用OpenSceneGraph实现的NeHe OpenGL教程 - 第三十九课
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简介
这节课NeHe课程主要向我们展示了将物理运动规律引入到三维场景中，模拟真实物体的位置变化过程。这节课分别模拟了如下几种运动方式：
（1）在重力作用下的抛物线运动；
（2）匀速运动
（3）一种类似于弹簧一样的来回运动
这些运动的方程在Physics.h头文件中描述的很清楚，稍有物理知识应该不难理解。
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实现
首先我们在场景中添加各种几何体：
root->addChild(createBackGroundGeode()); //网状背景 root->addChild(constantVelocityNode()); //匀速模拟 root->addChild(underGravitationNode()); // 重力模拟 root->addChild(massConnectedWithSpringNode()); //弹簧来回运动模拟另外需要添加场景中的说明文字：
osg::Node *timeEllapsedNode = glPrint(-15.0f, 14, 0, osg::Vec4(1,1,1,1), "Time elapsed (seconds): %.2f", timeElapsed); timeEllapsedNode->addUpdateCallback(new TimeEllapsedUpdateCallback); root->addChild(timeEllapsedNode); osg::Node *ratioNode = glPrint(-15.0f, 13, 0, osg::Vec4(1,1,1,1),"Slow motion ratio: %.2f", slowMotionRatio); ratioNode->addUpdateCallback(new RatioUpdateCallback); root->addChild(ratioNode); root->addChild(glPrint(-15.0f, 12, 0, osg::Vec4(1,1,1,1),"Press F2 for normal motion")); root->addChild(glPrint(-15.0f, 11, 0, osg::Vec4(1,1,1,1),"Press F3 for slow motion"));
接下来便是一系列的更新回调，按照物理运动的规律更新节点位置：
//Constant Callback
class ConstantPointUpdateCallback : public osg::Drawable::UpdateCallback
{
public:
virtual void update(osg::NodeVisitor*, osg::Drawable* drawable)
{
osg::Geometry *geometry = dynamic_cast<osg::Geometry*>(drawable);
if (!geometry)
return;
osg::Vec3Array *vertexArray = dynamic_cast<osg::Vec3Array*>(geometry->getVertexArray());
if (!vertexArray)
return;
vertexArray->clear();
for (int a = 0; a < constantVelocity->numOfMasses; ++a)
{
Mass* mass = constantVelocity->getMass(a);
Vector3D* pos = &mass->pos;
vertexArray->push_back(osg::Vec3(pos->x, pos->y, pos->z));
}
geometry->setVertexArray(vertexArray);
vertexArray->dirty();
}
};
class ConstantWordUpdateCallback : public osg::NodeCallback
{
public:
virtual void operator()(osg::Node* node, osg::NodeVisitor* nv)
{
osg::MatrixTransform *mt = dynamic_cast<osg::MatrixTransform*>(node);
if (!mt)
return;
for (int a = 0; a < constantVelocity->numOfMasses; ++a)
{
Mass* mass = constantVelocity->getMass(a);
Vector3D* pos = &mass->pos;
mt->setMatrix(osg::Matrix::translate(pos->x, pos->y + 1, pos->z));
}
traverse(node, nv);
}
};为了篇幅限制，这里只给出匀速运动的回调代码，其他部分参看附录中的源码。
我们需要在每帧中计算时间以及在每帧中更新物理运动的参数，这部分在交互的代码FRAME(帧循环事件)中给出：
case (osgGA::GUIEventAdapter::FRAME):
{
double dt = 0.0;
_currentTick = osg::Timer::instance()->tick();
if (_currentTick != _lastTick)
{
dt = osg::Timer::instance()->delta_s(_lastTick, _currentTick);
_lastTick = _currentTick;
}
dt /= slowMotionRatio;
timeElapsed += dt;
float maxPossible_dt = 0.1f;
int numOfIterations = (int)(dt / maxPossible_dt) + 1;
if (numOfIterations != 0)
dt = dt / numOfIterations;
for (int a = 0; a < numOfIterations; ++a)
{
constantVelocity->operate(dt);
motionUnderGravitation->operate(dt);
massConnectedWithSpring->operate(dt);
}
}此外在按下F2和F3时调整运动的速度：
if (ea.getKey() == osgGA::GUIEventAdapter::KEY_F2)
{
slowMotionRatio = 1.0f;
}
if (ea.getKey() == osgGA::GUIEventAdapter::KEY_F3)
{
slowMotionRatio = 10.0f;
}编译运行程序：
附：本课源码(源码中可能存在错误和不足，仅供参考)
#include "../osgNeHe.h"
#include "Physics1.h"
#include <QtCore/QTimer>
#include <QtGui/QApplication>
#include <QtGui/QVBoxLayout>
#include <osgViewer/Viewer>
#include <osgDB/ReadFile>
#include <osgQt/GraphicsWindowQt>
#include <osg/MatrixTransform>
#include <osgText/Text>
#include <osg/Point>
#include <osgGA/TrackballManipulator>
//////////////////////////////////////////////////////////////////////////
ConstantVelocity* constantVelocity = new ConstantVelocity();
MotionUnderGravitation* motionUnderGravitation =
new MotionUnderGravitation(Vector3D(0.0f, -9.81f, 0.0f));
MassConnectedWithSpring* massConnectedWithSpring = new MassConnectedWithSpring(2.0f);
float slowMotionRatio = 10.0f;
float timeElapsed = 0;
osg::Node* glPrint(GLfloat x, GLfloat y, GLfloat z, const osg::Vec4& fontColor, const char *string, ...)
{
char text[256];
va_list ap;
if (string == NULL)
return NULL;
va_start(ap, string);
vsprintf(text, string, ap);
va_end(ap);
osg::MatrixTransform *posMT = new osg::MatrixTransform;
posMT->setMatrix(osg::Matrix::translate(x, y, z));
osgText::Text *textWords = new osgText::Text;
textWords->setColor(fontColor);
textWords->setText(text);
textWords->setFont("Fonts/Arial.ttf");
textWords->setCharacterSize(1.0f);
osg::Geode *fontGeode = new osg::Geode;
fontGeode->addDrawable(textWords);
posMT->addChild(fontGeode);
return posMT;
}
//////////////////////////////////////////////////////////////////////////
//////////////////////////////////////////////////////////////////////////
//////////////////////////////////////////////////////////////////////////
class ManipulatorSceneHandler : public osgGA::GUIEventHandler
{
public:
ManipulatorSceneHandler()
{
_lastTick = osg::Timer::instance()->tick();
_currentTick = _lastTick;
}
public:
virtual bool handle(const osgGA::GUIEventAdapter& ea, osgGA::GUIActionAdapter& aa)
{
osgViewer::Viewer *viewer = dynamic_cast<osgViewer::Viewer*>(&aa);
if (!viewer)
return false;
if (!viewer->getSceneData())
return false;
if (ea.getHandled())
return false;
osg::Group *root = viewer->getSceneData()->asGroup();
switch(ea.getEventType())
{
case (osgGA::GUIEventAdapter::FRAME):
{
double dt = 0.0;
_currentTick = osg::Timer::instance()->tick();
if (_currentTick != _lastTick)
{
dt = osg::Timer::instance()->delta_s(_lastTick, _currentTick);
_lastTick = _currentTick;
}
dt /= slowMotionRatio;
timeElapsed += dt;
float maxPossible_dt = 0.1f;
int numOfIterations = (int)(dt / maxPossible_dt) + 1;
if (numOfIterations != 0)
dt = dt / numOfIterations;
for (int a = 0; a < numOfIterations; ++a)
{
constantVelocity->operate(dt);
motionUnderGravitation->operate(dt);
massConnectedWithSpring->operate(dt);
}
}
break;
case(osgGA::GUIEventAdapter::KEYDOWN):
{
if (ea.getKey() == osgGA::GUIEventAdapter::KEY_F2)
{
slowMotionRatio = 1.0f;
}
if (ea.getKey() == osgGA::GUIEventAdapter::KEY_F3)
{
slowMotionRatio = 10.0f;
}
}
break;
default: break;
}
return false;
}
osg::Timer_t _lastTick;
osg::Timer_t _currentTick;
};
//////////////////////////////////////////////////////////////////////////
//////////////////////////////////////////////////////////////////////////
//////////////////////////////////////////////////////////////////////////
//Constant Callback
class ConstantPointUpdateCallback : public osg::Drawable::UpdateCallback
{
public:
virtual void update(osg::NodeVisitor*, osg::Drawable* drawable)
{
osg::Geometry *geometry = dynamic_cast<osg::Geometry*>(drawable);
if (!geometry)
return;
osg::Vec3Array *vertexArray = dynamic_cast<osg::Vec3Array*>(geometry->getVertexArray());
if (!vertexArray)
return;
vertexArray->clear();
for (int a = 0; a < constantVelocity->numOfMasses; ++a)
{
Mass* mass = constantVelocity->getMass(a);
Vector3D* pos = &mass->pos;
vertexArray->push_back(osg::Vec3(pos->x, pos->y, pos->z));
}
geometry->setVertexArray(vertexArray);
vertexArray->dirty();
}
};
class ConstantWordUpdateCallback : public osg::NodeCallback
{
public:
virtual void operator()(osg::Node* node, osg::NodeVisitor* nv)
{
osg::MatrixTransform *mt = dynamic_cast<osg::MatrixTransform*>(node);
if (!mt)
return;
for (int a = 0; a < constantVelocity->numOfMasses; ++a)
{
Mass* mass = constantVelocity->getMass(a);
Vector3D* pos = &mass->pos;
mt->setMatrix(osg::Matrix::translate(pos->x, pos->y + 1, pos->z));
}
traverse(node, nv);
}
};
//Gravity Callback
class GravitationPointUpdateCallback : public osg::Drawable::UpdateCallback
{
public:
virtual void update(osg::NodeVisitor*, osg::Drawable* drawable)
{
osg::Geometry *geometry = dynamic_cast<osg::Geometry*>(drawable);
if (!geometry)
return;
osg::Vec3Array *vertexArray = dynamic_cast<osg::Vec3Array*>(geometry->getVertexArray());
if (!vertexArray)
return;
vertexArray->clear();
for (int a = 0; a < motionUnderGravitation->numOfMasses; ++a)
{
Mass* mass = motionUnderGravitation->getMass(a);
Vector3D* pos = &mass->pos;
vertexArray->push_back(osg::Vec3(pos->x, pos->y, pos->z));
}
geometry->setVertexArray(vertexArray);
vertexArray->dirty();
}
};
class GravitationWordUpdateCallback : public osg::NodeCallback
{
public:
virtual void operator()(osg::Node* node, osg::NodeVisitor* nv)
{
osg::MatrixTransform *mt = dynamic_cast<osg::MatrixTransform*>(node);
if (!mt)
return;
for (int a = 0; a < motionUnderGravitation->numOfMasses; ++a)
{
Mass* mass = motionUnderGravitation->getMass(a);
Vector3D* pos = &mass->pos;
mt->setMatrix(osg::Matrix::translate(pos->x, pos->y + 1, pos->z));
}
traverse(node, nv);
}
};
//SpringCallback
class SpringPointUpdateCallback : public osg::Drawable::UpdateCallback
{
public:
virtual void update(osg::NodeVisitor*, osg::Drawable* drawable)
{
osg::Geometry *geometry = dynamic_cast<osg::Geometry*>(drawable);
if (!geometry)
return;
osg::Vec3Array *vertexArray = dynamic_cast<osg::Vec3Array*>(geometry->getVertexArray());
if (!vertexArray)
return;
vertexArray->clear();
for (int a = 0; a < massConnectedWithSpring->numOfMasses; ++a)
{
Mass* mass = massConnectedWithSpring->getMass(a);
Vector3D* pos = &mass->pos;
vertexArray->push_back(osg::Vec3(pos->x, pos->y, pos->z));
}
geometry->setVertexArray(vertexArray);
vertexArray->dirty();
}
};
class SpringWordUpdateCallback : public osg::NodeCallback
{
public:
virtual void operator()(osg::Node* node, osg::NodeVisitor* nv)
{
osg::MatrixTransform *mt = dynamic_cast<osg::MatrixTransform*>(node);
if (!mt)
return;
for (int a = 0; a < massConnectedWithSpring->numOfMasses; ++a)
{
Mass* mass = massConnectedWithSpring->getMass(a);
Vector3D* pos = &mass->pos;
mt->setMatrix(osg::Matrix::translate(pos->x, pos->y + 1, pos->z));
}
traverse(node, nv);
}
};
class SpringLineUpdateCallback : public osg::Drawable::UpdateCallback
{
public:
virtual void update(osg::NodeVisitor*, osg::Drawable* drawable)
{
osg::Geometry *geometry = dynamic_cast<osg::Geometry*>(drawable);
if (!geometry)
return;
osg::Vec3Array *vertexArray = dynamic_cast<osg::Vec3Array*>(geometry->getVertexArray());
if (!vertexArray)
return;
vertexArray->clear();
for (int a = 0; a < massConnectedWithSpring->numOfMasses; ++a)
{
Mass* mass = massConnectedWithSpring->getMass(a);
Vector3D* pos = &mass->pos;
vertexArray->push_back(osg::Vec3(pos->x, pos->y, pos->z));
Vector3D *tmp = &massConnectedWithSpring->connectionPos;
vertexArray->push_back(osg::Vec3(tmp->x, tmp->y, tmp->z));
}
geometry->setVertexArray(vertexArray);
vertexArray->dirty();
}
};
class TimeEllapsedUpdateCallback : public osg::NodeCallback
{
public:
virtual void operator()(osg::Node* node, osg::NodeVisitor* nv)
{
osg::MatrixTransform *mt = dynamic_cast<osg::MatrixTransform*>(node);
if (!mt)
return;
osg::Geode *geode = dynamic_cast<osg::Geode*>(mt->getChild(0));
if (!geode)
return;
osgText::Text *text = dynamic_cast<osgText::Text*>(geode->getDrawable(0));
if (!text)
return;
std::stringstream os;
std::string str;
os.precision(2);
os << std::fixed << "Time elapsed (seconds): " << timeElapsed;
str = os.str();
text->setText(str);
traverse(node, nv);
}
};
class RatioUpdateCallback : public osg::NodeCallback
{
public:
virtual void operator()(osg::Node* node, osg::NodeVisitor* nv)
{
osg::MatrixTransform *mt = dynamic_cast<osg::MatrixTransform*>(node);
if (!mt)
return;
osg::Geode *geode = dynamic_cast<osg::Geode*>(mt->getChild(0));
if (!geode)
return;
osgText::Text *text = dynamic_cast<osgText::Text*>(geode->getDrawable(0));
if (!text)
return;
std::stringstream os;
std::string str;
os.precision(2);
os << std::fixed << "Slow motion ratio: " << slowMotionRatio;
str = os.str();
text->setText(str);
traverse(node, nv);
}
};
//绘制背景网格
osg::Geode* createBackGroundGeode()
{
osg::Geode *geode = new osg::Geode;
osg::Geometry *geometry = new osg::Geometry;
osg::Vec3Array *vertexArray = new osg::Vec3Array;
osg::Vec3Array *colorArray = new osg::Vec3Array;
colorArray->push_back(osg::Vec3(0, 0, 1.0));
geometry->setColorArray(colorArray, osg::Array::BIND_OVERALL);
for (float x = -20; x <= 20; x += 1.0f)
{
vertexArray->push_back(osg::Vec3(x, 20, 0));
vertexArray->push_back(osg::Vec3(x,-20, 0));
}
for (float y = -20; y <= 20; y += 1.0f)
{
vertexArray->push_back(osg::Vec3(20, y, 0));
vertexArray->push_back(osg::Vec3(-20, y, 0));
}
geometry->setVertexArray(vertexArray);
geometry->getOrCreateStateSet()->setMode(GL_LIGHTING, osg::StateAttribute::OFF);
geometry->addPrimitiveSet(new osg::DrawArrays(osg::PrimitiveSet::LINES, 0, vertexArray->size()));
geode->addDrawable(geometry);
return geode;
}
osg::Geode* createPoint(const osg::Vec3& pos, const osg::Vec3& color, float size)
{
osg::Geode *geode = new osg::Geode;
osg::Geometry *geometry = new osg::Geometry;
osg::Vec3Array *vertexArray = new osg::Vec3Array;
osg::Vec3Array *colorArray = new osg::Vec3Array;
colorArray->push_back(color);
geometry->setColorArray(colorArray, osg::Array::BIND_OVERALL);
vertexArray->push_back(pos);
geometry->setVertexArray(vertexArray);
geometry->addPrimitiveSet(new osg::DrawArrays(osg::PrimitiveSet::POINTS, 0, vertexArray->size()));
osg::Point *point = new osg::Point;
point->setSize(size);
geometry->getOrCreateStateSet()->setAttributeAndModes(point);
geometry->getOrCreateStateSet()->setMode(GL_LIGHTING, osg::StateAttribute::OFF);
geode->addDrawable(geometry);
return geode;
}
osg::Geode* createLine(const osg::Vec3& posBeg, const osg::Vec3& posEnd, const osg::Vec3& color)
{
osg::Geode *geode = new osg::Geode;
osg::Geometry *geometry = new osg::Geometry;
osg::Vec3Array *vertexArray = new osg::Vec3Array;
osg::Vec3Array *colorArray = new osg::Vec3Array;
vertexArray->push_back(posBeg);
vertexArray->push_back(posEnd);
geometry->setVertexArray(vertexArray);
colorArray->push_back(color);
geometry->setColorArray(colorArray, osg::Array::BIND_OVERALL);
geometry->addPrimitiveSet(new osg::DrawArrays(osg::PrimitiveSet::LINES, 0, vertexArray->size()));
geometry->getOrCreateStateSet()->setMode(GL_LIGHTING, osg::StateAttribute::OFF);
geode->addDrawable(geometry);
return geode;
}
//绘制Constant Velocity
osg::Node* constantVelocityNode()
{
osg::Group *constantVelocityGroup = new osg::Group;
for (int a = 0; a < constantVelocity->numOfMasses; ++a)
{
Mass* mass = constantVelocity->getMass(a);
Vector3D* pos = &mass->pos;
osg::Node *node = glPrint(pos->x, pos->y + 1, pos->z, osg::Vec4(1,0,0,1), "Mass with constant vel");
osg::Geode *geode = createPoint(osg::Vec3(pos->x, pos->y, pos->z), osg::Vec3(1,0,0), 4);
geode->getDrawable(0)->setUpdateCallback(new ConstantPointUpdateCallback);
node->addUpdateCallback(new ConstantWordUpdateCallback);
constantVelocityGroup->addChild(node);
constantVelocityGroup->addChild(geode);
}
return constantVelocityGroup;
}
//绘制motionUnderGravitation
osg::Node* underGravitationNode()
{
osg::Group *group = new osg::Group;
for (int a = 0; a < motionUnderGravitation->numOfMasses; ++a)
{
Mass* mass = motionUnderGravitation->getMass(a);
Vector3D* pos = &mass->pos;
osg::Node *wordNode = glPrint(pos->x, pos->y + 1, pos->z, osg::Vec4(1,1,0,1), "Motion under gravitation");
osg::Geode *pointNode = createPoint(osg::Vec3(pos->x, pos->y, pos->z), osg::Vec3(1,1,0), 4);
wordNode->addUpdateCallback(new GravitationWordUpdateCallback);
pointNode->getDrawable(0)->setUpdateCallback(new GravitationPointUpdateCallback);
group->addChild(wordNode);
group->addChild(pointNode);
}
return group;
}
//绘制massConnectedWithSpring
osg::Node* massConnectedWithSpringNode()
{
osg::Group *group = new osg::Group;
for (int a = 0; a < massConnectedWithSpring->numOfMasses; ++a)
{
Mass* mass = massConnectedWithSpring->getMass(a);
Vector3D* pos = &mass->pos;
osg::Node *wordNode = glPrint(pos->x, pos->y + 1, pos->z, osg::Vec4(0,1,0,1), "Mass connected with spring");
osg::Geode *pointNode = createPoint(osg::Vec3(pos->x, pos->y, pos->z), osg::Vec3(0,1,0), 8);
group->addChild(wordNode);
group->addChild(pointNode);
wordNode->addUpdateCallback(new SpringWordUpdateCallback);
pointNode->getDrawable(0)->setUpdateCallback(new SpringPointUpdateCallback);
Vector3D *tmp = &massConnectedWithSpring->connectionPos;
osg::Geode *lineNode = createLine(osg::Vec3(pos->x, pos->y, pos->z), osg::Vec3(tmp->x, tmp->y, tmp->z), osg::Vec3(0,1,0));
//Force the lineNode Draw Upon Background
lineNode->getOrCreateStateSet()->setMode(GL_DEPTH_TEST, osg::StateAttribute::OFF);
group->addChild(lineNode);
lineNode->getDrawable(0)->setUpdateCallback(new SpringLineUpdateCallback);
}
return group;
}
class ViewerWidget : public QWidget, public osgViewer::Viewer
{
public:
ViewerWidget(osg::Node *scene = NULL)
{
QWidget* renderWidget = getRenderWidget( createGraphicsWindow(0,0,100,100), scene);
QVBoxLayout* layout = new QVBoxLayout;
layout->addWidget(renderWidget);
layout->setContentsMargins(0, 0, 0, 1);
setLayout( layout );
connect( &_timer, SIGNAL(timeout()), this, SLOT(update()) );
_timer.start( 10 );
}
QWidget* getRenderWidget( osgQt::GraphicsWindowQt* gw, osg::Node* scene )
{
osg::Camera* camera = this->getCamera();
camera->setGraphicsContext( gw );
const osg::GraphicsContext::Traits* traits = gw->getTraits();
camera->setClearColor( osg::Vec4(0.0, 0.0, 0.0, 1.0) );
camera->setViewport( new osg::Viewport(0, 0, traits->width, traits->height) );
camera->setProjectionMatrixAsPerspective(45.0f, static_cast<double>(traits->width)/static_cast<double>(traits->height), 0.1f, 100.0f );
camera->setViewMatrixAsLookAt(osg::Vec3d(0, 0, 40), osg::Vec3d(0, 0, 0), osg::Vec3d(0, 1, 0));
//OSG默认会将点裁剪掉
camera->setCullingMode(
camera->getCullingMode() &
~osg::CullSettings::SMALL_FEATURE_CULLING);
addEventHandler(new ManipulatorSceneHandler);
this->setSceneData( scene );
return gw->getGLWidget();
}
osgQt::GraphicsWindowQt* createGraphicsWindow( int x, int y, int w, int h, const std::string& name="", bool windowDecoration=false )
{
osg::DisplaySettings* ds = osg::DisplaySettings::instance().get();
osg::ref_ptr<osg::GraphicsContext::Traits> traits = new osg::GraphicsContext::Traits;
traits->windowName = name;
traits->windowDecoration = windowDecoration;
traits->x = x;
traits->y = y;
traits->width = w;
traits->height = h;
traits->doubleBuffer = true;
traits->alpha = ds->getMinimumNumAlphaBits();
traits->stencil = ds->getMinimumNumStencilBits();
traits->sampleBuffers = ds->getMultiSamples();
traits->samples = ds->getNumMultiSamples();
return new osgQt::GraphicsWindowQt(traits.get());
}
virtual void paintEvent( QPaintEvent* event )
{
frame();
}
protected:
QTimer _timer;
};
osg::Node* buildScene()
{
osg::Group *root = new osg::Group;
root->addChild(createBackGroundGeode());
root->addChild(constantVelocityNode());
root->addChild(underGravitationNode());
root->addChild(massConnectedWithSpringNode());
osg::Node *timeEllapsedNode = glPrint(-15.0f, 14, 0, osg::Vec4(1,1,1,1), "Time elapsed (seconds): %.2f", timeElapsed);
timeEllapsedNode->addUpdateCallback(new TimeEllapsedUpdateCallback);
root->addChild(timeEllapsedNode);
osg::Node *ratioNode = glPrint(-15.0f, 13, 0, osg::Vec4(1,1,1,1),"Slow motion ratio: %.2f", slowMotionRatio);
ratioNode->addUpdateCallback(new RatioUpdateCallback);
root->addChild(ratioNode);
root->addChild(glPrint(-15.0f, 12, 0, osg::Vec4(1,1,1,1),"Press F2 for normal motion"));
root->addChild(glPrint(-15.0f, 11, 0, osg::Vec4(1,1,1,1),"Press F3 for slow motion"));
return root;
}
int main( int argc, char** argv )
{
QApplication app(argc, argv);
ViewerWidget* viewWidget = new ViewerWidget(buildScene());
viewWidget->setGeometry( 100, 100, 640, 480 );
viewWidget->show();
return app.exec();
}