Render All Ships Patch

Summary

This patch modifies P3 to render all ships on the scrollmap, not just the up to two ships spotted by each player ship or convoy.

Details

The first half of the draw_spotted_ships function at 004516B0 determines which ships should be rendered. It produces three things of interest:

the amount of ships that should be drawn
an array of ship indexes that should be drawn
an array of ship y coordinates

The rest of the function does not have to be modified.

The following function fixup_all_ships takes pointers to the two arrays as an argument, and returns the amount of ships that should be drawn. It only enqueues ships whose status is 0xf (merchant vessel at sea) and 0x12 (AI pirate vessel).

#include <stdint.h>
#define CLASS6_PTR 0x006DD7A0

inline void* get_ship_by_index(uint16_t index) {
    uint32_t ships_ptr =  *(uint32_t*) (CLASS6_PTR + 0x04);
    return (void*) ships_ptr + 0x180 * (uint32_t) index;
}

inline uint16_t get_ships_size() {
    return *(uint16_t*) (CLASS6_PTR + 0xf4);
}

inline uint16_t get_ship_status(void* ship) {
    return *(uint16_t*) (((uint32_t) ship) + 0x134);
}

inline uint16_t get_ship_y_high(void* ship) {
    return *(uint16_t*) (((uint32_t) ship) + 0x22);
}

uint32_t fixup_all_ships(uint32_t* spotted_y, uint32_t* spotted_index) {
    uint16_t ships_size = get_ships_size();
    int new_spotted_size = 0;

    for (uint16_t i = 0; i < ships_size; i++) {
        void* ship = get_ship_by_index(i);
        uint16_t status = get_ship_status(ship);

        if (status != 0x12 && status != 0xf) {
            continue;
        }

        spotted_y[new_spotted_size] = get_ship_y_high(ship);
        spotted_index[new_spotted_size] = i;

        new_spotted_size += 1;
    }

    return new_spotted_size;
}

Built with gcc 14.1 (-m32 -O3 -fno-stack-protector) this generates the following assembly:

fixup_all_ships:
        push    ebp
        push    edi
        push    esi
        push    ebx
        movzx   ebx, WORD PTR ds:7198868
        mov     esi, DWORD PTR [esp+20]
        mov     edi, DWORD PTR [esp+24]
        test    bx, bx
        je      .L6
        xor     ecx, ecx
        xor     eax, eax
.L5:
        lea     edx, [ecx+ecx*2]
        sal     edx, 7
        add     edx, DWORD PTR ds:7198628
        movzx   ebp, WORD PTR [edx+308]
        cmp     bp, 18
        je      .L7
        cmp     bp, 15
        jne     .L3
.L7:
        movzx   edx, WORD PTR [edx+34]
        mov     DWORD PTR [esi+eax*4], edx
        mov     DWORD PTR [edi+eax*4], ecx
        add     eax, 1
.L3:
        add     ecx, 1
        cmp     ebx, ecx
        jne     .L5
        pop     ebx
        pop     esi
        pop     edi
        pop     ebp
        ret
.L6:
        pop     ebx
        xor     eax, eax
        pop     esi
        pop     edi
        pop     ebp
        ret

A jump to fixup_all_ships has to be injected at 0x00451759 with the following assembly instructions. #ADDRESSOFPATCH needs to be replaced with the address of fixup_all_ships.

# save regs
push eax
push ecx
push edx

# call fixup_all_ships
mov eax, [esp+0x30]
mov ecx, [esp+0x2C]
push ecx
push eax
mov edx, #ADDRESSOFPATCH
call edx
mov ebp, eax
pop eax
pop eax

# restore regs
pop edx
pop ecx
pop eax

# jump to second part of draw_spotted_ships
mov eax, 0x00451B58
jmp eax

Patrician 3 Insights

Render All Ships Patch

Summary

Details

Patch