# assimp-go

A Handcrafted Open Asset Import Library (AssImp) wrapper for Go.

## Features

The following features are already implemented:

* Loading all supported model formats into a Scene object
* Mesh data
* Materials
* Textures and embedded textures
* Error reporting
* Enums relevant to the above operations

Unimplemented (yet) AssImp Scene objects:

* Animation
* Lights
* Camera
* Metadata

## Using assimp-go

### Requirements

To run the project you need:

* A recent version of [Go](https://golang.org/) installed (1.17+)
* A C/C++ compiler installed and in your path
  * Windows: [MingW](https://www.mingw-w64.org/downloads/#mingw-builds) or similar
  * Mac/Linux: Should be installed by default, but if not try [GCC](https://gcc.gnu.org/) or [Clang](https://releases.llvm.org/download.html)

Then simply clone and use `go run .`

> Note: that it might take a while to run the first time because of downloading/compiling dependencies.

`assimp-go` statically links AssImp using platform dependent libraries.
Currently only `Windows` libraries are available, but more should be easy to add by statically compiling assimp on the wanted platform. (Make a PR if you can help us get those binaries!)

### Getting Started

```Go
func main() {

    //Load this .fbx model with the following post processing flags
    scene, release, err := asig.ImportFile("my-cube.fbx", asig.PostProcessTriangulate | asig.PostProcessJoinIdenticalVertices)
    if err != nil {
            panic(err)
    }

    for i := 0; i < len(scene.Materials); i++ {

        m := scene.Materials[i]

        //Check how many diffuse textures are attached to this material
        texCount := asig.GetMaterialTextureCount(m, asig.TextureTypeDiffuse)
        fmt.Println("Texture count:", texCount)

        //If we have at least 1 diffuse texture attached to this material, load the first diffuse texture (index 0)
        if texCount > 0 {

            texInfo, err := asig.GetMaterialTexture(m, asig.TextureTypeDiffuse, 0)
            if err != nil {
                panic(err)
            }

            fmt.Printf("%v\n", texInfo)
        }
    }

    //Now that we are done with all our `asig.XYZ` calls we can release underlying C resources. 
    //
    //NOTE: Our Go objects (like scene, scene.Materials etc) will remain intact ;), but we must NOT use asig.XYZ calls on this scene and its children anymore
    release()
}
```

The `release()` function is used to free underlying C resources and should be called after all processing that requires C code is done.
`release()` Will not affect the returned Go structs like `Scene` or `Mesh`. Returned Go data will remain valid.

`asig.X` functions call into C and therefore should not be used on released objects. Calling any `asig.X` function after `release()` is **undefined**.

While `asig` functions should NOT be called on a Scene (or its objects) after they have been released, methods on structs (e.g. `myScene.XYZ`, `myMesh.ABCD()`) are **safe** even after release.

## Developing assimp-go

We link against static assimp libraries that are built for each platform and added to the `asig/libs` package.
Depending on the platform we select one of them and link against it when doing `go build`.

The general steps are:

- Copy assimp includes into `asig/assimp`
- Copy `zlib.h`, `zconf.h` and `irrXML.h` into `asig/zlib` and `asig/irrxml` respectively.
- Copy static libraries into `asig/libs`
- Generate the wrappers using `swig -go -c++ -intgosize 64 asig/asig.i`
- Add `#cgo LDFLAGS: -L ./staticLibs -l zlibstatic -l IrrXML -l assimp` at the top of the 'C' import in `asig.go`

> Note: When dealing with static libraries the compiler will probably (e.g. MinGW does this) ignore `lib` suffixes and `.a`/`.lib` suffixes.
So if your lib name is `libassimp.a` you need to pass it to CGO as `-l assimp`, otherwise you will get an error about library not found.

For platform specific steps:

**Windows**:

> Note: You must compile with the same C/C++ compiler you use with Go (e.g. if you use MinGW with Go, then compile assimp with MinGW by sepcifying the correct `-G` option)
---
> Note: If you get compilation errors with things like `File too big` or `can't write 166 bytes to section` then cmake isn't detecting you are using MinGW, so add this flag `-D CMAKE_COMPILER_IS_MINGW=TRUE`

Now assuming you are using MinGW on windows:

- Clone wanted release of assimp and run `cmake CMakeLists.txt -D BUILD_SHARED_LIBS=OFF -D ASSIMP_BUILD_ZLIB=ON -D ASSIMP_BUILD_ASSIMP_TOOLS=OFF -D ASSIMP_BUILD_TESTS=OFF -G "MinGW Makefiles"` in the root folder
- Run `cmake --build . --parallel 6`
- Copy the generated `*.lib` (or `*.a`) files into `asig/lib`