首先要具備射線拾取的基本知識和向量運算的基礎知識,屏幕點轉換爲三維點怎麼取轉換。
現在先看一下屏幕的點如何轉換爲三維點,代碼如下:
osg::Vec3 screenToWorld(osgViewer::Viewer* viewer,double dx,double dy)
{
osg::Camera *camera = viewer->getCamera();
osg::Matrix viewMat = camera->getViewMatrix(); //獲取當前視圖矩陣
osg::Matrix projMat = camera->getProjectionMatrix();//獲取投影矩陣
osg::Matrix windMat = camera->getViewport()->computeWindowMatrix();//獲取窗口矩陣
osg::Matrix MVPW = viewMat * projMat *windMat; //視圖-》投影-》窗口變換
osg::Matrix inverseMVPW = osg::Matrix::inverse(MVPW);
osg::Vec3 mouseWorld = osg::Vec3(dx, dy, 0) * inverseMVPW;
return mouseWorld;
}
好了,上述代碼完成從屏幕的二維點變換到世界的三維點,接下來實現以下鼠標點拾取物體,代碼如下:
//參數說明:firstPos:是當前攝像機的位置。endPos:爲偏移座標值,eye + curRayLineDir*100
//curRayLineDir = mouseWorldPos(屏幕點轉三維點使用上面的函數) - eye;
//curRayLineDir.normallize();
void CIntersectEventHandler::rayLinePick(const osg::Vec3& firstPos,const osg::Vec3& endPos)
{
osg::ref_ptr<osgUtil::LineSegmentIntersector> lineSegmentIntesector = \
new osgUtil::LineSegmentIntersector(firstPos,endPos);
osgUtil::IntersectionVisitor intersectionVisitor(lineSegmentIntesector);
m_matNode->accept(intersectionVisitor);//m_matNode爲你拾取的物體
osgUtil::LineSegmentIntersector::Intersections intersections;
if (lineSegmentIntesector->containsIntersections())
{
intersections = lineSegmentIntesector->getIntersections();
for(auto iter = intersections.begin(); iter != intersections.end(); ++iter)
{
osg::NodePath nodePath = iter->nodePath;
m_pickPoint = iter->getWorldIntersectPoint();
for(int i=0; i<nodePath.size(); ++i)
{
m_pickObj = dynamic_cast<osg::MatrixTransform*>(nodePath[i]);//拾取到的node
}
}
}
}
最後我要計算當前的鼠標拾取到物體之後移動的位置。代碼走你:
//我是在osgGA::GUIEventAdapter::DRAG進行拖拽的功能
if(m_pickObj && m_bLeftMouseBtn)//這個布爾值就是曉得鼠標的左鍵是否按下了。
{
//獲取當前的攝像機的位置
osg::Vec3 eye = viewer->getCamera()->getInverseViewMatrix().getTrans();
//計算當前攝像機與pick到的模型之間的距離是多少
osg::Vec3 offset = m_pickPoint - eye;
int dist = offset.length();
//計算當前的鼠標屏幕點映射到三維中的值
osg::Vec3 mouseWorldPos = screenToWorld(viewer,ea.getX(),ea.getY());
//計算當前鼠標三維點與攝像機的方向
osg::Vec3 rayDir = mouseWorldPos - eye;
rayDir.normalize();
//最後計算物體拖拽時最終的世界位置
osg::Vec3 curPos = eye + rayDir*dist;
m_pickObj->setMatrix(osg::Matrix::translate(curPos));
}
好了,拖拽功能完成,若有不足之處還請指出更正!
下面是演示效果: