite")
 print("Platform: {}".format(platform.upper()))
 
-# Configuration variables
+# Configuration variables for gma6
 
 load_address = 0x6A00 - 2
 seed = 0x49
@@ -288,9 +297,9 @@ insert_nops(data_block, 0x9FC1, 1)
 #       NOP
 
 insert_bytes(data_block, 0x9FD9, [
-    0xC8,                                   # INY
-    0xB1, 0x5B,                             # LDA (V),Y
-    0xAA                                    # TAX
+    0xC8,                               # INY
+    0xB1, 0x5B,                         # LDA (V),Y
+    0xAA                                # TAX
 ])
 
 lda_sta_block = get_offset(0x9FDD)
@@ -298,9 +307,9 @@ for n in range(lda_sta_block, lda_sta_block + 4 * 5):
     data_block[n] = data_block[n + 4]
 
 insert_bytes(data_block, 0x9FF1, [
-    0xC8,                                   # INY
-    0xB1, 0x5B,                             # LDA (V),Y
-    0xAA                                    # TAX
+    0xC8,                               # INY
+    0xB1, 0x5B,                         # LDA (V),Y
+    0xAA                                # TAX
 ])
 insert_nops(data_block, 0x9FF5, 2)
 
@@ -316,7 +325,7 @@ insert_nops(data_block, 0x9FF5, 2)
 # To:   JMP PATCH2
 
 insert_bytes(data_block, 0xA010, [
-    0x4C, patch2 % 256, patch2 // 256       # JMP PATCH2
+    0x4C, patch2 % 256, patch2 // 256   # JMP PATCH2
 ])
 
 # LL9 (Part 11)
@@ -359,6 +368,91 @@ elite_file.close()
 
 print("[ Modify  ] append file extra.bin")
 
+# We now move on to the routines for drawing flicker-free planets
+
+# Set the addresses for the extra routines (LLX30, PATCH1, PATCH2) that we will
+# append to the end of the main game code (where there is a bit of free space)
+
+erasep = 0xCD3B
+patch4 = 0x69D0
+patch5 = 0x69D5
+
+# PL9 (Part 1 of 3)
+#
+# We have already assembled the modified part 1 of PL9 in BeebAsm and saved
+# it as the binary file pl9.bin, so now we drop this over the top of the
+# existing routine (the new routine is slightly bigger, so it ends by jumping
+# to PATCH6, which contains the spill-over).
+
+insert_binary_file(data_block, 0x7D8C, "pl9.bin")
+
+# PL9 (Part 2 of 3)
+#
+# The above modification moves PL20, so we need to modify the branch instruction
+# at the start of part 2 of PL9.
+
+insert_bytes(data_block, 0x7DA8, [
+    0x90, 0xEB                          # BCC PL20
+])
+
+# PL9 (Part 3 of 3)
+#
+# The above modification moves PL20, so we need to modify the branch instruction
+# at the start of part 3 of PL9.
+
+insert_bytes(data_block, 0x7DE2, [
+    0x30, 0xB1                          # BMI PL20
+])
+
+# WPLS2
+#
+# We have already assembled the modified part 1 of PL9 in BeebAsm and saved
+# it as the binary file pl9.bin, so now we drop this over the top of the
+# existing routine (which is quite a bit longer, so there is room).
+
+insert_binary_file(data_block, 0x80BB, "wpls2.bin")
+
+# PLS22
+#
+# This is the modification on either side of PL40, with the label moving two
+# bytes backwards to accommodate the modified code.
+#
+# From: BCS PL40
+#       ...
+#       STA CNT2
+#       JMP PLL4
+#      .PL40
+#       RTS
+#
+# To:   BCS PL40
+#       ...
+#       JMP PATCH4
+#      .PL40
+#       JMP EraseRestOfPlanet
+
+insert_bytes(data_block, 0x7F04, [
+    0xB0, 0x0A                          # BCS PL40
+])
+insert_bytes(data_block, 0x7F0D, [
+    0x4C, patch4 % 256, patch4 // 256,  # JMP PATCH4
+    0x4C, erasep % 256, erasep // 256   # JMP EraseRestOfPlanet
+])
+
+# CIRCLE2
+#
+# This is the modification at the start of the routine.
+#
+# From: LDX #&FF
+#       STX FLAG
+#
+# To:   JSR PATCH5
+#       NOP
+
+insert_bytes(data_block, 0x805E, [
+    0x20, patch5 % 256, patch5 // 256  # JSR PATCH5
+])
+insert_nops(data_block, 0x8061, 1)
+
 # All the modifications are done, so write the output file for gma6.modified,
 # which we can use for debugging
 
@@ -386,6 +480,165 @@ output_file.close()
 
 print("[ Save    ] gma6.encrypted")
 
+# Configuration variables for gma5
+
+load_address = 0x1D00 - 2
+seed = 0x36
+scramble_from = 0x1D00
+scramble_to = 0x1D00 + (0x21D4 - 3)    # File size - 3
+
+# Set up an array to hold the gma5 binary, so we can modify it
+
+data_block = bytearray()
+
+# Load the gma5 code file into data_block
+
+elite_file = open("gma5", "rb")
+data_block.extend(elite_file.read())
+elite_file.close()
+
+print()
+print("[ Read    ] gma5")
+
+# Decrypt the gma5 code file
+
+updated_seed = seed
+
+for n in range(scramble_to, scramble_from - 1, -1):
+    new = (data_block[n - load_address] - updated_seed) % 256
+    data_block[n - load_address] = new
+    updated_seed = new
+
+print("[ Decrypt ] gma5")
+
+# Write an output file containing the decrypted but unmodified gma5 code, which
+# we can use for debugging
+
+output_file = open("gma5.decrypted", "wb")
+output_file.write(data_block)
+output_file.close()
+
+print("[ Save    ] gma5.decrypted")
+
+# BLINE
+#
+# We have already assembled the modified BLINE in BeebAsm and saved it as the
+# binary file bline.bin, so now we drop this over the top of the existing
+# routine (the new routine is slightly bigger, so it ends by jumping to PATCH3,
+# which contains the spill-over).
+
+insert_binary_file(data_block, 0x2977, "bline.bin")
+
+# All the modifications are done, so write the output file for gma5.modified,
+# which we can use for debugging
+
+output_file = open("gma5.modified", "wb")
+output_file.write(data_block)
+output_file.close()
+
+print("[ Save    ] gma5.modified")
+
+# Encrypt the gma5 code file
+
+for n in range(scramble_from, scramble_to):
+    data_block[n - load_address] = (data_block[n - load_address] + data_block[n + 1 - load_address]) % 256
+
+data_block[scramble_to - load_address] = (data_block[scramble_to - load_address] + seed) % 256
+
+print("[ Encrypt ] gma5.modified")
+
+# Write the output file for gma5.encrypted, which contains our modified game
+# binary with the flicker-free code
+
+output_file = open("gma5.encrypted", "wb")
+output_file.write(data_block)
+output_file.close()
+
+print("[ Save    ] gma5.encrypted")
+
+# Configuration variables for gma4
+
+load_address = 0x4000 - 2
+seed = 0x8E
+scramble_from = 0x75E4
+scramble_to = 0x865A
+
+# Set up an array to hold the gma4 binary, so we can modify it
+
+data_block = bytearray()
+
+# Load the gma4 code file into data_block
+
+elite_file = open("gma4", "rb")
+data_block.extend(elite_file.read())
+elite_file.close()
+
+print()
+print("[ Read    ] gma4")
+
+# Decrypt the gma4 code file
+
+updated_seed = seed
+
+for n in range(scramble_to, scramble_from - 1, -1):
+    new = (data_block[n - load_address] - updated_seed) % 256
+    data_block[n - load_address] = new
+    updated_seed = new
+
+print("[ Decrypt ] gma4")
+
+# Write an output file containing the decrypted but unmodified gma4 code, which
+# we can use for debugging
+
+output_file = open("gma4.decrypted", "wb")
+output_file.write(data_block)
+output_file.close()
+
+print("[ Save    ] gma4.decrypted")
+
+# We now insert the four extra routines required by the modifications into
+# the unused space just after the sprites:
+#
+#   PATCH3
+#   PATCH4
+#   PATCH5
+#   PATCH6
+#
+# We have already assembled these in BeebAsm and saved them as the binary file
+# extra2.bin, so we simply insert this file at the correct address. The contents
+# of the GMA4 file is moved after decryption, so although the routines end up at
+# $69C0, they actually get loaded and decrypted at $7C3A, so that's the address
+# we use when inserting the code into the gm4 file:
+
+insert_binary_file(data_block, 0x7C3A, "extra2.bin")
+
+# All the modifications are done, so write the output file for gma4.modified,
+# which we can use for debugging
+
+output_file = open("gma4.modified", "wb")
+output_file.write(data_block)
+output_file.close()
+
+print("[ Save    ] gma4.modified")
+
+# Encrypt the gma4 code file
+
+for n in range(scramble_from, scramble_to):
+    data_block[n - load_address] = (data_block[n - load_address] + data_block[n + 1 - load_address]) % 256
+
+data_block[scramble_to - load_address] = (data_block[scramble_to - load_address] + seed) % 256
+
+print("[ Encrypt ] gma4.modified")
+
+# Write the output file for gma4.encrypted, which contains our modified game
+# binary with the flicker-free code
+
+output_file = open("gma4.encrypted", "wb")
+output_file.write(data_block)
+output_file.close()
+
+print("[ Save    ] gma4.encrypted")
+
 # Finally, we need to remove the disk protection from gma1, as described here:
 # https://www.lemon64.com/forum/viewtopic.php?t=67762&start=90