用OpenSceneGraph实现的NeHe OpenGL教程 - 第四十一课

• 简介

这节课也是在场景中添加雾效的效果，与之类似的是第十六课，所不同的是这节课使用了雾坐标来计算雾效。为了能运行这一课，你的显卡必须支持GL_EXT_fot_coord扩展。

• 实现

这节课的实现过程比较简单，在OSG中为几何体的顶点封装好了顶点的各项属性，包括顶点坐标、顶点纹理坐标、顶点颜色，当然也包括本课中的雾坐标。

首先我们还是添加顶点的各项数据：

	osg::Geode *geode = new osg::Geode;
	osg::Geometry *geometry = new osg::Geometry;
	osg::Vec3Array *vertexArray = new osg::Vec3Array;
	osg::FloatArray *fogArray = new osg::FloatArray;
	osg::Vec2Array *textureArray = new osg::Vec2Array;
        vertexArray->push_back(osg::Vec3(-2.5f,-2.5f,-15.0f));
        vertexArray->push_back(osg::Vec3(2.5f,-2.5f,-15.0f));
        vertexArray->push_back(osg::Vec3(2.5f,2.5f,-15.0f));
        vertexArray->push_back(osg::Vec3(-2.5f,2.5f,-15.0f));
        textureArray->push_back(osg::Vec2(0.0f, 0.0f));
        textureArray->push_back(osg::Vec2(1.0f, 0.0f));
        textureArray->push_back(osg::Vec2(1.0f, 1.0f));
        textureArray->push_back(osg::Vec2(0.0f, 1.0f));
        fogArray->push_back(1.0f);
        fogArray->push_back(1.0f);
        fogArray->push_back(1.0f);
        fogArray->push_back(1.0f);
        ......

接着读取纹理：

	osg::Texture2D *texture2D = new osg::Texture2D;
	texture2D->setFilter(osg::Texture::MAG_FILTER, osg::Texture::LINEAR);
	texture2D->setFilter(osg::Texture::MIN_FILTER, osg::Texture::LINEAR);
	texture2D->setImage(osgDB::readImageFile("Data/Wall.bmp"));
	geometry->getOrCreateStateSet()->setTextureAttributeAndModes(0, texture2D);

启用雾效特效：

	osg::Fog *fog = new osg::Fog;
	fog->setMode(osg::Fog::LINEAR);
	fog->setColor(osg::Vec4(fogColor[0], fogColor[1],fogColor[2],fogColor[3]));
	fog->setStart(0.0f);
	fog->setEnd(1.0f);
	fog->setFogCoordinateSource(osg::Fog::FOG_COORDINATE);

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 <osg/Texture2D>
#include <osg/Fog>


GLfloat	fogColor[4] = {0.6f, 0.3f, 0.0f, 1.0f};

osg::MatrixTransform *g_Trans = NULL;

class ManipulatorSceneHandler : public osgGA::GUIEventHandler
{
public:
	ManipulatorSceneHandler()
	{
	}

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;

		switch (ea.getEventType())
		{
		case(osgGA::GUIEventAdapter::KEYDOWN):
			{
				if (ea.getKey() == osgGA::GUIEventAdapter::KEY_Up)
				{
					if (!g_Trans)
						return false;

					osg::Vec3 trans = g_Trans->getMatrix().getTrans();
					if(trans.z() < 14.0f)
						trans += osg::Vec3(0,0,1);

					g_Trans->setMatrix(osg::Matrix::translate(trans));
				}

				if (ea.getKey() == osgGA::GUIEventAdapter::KEY_Down)
				{
					if (!g_Trans)
						return false;

					osg::Vec3 trans = g_Trans->getMatrix().getTrans();
					if(trans.z() >-19.0f)
						trans -= osg::Vec3(0,0,1);

					g_Trans->setMatrix(osg::Matrix::translate(trans));
				}
			}
			break;

		default: break;
		}
		return false;
		}
};





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, 0.5) );
		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, 0), osg::Vec3d(0, 0, -1), osg::Vec3d(0, 1, 0));

		this->setSceneData( scene );
		this->addEventHandler(new ManipulatorSceneHandler);
		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 *zoomMT = new osg::MatrixTransform;
	zoomMT->setMatrix(osg::Matrix::translate(0,0,-19.0));
	g_Trans = zoomMT;

	osg::Geode *geode = new osg::Geode;
	osg::Geometry *geometry = new osg::Geometry;
	osg::Vec3Array *vertexArray = new osg::Vec3Array;
	osg::FloatArray *fogArray = new osg::FloatArray;
	osg::Vec2Array *textureArray = new osg::Vec2Array;

	vertexArray->push_back(osg::Vec3(-2.5f,-2.5f,-15.0f));
	vertexArray->push_back(osg::Vec3(2.5f,-2.5f,-15.0f));
	vertexArray->push_back(osg::Vec3(2.5f,2.5f,-15.0f));
	vertexArray->push_back(osg::Vec3(-2.5f,2.5f,-15.0f));
	textureArray->push_back(osg::Vec2(0.0f, 0.0f));
	textureArray->push_back(osg::Vec2(1.0f, 0.0f));
	textureArray->push_back(osg::Vec2(1.0f, 1.0f));
	textureArray->push_back(osg::Vec2(0.0f, 1.0f));
	fogArray->push_back(1.0f);
	fogArray->push_back(1.0f);
	fogArray->push_back(1.0f);
	fogArray->push_back(1.0f);

	vertexArray->push_back(osg::Vec3(-2.5f,-2.5f,-15.0f));
	vertexArray->push_back(osg::Vec3(2.5f,-2.5f,-15.0f));
	vertexArray->push_back(osg::Vec3(2.5f,-2.5f,15.0f));
	vertexArray->push_back(osg::Vec3(-2.5f,-2.5f,15.0f));
	textureArray->push_back(osg::Vec2(0.0f, 0.0f));
	textureArray->push_back(osg::Vec2(1.0f, 0.0f));
	textureArray->push_back(osg::Vec2(1.0f, 1.0f));
	textureArray->push_back(osg::Vec2(0.0f, 1.0f));
	fogArray->push_back(1.0f);
	fogArray->push_back(1.0f);
	fogArray->push_back(0.0f);
	fogArray->push_back(0.0f);

	vertexArray->push_back(osg::Vec3(-2.5f,2.5f,-15.0f));
	vertexArray->push_back(osg::Vec3(2.5f,2.5f,-15.0f));
	vertexArray->push_back(osg::Vec3(2.5f,2.5f,15.0f));
	vertexArray->push_back(osg::Vec3(-2.5f,2.5f,15.0f));
	textureArray->push_back(osg::Vec2(0.0f, 0.0f));
	textureArray->push_back(osg::Vec2(1.0f, 0.0f));
	textureArray->push_back(osg::Vec2(1.0f, 1.0f));
	textureArray->push_back(osg::Vec2(0.0f, 1.0f));
	fogArray->push_back(1.0f);
	fogArray->push_back(1.0f);
	fogArray->push_back(0.0f);
	fogArray->push_back(0.0f);

	vertexArray->push_back(osg::Vec3(2.5f,-2.5f,15.0f));
	vertexArray->push_back(osg::Vec3(2.5f,2.5f,15.0f));
	vertexArray->push_back(osg::Vec3(2.5f,2.5f,-15.0f));
	vertexArray->push_back(osg::Vec3(2.5f,-2.5f,-15.0f));
	textureArray->push_back(osg::Vec2(0.0f, 0.0f));
	textureArray->push_back(osg::Vec2(0.0f, 1.0f));
	textureArray->push_back(osg::Vec2(1.0f, 1.0f));
	textureArray->push_back(osg::Vec2(1.0f, 0.0f));
	fogArray->push_back(0.0f);
	fogArray->push_back(0.0f);
	fogArray->push_back(1.0f);
	fogArray->push_back(1.0f);

	vertexArray->push_back(osg::Vec3(-2.5f,-2.5f,15.0f));
	vertexArray->push_back(osg::Vec3(-2.5f,2.5f,15.0f));
	vertexArray->push_back(osg::Vec3(-2.5f,2.5f,-15.0f));
	vertexArray->push_back(osg::Vec3(-2.5f,-2.5f,-15.0f));
	textureArray->push_back(osg::Vec2(0.0f, 0.0f));
	textureArray->push_back(osg::Vec2(0.0f, 1.0f));
	textureArray->push_back(osg::Vec2(1.0f, 1.0f));
	textureArray->push_back(osg::Vec2(1.0f, 0.0f));
	fogArray->push_back(0.0f);
	fogArray->push_back(0.0f);
	fogArray->push_back(1.0f);
	fogArray->push_back(1.0f);

	geometry->setVertexArray(vertexArray);
	geometry->setTexCoordArray(0, textureArray);
	geometry->setFogCoordArray(fogArray, osg::Array::BIND_PER_VERTEX);
	geometry->getOrCreateStateSet()->setMode(GL_LIGHTING, osg::StateAttribute::OFF);
	
	osg::Texture2D *texture2D = new osg::Texture2D;
	texture2D->setFilter(osg::Texture::MAG_FILTER, osg::Texture::LINEAR);
	texture2D->setFilter(osg::Texture::MIN_FILTER, osg::Texture::LINEAR);
	texture2D->setImage(osgDB::readImageFile("Data/Wall.bmp"));
	geometry->getOrCreateStateSet()->setTextureAttributeAndModes(0, texture2D);

	osg::Fog *fog = new osg::Fog;
	fog->setMode(osg::Fog::LINEAR);
	fog->setColor(osg::Vec4(fogColor[0], fogColor[1],fogColor[2],fogColor[3]));
	fog->setStart(0.0f);
	fog->setEnd(1.0f);
	fog->setFogCoordinateSource(osg::Fog::FOG_COORDINATE);
	
	geometry->getOrCreateStateSet()->setAttributeAndModes(fog);

	geometry->addPrimitiveSet(new osg::DrawArrays(osg::PrimitiveSet::QUADS, 0, vertexArray->size()));
	geode->addDrawable(geometry);

	zoomMT->addChild(geode);
	root->addChild(zoomMT);

	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();
}