用OpenSceneGraph实现的NeHe OpenGL教程 - 第六课

• 简介

本节课要实现的内容是为立方体的六个面添加纹理

纹理映射(Texture Mapping)是OpenGL程序开发中的一个重要概念。纹理是一个数组的概念，其中每一个数据(RGB颜色以及Alpha值，或者其他系统及用户定义的类型)称为一个纹素(texel)。在描绘具有真实感物体时，使用一幅真实拍摄的照片作为纹理贴到几何体的表面，可以大大丰富物体的表现效果。

OSG使用派生自StateAttribute的Texture类来定义一个纹理对象，其6个子类对象(Texture1D Texture2D等)分别表示一维纹理、二维纹理等

• 实现

首先我们先要将纹理坐标加入到几何体Geometry的纹理数组之中

float textureVertices[][2] = {
	//Front Face
	{0.0f, 0.0f},
	{1.0f, 0.0f},
	{1.0f, 1.0f},
	{0.0f, 1.0f},
	// Back Face
	{1.0f, 0.0f},
	{1.0f, 1.0f},
	{0.0f, 1.0f},
	{0.0f, 0.0f},
	// Top Face
	{0.0f, 1.0f},
	{0.0f, 0.0f},
	{1.0f, 0.0f},
	{1.0f, 1.0f},
	// Bottom Face
	{1.0f, 1.0f},
	{0.0f, 1.0f},
	{0.0f, 0.0f},
	{1.0f, 0.0f},
	// Right face
	{1.0f, 0.0f},
	{1.0f, 1.0f},
	{0.0f, 1.0f},
	{0.0f, 0.0f},
	// Left Face
	{0.0f, 0.0f},
	{1.0f, 0.0f},
	{1.0f, 1.0f},
	{0.0f, 1.0f}
};

	osg::Vec2Array* texcoords = new osg::Vec2Array;
	for (unsigned i = 0; i < sizeof(textureVertices); ++i)
	{
		texcoords->push_back(osg::Vec2(textureVertices[i][0], textureVertices[i][1]));
	}
	quadGeometry->setTexCoordArray(0,texcoords);

接着我们声明一个二维纹理对象Texture2D，并按NeHe第六课的要求对二维纹理作一些设置

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

在NeHe第六课中用到了auxDIBImageLoad函数来读取一个bmp类型的图片，在OSG中我们不需要这么做，OSG实现了强大的文件读写机制，通过插件的方式提供了各种模型，图片和其他类型文件的解析和转换支持，并可以很方便地进行扩展。OSG目前支持的图片格式包括bmp、dds、jpg、jpg2、rgb、svg、tga、tiff等等，在这里我们直接使用osgDB库中的readImageFile来加载bmp图片作为纹理使用

最后将纹理设置给节点

quadGeode->getOrCreateStateSet()->setTextureAttributeAndModes(0, texture2D);

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/NodeVisitor>
#include <osg/AnimationPath>

#include <osg/Texture2D>

float textureVertices[][2] = {
	//Front Face
	{0.0f, 0.0f},
	{1.0f, 0.0f},
	{1.0f, 1.0f},
	{0.0f, 1.0f},
	// Back Face
	{1.0f, 0.0f},
	{1.0f, 1.0f},
	{0.0f, 1.0f},
	{0.0f, 0.0f},
	// Top Face
	{0.0f, 1.0f},
	{0.0f, 0.0f},
	{1.0f, 0.0f},
	{1.0f, 1.0f},
	// Bottom Face
	{1.0f, 1.0f},
	{0.0f, 1.0f},
	{0.0f, 0.0f},
	{1.0f, 0.0f},
	// Right face
	{1.0f, 0.0f},
	{1.0f, 1.0f},
	{0.0f, 1.0f},
	{0.0f, 0.0f},
	// Left Face
	{0.0f, 0.0f},
	{1.0f, 0.0f},
	{1.0f, 1.0f},
	{0.0f, 1.0f}
};

float QuadVertices[][3] = {

	{-1.0f, -1.0f,  1.0f},
	{ 1.0f, -1.0f,  1.0f},
	{ 1.0f,  1.0f,  1.0f},
	{-1.0f,  1.0f,  1.0f},

	{-1.0f, -1.0f, -1.0f},
	{-1.0f,  1.0f, -1.0f},
	{ 1.0f,  1.0f, -1.0f},
	{ 1.0f, -1.0f, -1.0f},

	{-1.0f,  1.0f, -1.0f},
	{-1.0f,  1.0f,  1.0f},
	{ 1.0f,  1.0f,  1.0f},
	{ 1.0f,  1.0f, -1.0f},

	{-1.0f, -1.0f, -1.0f},
	{ 1.0f, -1.0f, -1.0f},
	{ 1.0f, -1.0f,  1.0f},
	{-1.0f, -1.0f,  1.0f},

	{ 1.0f, -1.0f, -1.0f},
	{ 1.0f,  1.0f, -1.0f},
	{ 1.0f,  1.0f,  1.0f},
	{ 1.0f, -1.0f,  1.0f},

	{-1.0f, -1.0f, -1.0f},
	{-1.0f, -1.0f,  1.0f},
	{-1.0f,  1.0f,  1.0f},
	{-1.0f,  1.0f, -1.0f}

};


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 *quadMT = new osg::MatrixTransform;
	quadMT->setMatrix(osg::Matrix::translate(0.0, 0.0, -5.0));

	osg::AnimationPathCallback *quadAnimationCallback = 
		new osg::AnimationPathCallback(osg::Vec3d(0, 0, 0), osg::Vec3(1, 1, 1), 2.5);
	osg::MatrixTransform *quadRotMT = new osg::MatrixTransform;
	quadRotMT->setUpdateCallback(quadAnimationCallback);

	osg::Geometry *quadGeometry = new osg::Geometry;
	osg::Vec3Array *quadVertexArray = new osg::Vec3Array;
	for (unsigned i = 0; i < sizeof(QuadVertices); ++i)
	{
		quadVertexArray->push_back(osg::Vec3(QuadVertices[i][0], QuadVertices[i][1], QuadVertices[i][2]));
	}
	quadGeometry->setVertexArray(quadVertexArray);

	osg::Vec2Array* texcoords = new osg::Vec2Array;
	for (unsigned i = 0; i < sizeof(textureVertices); ++i)
	{
		texcoords->push_back(osg::Vec2(textureVertices[i][0], textureVertices[i][1]));
	}
	quadGeometry->setTexCoordArray(0,texcoords);

	int first = 0;
	for (unsigned i = 0; i < 6; ++i)
	{
		osg::DrawArrays *vertexIndices = new osg::DrawArrays(osg::PrimitiveSet::QUADS, first, 4);
		first += 4;
		quadGeometry->addPrimitiveSet(vertexIndices);
	}

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

	osg::Geode *quadGeode = new osg::Geode;
	quadGeode->getOrCreateStateSet()->setTextureAttributeAndModes(0, texture2D);
	quadGeode->getOrCreateStateSet()->setMode(GL_LIGHTING, osg::StateAttribute::OFF);
	quadGeode->addDrawable(quadGeometry);
	quadRotMT->addChild(quadGeode);
	quadMT->addChild(quadRotMT);

	root->addChild(quadMT);

	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();
}