用OpenSceneGraph实现的NeHe OpenGL教程 - 第八课
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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)
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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
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
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
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)
#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();
}