OpenSceneGraph实现的NeHe OpenGL教程 - 第八课

简介

本课是在第七课的基础上实现将立方体变透明的效果，其中用到了OpenGL中的混合(Blend)

实现

在OpenGL中如何实现混合以及混合实现的原理和过程在NeHe教程中已经解释的很清楚了，在这里就不在赘述，本课主要探讨在OSG中实现混合的效果，混合同样是作为一种StateSet的方式来进行处理的，OSG中的混合主要涉及到一下几个类BlendFunc、BlendEquation和BlendColor，对应于OpenGL中的glBlendFunc 、glBlendEquation和glBlendColor三个函数，对混合的参数进行一些设置。本课中我们参考NeHe教程中设置混合的计算方式定义如下的BlendFunc

[cpp] view
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osg::BlendFunc *blendFunc = new osg::BlendFunc(GL_SRC_ALPHA, GL_ONE, 0.5, 0.5);

quadGeometry->getOrCreateStateSet()->setAttribute(blendFunc,

osg::StateAttribute::ON);

需要注意的是我们需要将初始的清除背景的颜色的alpha值设置为0.5

[cpp] view
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camera->setClearColor( osg::Vec4(0.0, 0.0, 0.0, 0.5) );

在按下键盘上B键的时候开启和关闭混合模式

[cpp] view
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if (ea.getKey()== osgGA::GUIEventAdapter::KEY_B)

{

static int i = 0;

if (i % 2 == 0) {

root->getOrCreateStateSet()->setMode(GL_BLEND, osg::StateAttribute::ON);

} else {

root->getOrCreateStateSet()->setMode(GL_BLEND, osg::StateAttribute::OFF);

}

++i;

}

其他的代码与第七课相同，编译运行程序后点击B键时可以看到透明的效果。

附：本课源码(源码中可能存在错误和不足，仅供参考)

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#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/Texture2D>

#include <osgGA/GUIEventAdapter>

#include <osg/Light>

#include <osg/LightModel>

#include <osg/LightSource>

#include <osg/BlendFunc>

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}

};

float normalVertics[][3] = {

// Front Face

{ 0.0f, 0.0f, 1.0f},

// Back Face

{ 0.0f, 0.0f,-1.0f},

// Top Face

{ 0.0f, 1.0f, 0.0f},

// Bottom Face

{ 0.0f,-1.0f, 0.0f},

// Right face

{ 1.0f, 0.0f, 0.0f},

// Left Face

{-1.0f, 0.0f, 0.0f}

};

//////////////////////////////////////////////////////////////////////////

//FindFirstNamedNodeVisitor用来遍历寻找与指定名称相同的节点

class FindFirstNamedNodeVisitor : public osg::NodeVisitor

{

public:

FindFirstNamedNodeVisitor(const std::string& name):

osg::NodeVisitor(osg::NodeVisitor::TRAVERSE_ALL_CHILDREN),

_name(name), _foundNode(NULL) {}

virtual void apply(osg::Node& node)

{

if (node.getName()==_name)

{

_foundNode = &node;

return;

}

traverse(node);

}

std::string _name;

osg::Node *_foundNode;

};

//////////////////////////////////////////////////////////////////////////

//RotateCallback

class RotateCallback : public osg::NodeCallback

{

public:

RotateCallback(osg::Vec3d rotateAxis, double rotateSpeed) :

osg::NodeCallback(),

_rotateAxis(rotateAxis),

_rotateSpeed(rotateSpeed),

_rotateAngle(0.0)

{

//Nop

}

void setRotateSpeed(double speed)

{

_rotateSpeed = speed;

}

double getRotateSpeed() const

{

return _rotateSpeed;

}

virtual void operator()(osg::Node* node, osg::NodeVisitor* nv)

{

osg::MatrixTransform *currentMT = dynamic_cast<osg::MatrixTransform*>(node);

if (currentMT)

{

//获取当前的平移位置

osg::Vec3d currentTranslate = currentMT->getMatrix().getTrans();

osg::Matrix newMatrix = osg::Matrix::rotate(_rotateAngle, _rotateAxis) * osg::Matrix::translate(currentTranslate);

currentMT->setMatrix(newMatrix);

_rotateAngle += _rotateSpeed;

}

traverse(node, nv);

}

private:

osg::Vec3d _rotateAxis; //旋转轴

double _rotateSpeed; //旋转速度

double _rotateAngle; //当前旋转的角度

};

//////////////////////////////////////////////////////////////////////////

class ManipulatorSceneHandler : public osgGA::GUIEventHandler

{

public:

ManipulatorSceneHandler()

{

}

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;

osg::Group *root = viewer->getSceneData()->asGroup();

switch(ea.getEventType())

{

case(osgGA::GUIEventAdapter::KEYDOWN):

{

if (ea.getKey() == osgGA::GUIEventAdapter::KEY_Left)

{

FindFirstNamedNodeVisitor fnv("yRotMT");

root->accept(fnv);

osg::Node *mtNode = fnv._foundNode;

osg::MatrixTransform *yRotMT = dynamic_cast<osg::MatrixTransform*>(mtNode);

if (!yRotMT)

return false;

RotateCallback *rotCallback = dynamic_cast<RotateCallback*>(yRotMT->getUpdateCallback());

if (!rotCallback)

return false;

double speed = rotCallback->getRotateSpeed();

speed += 0.02;

rotCallback->setRotateSpeed(speed);

}

if (ea.getKey() == osgGA::GUIEventAdapter::KEY_Right)

{

FindFirstNamedNodeVisitor fnv("yRotMT");

root->accept(fnv);

osg::Node *mtNode = fnv._foundNode;

osg::MatrixTransform *yRotMT = dynamic_cast<osg::MatrixTransform*>(mtNode);

if (!yRotMT)

return false;

RotateCallback *rotCallback = dynamic_cast<RotateCallback*>(yRotMT->getUpdateCallback());

if (!rotCallback)

return false;

double speed = rotCallback->getRotateSpeed();

speed -= 0.02;

rotCallback->setRotateSpeed(speed);

}

if (ea.getKey() == osgGA::GUIEventAdapter::KEY_Up)

{

FindFirstNamedNodeVisitor fnv("xRotMT");

root->accept(fnv);

osg::Node *mtNode = fnv._foundNode;

osg::MatrixTransform *xRotMT = dynamic_cast<osg::MatrixTransform*>(mtNode);

if (!xRotMT)

return false;

RotateCallback *rotCallback = dynamic_cast<RotateCallback*>(xRotMT->getUpdateCallback());

if (!rotCallback)

return false;

double speed = rotCallback->getRotateSpeed();

speed += 0.02;

rotCallback->setRotateSpeed(speed);

}

if (ea.getKey()== osgGA::GUIEventAdapter::KEY_Down)

{

FindFirstNamedNodeVisitor fnv("xRotMT");

root->accept(fnv);

osg::Node *mtNode = fnv._foundNode;

osg::MatrixTransform *xRotMT = dynamic_cast<osg::MatrixTransform*>(mtNode);

if (!xRotMT)

return false;

RotateCallback *rotCallback = dynamic_cast<RotateCallback*>(xRotMT->getUpdateCallback());

if (!rotCallback)

return false;

double speed = rotCallback->getRotateSpeed();

speed -= 0.02;

rotCallback->setRotateSpeed(speed);

}

if (ea.getKey()== osgGA::GUIEventAdapter::KEY_Page_Up)

{

FindFirstNamedNodeVisitor fnv("zoomMT");

root->accept(fnv);

osg::Node *mtNode = fnv._foundNode;

osg::MatrixTransform *zoomMT = dynamic_cast<osg::MatrixTransform*>(mtNode);

if (!zoomMT)

return false;

osg::Vec3 trans = zoomMT->getMatrix().getTrans();

trans.set(trans.x(), trans.y(), trans.z() + 0.2);

zoomMT->setMatrix(osg::Matrix::translate(trans));

}

if (ea.getKey()== osgGA::GUIEventAdapter::KEY_Page_Down)

{

FindFirstNamedNodeVisitor fnv("zoomMT");

root->accept(fnv);

osg::Node *mtNode = fnv._foundNode;

osg::MatrixTransform *zoomMT = dynamic_cast<osg::MatrixTransform*>(mtNode);

if (!zoomMT)

return false;

osg::Vec3 trans = zoomMT->getMatrix().getTrans();

trans.set(trans.x(), trans.y(), trans.z() - 0.2);

zoomMT->setMatrix(osg::Matrix::translate(trans));

}

if (ea.getKey()== osgGA::GUIEventAdapter::KEY_L)

{

static int i = 0;

if (i % 2 == 0) {

root->getOrCreateStateSet()->setMode(GL_LIGHTING, osg::StateAttribute::ON);

} else {

root->getOrCreateStateSet()->setMode(GL_LIGHTING, osg::StateAttribute::OFF);

}

++i;

}

if (ea.getKey()== osgGA::GUIEventAdapter::KEY_B)

{

static int i = 0;

if (i % 2 == 0) {

root->getOrCreateStateSet()->setMode(GL_BLEND, osg::StateAttribute::ON);

} else {

root->getOrCreateStateSet()->setMode(GL_BLEND, osg::StateAttribute::OFF);

}

++i;

}

if (ea.getKey()== osgGA::GUIEventAdapter::KEY_F)

{

FindFirstNamedNodeVisitor fnv("quadGeode");

root->accept(fnv);

osg::Node *mtNode = fnv._foundNode;

osg::Geode *quadGeode = dynamic_cast<osg::Geode*>(mtNode);

if (!quadGeode)

return false;

osg::Texture2D *texture2D = dynamic_cast<osg::Texture2D*>(quadGeode->getOrCreateStateSet()->getTextureAttribute(0, osg::StateAttribute::TEXTURE));

static int i = 0;

if (i % 3 == 0) {

texture2D->setFilter(osg::Texture::MIN_FILTER, osg::Texture::LINEAR);

texture2D->setFilter(osg::Texture::MAG_FILTER, osg::Texture::LINEAR);

} else if (i % 3 == 1) {

texture2D->setFilter(osg::Texture::MIN_FILTER, osg::Texture::LINEAR);

texture2D->setFilter(osg::Texture::MAG_FILTER, osg::Texture::LINEAR_MIPMAP_NEAREST);

} else {

texture2D->setFilter(osg::Texture::MIN_FILTER, osg::Texture::NEAREST);

texture2D->setFilter(osg::Texture::MAG_FILTER, osg::Texture::NEAREST);

}

++i;

}

}

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

osg::StateSet* globalStateset = camera->getStateSet();

if (globalStateset)

{

osg::LightModel* lightModel = new osg::LightModel;

lightModel->setAmbientIntensity(osg::Vec4(0,0,0,0));

globalStateset->setAttributeAndModes(lightModel, osg::StateAttribute::ON);

}

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::Light* light = new osg::Light();

light->setLightNum(0);

light->setAmbient(osg::Vec4(0.5f, 0.5f, 0.5f, 1.0f));

light->setDiffuse(osg::Vec4(1.0f, 1.0f, 1.0f, 1.0f));

light->setPosition(osg::Vec4(0.0f, 0.0f, 2.0f, 1.0f));

osg::LightSource* lightsource = new osg::LightSource();

lightsource->setLight (light);

root->addChild (lightsource);

osg::MatrixTransform *quadMT = new osg::MatrixTransform;

quadMT->setName("zoomMT");

quadMT->setMatrix(osg::Matrix::translate(0.0, 0.0, -5.0));

osg::MatrixTransform *quadXRotMT = new osg::MatrixTransform;

quadXRotMT->setName("xRotMT");

RotateCallback *xRotCallback = new RotateCallback(osg::X_AXIS, 0.0);

quadXRotMT->setUpdateCallback(xRotCallback);

osg::MatrixTransform *quadYRotMT = new osg::MatrixTransform;

quadYRotMT->setName("yRotMT");

RotateCallback *yRotCallback = new RotateCallback(osg::Y_AXIS, 0.0);

quadYRotMT->setUpdateCallback(yRotCallback);

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::Vec4Array *colorArray = new osg::Vec4Array;

colorArray->push_back(osg::Vec4(1.0f, 1.0f, 1.0f, 0.5));

quadGeometry->setColorArray(colorArray, osg::Array::BIND_OVERALL);

osg::BlendFunc *blendFunc = new osg::BlendFunc(GL_SRC_ALPHA, GL_ONE, 0.5, 0.5);

quadGeometry->getOrCreateStateSet()->setRenderingHint(

osg::StateSet::TRANSPARENT_BIN );

quadGeometry->getOrCreateStateSet()->setAttribute(blendFunc,

osg::StateAttribute::ON);

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);

osg::Vec3Array *quadNormalArray = new osg::Vec3Array;

for (unsigned i = 0; i < sizeof(normalVertics); ++i)

{

quadNormalArray->push_back(osg::Vec3(normalVertics[i][0], normalVertics[i][1], normalVertics[i][2]));

}

quadGeometry->setNormalArray(quadNormalArray, osg::Array::BIND_PER_PRIMITIVE_SET);

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/Glass.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::Geode *quadGeode = new osg::Geode;

quadGeode->setName("quadGeode");

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

quadGeode->addDrawable(quadGeometry);

quadYRotMT->addChild(quadGeode);

quadXRotMT->addChild(quadYRotMT);

quadMT->addChild(quadXRotMT);

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();

}