User talk:Morgan525
Modding Tank/Cannon into a Tank/Chaingun
Many people have questions about this. It's fairly easy to change the ammo type of the Tank/Cannon turrent and damage into a AP/rifle and then giving the turret autofire. The real problem is changing the amount of ammo in the tank and not cause problems with the amount of ammo in your base stores. In the executable there are various places that handle updating the amount of ammo for the various events: adding a tank onto a craft(checking if the base has the proper amount of ammo for the tank and removing that amount from base stores, if so), removing the tank from a craft (adding the ammo back to base stores), post-interception-battle (adding the remaining ammo from the tank into base stores and attempting to add the tank back onto the craft), and post base defense (adding the remaining ammo to base stores.) In addition, there is the routine that sets the amount of ammo for the tank in battlescape. If you miss any of these areas, your ammo supply quickly spirals out of control or you get no benefit for the changes you have made.
The DOS version of the game makes it much simpler to adjust the stats, but I have lost the notes on the offsets. The problem with the CE version is the way the compiler wrote the calculations. In the code, the value was calculated by using multiples of five with bit-shifts to get to 30. This means you can't choose any amount for your ammo. I rewrote these lines to make it simpler to understand and give more freedom to choose the value(Feel free to use these changes. I gave my tank 60 rounds {3Ch}. However, unless you want to deduce for yourself how to modify the proper locations, don't increase the amount of ammo over 63. [This has to do with how the game uses bit-shifts to calculate remaining ammo during the post-tatical phase]):
TANK/CANNON AMMO ALTERATION
POST-TACTICAL PHASE BASE/CRAFT INVENTORY UPDATE
0x449C53: B8 3C 00 00 00 0F AF C2 90 90 3B F0 7D 2C 66 0F B6 D2 66 01 17 B8 89 88 88 88 F7 EE 03 D6 C7 44 24 10 01 00 00 00 C1 FA 05 8B C2 C1 E8 1F 03 D0 88 55 2C 66 0F B6
D2 66 29 17 66 0F B6 45 00 8B D0 C1 E2 0B 2B D0 C1 E2 04 03 D0 C1 E2 02 66 02 91 1A 01 00 00 90 90
.text:00449C53 mov eax, 3Ch
.text:00449C58 imul eax, edx
.text:00449C5B nop
.text:00449C5C nop
.text:00449C5D cmp esi, eax
.text:00449C5F jge short loc_449C8D
.text:00449C61 movzx dx, dl
.text:00449C65 add [edi], dx
.text:00449C68 mov eax, 88888889h
.text:00449C6D imul esi
.text:00449C6F add edx, esi
.text:00449C71 mov [esp+30h+var_20], 1
.text:00449C79 sar edx, 5
.text:00449C7C mov eax, edx
.text:00449C7E shr eax, 1Fh
.text:00449C81 add edx, eax
.text:00449C83 mov [ebp+2Ch], dl
.text:00449C86 movzx dx, dl
.text:00449C8A sub [edi], dx
.text:00449C8D movzx ax, byte ptr [ebp+0]
.text:00449C92 mov edx, eax
.text:00449C94 shl edx, 0Bh
.text:00449C97 sub edx, eax
.text:00449C99 shl edx, 4
.text:00449C9C add edx, eax
.text:00449C9E shl edx, 2
.text:00449CA1 db 66h
.text:00449CA1 add dl, [ecx+11Ah]
.text:00449CA8 nop
.text:00449CA9 nop
0x449DFA: B8 3C 00 00 00 0F AF C2 3B F0 7D 2E 90 90 66 0F B6 D2 66 01 17 B8 89 88 88 88 F7 EE 03 D6 C7 44 24 10 01 00 00 00 C1 FA 05 8B C2 C1 E8 1F 03 D0 88 55 00 66 0F B6
D2 66 29 17 66 0F B6 45 00 8B D0 C1 E2 0B 2B D0 C1 E2 04 03 D0 C1 E2 02 66 01 91 1A 01 00 00 90 90
.text:00449DFA mov eax, 3Ch
.text:00449DFF imul eax, edx
.text:00449E02 cmp esi, eax
.text:00449E04 jge short loc_449E34
.text:00449E06 nop
.text:00449E07 nop
.text:00449E08 movzx dx, dl
.text:00449E0C add [edi], dx
.text:00449E0F mov eax, 88888889h
.text:00449E14 imul esi
.text:00449E16 add edx, esi
.text:00449E18 mov [esp+30h+var_20], 1
.text:00449E20 sar edx, 5
.text:00449E23 mov eax, edx
.text:00449E25 shr eax, 1Fh
.text:00449E28 add edx, eax
.text:00449E2A mov [ebp+0], dl
.text:00449E2D movzx dx, dl
.text:00449E31 sub [edi], dx
.text:00449E34 movzx ax, byte ptr [ebp+0]
.text:00449E39 mov edx, eax
.text:00449E3B shl edx, 0Bh
.text:00449E3E sub edx, eax
.text:00449E40 shl edx, 4
.text:00449E43 add edx, eax
.text:00449E45 shl edx, 2
.text:00449E48 add [ecx+11Ah], dx
.text:00449E4F nop
.text:00449E50 nop
[TANK/CHAINGUN AMMO AMOUNT SET FOR TACTICAL REFERENCE]
0x44ED27: C6 45 76 3C
.text:0044ED27 mov byte ptr [ebp+76h], 3Ch
[TANK/CHAINGUN AMMO CHECK IN BASE INVENTORY AND ALTERATION OF AMOUNT]
0x456410: 66 83 84 90 1A 01 00 00 3C
.text:00456410 add word ptr [eax+edx*4+11Ah], 3Ch
0x4564F1: 66 83 F9 3C
.text:004564F1 cmp cx, 3Ch
0x456512: 83 C1 C4
.text:00456512 add ecx, 0FFFFFFC4h (add ecx, -3Ch)
[Alternate option]
0x456512: 83 E9 3C
.text:00456512 sub ecx, 3Ch
TANK STATS start at offset 47573B
TANK UFOpaedia info 4752B0~4752CF
Functions used in UFOloader's new interception routines
For those that might want to know how accuracy is calculated with the new options for interception turned on:
X-Craft Accuracy
[(1+((3-(.5*(difficulty level-1)))/UFOsize)/2 ] * Weapon Accuracy ....... [beginner=1..superhuman=5]
Diff Ship Size
VS S M L VL
begin 0.8 0.875 1 1.25 2
exp 0.75 0.8125 0.91667 1.125 1.75
vet 0.7 0.75 0.83333 1 1.5
Genius 0.65 0.6875 0.75 0.875 1.25
Super 0.6 0.625 0.66667 0.75 1
UFO Accuracy
60 + (difficulty level *3) - [Cautious Mode bonus (10)]
Comparison of Damage routines
To explain, first the memory address of the Xcraft weapon is loaded to eax. Then the damage value is read from (eax+6) and loaded into bx. This value is sent to the random function where the value generated is returned through eax. Thereafter, the base value (ebx) is added to the random value (eax) for a range of 100-200%. The value of eax has edx subtracted from it (after extensive testing of several encounters and having edx displayed for each attack, edx always seems to be 0). eax is bit-shifted 1 space to the right {divided by two} and the final amount added to the amount of damage the craft has sustained (edi+0Ah). The result is that Xcraft weapons do 50-100% damage.
In the UFO case: the memory location for the UFO stats are set in ecx. Then the UFO weapon power is read (ecx+16h) and put into dx. Then this value is sent to the random funtion and again returned through eax (or ax as is the case here). ecx is set to zero and the random value is checked to see if zero was generated [cmp(compare) ax, cx]. If this is true, the program jumps past the section to assign damage to the Xcraft.
- The main routine for interdiction in DOS1.4 version is from 330B0~336A8.
Feedback
Any questions or feedback one may have....