在三維空間中,人們通常需要對平面等形體進行旋轉,拖拽等操作。比如下面的過程:
- 將平面繞平面的Y軸旋轉一定角度
- 將其繞平面自身的X軸旋轉一定角度
- 將平面向向量方向(1, 2, 3)移動一段距離。
這樣複雜的操作通常需要我們使用vtkActor提供的操作函數:
void vtkProp3D::RotateY (double angle)
void vtkProp3D::RotateX (double angle)
void vtkProp3D::AddPosition (double deltaX,double deltaY,double deltaZ)
控制運動的接口我們找到了,但是傳入的參數還需要認真思考如何計算。
通常,我們是在事件中計算位置移動向量,或者旋轉角度,這裏就需要用到vtkRenderWindowInteractor提供的GetEventPosition和GetLastEventPosition函數。他們幫助我們計算Display座標系的光標座標值。
平移向量是向量 GetEventPosition => GetLastEventPosition 在平面法向量上的投影。
旋轉角度則是 planeOrigin => GetLastEventPosition 與 planeOrigin => GetEventPosition的向量夾角。
如此可知,每一次運動,都需要知道平面中心點或者平面的法向量。同時,在一次運動結束之後,平面中心點或者平面法向量都應該更新。
在文章 【VTK】平面的平移和旋轉 的末尾片段我有介紹到如何求解actor在線性變化後的平面原點和平面法向量。下面指明一下注意事項:
由actor matrix構造出來的vtkTransform對象不要在求解origin之後又立馬求解normal。
#include <stdio.h>
#include <vtkSmartPointer.h>
#include <vtkSphereSource.h>
#include <vtkActor.h>
#include <vtkPlaneSource.h>
#include <vtkRenderer.h>
#include <vtkRenderWindow.h>
#include <vtkPolyDataMapper.h>
#include <vtkProperty.h>
#include <vtkRenderWindowInteractor.h>
#include <vtkLight.h>
#include <vtkCamera.h>
#include <vtkActor2D.h>
#include <vtkTransform.h>
using namespace std;
int main()
{
setbuf( stdout, NULL );
vtkSmartPointer<vtkPlaneSource> plane =
vtkSmartPointer<vtkPlaneSource>::New();
vtkSmartPointer<vtkPolyDataMapper> mapper =
vtkSmartPointer<vtkPolyDataMapper>::New();
mapper->SetInputConnection( plane->GetOutputPort() );
vtkSmartPointer<vtkActor> actor =
vtkSmartPointer<vtkActor>::New();
actor->SetMapper( mapper );
double oldNormal[3] = { 0, 0, -1 };
double oldOrigin[3] = { 0, 0, 0 };
actor->RotateY( 45 );
// actor->AddPosition( 1, -1, 1 );
vtkSmartPointer<vtkTransform> transform =
vtkSmartPointer<vtkTransform>::New();
transform->SetMatrix( actor->GetMatrix() );
double *newNormal = transform->TransformDoubleVector( oldNormal );
vtkSmartPointer<vtkTransform> transform2 =
vtkSmartPointer<vtkTransform>::New();
transform2->SetMatrix( actor->GetMatrix() );
double *newOrigin = transform2->TransformDoublePoint( oldOrigin );
printf( "newNormal: %lf, %lf, %lf\n", newNormal[0], newNormal[1], newNormal[2] );
printf( "newOrigin: %lf, %lf, %lf\n", newOrigin[0], newOrigin[1], newOrigin[2] );
/*
newOrigin: 0.000000, 0.000000, 0.000000
newNormal: -0.707107, 0.000000, -0.707107 (-cos45)
*/
vtkSmartPointer<vtkRenderer> renderer =
vtkSmartPointer<vtkRenderer>::New();
renderer->AddActor(actor);
renderer->SetBackground( 0, 0, 0 );
vtkSmartPointer<vtkRenderWindow> renderWindow =
vtkSmartPointer<vtkRenderWindow>::New();
renderWindow->AddRenderer( renderer );
vtkSmartPointer<vtkRenderWindowInteractor> renderWindowInteractor =
vtkSmartPointer<vtkRenderWindowInteractor>::New();
renderWindowInteractor->SetRenderWindow( renderWindow );
renderWindowInteractor->GetLastEventPosition();
renderer->ResetCamera();
renderWindow->Render();
renderWindowInteractor->Start();
return 0;
}
比如上面例子中的double *newOrigin = transform2->TransformDoublePoint( oldOrigin );
如果我是繼續使用了transform,那麼origin與normal的數值就是一樣的了。先計算誰誰就錯了。
錯誤結果:
newNormal: 0.000000, 0.000000, 0.000000
newOrigin: 0.000000, 0.000000, 0.000000
這是爲什麼呢?
看看兩個函數的實現:
double *TransformDoublePoint(double x, double y, double z) {
this->InternalDoublePoint[0] = x;
this->InternalDoublePoint[1] = y;
this->InternalDoublePoint[2] = z;
this->TransformPoint(this->InternalDoublePoint,this->InternalDoublePoint);
return this->InternalDoublePoint; };
//------------------------------------------------------------------------
double *TransformDoubleVector(double x, double y, double z) {
this->InternalDoublePoint[0] = x;
this->InternalDoublePoint[1] = y;
this->InternalDoublePoint[2] = z;
this->TransformVector(this->InternalDoublePoint,this->InternalDoublePoint);
return this->InternalDoublePoint; };
vtkLinearTransform將計算結果全都存儲在InternalDoublePoint中了,所以例子中的newOrigin和newNormal最終指向同一個double數組,這個數組存儲着最後一次計算的結果,即newOrigin。