可通过小球进行旋转的十字光标（vtkResliceCursor)

        前一段事件看到VTK的一个例子：

该案例是vtk.js写的，觉得很有意思，个人正好也要用到，于是萌生了用C++修改VTK源码来实现该功能的想法。原本以为很简单，只需要修改一下vtkResliceCursor就可以了，加上小球，加上几个Actor，就能实现，没想到该功能整花了我差不多一个月的时间。但也学到了不少知识，下面就该功能的实现效果和方法做个大致解说：

我实现的效果：

实现方法：

1，首先在vtkResliceCursor中定义六个小球的位置。因为是X，Y，Z三个轴，每个轴上两个小球，所以总共有六个小球。代码：

void vtkResliceCursor::BuildCursorGeometryWithoutHole()
{// 其他源码省略.......for (int i = 0; i < 3; i++){//wulc{this->SpherePoints[0][i] = this->Center[i] - sphereLength * this->XAxis[i];this->SpherePoints[1][i] = this->Center[i] + sphereLength * this->XAxis[i];this->SpherePoints[2][i] = this->Center[i] - sphereLength * this->YAxis[i];this->SpherePoints[3][i] = this->Center[i] + sphereLength * this->YAxis[i];this->SpherePoints[4][i] = this->Center[i] - sphereLength * this->ZAxis[i];this->SpherePoints[5][i] = this->Center[i] + sphereLength * this->ZAxis[i];}}// 其他源码省略.......
}sphereLength 是一个自定义的常数，也就是中心到小球的距离。可以是 30 ，40 ，50 .。。。。

 除此之外我们还要定义一个函数，通过该函数可以获取这六个小球的坐标。比如 GetPointPosition(double p[6][3]);

2,在vtkResliceCursorPicker中判断鼠标是否靠近小球中心位置，靠近小球坐标时，将鼠标光标变为手掌形状。判断方法就是鼠标的位置和小球位置的距离，其中有现成的代码：

/----------------wulc---------------------------------------------------
int vtkResliceCursorPicker::IntersectPointWithPoint(double p1[3], double p2[3], double Points[], double tol)
{double pts[6][3] = { {0,0,0} };for (size_t i = 0; i < 6; i++){pts[i][0] = Points[3*i];pts[i][1] = Points[3*i + 1];pts[i][2] = Points[3 * i + 2];}int j = 0;for ( ; j < 6; j++){double X[4] = { pts[j][0], pts[j][1], pts[j][2], 1 };int i;double ray[3], rayFactor, projXYZ[3];for (i = 0; i < 3; i++){ray[i] = p2[i] - p1[i];}if ((rayFactor = vtkMath::Dot(ray, ray)) == 0.0){return 0;}const double t = (ray[0] * (X[0] - p1[0]) +ray[1] * (X[1] - p1[1]) +ray[2] * (X[2] - p1[2])) / rayFactor;if (t >= 0.0 && t <= 1.0){for (i = 0; i < 3; i++){projXYZ[i] = p1[i] + t * ray[i];if (fabs(X[i] - projXYZ[i]) > tol){break;}}if (i > 2) // within tolerance{return 1;}}}return 0;
}

 3，最后要在vtkResliceCursorActor类中添加小球，代码：

//wulcif (this->Renderer == nullptr) return;if (axisNormal == 1)//x-z平面{double* position = this->CursorAlgorithm->GetResliceCursor()->GetSpherePostion(2);if (fabs(position[0] - 0.0) > 0.001 || fabs(position[1] - 0.0) > 0.001 || fabs(position[2] - 0.0) > 0.001){this->SphereActor[2]->GetProperty()->SetColor(1, 0, 0);this->SphereActor[3]->GetProperty()->SetColor(1, 0, 0);this->SphereActor[2]->SetPosition(position[0], position[1], position[2]);this->SphereActor[3]->SetPosition(position[3], position[4], position[5]);position = this->CursorAlgorithm->GetResliceCursor()->GetSpherePostion(0);this->SphereActor[0]->GetProperty()->SetColor(0, 0, 1);this->SphereActor[1]->GetProperty()->SetColor(0, 0, 1);this->SphereActor[0]->SetPosition(position[0], position[1], position[2]);this->SphereActor[1]->SetPosition(position[3], position[4], position[5]);}}else if (axisNormal == 2)//x-y平面{double* position = this->CursorAlgorithm->GetResliceCursor()->GetSpherePostion(0);if (fabs(position[0] - 0.0) > 0.001 || fabs(position[1] - 0.0) > 0.001 || fabs(position[2] - 0.0) > 0.001){this->SphereActor[0]->GetProperty()->SetColor(0, 1, 0);this->SphereActor[1]->GetProperty()->SetColor(0, 1, 0);this->SphereActor[0]->SetPosition(position[0], position[1], position[2]);this->SphereActor[1]->SetPosition(position[3], position[4], position[5]);position = this->CursorAlgorithm->GetResliceCursor()->GetSpherePostion(1);this->SphereActor[2]->GetProperty()->SetColor(1, 0, 0);this->SphereActor[3]->GetProperty()->SetColor(1, 0, 0);this->SphereActor[2]->SetPosition(position[0], position[1], position[2]);this->SphereActor[3]->SetPosition(position[3], position[4], position[5]);}}else if (axisNormal == 0) //y-z平面{double* position = this->CursorAlgorithm->GetResliceCursor()->GetSpherePostion(2);if (fabs(position[0] - 0.0) > 0.001 || fabs(position[1] - 0.0) > 0.001 || fabs(position[2] - 0.0) > 0.001){this->SphereActor[0]->GetProperty()->SetColor(0, 1, 0);this->SphereActor[1]->GetProperty()->SetColor(0, 1, 0);this->SphereActor[0]->SetPosition(position[0], position[1], position[2]);this->SphereActor[1]->SetPosition(position[3], position[4], position[5]);position = this->CursorAlgorithm->GetResliceCursor()->GetSpherePostion(1);this->SphereActor[2]->GetProperty()->SetColor(0, 0, 1);this->SphereActor[3]->GetProperty()->SetColor(0, 0, 1);this->SphereActor[2]->SetPosition(position[0], position[1], position[2]);this->SphereActor[3]->SetPosition(position[3], position[4], position[5]);}}

这就可以了，欢迎小伙伴能够一块讨论。