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我正在用 Java 3D API 编写一个小游戏，我使用 javax.media.j3d.BoundingBox 的对象来存储模型的边界。

BoundingBox 的构造函数如下：

public BoundingBox(Point3d lower, Point3d upper) {
    boundId = BOUNDING_BOX;
    this.lower = new Point3d(lower);
    this.upper = new Point3d(upper);
    updateBoundsStates();
}

现在我想平移和旋转 BoundingBox，因为模型本身会这样做，并且我使用以下 BoundingBox 方法：

/** 
 * Transforms this bounding box by the given matrix.
 * @param matrix a transformation matrix
 */
public void transform(Transform3D matrix) {
    if(boundsIsInfinite)
        return;

    if (tmpP3d == null) 
        tmpP3d = new Point3d();

    double ux, uy, uz, lx, ly, lz;
    ux = upper.x; 
    uy = upper.y; 
    uz = upper.z;

    lx = lower.x; 
    ly = lower.y; 
    lz = lower.z;

    tmpP3d.set(ux, uy, uz);
    matrix.transform( tmpP3d );

    upper.x = tmpP3d.x;
    upper.y = tmpP3d.y;
    upper.z = tmpP3d.z;

    lower.x = tmpP3d.x;
    lower.y = tmpP3d.y;
    lower.z = tmpP3d.z;

    tmpP3d.set(lx, uy, uz);
    matrix.transform( tmpP3d );

    if ( tmpP3d.x  > upper.x ) upper.x = tmpP3d.x;
    if ( tmpP3d.y  > upper.y ) upper.y = tmpP3d.y;
    if ( tmpP3d.z  > upper.z ) upper.z = tmpP3d.z;

    if ( tmpP3d.x  < lower.x ) lower.x = tmpP3d.x;
    if ( tmpP3d.y  < lower.y ) lower.y = tmpP3d.y;
    if ( tmpP3d.z  < lower.z ) lower.z = tmpP3d.z;

    tmpP3d.set(lx, ly, uz);
    matrix.transform( tmpP3d );

    if ( tmpP3d.x  > upper.x ) upper.x = tmpP3d.x;
    if ( tmpP3d.y  > upper.y ) upper.y = tmpP3d.y;
    if ( tmpP3d.z  > upper.z ) upper.z = tmpP3d.z;

    if ( tmpP3d.x  < lower.x ) lower.x = tmpP3d.x;
    if ( tmpP3d.y  < lower.y ) lower.y = tmpP3d.y;
    if ( tmpP3d.z  < lower.z ) lower.z = tmpP3d.z;

    tmpP3d.set(ux, ly, uz);
    matrix.transform( tmpP3d );

    if ( tmpP3d.x > upper.x ) upper.x = tmpP3d.x;
    if ( tmpP3d.y > upper.y ) upper.y = tmpP3d.y;
    if ( tmpP3d.z > upper.z ) upper.z = tmpP3d.z;

    if ( tmpP3d.x < lower.x ) lower.x = tmpP3d.x;
    if ( tmpP3d.y < lower.y ) lower.y = tmpP3d.y;
    if ( tmpP3d.z < lower.z ) lower.z = tmpP3d.z;

    tmpP3d.set(lx, uy, lz);
    matrix.transform( tmpP3d );

    if ( tmpP3d.x > upper.x ) upper.x = tmpP3d.x;
    if ( tmpP3d.y > upper.y ) upper.y = tmpP3d.y;
    if ( tmpP3d.z > upper.z ) upper.z = tmpP3d.z;

    if ( tmpP3d.x < lower.x ) lower.x = tmpP3d.x;
    if ( tmpP3d.y < lower.y ) lower.y = tmpP3d.y;
    if ( tmpP3d.z < lower.z ) lower.z = tmpP3d.z;

    tmpP3d.set(ux, uy, lz);
    matrix.transform( tmpP3d );

    if ( tmpP3d.x > upper.x ) upper.x = tmpP3d.x;
    if ( tmpP3d.y > upper.y ) upper.y = tmpP3d.y;
    if ( tmpP3d.z > upper.z ) upper.z = tmpP3d.z;

    if ( tmpP3d.x < lower.x ) lower.x = tmpP3d.x;
    if ( tmpP3d.y < lower.y ) lower.y = tmpP3d.y;
    if ( tmpP3d.z < lower.z ) lower.z = tmpP3d.z;

    tmpP3d.set(lx, ly, lz);
    matrix.transform( tmpP3d );

    if ( tmpP3d.x > upper.x ) upper.x = tmpP3d.x;
    if ( tmpP3d.y > upper.y ) upper.y = tmpP3d.y;
    if ( tmpP3d.z > upper.z ) upper.z = tmpP3d.z;

    if ( tmpP3d.x < lower.x ) lower.x = tmpP3d.x;
    if ( tmpP3d.y < lower.y ) lower.y = tmpP3d.y;
    if ( tmpP3d.z < lower.z ) lower.z = tmpP3d.z;

    tmpP3d.set(ux, ly, lz);
    matrix.transform( tmpP3d );

    if ( tmpP3d.x > upper.x ) upper.x = tmpP3d.x;
    if ( tmpP3d.y > upper.y ) upper.y = tmpP3d.y;
    if ( tmpP3d.z > upper.z ) upper.z = tmpP3d.z;

    if ( tmpP3d.x < lower.x ) lower.x = tmpP3d.x;
    if ( tmpP3d.y < lower.y ) lower.y = tmpP3d.y;
    if ( tmpP3d.z < lower.z ) lower.z = tmpP3d.z;

    if (VirtualUniverse.mc.releaseBoundingBoxMemory) {
        // Free memory
        tmpP3d = null;
    }
}

但是：如果您使用此方法旋转 BoundingBox，它会生成一个新的 BoundingBox，它的体积可能比旧的要大。如果您精确旋转 90、180、270 或 360 度，它只会提供相同的音量。

附加信息：我必须手动计算 BoundingBox，因为我通过在模型上调用 setAutoComputeBounds(false) 和 setBounds(XYZ) 来使用手动边界（而不是自动计算的太大的边界）（在这种情况下，它实际上是 javax. media.j3d 指向 javax.media.j3d.SharedGroup），并且似乎 Java 3d 引擎（至少在这种情况下）在相应模型的平移/旋转的情况下不会自动重新计算您的手动边界。

我的问题是：我必须如何（重新）实现上面显示的方法 transform() 以获得始终具有相同体积的边界框？

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1 回答 1

2

BoundingBox 实际上总是与轴对齐，无论它的两个点在哪里。两点不能定义任意立方体。无论你如何重写变换函数，它都不起作用。

You might consider the BoundingPolytope class. It provides more general bounds, formed from planes, though it does have a constructor which accepts another Bounds object, so you need not actually define the planes yourself.

于 2012-06-27T12:29:57.537 回答