OSG Notes: Set DO_NOT_COMPUTE_NEAR_FAR to manually calculate far and near planes

问题

When implementing a joystick for orthographic projection,缩放平移后,A situation where a graphics part message is generated.没研究透osgAutomatic calculation algorithm,For the time being, I think that the automatic calculation of the far and near planes may not be a problem for perspective projection,But the orthographic projection does.

思路（记录下,Not strictly scrutinized,不保证正确性）

left, right, top, bottomUse the radius of the model to enclose the sphere.The distance idea between the far and near planes is shown in the figure below,zHalf the length of the shaft shall be taken as the maximum possible length（That is, the distance from the viewpoint along the line of sight to the other side of the bounding box）,This will ensure how to rotate the model,The models are all within the observation range with the eye as the coordinate origin.

代码

#include <iostream>
#include <osgViewer/Viewer>
#include <osg/Group>
#include <osg/ShapeDrawable>
#include <osgGA/GUIEventHandler>
#include <osg/Viewport>
#include <osg/NodeCallback>
#include <osgGA/StandardManipulator>
#include <osgGA/EventVisitor>

using namespace std;


class MyGUIEventHandler : public osgGA::GUIEventHandler
{
    
public:
	virtual bool handle(const osgGA::GUIEventAdapter& ea, osgGA::GUIActionAdapter& aa,
		osg::Object* pObject, osg::NodeVisitor* pNodeVisitor)
	{
    
		osgViewer::Viewer* pViewer = dynamic_cast<osgViewer::Viewer*>(aa.asView());
		if (!pViewer || !pViewer->getSceneData() )
		{
    
			return false;
		}
		osg::ref_ptr<osg::Camera> pCamera = pViewer->getCamera();
		if (!pCamera)
		{
    
			return false;
		}
		osg::Viewport* pViewport = pCamera->getViewport();
		if (!pViewport)
		{
    
			return false;
		}
		osgGA::StandardManipulator* pManipulator = dynamic_cast<osgGA::StandardManipulator*>(
			pViewer->getCameraManipulator());
		if (!pManipulator)
		{
    
			return false;
		}

		double aspecRadio = double(pViewport->width()) / double(pViewport->height());

		osg::BoundingSphere modelBound = pViewer->getSceneData()->getBound();
		double dModelHalfSize = modelBound.radius();
		static double s_dScale = 1.0;

		switch (ea.getEventType())
		{
    
		case osgGA::GUIEventAdapter::EventType::KEYDOWN:
		{
    
			bool bZoom = false;
			if (int(osgGA::GUIEventAdapter::KeySymbol::KEY_R) == ea.getKey())
			{
    
				s_dScale = 1.0; //恢复
				bZoom = true;
			}
			else if (int(osgGA::GUIEventAdapter::KeySymbol::KEY_D) == ea.getKey())
			{
    
				s_dScale *= 1.2; //缩小
				bZoom = true;
			}
			else if (int(osgGA::GUIEventAdapter::KeySymbol::KEY_U) == ea.getKey())
			{
    
				s_dScale *= 0.8;//放大
				bZoom = true;
			}
			else
			{
    
				bZoom = false; //Corrects near and far planes
			}



			//Calculate the eye-to-viewpoint distance using the joystick's viewing matrix,The result of using the camera is wrong
// osg::Vec3d eye0;
// osg::Vec3d center0;
// osg::Vec3d up0;
// pCamera->getViewMatrixAsLookAt(eye0, center0, up0);
// double dDistance0 = (eye0 - center0).length();

			double left = 0.0;
			double right = 0.0;
			double bottom = 0.0;
			double top = 0.0;
			double zNear = 0.0;
			double zFar = 0.0;
			if (pViewer->getCamera()->getProjectionMatrixAsOrtho(left, right, bottom, top, zNear, zFar))
			{
    //正交投影

				osg::Vec3d eye1;
				osg::Vec3d center1;
				osg::Vec3d up1;
				pManipulator->getTransformation(eye1, center1, up1);
				double dDistance1 = (eye1 - center1).length();
				double dDistance2 = (center1 - modelBound.center()).length();

				std::cout << "dDistance1:" << dDistance1
					<< ", dDistance2:" << dDistance2 << std::endl;


				if (bZoom)//Scaling of orthographic projections
				{
    
					double dHalfRange = dModelHalfSize * s_dScale;
					if (aspecRadio > 1.0)
					{
    
						pViewer->getCamera()->setProjectionMatrixAsOrtho(
							-dHalfRange*aspecRadio, dHalfRange*aspecRadio,
							-dHalfRange, dHalfRange, zNear * s_dScale, zFar * s_dScale);
					}
					else
					{
    
						pViewer->getCamera()->setProjectionMatrixAsOrtho(
							-dHalfRange, dHalfRange,
							-dHalfRange*aspecRadio, dHalfRange*aspecRadio,
							zNear * s_dScale, zFar * s_dScale);
					}
				}
				else //Corrects near and far planes
				{
    
					double dHalfRangeZ = dDistance1 + dDistance2 + dModelHalfSize*0.7;
					pViewer->getCamera()->setProjectionMatrixAsOrtho(
						left, right, bottom, top, -dHalfRangeZ, dHalfRangeZ);
				}
			}

			break;
		}

		}
		return osgGA::GUIEventHandler::handle(ea, aa, pObject, pNodeVisitor);
	}


};



int main(int argc, char** argv)
{
    
	osgViewer::Viewer* pViewer = new osgViewer::Viewer();

	osg::ref_ptr<osg::Group> pRoot = new osg::Group();
	osg::ref_ptr<osg::Geode> pGeode = new osg::Geode();
	pRoot->addChild(pGeode);


	osg::ref_ptr<osg::Box> pBox = new osg::Box(osg::Vec3(0, 0, 0), 100.0);
	pGeode->addDrawable(new osg::ShapeDrawable(pBox));

	const osg::BoundingSphere& boundingSphere = pRoot->getBound();


	pViewer->addEventHandler(new MyGUIEventHandler());

	pViewer->setSceneData(pRoot);
	pViewer->getCamera()->setClearColor(osg::Vec4(0, 0, 0, 1.0));
	pViewer->setUpViewInWindow(450, 220, 720, 450);
	pViewer->realize();

	//Far and near planes are not automatically calculated
	pViewer->getCamera()->setComputeNearFarMode(
		osg::CullSettings::ComputeNearFarMode::DO_NOT_COMPUTE_NEAR_FAR);

	//Set a default projection range
	const osg::Viewport* pViewport = pViewer->getCamera()->getViewport();
	if (pViewport)
	{
    
		double dHalfRange = 100;
		double aspecRadio = double(pViewport->width()) / double(pViewport->height());
		if (aspecRadio > 1.0)
		{
    
			pViewer->getCamera()->setProjectionMatrixAsOrtho(
				-dHalfRange*aspecRadio, dHalfRange*aspecRadio, 
				-dHalfRange, dHalfRange, -dHalfRange, dHalfRange);
		}
		else
		{
    
			pViewer->getCamera()->setProjectionMatrixAsOrtho(
				-dHalfRange, dHalfRange,
				-dHalfRange*aspecRadio, dHalfRange*aspecRadio, -dHalfRange, dHalfRange);
		}
	}
	//aspecRadio
	

	pViewer->run();

	return 0;
}

截图

• Axonometric view,正方体,Correct near and far planes are not calculated
  

• After manually calculating the far and near planes