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();}