hi, I’m trying to convert some C code (full code i...

# kotlin-native

[Adam S]

hi, I’m trying to convert some C code (full code in 🧵) to Kotlin Native

Model model = LoadModel("resources/model.obj")
Texture2D texture = LoadTexture("resources/texture.png");
model.materials[0].maps[MATERIAL_MAP_DIFFUSE].texture = texture; // Set map diffuse texture

I can get close, but for some reason the generated cinterop Kotlin code has texture as a val, not a var

val model: CValue<Model> = LoadModel("resources/model.obj")
val texture: CValue<Texture> = LoadTexture("resources/texture.png")

model.useContents {
  // model.materials[0].maps[MATERIAL_MAP_DIFFUSE].texture = texture
  materials!![0].maps!![MATERIAL_MAP_DIFFUSE].texture = texture // ERROR val cannot be reassigned
}

any hints are appreciated!

[Adam S]

lib.c

lib.c

[vbsteven]

What does IDEA say the type of .texture is? when you have over it?

[Adam S]

snip.kt

snip.kt

[Adam S]

texture is a class Texture(rawPtr: kotlinx.cinterop.NativePtr) : CStructVar

[Oleg Yukhnevich]

https://kotlinlang.slack.com/archives/C3SGXARS6/p1593990644146500
Looks relevant
Seems it’s not possible directly to set, only to copy

[Landry Norris]

The texture is stored by value. When you set the value in C, it's not just changing a reference like in Kotlin. It's copying the fields one-by-one (I'm sure some implementations may copy all the memory of the struct instead, but same effect). This goes against Kotlin's set method, so you can just copy the relevant fields (or memset if you feel like being efficient, but dangerous)

[Adam S]

so you can just copy the relevant fields (or memset if you feel like being efficient, but dangerous)

how? :) The problem is that texture is a val

[Adam S]

alright, I think I figured it out. I misread the thread that Oleg posted and thought it wasn’t possible, but it suggested using the ‘place’ function

this seems to work:

val model: CValue<Model> = LoadModel("resources/model.obj")
val texture: CValue<Texture> = LoadTexture("resources/texture.png")

model.useContents {
  texture.place(materials!![0].maps!![MATERIAL_MAP_DIFFUSE].texture.ptr)
}