用OpenSceneGraph实现的NeHe OpenGL教程 - 第十三课
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简介
NeHe这节课主要讨论如何使用OpenGL显示2D文字。OpenGL显示2D文字是通过wglUseFontBitmaps函数创建了一系列的显示列表来实现的。通过阅读NeHe教程，读者应该能感觉到在OpenGL中显示文字还是比较麻烦的。在OSG中显示2D文字相对来说比较简单，OSG提供了专门用来处理文字的库osgText(包括二维和三维字体)
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实现
首先创建文字节点，由于osgText::Text继承于osg::Drawable可绘制物体，因此创建文本之后直接将其添加到叶节点中
osg::Group *root = new osg::Group;
osg::MatrixTransform *moveMT = new osg::MatrixTransform;
moveMT->setMatrix(osg::Matrix::translate(0, 0, -10));
root->addChild(moveMT);
osg::Geode *fontGeode = new osg::Geode;
osgText::Text *text = new osgText::Text;
text->setCharacterSize(0.4f);
text->setUpdateCallback(new FontColorCallback);
text->setText("OpenGL NeHe");
text->setFont("fonts/arial.ttf");
fontGeode->addDrawable(text);
moveMT->addChild(fontGeode);
return root;对于OSG中的Text类，它提供了丰富的成员函数允许用户自由地调整排版格式、采用不同的位置和姿态、使用不同的颜色等操作。
由于场景中需要不断修改字体的颜色，我们使用Drawable的UpdateCallback来完成
class FontColorCallback : public osg::Drawable::UpdateCallback
{
public:
virtual void update(osg::NodeVisitor*, osg::Drawable* drawable)
{
if (dynamic_cast<osgText::Text*>(drawable))
{
osgText::Text *text = dynamic_cast<osgText::Text*>(drawable);
text->setColor(osg::Vec4(1.0f*float(cos(cnt1)),1.0f*float(sin(cnt2)),1.0f-0.5f*float(cos(cnt1+cnt2)), 1));
std::stringstream os;
std::string str;
os.precision(2);
os << std::fixed << "Active OpenGL Text With NeHe - " << cnt1;
str = os.str();
text->setText(str);
text->setPosition(osg::Vec3(-4.5f+0.5f*float(cos(cnt1)), 1.92f*float(sin(cnt2)),0));
cnt1+=0.051f;
cnt2+=0.005f;
}
}
};在每帧中修改字体的颜色和位置，与NeHe教程中的模式一样
最后编译运行程序：
附：本课源码(源码中可能存在不足和错误，仅供参考)
#include "../osgNeHe.h"
#include <QtCore/QTimer>
#include <QtGui/QApplication>
#include <QtGui/QVBoxLayout>
#include <osgViewer/Viewer>
#include <osgDB/ReadFile>
#include <osgQt/GraphicsWindowQt>
#include <osg/MatrixTransform>
#include <osgDB/ReadFile>
#include <osgText/Text>
#include <iostream>
#include <sstream>
float cnt1, cnt2;
class FontColorCallback : public osg::Drawable::UpdateCallback
{
public:
virtual void update(osg::NodeVisitor*, osg::Drawable* drawable)
{
if (dynamic_cast<osgText::Text*>(drawable))
{
osgText::Text *text = dynamic_cast<osgText::Text*>(drawable);
text->setColor(osg::Vec4(1.0f*float(cos(cnt1)),1.0f*float(sin(cnt2)),1.0f-0.5f*float(cos(cnt1+cnt2)), 1));
std::stringstream os;
std::string str;
os.precision(2);
os << std::fixed << "Active OpenGL Text With NeHe - " << cnt1;
str = os.str();
text->setText(str);
text->setPosition(osg::Vec3(-4.5f+0.5f*float(cos(cnt1)), 1.92f*float(sin(cnt2)),0));
cnt1+=0.051f;
cnt2+=0.005f;
}
}
};
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, 1), osg::Vec3d(0, 0, 0), osg::Vec3d(0, 1, 0));
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;
osg::MatrixTransform *moveMT = new osg::MatrixTransform;
moveMT->setMatrix(osg::Matrix::translate(0, 0, -10));
root->addChild(moveMT);
osg::Geode *fontGeode = new osg::Geode;
osgText::Text *text = new osgText::Text;
text->setCharacterSize(0.4f);
text->setUpdateCallback(new FontColorCallback);
text->setText("OpenGL NeHe");
text->setFont("fonts/arial.ttf");
fontGeode->addDrawable(text);
moveMT->addChild(fontGeode);
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();
}