OpenSceneGraph实现的NeHe OpenGL教程 - 第三十六课

简介

这节课NeHe课程向我们介绍了如何读取帧缓存中的像素值，并把 它作为场景中的纹理加载到几何体上。也就是我们常说的渲染到纹理(Render To Texture)功能，也称纹理烘培。这一功能主要有两个作用：第一是实现场景离屏渲染之后的后置处理；第二是实现多种不同场景的融合显示效果。

实现

首先创建我们场景中需要显示的Helix模型，代码如下：

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osg::Geode* createHelix()

接下来我们需要将这个模型加载的场景写到纹理中去，在OSG中可以通过创建渲染到纹理的相机完成这样的操作：

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osg::Camera* createRenderToTextureCamera(int w, int h)

{

osg::Camera *rtt = new osg::Camera;

rtt->setClearColor(osg::Vec4(0.0f, 0.0f, 0.5f, 0.5));

rtt->setClearMask(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

rtt->setReferenceFrame(osg::Transform::ABSOLUTE_RF);

rtt->setViewport(0, 0, w, h);

rtt->setRenderOrder(osg::Camera::PRE_RENDER);

rtt->setRenderTargetImplementation(osg::Camera::FRAME_BUFFER_OBJECT);

rtt->setProjectionMatrixAsPerspective(45.0f, static_cast<double>(640)/static_cast<double>(480), 0.1f, 100.0f );

rtt->setViewMatrixAsLookAt(osg::Vec3d(0, 5, 50), osg::Vec3d(0, 0, 0), osg::Vec3d(0, 1, 0));

osg::MatrixTransform *zoomMT = new osg::MatrixTransform;

zoomMT->setMatrix(osg::Matrix::translate(0,0,-50));

osg::MatrixTransform *xRotMT = new osg::MatrixTransform;

xRotMT->addUpdateCallback(new RotAxisCallback(osg::X_AXIS, 0.02));

osg::MatrixTransform *yRotMT = new osg::MatrixTransform;

yRotMT->addUpdateCallback(new RotAxisCallback(osg::Y_AXIS, 0.01));

zoomMT->addChild(xRotMT);

xRotMT->addChild(yRotMT);

yRotMT->addChild(createHelix());

rtt->addChild(zoomMT);

return rtt;

}

通过设置相机渲染方式是PRE_RENDER可以保证在渲染其他场景之前先渲染这个相机中的场景，并通过下面的操作将其保存到纹理之中：

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g_Texture = createTexture(128,128);

osg::Camera *rttCamera = createRenderToTextureCamera(128, 128);

rttCamera->attach(osg::Camera::COLOR_BUFFER, g_Texture);

这样我们需要的纹理就创建好了。

接下来加载使用纹理的几何体：

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osg::Node* createBlur(int times, float inc)

同时在几何体的更新中不断修改纹理坐标的位置，实现微小的偏移，整个场景看起来像一种运动模糊的效果：

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class BlurGeometryUpdateCallback : public osg::Drawable::UpdateCallback

最后把所有这些部分添加到场景根节点中，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)

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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/AnimationPath>

#include <osg/Material>

#include <osg/LightSource>

#include <osg/BlendFunc>

#include <osg/Texture2D>

#include <osg/State>

float angle;

float vertexes[4][3];

float normal[3];

osg::Texture2D *g_Texture;

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

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

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

void ReduceToUnit(float vector[3]) // Reduces A Normal Vector (3 Coordinates)

{ // To A Unit Normal Vector With A Length Of One.

float length; // Holds Unit Length

// Calculates The Length Of The Vector

length = (float)sqrt((vector[0]*vector[0]) + (vector[1]*vector[1]) + (vector[2]*vector[2]));

if(length == 0.0f) // Prevents Divide By 0 Error By Providing

length = 1.0f; // An Acceptable Value For Vectors To Close To 0.

vector[0] /= length; // Dividing Each Element By

vector[1] /= length; // The Length Results In A

vector[2] /= length; // Unit Normal Vector.

}

void calcNormal(float v[3][3], float out[3]) // Calculates Normal For A Quad Using 3 Points

{

float v1[3],v2[3]; // Vector 1 (x,y,z) & Vector 2 (x,y,z)

static const int x = 0; // Define X Coord

static const int y = 1; // Define Y Coord

static const int z = 2; // Define Z Coord

// Finds The Vector Between 2 Points By Subtracting

// The x,y,z Coordinates From One Point To Another.

// Calculate The Vector From Point 1 To Point 0

v1[x] = v[0][x] - v[1][x]; // Vector 1.x=Vertex[0].x-Vertex[1].x

v1[y] = v[0][y] - v[1][y]; // Vector 1.y=Vertex[0].y-Vertex[1].y

v1[z] = v[0][z] - v[1][z]; // Vector 1.z=Vertex[0].y-Vertex[1].z

// Calculate The Vector From Point 2 To Point 1

v2[x] = v[1][x] - v[2][x]; // Vector 2.x=Vertex[0].x-Vertex[1].x

v2[y] = v[1][y] - v[2][y]; // Vector 2.y=Vertex[0].y-Vertex[1].y

v2[z] = v[1][z] - v[2][z]; // Vector 2.z=Vertex[0].z-Vertex[1].z

// Compute The Cross Product To Give Us A Surface Normal

out[x] = v1[y]*v2[z] - v1[z]*v2[y]; // Cross Product For Y - Z

out[y] = v1[z]*v2[x] - v1[x]*v2[z]; // Cross Product For X - Z

out[z] = v1[x]*v2[y] - v1[y]*v2[x]; // Cross Product For X - Y

ReduceToUnit(out); // Normalize The Vectors

}

class RotAxisCallback : public osg::NodeCallback

{

public:

RotAxisCallback(const osg::Vec3& axis, double rotSpeed = 0.0, double currentAngle = 0.0)

: _rotAxis(axis), _rotSpeed(rotSpeed), _currentAngle(currentAngle){ }

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

{

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

if (!rotMT)

return;

_currentAngle += _rotSpeed;

rotMT->setMatrix(osg::Matrix::rotate(_currentAngle, _rotAxis));

traverse(node, nv);

}

void setRotateSpeed(double speed)

{

_rotSpeed = speed;

}

double getRotateSpeed() const

{

return _rotSpeed;

}

double getCurrentAngle() const

{

return _currentAngle;

}

private:

osg::Vec3 _rotAxis;

double _currentAngle;

double _rotSpeed;

};

osg::Geode* createHelix()

{

GLfloat x; // Helix x Coordinate

GLfloat y; // Helix y Coordinate

GLfloat z; // Helix z Coordinate

GLfloat phi; // Angle

GLfloat theta; // Angle

GLfloat v,u; // Angles

GLfloat r = 1.5f; // Radius Of Twist

int twists = 5; // 5 Twists

osg::Geode *geode = new osg::Geode;

osg::Geometry *geometry = new osg::Geometry;

osg::Vec3Array *vertexArray = new osg::Vec3Array;

osg::Vec3Array *normalArray = new osg::Vec3Array;

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

for(int phi=0; phi <= 360; phi+=20.0) // 360 Degrees In Steps Of 20

{

for(int theta=0; theta<=360*twists; theta+=20.0) // 360 Degrees * Number Of Twists In Steps Of 20

{

v=(phi/180.0f*3.142f); // Calculate Angle Of First Point ( 0 )

u=(theta/180.0f*3.142f); // Calculate Angle Of First Point ( 0 )

x=float(cos(u)*(2.0f+cos(v) ))*r; // Calculate x Position (1st Point)

y=float(sin(u)*(2.0f+cos(v) ))*r; // Calculate y Position (1st Point)

z=float((( u-(2.0f*3.142f)) + sin(v) ) * r); // Calculate z Position (1st Point)

vertexes[0][0]=x; // Set x Value Of First Vertex

vertexes[0][1]=y; // Set y Value Of First Vertex

vertexes[0][2]=z; // Set z Value Of First Vertex

v=(phi/180.0f*3.142f); // Calculate Angle Of Second Point ( 0 )

u=((theta+20)/180.0f*3.142f); // Calculate Angle Of Second Point ( 20 )

x=float(cos(u)*(2.0f+cos(v) ))*r; // Calculate x Position (2nd Point)

y=float(sin(u)*(2.0f+cos(v) ))*r; // Calculate y Position (2nd Point)

z=float((( u-(2.0f*3.142f)) + sin(v) ) * r); // Calculate z Position (2nd Point)

vertexes[1][0]=x; // Set x Value Of Second Vertex

vertexes[1][1]=y; // Set y Value Of Second Vertex

vertexes[1][2]=z; // Set z Value Of Second Vertex

v=((phi+20)/180.0f*3.142f); // Calculate Angle Of Third Point ( 20 )

u=((theta+20)/180.0f*3.142f); // Calculate Angle Of Third Point ( 20 )

x=float(cos(u)*(2.0f+cos(v) ))*r; // Calculate x Position (3rd Point)

y=float(sin(u)*(2.0f+cos(v) ))*r; // Calculate y Position (3rd Point)

z=float((( u-(2.0f*3.142f)) + sin(v) ) * r); // Calculate z Position (3rd Point)

vertexes[2][0]=x; // Set x Value Of Third Vertex

vertexes[2][1]=y; // Set y Value Of Third Vertex

vertexes[2][2]=z; // Set z Value Of Third Vertex

v=((phi+20)/180.0f*3.142f); // Calculate Angle Of Fourth Point ( 20 )

u=((theta)/180.0f*3.142f); // Calculate Angle Of Fourth Point ( 0 )

x=float(cos(u)*(2.0f+cos(v) ))*r; // Calculate x Position (4th Point)

y=float(sin(u)*(2.0f+cos(v) ))*r; // Calculate y Position (4th Point)

z=float((( u-(2.0f*3.142f)) + sin(v) ) * r); // Calculate z Position (4th Point)

vertexes[3][0]=x; // Set x Value Of Fourth Vertex

vertexes[3][1]=y; // Set y Value Of Fourth Vertex

vertexes[3][2]=z; // Set z Value Of Fourth Vertex

calcNormal(vertexes,normal); // Calculate The Quad Normal

normalArray->push_back(osg::Vec3(normal[0],normal[1],normal[2]));

normalArray->push_back(osg::Vec3(normal[0],normal[1],normal[2]));

normalArray->push_back(osg::Vec3(normal[0],normal[1],normal[2]));

normalArray->push_back(osg::Vec3(normal[0],normal[1],normal[2]));

// Render The Quad

vertexArray->push_back(osg::Vec3(vertexes[0][0],vertexes[0][1],vertexes[0][2]));

vertexArray->push_back(osg::Vec3(vertexes[1][0],vertexes[1][1],vertexes[1][2]));

vertexArray->push_back(osg::Vec3(vertexes[2][0],vertexes[2][1],vertexes[2][2]));

vertexArray->push_back(osg::Vec3(vertexes[3][0],vertexes[3][1],vertexes[3][2]));

}

}

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

geometry->setVertexArray(vertexArray);

geometry->setNormalArray(normalArray, osg::Array::BIND_PER_VERTEX);

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

osg::Material *helixMat = new osg::Material;

helixMat->setAmbient(osg::Material::FRONT_AND_BACK, osg::Vec4(0.4f,0.2f,0.8f,1.0f));

helixMat->setDiffuse(osg::Material::FRONT_AND_BACK, osg::Vec4(0.4f,0.2f,0.8f,1.0f));

helixMat->setSpecular(osg::Material::FRONT_AND_BACK, osg::Vec4(1.0f,1.0f,1.0f,1.0f));

helixMat->setShininess(osg::Material::FRONT, 128.0f);

geometry->getOrCreateStateSet()->setAttributeAndModes(helixMat);

geometry->getOrCreateStateSet()->setMode(GL_LIGHT0, osg::StateAttribute::ON);

geode->addDrawable(geometry);

return geode;

}

class ViewerWidget : public QWidget, public osgViewer::Viewer

{

public:

ViewerWidget(osg::Node *scene = NULL)

{

QWidget* renderWidget = getRenderWidget( createGraphicsWindow(0,0,640,480), 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, 5, 50), 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;

};

class BlurGeometryUpdateCallback : public osg::Drawable::UpdateCallback

{

public:

BlurGeometryUpdateCallback(int renderTimes, float inc) : _times(renderTimes), _inc(inc){ }

void update(osg::NodeVisitor*, osg::Drawable* d)

{

osg::Geometry *geometry = dynamic_cast<osg::Geometry*>(d);

if (!geometry)

return;

osg::Vec2Array *texArray = dynamic_cast<osg::Vec2Array*>(geometry->getTexCoordArray(0));

if(!texArray)

return;

osg::Vec4Array *colorArray = dynamic_cast<osg::Vec4Array*>(geometry->getColorArray());

if(!colorArray)

return;

float spost = 0.0f;

float alphainc = 0.9f / _times;

float alpha = 0.2f;

alphainc = alpha / _times;

texArray->clear();

colorArray->clear();

for (int num = 0;num < _times;num++)

{

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

texArray->push_back(osg::Vec2(0+spost,1-spost));

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

texArray->push_back(osg::Vec2(0+spost,0+spost));

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

texArray->push_back(osg::Vec2(1-spost,0+spost));

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

texArray->push_back(osg::Vec2(1-spost,1-spost));

spost += _inc;

alpha = alpha - alphainc;

}

texArray->dirty();

colorArray->dirty();

}

int _times;

float _inc;

};

osg::Node* createBlur(int times, float inc)

{

float spost = 0.0f;

float alphainc = 0.9f / times;

float alpha = 0.2f;

alphainc = alpha / times;

osg::BlendFunc *blendFunc = new osg::BlendFunc(osg::BlendFunc::SRC_ALPHA, osg::BlendFunc::ONE);

osg::Geode *geode = new osg::Geode;

osg::Geometry *geometry = new osg::Geometry;

geometry->setUpdateCallback(new BlurGeometryUpdateCallback(times, inc));

osg::Vec2Array *vertexArray = new osg::Vec2Array;

osg::Vec2Array *texArray = new osg::Vec2Array;

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

for (int num = 0;num < times;num++)

{

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

vertexArray->push_back(osg::Vec2(0,0));

texArray->push_back(osg::Vec2(0+spost,1-spost));

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

vertexArray->push_back(osg::Vec2(0,480));

texArray->push_back(osg::Vec2(0+spost,0+spost));

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

vertexArray->push_back(osg::Vec2(640,480));

texArray->push_back(osg::Vec2(1-spost,0+spost));

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

vertexArray->push_back(osg::Vec2(640,0));

texArray->push_back(osg::Vec2(1-spost,1-spost));

}

geometry->setVertexArray(vertexArray);

geometry->setTexCoordArray(0, texArray, osg::Array::BIND_PER_VERTEX);

geometry->setColorArray(colorArray, osg::Array::BIND_PER_VERTEX);

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

geometry->getOrCreateStateSet()->setAttributeAndModes(blendFunc);

geometry->getOrCreateStateSet()->setTextureAttributeAndModes(0, g_Texture);

geometry->getOrCreateStateSet()->setMode(GL_DEPTH_TEST, osg::StateAttribute::OFF);

geometry->getOrCreateStateSet()->setMode(GL_LIGHT0, osg::StateAttribute::ON);

geode->addDrawable(geometry);

return geode;

}

osg::Camera* createBlurHUD()

{

osg::Camera* camera = new osg::Camera;

camera->setProjectionMatrix(osg::Matrix::ortho2D(0,640,0,480));

camera->setReferenceFrame(osg::Transform::ABSOLUTE_RF);

camera->setViewMatrix(osg::Matrix::identity());

camera->setRenderOrder(osg::Camera::POST_RENDER);

camera->setAllowEventFocus(false);

camera->addChild(createBlur(25, 0.02f));

return camera;

}

osg::Texture2D* createTexture(int w, int h)

{

osg::Texture2D *texture = new osg::Texture2D;

texture->setInternalFormat(GL_RGBA);

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

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

texture->setTextureSize(w,h);

return texture;

}

osg::Camera* createRenderToTextureCamera(int w, int h)

{

osg::Camera *rtt = new osg::Camera;

rtt->setClearColor(osg::Vec4(0.0f, 0.0f, 0.5f, 0.5));

rtt->setClearMask(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

rtt->setReferenceFrame(osg::Transform::ABSOLUTE_RF);

rtt->setViewport(0, 0, w, h);

rtt->setRenderOrder(osg::Camera::PRE_RENDER);

rtt->setRenderTargetImplementation(osg::Camera::FRAME_BUFFER_OBJECT);

rtt->setProjectionMatrixAsPerspective(45.0f, static_cast<double>(640)/static_cast<double>(480), 0.1f, 100.0f );

rtt->setViewMatrixAsLookAt(osg::Vec3d(0, 5, 50), osg::Vec3d(0, 0, 0), osg::Vec3d(0, 1, 0));

osg::MatrixTransform *zoomMT = new osg::MatrixTransform;

zoomMT->setMatrix(osg::Matrix::translate(0,0,-50));

osg::MatrixTransform *xRotMT = new osg::MatrixTransform;

xRotMT->addUpdateCallback(new RotAxisCallback(osg::X_AXIS, 0.02));

osg::MatrixTransform *yRotMT = new osg::MatrixTransform;

yRotMT->addUpdateCallback(new RotAxisCallback(osg::Y_AXIS, 0.01));

zoomMT->addChild(xRotMT);

xRotMT->addChild(yRotMT);

yRotMT->addChild(createHelix());

rtt->addChild(zoomMT);

return rtt;

}

osg::Node* buildScene()

{

GLfloat light0pos[4]= {0.0f, 5.0f, 10.0f, 1.0f};

GLfloat light0ambient[4]= {0.2f, 0.2f, 0.2f, 1.0f};

GLfloat light0diffuse[4]= {0.3f, 0.3f, 0.3f, 1.0f};

GLfloat light0specular[4]={0.8f, 0.8f, 0.8f, 1.0f};

osg::Group *root = new osg::Group;

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

light->setLightNum(0);

light->setAmbient(osg::Vec4(light0ambient[0],light0ambient[1],light0ambient[2],light0ambient[3]));

light->setDiffuse(osg::Vec4(light0diffuse[0],light0diffuse[1],light0diffuse[2],light0diffuse[3]));

light->setPosition(osg::Vec4(light0pos[0], light0pos[1],light0pos[2],light0pos[3]));

light->setSpecular(osg::Vec4(light0specular[0],light0specular[1],light0specular[2],light0specular[3]));

osg::LightSource *lightSource = new osg::LightSource;

lightSource->setLight(light);

root->addChild(lightSource);

osg::MatrixTransform *zoomMT = new osg::MatrixTransform;

zoomMT->setMatrix(osg::Matrix::translate(0,0,-50));

osg::MatrixTransform *xRotMT = new osg::MatrixTransform;

xRotMT->addUpdateCallback(new RotAxisCallback(osg::X_AXIS, 0.02));

osg::MatrixTransform *yRotMT = new osg::MatrixTransform;

yRotMT->addUpdateCallback(new RotAxisCallback(osg::Y_AXIS, 0.01));

zoomMT->addChild(xRotMT);

xRotMT->addChild(yRotMT);

yRotMT->addChild(createHelix());

g_Texture = createTexture(128,128);

osg::Camera *rttCamera = createRenderToTextureCamera(128, 128);

rttCamera->attach(osg::Camera::COLOR_BUFFER, g_Texture);

root->addChild(rttCamera);

root->addChild(zoomMT);

root->addChild(createBlurHUD());

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();

}