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我已经在互联网上玩了一段时间的一些算法，但我似乎无法让它们工作，所以我在这里抛出这个问题；

我正在尝试从一个点渲染速度矢量线。画线并不困难：只需velocity.length在图中插入一条带长度的线。这使线以 y 轴方向的点为中心。我们现在需要在适当的旋转和平移中得到它。

平移向量不难计算：它是速度向量的一半。然而，旋转矩阵对我来说非常难以捉摸。给定一个方向向量<x, y, z>，我需要什么矩阵？

编辑1：看；如果你不明白这个问题，你可能无法给我答案。

这是我目前拥有的：

                    Vector3f 翻译 = 新 Vector3f();
                    平移.scale(1f/2f, body.velocity);

                    Vector3f vec_z = (Vector3f) body.velocity.clone();
                    vec_z.normalize();

                    Vector3f vec_y; // 参考向量，稍后会更正
                    如果（vec_z.x == 0 && vec_z.z == 0）{
                        vec_y = new Vector3f(-vec_z.y, 0f, 0f); // 可以优化
                    } 别的 {
                        vec_y = new Vector3f(0f, 1f, 0f);
                    }
                    Vector3f vec_x = new Vector3f();
                    vec_x.cross(vec_y, vec_z);
                    vec_z.normalize();

                    vec_y.cross(vec_x, vec_z);
                    vec_y.normalize();
                    vec_y.negate();

                    Matrix3f 旋转 = 新 Matrix3f(
                        vec_z.z, vec_z.x, vec_z.y,
                        vec_x.z, vec_x.x, vec_x.y,
                        vec_y.z、vec_y.x、vec_y.y
                    );

                    arrowTransform3D.set（旋转，平移，1f）；

根据这篇文章。是的，我已经尝试过标准旋转矩阵（vec_x.x、vec_y.x 等）但没有奏效。我一直在旋转列和行以查看是否有任何效果。

编辑2：

对我评论的粗鲁措辞表示歉意。

So it looks like there were a combination of two errors; one of which House MD pointed out (really bad naming of variables: vec_z was actually vec_y, and so on), and the other was that I needed to invert the matrix before passing it off to the rendering engine (transposing was close!). So the modified code is:

                    Vector3f vec_y = (Vector3f) body.velocity.clone();
                    vec_y.normalize();

                    Vector3f vec_x; // reference vector, will correct later
                    if (vec_y.x == 0 && vec_y.z == 0) {
                        vec_x = new Vector3f(-vec_y.y, 0f, 0f); // could be optimized
                    } else {
                        vec_x = new Vector3f(0f, 1f, 0f);
                    }

                    Vector3f vec_z = new Vector3f();
                    vec_z.cross(vec_x, vec_y);
                    vec_z.normalize();

                    vec_x.cross(vec_z, vec_y);
                    vec_x.normalize();
                    vec_x.negate();

                    Matrix3f rotation = new Matrix3f(
                        vec_x.x, vec_x.y, vec_x.z,
                        vec_y.x, vec_y.y, vec_y.z,
                        vec_z.x, vec_z.y, vec_z.z
                    );
                    rotation.invert();
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2 回答 2

1

This should do you

于 2008-10-19T11:25:05.487 回答
0

Dupe.

The question there involves getting a rotation to a certain axis, whereas I'm concerned with getting a rotation matrix.

Gee, I wonder if you could turn convert one to the other?

BTW, your current solution of picking an arbitrary y axis and then reorthogonalising should work fine; it looks bugged though, or at least badly written. 'z_vec' is not a good variable-name for the y-axis. What's with the 'z,x,y' ordering, anyway?

If it still doesn't work, try making random changes until it does - transpose the matrix, negate vectors until you have an even number of sign errors, that kind of thing.

Also your tone of voice comes across as sort-of rude, given that you're asking strangers to spend their time helping you.

于 2008-10-19T11:52:20.707 回答