本文介绍了一个基于OpenSceneGraph (OSG) 的指南针组件实现细节，该组件能够显示方向信息并随场景旋转。文章深入讲解了如何利用OSG API创建定制化的视觉元素，并通过代码示例展示了指南针的设计和集成。
//**********************Compass.h**********************
#include <osg/MatrixTransform>
#include <osg/Projection>
#include <osg/Vec4>
#include <osg/NodeVisitor>
#include <osg/ClipPlane>
#include <osg/Viewport>
class Compass : public osg::Projection
{
public:
Compass( osg::Viewport *vp);
protected:
virtual void traverse(osg::NodeVisitor&);
//static const osg::Vec4 color;
private:
osg::ref_ptr<osg::MatrixTransform> _tx;
osg::ref_ptr<osg::MatrixTransform> _ltx;
osg::ref_ptr<osg::ClipPlane> _clipPlane;
osg::ref_ptr<osg::Geode> _makeGeode();
osg::ref_ptr<osg::Geode> _lineGeode();
};
//********************************Compass.cpp********************************
#include <stdio.h>
#include <osg/Geode>
#include <osg/Geometry>
#include <osg/MatrixTransform>
#include <osg/LineWidth>
#include <osgText/Text>
#include <osgUtil/CullVisitor>
#include <osg/ClipPlane>
#include "Compass.h"
//const osg::Vec4 Compass::color = osg::Vec4( 0, 0.6, 0, 1.0 );
osg::Vec4 color( 0, 0.6, 0, 1.0 );
Compass::Compass(osg::Viewport *vp)
{
osg::ref_ptr<osg::StateSet> stateSet = new osg::StateSet;
stateSet->setMode(GL_DEPTH_TEST, osg::StateAttribute::OFF | osg::StateAttribute::OVERRIDE );
stateSet->setMode( GL_LIGHTING, osg::StateAttribute::OFF | osg::StateAttribute::OVERRIDE );
stateSet->setTextureMode( 0, GL_TEXTURE_2D, osg::StateAttribute::OFF );
stateSet->setRenderBinDetails( 110, "RenderBin" );
stateSet->setAttribute( vp );
double ar = 120.0/640.0;
setMatrix( osg::Matrix::frustum( -0.35, 0.35, -0.35 * ar, 0.35 * ar, 1.0, 10000.0 ));
//setMatrix( osg::Matrix::ortho2D( -1, 1, 0, 2 * ar ));
_clipPlane = new osg::ClipPlane( 0, osg::Plane( 0.0, -1.0, 0.0, 0.0 ));
stateSet->setAttributeAndModes( _clipPlane.get() );
stateSet->setAttributeAndModes( new osg::LineWidth( 4.0 ));
setStateSet( stateSet.get());
setCullingActive( false );
_tx = new osg::MatrixTransform;
_tx->setReferenceFrame( osg::Transform::ABSOLUTE_RF );
_tx->addChild( _makeGeode().get() );
addChild(_tx.get());
_ltx = new osg::MatrixTransform;
_ltx->addChild(_lineGeode().get());
_tx->addChild( _ltx.get() );
}
osg::ref_ptr<osg::Geode> Compass::_lineGeode()
{
osg::ref_ptr<osg::Vec3Array> coords = new osg::Vec3Array;
coords->push_back( osg::Vec3(-0.03, -1.0, -0.07) );
coords->push_back( osg::Vec3( 0.0, -1.0, -0.01) );
coords->push_back( osg::Vec3( 0.0, -1.0, -0.01) );
coords->push_back( osg::Vec3( 0.03, -1.0, -0.07) );
/*
coords->push_back( osg::Vec3(-0.03, -1.0, 0.15) );
coords->push_back( osg::Vec3( 0.0, -1.0, 0.11) );
coords->push_back( osg::Vec3( 0.0, -1.0, 0.11) );
coords->push_back( osg::Vec3( 0.03, -1.0, 0.15) );
*/
osg::ref_ptr<osg::Vec4Array> colors = new osg::Vec4Array;
colors->push_back( color );
osg::ref_ptr<osg::Geometry> geometry = new osg::Geometry;
geometry->setVertexArray(coords.get());
geometry->setColorArray(colors.get());
geometry->setColorBinding(osg::Geometry::BIND_OVERALL);
geometry->addPrimitiveSet( new osg::DrawArrays(osg::PrimitiveSet::LINES, 0, coords->size()));
osg::ref_ptr<osg::Geode> geode = new osg::Geode;
geode->addDrawable( geometry.get() );
return geode;
}
osg::ref_ptr<osg::Geode> Compass::_makeGeode()
{
osg::ref_ptr<osg::Vec3Array> coords = new osg::Vec3Array;
osg::ref_ptr<osg::Vec4Array> colors = new osg::Vec4Array;
osg::ref_ptr<osg::Geode> geode = new osg::Geode;
for( int i = 0; i < 360; i += 5 )
{
double a = osg::DegreesToRadians( double(i-180) );
coords->push_back( osg::Vec3( sin(-a), cos(-a), 0.0 ));
if( !(i%10 ) )
coords->push_back( osg::Vec3( sin(-a), cos(-a), 0.06 ));
else
coords->push_back( osg::Vec3( sin(-a), cos(-a), 0.02 ));
if( !(i % 30 ))
{
osg::ref_ptr<osgText::Text> text = new osgText::Text;
text->setFont( "fonts/arial.ttf" );
text->setAlignment( osgText::Text::CENTER_CENTER );
text->setFontResolution(100,100);
text->setCharacterSize( 0.1 );
text->setColor( color );
osg::Matrix m = osg::Matrix::rotate( osg::PI*0.5, 1, 0, 0 ) *
osg::Matrix::rotate( osg::PI + a, 0, 0, 1 );
osg::Quat q;
q.set( m );
text->setRotation( q );
char buff[8];
(i == 0 ) ? sprintf( buff, "N" ):
(i == 90 ) ? sprintf( buff, "W" ):
(i == 180 ) ? sprintf( buff, "S" ):
(i == 270 ) ? sprintf( buff, "E" ): sprintf( buff, "%2d", (((360-i)%360)/10));
text->setText( buff );
text->setPosition( osg::Vec3( sin(-a), cos(-a), 0.1 ));
geode->addDrawable( text.get() );
}
}
colors->push_back( color );
osg::ref_ptr<osg::Geometry> geometry = new osg::Geometry;
geometry->setVertexArray(coords.get());
geometry->setColorArray(colors.get());
geometry->setColorBinding(osg::Geometry::BIND_OVERALL);
geometry->addPrimitiveSet( new osg::DrawArrays(osg::PrimitiveSet::LINES, 0, coords->size()));
//geometry->getOrCreateStateSet()->setAttributeAndModes( new osg::LineWidth( 4.0 ));
geode->addDrawable( geometry.get() );
return geode;
}
void Compass::traverse(osg::NodeVisitor&nv)
{
if( nv.getVisitorType() == osg::NodeVisitor::CULL_VISITOR )
{
osgUtil::CullVisitor *cv = dynamic_cast<osgUtil::CullVisitor *>(&nv);
osg::Matrix ivm = cv->getState()->getInitialViewMatrix();
ivm(3,0) = ivm(3,1) = ivm(3,2) = 0.0;
osg::Vec3 v = osg::Vec3(0,1,0) * ivm * osg::Matrix::rotate( osg::PI*0.5, 1, 0, 0 );
double a = atan2( v[0], v[1] );
_tx->setMatrix( osg::Matrix::rotate( -a, 0, 0, 1 ) *
osg::Matrix::translate( 0.0, 3.0, -0.05 ) *
osg::Matrix::rotate( -osg::PI*0.5, 1, 0, 0 ) );
osg::Vec4d cp = osg::Vec4d(0.0, -1.0, 0.0, -0.75 ) * osg::Matrix::rotate( a, 0, 0, 1 );
_clipPlane->setClipPlane( cp );
_ltx->setMatrix( osg::Matrix::rotate( a, 0, 0, 1 ) );
}
osg::Projection::traverse( nv );
}
//*************main.cpp***********************
#include <osgDB/ReadFile>
#include <osgUtil/Optimizer>
#include <osgViewer/Viewer>
#include <osg/NodeCallback>
#include <osg/StateSet>
#include <osg/LightModel>
#include <osgGA/TrackballManipulator>
#include <osgGA/StateSetManipulator>
#include <osgGA/GUIEventHandler>
#include <osgViewer/ViewerEventHandlers>
#include "Compass.h"
int main(int argc, char **argv)
{
// Parse command line arguments
osg::ArgumentParser args( &argc, argv );
osg::ref_ptr<osg::Group> root = new osg::Group;
// Set up the viewer
osgViewer::Viewer viewer(args);
// Set the clear color to black
// viewer.getCamera()->setClearColor(osg::Vec4(0,0,0,1));
// Use a default camera manipulator
osgGA::TrackballManipulator* manip = new osgGA::TrackballManipulator;
viewer.setCameraManipulator(manip);
// Initially, place the TrackballManipulator so it's in the center of the scene
manip->setHomePosition(osg::Vec3(0,0,0), osg::Vec3(0,1,0), osg::Vec3(0,0,1));
manip->home(0);
// Add some useful handlers to see stats, wireframe and onscreen help
viewer.addEventHandler(new osgViewer::StatsHandler);
viewer.addEventHandler(new osgGA::StateSetManipulator(root->getOrCreateStateSet()));
viewer.addEventHandler(new osgViewer::HelpHandler);
// Tell the viewer what to display for a help message
viewer.getUsage(*args.getApplicationUsage());
// Load up the models specified on the command line
osg::ref_ptr<osg::Node> model = osgDB::readNodeFile("dumptruck.osg");
if( model.valid() )
root->addChild( model.get() );
// Add a compass model so we can see which way we are facing
osg::ref_ptr<osg::Viewport> vp = new osg::Viewport( 320, 20, 640, 100 );
root->addChild( new Compass( vp.get() ));
// Set some acceptable defaults.
double latitude = 38.4765; // San Francisco, California
double longitude = -122.493;
//Experiment with setting the LightModel to very dark to get better sun lighting effects
{
osg::ref_ptr<osg::StateSet> sset = root->getOrCreateStateSet();
osg::ref_ptr<osg::LightModel> lightModel = new osg::LightModel;
lightModel->setAmbientIntensity( osg::Vec4( 0.0025, 0.0025,0.0025, 1.0 ));
sset->setAttributeAndModes( lightModel.get() );
}
osgUtil::Optimizer optimizer;
optimizer.optimize(root.get());
// set the scene to render
viewer.setSceneData(root.get());
// Realize the viewer
viewer.realize();
while( !viewer.done() )
{
viewer.frame();
}
return 0;
}
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