VR中的变换矩阵问题 [英] questions of transform matrix in VR

问题描述

我对OpenVR api中的矩阵转换有疑问.

I have a problem about matrix transformation in OpenVR api.

m_compositor->WaitGetPoses(m_rTrackedDevicePose, vr::k_unMaxTrackedDeviceCount, nullptr, 0);

在openvr提供的演示中:

in the demo which the openvr gives:

const Matrix4 & matDeviceToTracking = m_rmat4DevicePose[ unTrackedDevice ];
        Matrix4 matMVP = GetCurrentViewProjectionMatrix( nEye ) * matDeviceToTracking;
        glUniformMatrix4fv( m_nRenderModelMatrixLocation, 1, GL_FALSE, matMVP.get() );

其中GetCurrentViewProjectionMatrix用

where GetCurrentViewProjectionMatrix is calculated with

Matrix4 CMainApplication::GetCurrentViewProjectionMatrix( vr::Hmd_Eye nEye )
{
    Matrix4 matMVP;
    if( nEye == vr::Eye_Left )
    {
        matMVP = m_mat4ProjectionLeft * m_mat4eyePosLeft * m_mat4HMDPose;
    }
    else if( nEye == vr::Eye_Right )
    {
        matMVP = m_mat4ProjectionRight * m_mat4eyePosRight *  m_mat4HMDPose;
    }

    return matMVP;
}

问题是:

1，matDeviceToTracking将从哪个空间转换到哪个空间?

1, which space is matDeviceToTracking transformed from to which space?

2，如果我已经有了modelview矩阵，并且已经可以使用hmd旋转了，如何正确渲染rendermodel?我尝试使用projection*modelview*m_rmat4DevicePose[ unTrackedDevice ]，但没有效果.

2, If I have modelview matrix already, and already can rotate with hmd, how can I render the rendermodel correctly? I tried using projection*modelview*m_rmat4DevicePose[ unTrackedDevice ] but there is no effect.

推荐答案

1.

在示例代码中，matDeviceToTracking是对m_rmat4DevicePose[unTrackedDevice]的引用，该引用是从TrackedDevicePose_t::mDeviceToAbsoluteTracking复制而来的.这是一个从模型空间到世界空间的映射模型.

In the sample code, the matDeviceToTracking is a reference to m_rmat4DevicePose[unTrackedDevice], which is copied from TrackedDevicePose_t::mDeviceToAbsoluteTracking. This is a model matrix mapping from the model space to the world space.

尽管有一个陷阱.如果您从示例中包含了UpdateHMDMatrixPose()函数，则该函数会在更新m_mat4HMDPose的值时反转m_rmat4DevicePose[vr::k_unTrackedDeviceIndex_Hmd]，从而使m_rmat4DevicePose[0]从世界空间映射到模型/HMD视图空间，而恰恰相反数组中的其他矩阵.

There is one pitfall, though. If you included the UpdateHMDMatrixPose() function from the sample, this function inverts m_rmat4DevicePose[vr::k_unTrackedDeviceIndex_Hmd] while updating the value of m_mat4HMDPose, leaving m_rmat4DevicePose[0] mapping from the world space to the model/HMD view space, exactly the other way around to the other matrices in the array.

2.

如果您已经具有模型视图矩阵，则只需将投影矩阵乘以它即可获得MVP矩阵.要渲染到HMD中，请分别对左眼和右眼使用m_mat4ProjectionLeft * m_mat4eyePosLeft * modelview和m_mat4ProjectionRight * m_mat4eyePosRight * modelview.为了在监视器上渲染，您可以生成自己的视锥并将其乘以模型视图矩阵.以下网站是有关如何创建投影矩阵的良好参考: http://www.songho.ca/opengl/gl_projectionmatrix.html

If you already have the model-view matrix, then you only need to multiply the projection matrix by it to obtain the MVP matrix. For rendering into the HMD, use m_mat4ProjectionLeft * m_mat4eyePosLeft * modelview and m_mat4ProjectionRight * m_mat4eyePosRight * modelview for left and right eye, respectively. For rendering on a monitor, you can generate your own frustum and multiply it by your model-view matrix. The following website is a good reference on how to create a projection matrix: http://www.songho.ca/opengl/gl_projectionmatrix.html

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