java – 将3D世界(arcore锚/姿势)转换为相应的2D屏幕坐标

首先,我们需要计算从世界转换的矩阵 – >屏幕：

public float[] calculateWorld2CameraMatrix(float[] modelmtx,float[] viewmtx,float[] prjmtx) {

    float scaleFactor = 1.0f;
    float[] scaleMatrix = new float[16];
    float[] modelXscale = new float[16];
    float[] viewXmodelXscale = new float[16];
    float[] world2screenMatrix = new float[16];

    Matrix.setIdentityM(scaleMatrix,0);
    scaleMatrix[0] = scaleFactor;
    scaleMatrix[5] = scaleFactor;
    scaleMatrix[10] = scaleFactor;

    Matrix.multiplyMM(modelXscale,modelmtx,scaleMatrix,0);
    Matrix.multiplyMM(viewXmodelXscale,viewmtx,modelXscale,0);
    Matrix.multiplyMM(world2screenMatrix,prjmtx,viewXmodelXscale,0);

    return world2screenMatrix;

}

一旦我们有了这个矩阵,那么我们可以将点从3D世界投影到2D,但在这个投影中我们必须从NDC坐标转换为屏幕.以下是执行此转换的方法：

double[] world2Screen(int screenWidth,int screenHeight,float[] world2cameraMatrix)
  {
    float[] origin = {0f,0f,1f};
    float[] ndcCoord = new float[4];
    Matrix.multiplyMV(ndcCoord,world2cameraMatrix,origin,0);

    ndcCoord[0] = ndcCoord[0]/ndcCoord[3];
    ndcCoord[1] = ndcCoord[1]/ndcCoord[3];

    double[] pos_2d = new double[]{0,0};
    pos_2d[0] = screenWidth  * ((ndcCoord[0] + 1.0)/2.0);
    pos_2d[1] = screenHeight * (( 1.0 - ndcCoord[1])/2.0);

    return pos_2d;
  }

最后,一个简单的用法示例：

DisplayMetrics displayMetrics = new DisplayMetrics();
        getWindowManager().getDefaultDisplay().getMetrics(displayMetrics);
        int height = displayMetrics.heightPixels;
        int width = displayMetrics.widthPixels;

        // Get projection matrix.
        float[] projmtx = new float[16];
        camera.getProjectionMatrix(projmtx,0.1f,100.0f);

        // Get camera matrix and draw.
        float[] viewmtx = new float[16];
        camera.getViewMatrix(viewmtx,0);

        float[] anchorMatrix = new float[16];
        anchor.getPose().toMatrix(anchorMatrix,0);
        float[] world2screenMatrix =    
  virtualObject.calculateWorld2CameraMatrix(anchorMatrix,projmtx);
        double[] anchor_2d =  world2Screen(width,height,world2screenMatrix);