OSG立体模式下动态修改相机远近裁剪面的实现

1. 非立体模式下动态修改相机远近裁剪面

class GLB_DLLCLASS_EXPORT CGlbGlobeClipHandler : public osg::NodeCallback
    {

　　struct CustomProjClamper : public osg::CullSettings::ClampProjectionMatrixCallback
 　　{

　　　　template<class matrix_type, class value_type>
            bool _clampProjectionMatrix(matrix_type& projection, double& znear, double& zfar, value_type nearFarRatio) const

　　　　{....}

　　...........

　　}

}

mpr_cliphandler = new CGlbGlobeClipHandler(p_globe);
mpr_p_root->setUpdateCallback((osg::NodeCallback*)mpr_cliphandler);

在根节点回调中mpr_cliphandler计算CustomProjClamper的成员变量double _nearFarRatio的值，然后在_clampProjectionMatrix中使用它来计算最远最近裁剪面.

osg::ref_ptr<osg::CullSettings::ClampProjectionMatrixCallback> clamper = new CGlbGlobeClipHandler::CustomProjClamper();

mpr_cliphandler->mpr_p_clampers[mpr_osgviewer->getCamera()] = clamper;
mpr_osgviewer->getCamera()->setClampProjectionMatrixCallback(clamper.get());   

2. 立体模式下动态修改相机远近裁剪面

在osg3.2.1版本上测试发现，红绿立体模式、Quad_Buffer立体模式下以上代码不起作用，不能动态修改远近裁剪面 。

追踪源代码发现在 osgUtil的SceneView类 void SceneView::cull()中以下代码

 _cullVisitorLeft->setDatabaseRequestHandler(_cullVisitor->getDatabaseRequestHandler());
 _cullVisitorLeft->setClampProjectionMatrixCallback(_cullVisitor->getClampProjectionMatrixCallback());
 _cullVisitorLeft->setTraversalMask(_cullMaskLeft);
 computeLeftEyeViewport(getViewport());
 bool computeNearFar = cullStage(computeLeftEyeProjection(getProjectionMatrix()),computeLeftEyeView(getViewMatrix()),_cullVisitorLeft.get(),_stateGraphLeft.get(),_renderStageLeft.get(),_viewportLeft.get());


 // set up the right eye.
 _cullVisitorRight->setDatabaseRequestHandler(_cullVisitor->getDatabaseRequestHandler());
 _cullVisitorRight->setClampProjectionMatrixCallback(_cullVisitor->getClampProjectionMatrixCallback());
 _cullVisitorRight->setTraversalMask(_cullMaskRight);
 computeRightEyeViewport(getViewport());
 computeNearFar = cullStage(computeRightEyeProjection(getProjectionMatrix()),computeRightEyeView(getViewMatrix()),_cullVisitorRight.get(),_stateGraphRight.get(),_renderStageRight.get(),_viewportRight.get());

if (computeNearFar)
 {
       CullVisitor::value_type zNear = osg::minimum(_cullVisitorLeft->getCalculatedNearPlane(),_cullVisitorRight->getCalculatedNearPlane());
       CullVisitor::value_type zFar =  osg::maximum(_cullVisitorLeft->getCalculatedFarPlane(),_cullVisitorRight->getCalculatedFarPlane());
       _cullVisitor->clampProjectionMatrix(getProjectionMatrix(),zNear,zFar);
 }

跟踪发现_cullVisitor中的_clampProjectionMatrixCallback对象为空，说明对主camera设置ClampProjectionMatrixCallback不能影响到_cullVisitor的_clampProjectionMatrixCallback。

这样解决办法就出来了，将主camera用到的ClampProjectionMatrixCallback对象设置一份给_cullVisitor就可以了!!!!!!!!!!

经测试通过，方法可行............................OK