Exploring IV’s vehicle liveries

Hi,

I had a look at the vehicle livery system of IV earlier today. Yard1 – once again – asked me whether I could take a look at this, since he said IV would limit the amount of liveries to four per vehicle even if more than four textures were added to the WTD file.

Edit: Video: Click here.

So I launched IDA and took a look at the native function SET_CAR_LIVERY to find out how changing a livery works at all. The second argument for the native is the livery texture index, ranging from 0-3 normally. A quick back trace led to the following code:

mov ecx, [ebx+eax*4+CVehicleModelInfo.m_adwLiveryTextureHashes]
movsx edx, [ebx+CVehicleModelInfo.__parent.m_wTxdId]

 

The register EAX holds the index of the texture and since it’s multiplied by 4 we know each entry has the size of 4 bytes, a DWORD. When passing a value from 0-3 to the native, the name of the texture as a hash is returned. However when passing 4, we get CDCDCDCD, so unallocated memory. This leads to the conclusion that the game either didn’t load our 5th texture or that we’re dealing with an array of size 4. The latter is the case. We only have a dwHashes[3] here, so anything past 4 textures will simply not be stored and thus can’t be retrieved later. Note that higher values might lead to unexpected behavior, since no range check is done and the code will just grab the value from memory exceeding the array bounds.

How to allow more liveries then? Simply hook into the function and change the specific location to return the hash for modelName_sign_n to bypass the array limitation. This way it wil look up the texture later by hash (it’s loaded by the game already) and assign it to the vehicle. Using such a simpe hook, you can extend the allowed range to any number you like. I might post an example later which does this for you.

On another note, I’m currently doing a research project on the texture/model loading of the rage engine and how it is stored/used in EFLC with cp702 which is getting along pretty good so far. I hope to be able to tell you more about this soon!

Lennart

4 thoughts on “Exploring IV’s vehicle liveries

  1. Firstyminator

    Wow… Awesome work there LMS. You extend the Gtaiv experience to unlimited heights! Very impressed of your research and work!

    Reply
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