用OpenSceneGraph实现的NeHe OpenGL教程 - 第十五课

• 简介

NeHe这节课主要讨论OpenGL怎样给文字赋予纹理贴图。OpenGL使用glTexGen函数给文字自动生成纹理坐标。在OSG中，使用osg::TexGen这个继承自StateAttribute的类来实现相同的效果

• 实现

首先将创建3D的字体，代码如下：

    osg::Geode *fontGeode = new osg::Geode;

    osg::Image *textureImage = osgDB::readImageFile("Data/Lights.bmp");
    osg::Texture2D *texture2D = new osg::Texture2D;
    texture2D->setImage(textureImage);
    texture2D->setFilter(osg::Texture::MIN_FILTER, osg::Texture::NEAREST);
    texture2D->setFilter(osg::Texture::MAG_FILTER, osg::Texture::NEAREST);

    osg::TexGen *texGen = new osg::TexGen;
    texGen->setMode(osg::TexGen::OBJECT_LINEAR);

    osgText::Text3D *text = new osgText::Text3D;
    text->setCharacterSize(3.0f);
    text->setCharacterDepth(0.5f);
    text->setText("N");
    text->setFont("fonts/Wingding.ttf");
    text->getOrCreateStateSet()->setTextureAttributeAndModes(0, texture2D);
    fontGeode->getOrCreateStateSet()->setTextureAttributeAndModes(0, texGen);
    fontGeode->addDrawable(text);

设置字体为系统中的Wingding.tff字体，就可以实现骷髅头的效果。

可以看到我们按照NeHe教程中的实现方式，将texGen状态属性添加到字体Drawable之中，实现了纹理的自动计算

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 <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 <osgText/Text3D>

#include <osg/AnimationPath>

#include <iostream>
#include <sstream>

#include <osg/TexGen>

float rot = 0.0;

class FontColorCallback : public osg::Drawable::UpdateCallback
{
public:

	virtual void update(osg::NodeVisitor*, osg::Drawable* drawable)
	{
		if (dynamic_cast<osgText::Text3D*>(drawable))
		{
			osgText::Text3D *text = dynamic_cast<osgText::Text3D*>(drawable);
			text->setText("N");
			rot+=0.5f;
		}
	}
};



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::MatrixTransform *rotX = new osg::MatrixTransform;
	rotX->setUpdateCallback(new osg::AnimationPathCallback(osg::Vec3d(0, 0, 0), osg::X_AXIS, 0.5));
	osg::MatrixTransform *rotY = new osg::MatrixTransform;
	rotY->setUpdateCallback(new osg::AnimationPathCallback(osg::Vec3d(0, 0, 0), osg::Y_AXIS, 0.4));
	osg::MatrixTransform *rotZ = new osg::MatrixTransform;
	rotZ->setUpdateCallback(new osg::AnimationPathCallback(osg::Vec3d(0, 0, 0), osg::Z_AXIS, 0.3));

	moveMT->addChild(rotX);
	rotX->addChild(rotY);
	rotY->addChild(rotZ);

	osg::Geode *fontGeode = new osg::Geode;

	osg::Image *textureImage = osgDB::readImageFile("Data/Lights.bmp");
	osg::Texture2D *texture2D = new osg::Texture2D;
	texture2D->setImage(textureImage);
	texture2D->setFilter(osg::Texture::MIN_FILTER, osg::Texture::NEAREST);
	texture2D->setFilter(osg::Texture::MAG_FILTER, osg::Texture::NEAREST);

	osg::TexGen *texGen = new osg::TexGen;
	texGen->setMode(osg::TexGen::OBJECT_LINEAR);

	osgText::Text3D *text = new osgText::Text3D;
	text->setCharacterSize(3.0f);
	text->setCharacterDepth(0.5f);
	text->setText("N");
	text->setFont("fonts/Wingding.ttf");
	text->getOrCreateStateSet()->setTextureAttributeAndModes(0, texture2D);
	fontGeode->getOrCreateStateSet()->setTextureAttributeAndModes(0, texGen);
	fontGeode->addDrawable(text);

	rotZ->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();
}