Needle colour mod

This article refers to a Stunts mod coded by Cas with quite some work from Daniel3D by editing the Restunts source and recompiling it, which allows to configure the instrument needle colour as seen from a car cockpit for each car individually.

History

On 22 August 2021, Ryoma created a thread where he mentioned he had had some success changing the instrument needle colour by creating a mask for one of his cars. Daniel3D noted that this wasn't a complete solution and decided to look into the Restunts code to find a better way to do it. He realised the instrument needle colour was actually defined by reference and not hard-coded, as there is a needle_meter_color pointer in the code.

This called the attention of Cas, who noticed that the pointer actually referenced a constant field, yet, it could be changed for a pointer to a variable. He correctly guessed that there should be a field in memory at a static offset relative to needle_meter_color that would lay within the car RES information and be currently unused, so changing this pointer to make reference to that field would allow for cars to have a configurable needle colour.

Originally, the idea was to just patch the binary by finding the pointer value and replace it, but this turned out to be challenging, so Daniel3D helped with recompilation of the source. Red #5 field was chosen because its default value is 16, which is white in Stunts. This worked flawlessly and it's the first version of the mod.

Then, Cas thought it could be possible to configure different colours for the two instrument needles, but this would require to push new code into the source. Both Cas and Daniel3D worked hard to get this done because this would produce artifacts and made the code unstable. With some padding bytes and several tries, they finally got it working. This is the new version and it has so far proved very stable, although it's impossible to confirm it can never lead to errors.