用OpenSceneGraph实现的NeHe OpenGL教程 - 第四十七课
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简介
NeHe教程在这节课向我们介绍了Cg编程技术。Gg是nVidio公司面向GPU的语言，类似的语言还有微软的HLSL,OpenGL的GLSL,ATI的shaderMonker。关于可编程的着色语言可以在网络上找到很多的学习资源，这也是新式OpenGL的特点之一。可以预见未来随着GPU的发展，越来越多的固定管线部分可以被可编程的部分所替代。考虑到在OSG中使用GLSL比较方便，本课使用GLSL来实现。
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实现
在OSG中可编程的Shader部分是通过osg::Program和osg::Shader进行了封装，同时把osg::Progarm作为一种StateAttribute添加到节点之中。
首先创建网状的场景
osg::Geode* createFlagGeode()
{
osg::Geode* geode = new osg::Geode;
osg::Geometry *geometry = new osg::Geometry;
osg::Vec3Array *vertexArray = new osg::Vec3Array;
for (int x = 0; x < SIZE - 1; x++)
{
for (int z = 0; z < SIZE - 1; z++)
{
vertexArray->push_back(osg::Vec3(mesh[x][z][0], mesh[x][z][1], mesh[x][z][2]));
vertexArray->push_back(osg::Vec3(mesh[x+1][z][0], mesh[x+1][z][1], mesh[x+1][z][2]));
wave_movement += 0.00001f;
if (wave_movement > TWO_PI)
wave_movement = 0.0f;
}
}
geometry->setVertexArray(vertexArray);
osg::PolygonMode *pm = new osg::PolygonMode(osg::PolygonMode::FRONT_AND_BACK, osg::PolygonMode::LINE);
geometry->addPrimitiveSet(new osg::DrawArrays(osg::PrimitiveSet::TRIANGLE_STRIP, 0, vertexArray->size()));
geometry->getOrCreateStateSet()->setMode(GL_LIGHTING, osg::StateAttribute::OFF);
geometry->getOrCreateStateSet()->setAttributeAndModes(pm);
osg::Uniform *uniform = new osg::Uniform("animStep", wave_movement);
uniform->setUpdateCallback(new MoveUpdateCallback);
geometry->getStateSet()->addUniform(uniform);
osg::Shader *vertexShader = new osg::Shader(osg::Shader::VERTEX, vShader);
osg::Shader *fragmentShader = new osg::Shader(osg::Shader::FRAGMENT, fShader);
osg::Program *program = new osg::Program();
program->addShader(vertexShader);
program->addShader(fragmentShader);
geometry->getOrCreateStateSet()->setAttributeAndModes(program);
geode->addDrawable(geometry);
return geode;
}
在OSG中Shader可以写到单独的文件中，使用osgDB::readShaderFile来读取，对于简单的shader可以直接写到字符串中：
VertexShader：
static const char* vShader = {
"#version 330\n"
"in vec4 inVertex;\n"
"uniform float animStep;\n"
"void main(){\n"
"vec4 tmp = inVertex;\n"
"tmp.y = ( sin(animStep + (tmp.x / 5.0) ) + sin(animStep + (tmp.z / 4.0) ) ) * 2.5;\n"
"gl_Position = gl_ModelViewProjectionMatrix * tmp;\n"
"}\n"
};
FragmentShader:
static const char* fShader = {
"#version 330\n"
"out vec4 fragColor;\n"
"void main(){\n"
"fragColor = vec4(0.5, 1.0, 0.5, 1.0);\n"
"}\n"
};
在顶点Shader中不断的修改网状几何体的y值，形成一种类似于正弦波的效果，带代码中需要我们修改Uniform的值，让模型呈现动态的效果。
可以在Uniform的回调中完成：
class MoveUpdateCallback : public osg::Uniform::Callback
{
virtual void operator()(osg::Uniform *uniform, osg::NodeVisitor *nv)
{
if(!uniform)
return;
float animStep;
uniform->get(animStep);
//按照NeHe课程中方式每帧改变64*64*0.00001
for (int x = 0; x < SIZE - 1; x++)
{
for (int z = 0; z < SIZE - 1; z++)
{
wave_movement += 0.00001f;
if (wave_movement > TWO_PI)
wave_movement = 0.0f;
}
}
animStep = wave_movement;
uniform->set(animStep);
}
};
把节点添加到根节点下，编译运行程序：
附：本课源码（源码中可能存在错误和不足之处，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/PolygonMode>
#include <osg/Shader>
#include <osg/Uniform>
#include <osg/Program>
//////////////////////////////////////////////////////////////////////////
#define TWO_PI 6.2831853071
#define SIZE 64
GLfloat mesh[SIZE][SIZE][3];
GLfloat wave_movement = 0.0f;
//////////////////////////////////////////////////////////////////////////
static const char* vShader = {
"#version 330\n"
"in vec4 inVertex;\n"
"uniform float animStep;\n"
"void main(){\n"
"vec4 tmp = inVertex;\n"
"tmp.y = ( sin(animStep + (tmp.x / 5.0) ) + sin(animStep + (tmp.z / 4.0) ) ) * 2.5;\n"
"gl_Position = gl_ModelViewProjectionMatrix * tmp;\n"
"}\n"
};
static const char* fShader = {
"#version 330\n"
"out vec4 fragColor;\n"
"void main(){\n"
"fragColor = vec4(0.5, 1.0, 0.5, 1.0);\n"
"}\n"
};
class MoveUpdateCallback : public osg::Uniform::Callback
{
virtual void operator()(osg::Uniform *uniform, osg::NodeVisitor *nv)
{
if(!uniform)
return;
float animStep;
uniform->get(animStep);
//按照NeHe课程中方式每帧改变64*64*0.00001
for (int x = 0; x < SIZE - 1; x++)
{
for (int z = 0; z < SIZE - 1; z++)
{
wave_movement += 0.00001f;
if (wave_movement > TWO_PI)
wave_movement = 0.0f;
}
}
animStep = wave_movement;
uniform->set(animStep);
}
};
void initialize()
{
for (int x = 0; x < SIZE; x++)
{
for (int z = 0; z < SIZE; z++)
{
mesh[x][z][0] = (float) (SIZE / 2) - x;
mesh[x][z][1] = 0.0f;
mesh[x][z][2] = (float) (SIZE / 2) - z;
}
}
}
osg::Geode* createFlagGeode()
{
osg::Geode* geode = new osg::Geode;
osg::Geometry *geometry = new osg::Geometry;
osg::Vec3Array *vertexArray = new osg::Vec3Array;
for (int x = 0; x < SIZE - 1; x++)
{
for (int z = 0; z < SIZE - 1; z++)
{
vertexArray->push_back(osg::Vec3(mesh[x][z][0], mesh[x][z][1], mesh[x][z][2]));
vertexArray->push_back(osg::Vec3(mesh[x+1][z][0], mesh[x+1][z][1], mesh[x+1][z][2]));
wave_movement += 0.00001f;
if (wave_movement > TWO_PI)
wave_movement = 0.0f;
}
}
geometry->setVertexArray(vertexArray);
osg::PolygonMode *pm = new osg::PolygonMode(osg::PolygonMode::FRONT_AND_BACK, osg::PolygonMode::LINE);
geometry->addPrimitiveSet(new osg::DrawArrays(osg::PrimitiveSet::TRIANGLE_STRIP, 0, vertexArray->size()));
geometry->getOrCreateStateSet()->setMode(GL_LIGHTING, osg::StateAttribute::OFF);
geometry->getOrCreateStateSet()->setAttributeAndModes(pm);
osg::Uniform *uniform = new osg::Uniform("animStep", wave_movement);
uniform->setUpdateCallback(new MoveUpdateCallback);
geometry->getStateSet()->addUniform(uniform);
osg::Shader *vertexShader = new osg::Shader(osg::Shader::VERTEX, vShader);
osg::Shader *fragmentShader = new osg::Shader(osg::Shader::FRAGMENT, fShader);
osg::Program *program = new osg::Program();
program->addShader(vertexShader);
program->addShader(fragmentShader);
geometry->getOrCreateStateSet()->setAttributeAndModes(program);
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, 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(0.0f, 25.0f, -45.0f), 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()
{
initialize();
osg::Group *root = new osg::Group;
root->addChild(createFlagGeode());
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();
}