如何从 jna 引用指针中检索 java class

Question

我正在用 jna 移植 openvr sample to jogl, after we created the binding。

几乎在最后（在渲染控制器和跟踪基站之前），我在尝试从 C++ 中的引用指针检索 java 中的模型 class 时遇到了困难。

C++代码here:

while ( 1 )
{
    error = vr::VRRenderModels()->LoadRenderModel_Async( pchRenderModelName, &pModel );
    if ( error != vr::VRRenderModelError_Loading )
        break;

    ThreadSleep( 1 );
}

LoadRenderModel_Async here:

/** Loads and returns a render model for use in the application. pchRenderModelName should be a render model name
* from the Prop_RenderModelName_String property or an absolute path name to a render model on disk. 
*
* The resulting render model is valid until VR_Shutdown() is called or until FreeRenderModel() is called. When the 
* application is finished with the render model it should call FreeRenderModel() to free the memory associated
* with the model.
*
* The method returns VRRenderModelError_Loading while the render model is still being loaded.
* The method returns VRRenderModelError_None once loaded successfully, otherwise will return an error. */
virtual EVRRenderModelError LoadRenderModel_Async( const char *pchRenderModelName, RenderModel_t **ppRenderModel ) = 0;

jna翻译为(here):

public interface LoadRenderModel_Async_callback extends Callback {

    int apply(Pointer pchRenderModelName, PointerByReference ppRenderModel);
};

在 java 我正在尝试以这种方式加载模型 (here):

int error;
PointerByReference modelPtrRef = new PointerByReference();

while (true) {

    Pointer stringPointer = new Memory(modelName.length());

    error = renderModels.LoadRenderModel_Async.apply(stringPointer, modelPtrRef);

    if (error != VR.EVRRenderModelError.VRRenderModelError_Loading) {
        break;
    }

    try {
        Thread.sleep(1);
    } catch (InterruptedException ex) {
        Logger.getLogger(ModelsRender.class.getName()).log(Level.SEVERE, null, ex);
    }
}

RenderModel_t m = new RenderModel_t(modelPtrRef.getValue());
m.read();

但是 m 是空的，也就是说 vertexData 是 null 而 vertexCount 是 0，在 c++ 上我有有效的值..

如何从 C++ 中的引用指针中检索 java class？

Answer 1

已解决，我需要创建一个指针 modelPtr，然后创建一个指向指针 modelPtrPtr 的指针并将其传递给 LoadRenderModel_Async。

最后，我实例化了一个模型 class，方法是将指针的值传递给一个指针，read() 从本机到堆内存中检索值：

    RenderModel_t.ByReference modelPtr = new RenderModel_t.ByReference();

    if (errorBuffer.get(0) != VR.EVRRenderModelError.VRRenderModelError_None) {
        return null;
    }

    int error;
    PointerByReference modelPtrPtr = new PointerByReference(modelPtr.getPointer());

    while (true) {

        Pointer stringPointer = new Memory(modelName.length() + 1);
        stringPointer.setString(0, modelName);

        error = renderModels.LoadRenderModel_Async.apply(stringPointer, modelPtrPtr);

        if (error != VR.EVRRenderModelError.VRRenderModelError_Loading) {
            break;
        }

        try {
            Thread.sleep(1);
        } catch (InterruptedException ex) {
            Logger.getLogger(ModelsRender.class.getName()).log(Level.SEVERE, null, ex);
        }
    }
    RenderModel_t model = new RenderModel_t(modelPtrPtr.getValue());
    model.read();

Answer 2

这里有一些更简单的东西：

if (errorBuffer.get(0) != VR.EVRRenderModelError.VRRenderModelError_None) {
    return null;
}

int error;
PointerByReference pref = new PointerByReference();

while (true) {

    error = renderModels.LoadRenderModel_Async.apply(modelName, pref);

    if (error != VR.EVRRenderModelError.VRRenderModelError_Loading) {
        break;
    }

    try {
        Thread.sleep(1);
    } catch (InterruptedException ex) {
        Logger.getLogger(ModelsRender.class.getName()).log(Level.SEVERE, null, ex);
    }
}
RenderModel_t model = new RenderModel_t(pref.getValue());


public class RenderModel_t {
    public RenderModel_t(Pointer p) {
        super(p);
        read();
    }
}

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