Prince of Persia

Posted: **September 25th, 2015, 5:08 pm**

Can an easy hex edit of PRINCE.EXE be made to make the chomper remove 1 hit point instead of killing the prince?

Posted: **September 26th, 2015, 5:06 pm**

Norbert wrote: Can an easy hex edit of PRINCE.EXE be made to make the chomper remove 1 hit point instead of killing the prince?

The relevant part of the disassembly:

Code: Select all

seg004:0811 B8 64 00                             mov     ax, 100
seg004:0814 50                                   push    ax              ; count
seg004:0815 9A BD 06 CB 06                       call    take_hp
seg004:081A B8 2E 00                             mov     ax, sound_46_something_chopped
seg004:081D 50                                   push    ax              ; sound_id
seg004:081E 9A C5 12 00 00                       call    play_sound
seg004:0823 B8 36 00                             mov     ax, 54          ; chomped
seg004:0826 50                                   push    ax              ; seq_index
seg004:0827 9A 0A 00 DE 05                       call    seqtbl_offset_char

Search: B8 64 00 50 9A BD 06 CB 06 B8 2E 00 50 9A C5 12 00 00 B8 36 00 50
Change:
* 0x64 -> 0x01 (how many HP to take)
* 0x36 -> what do you want instead of being chomped:
0x11 = seq_17_soft_land
0x1A = seq_26_crouch_while_running
0x32 = seq_50_crouch
0x4F = seq_79_crouch_hop
See types.h of SDLPoP for other numbers.

Now, if the prince had only 1 HP then there might be a problem...

You might also want to remove blood:

Code: Select all

seg004:07C0 8A 1E ED 42                          mov     bl, curr_tile_pos
seg004:07C4 2A FF                                sub     bh, bh
seg004:07C6 8B 36 88 5F                          mov     si, curr_room_modif
seg004:07CA 80 08 80                             or      byte ptr [bx+si], 80h ; put blood
seg004:07CD 80 3E 22 3D B2                       cmp     char_frame, 178 ; chopped

Search: 80 08 80 80, change to 80 08 00 80

What is your goal, by the way?
Maybe you are making some new mod where the chomper (graphics) is replaced with something different?

Posted: **October 16th, 2015, 8:07 am**

Neat.

David wrote:What is your goal, by the way?

To be honest I was merely curious to see the modified chomper in action. I just have and it's quite fun to see the chomper just take one hitpoint. I hope it didn't take too much effort on your part to find the hex modifications necessary for it. I tried to make sure you wouldn't put in a lot of effort finding them - if that would've been necessary - by including "an easy hex edit" in my question, but now that I'm thinking about it, that phrase is multi-interpretable. It could also refer to how easy the edit(s) is (are) to apply after being found.

David wrote:Now, if the prince had only 1 HP then there might be a problem...

Yes, it causes a problem, because the game basically hangs. If there was a way to fix this, maybe the modifications could be used for the easiest setting of King of Persia. But it's probably better if you focus your energy on other things.

Posted: **January 31st, 2021, 6:06 pm**

Norbert wrote: ↑October 16th, 2015, 8:07 am
David wrote:Now, if the prince had only 1 HP then there might be a problem...
[...] If there was a way to fix this, [...]

Is there?
I think once fixed this is an interesting modification, because it changes the impact of chomper usage in levels.

Prince of Persia

Question: hex edit to make chomper -1hp instead of kill?

Question: hex edit to make chomper -1hp instead of kill?

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Re: Question: hex edit to make chomper -1hp instead of kill?

Re: Question: hex edit to make chomper -1hp instead of kill?