:wave: Quick question. I using a C API using Kotli...

# kotlin-native

[dwursteisen]

👋
Quick question.
I using a C API using Kotlin/Native.
Using C interrop, I can use the generated object Model which has a field val transform: Matrix
I want to update this transform matrix but I haven’t found a way to do it.

val model = cValue<Model> { }
// ...
model.useContents {
    // create a copy so update are lost 
    transform.useContents {
       m1 = ...
    }  
}

generated code by cinterop:

public final class Model {
   // ...
   val transform: Matrix
}

header definition:
• Model: https://github.com/raysan5/raylib/blob/master/src/raylib.h#L365
• Matrix: https://github.com/raysan5/raylib/blob/master/src/raylib.h#L195

[Artyom Degtyarev [JB]]

Hello! Can you tell, what exactly you’re trying to do here?

[dwursteisen]

Hello!

I’m trying to call raylib (a little game engine in C) using Kotlin/Native.

You can rotate models (ie: a 3D object) using transformation.
ie: by assigning a matrix which contains all my rotations.

You can see an example (in C) here:

• https://github.com/raysan5/raylib/blob/master/examples/models/models_yaw_pitch_roll.c#L105
• https://www.raylib.com/examples/web/models/loader.html?name=models_yaw_pitch_roll
So I’m trying to do the same things but using Kotlin/Native:

val model : CValue<Model> = LoadModel("…")

// ...

DrawModel(model, cubePosition, 1f, Colors.WHITE)

Where I got some issues, is how to update my transform matrix from my model.

cinterop produce this Kotlin model:

class Model(val transform: Matrix, …)

I can’t reasign the transform matrix. So I’m trying now to update the matrix (each fiels of the matrix are var).

But I’m little confuse about how to do it

-----
Wait…While typing this text, I may get my mistake: I didn’t correctly use copy (I was still using the old reference of model, and not the “copied” model):

val model = LoadModel(…).copy {
        val matrix = rotatedMatrix(x, y, z)
        matrix.useContents {
            transform.m0 = matrix.m0
            // ...
            transform.m15 = matrix.m15
        }
}

It seems to work.

But I’m bit surprised that I need to “copy” an object while I just want to mutate one of its fields 🤔 .

Anyway, thanks you 😛 You help me to search deeper!