Learning OSG programing---osgShape

本例示范了osg中Shape ---- 基本几何元素的绘制过程。参照osg官方文档，Shape 类包含以下子类：

在示例程序中，函数createShapes函数用于生成需要绘制的几何形状。

osg::Geode* createShapes(osg::ArgumentParser& arguments)
{
    osg::Geode* geode = new osg::Geode();


    // ---------------------------------------
    // Set up a StateSet to texture the objects
    // ---------------------------------------
    osg::StateSet* stateset = new osg::StateSet();
　　//设置材质图片
    osg::ref_ptr<osg::Image> image = osgDB::readRefImageFile( "Images/lz.rgb" );
    if (image)
    {
        osg::Texture2D* texture = new osg::Texture2D;
        texture->setImage(image);
        texture->setFilter(osg::Texture::MIN_FILTER, osg::Texture::LINEAR);
        stateset->setTextureAttributeAndModes(0,texture, osg::StateAttribute::ON);
    }

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

    geode->setStateSet( stateset );


    float radius = 0.8f;
    float height = 1.0f;

    osg::TessellationHints* hints = new osg::TessellationHints;
    hints->setDetailRatio(0.5f);
　　//建立各种几何实体
    geode->addDrawable(new osg::ShapeDrawable(new osg::Sphere(osg::Vec3(0.0f,0.0f,0.0f),radius),hints));
    geode->addDrawable(new osg::ShapeDrawable(new osg::Box(osg::Vec3(2.0f,0.0f,0.0f),2*radius),hints));
    geode->addDrawable(new osg::ShapeDrawable(new osg::Cone(osg::Vec3(4.0f,0.0f,0.0f),radius,height),hints));
    geode->addDrawable(new osg::ShapeDrawable(new osg::Cylinder(osg::Vec3(6.0f,0.0f,0.0f),radius,height),hints));
    geode->addDrawable(new osg::ShapeDrawable(new osg::Capsule(osg::Vec3(8.0f,0.0f,0.0f),radius,height),hints));
　　//用于控制平面的高程起伏
    osg::HeightField* grid = new osg::HeightField;
    if (arguments.read("--large"))　　　　　　//大范围
    {
        unsigned int numX = 512;
        unsigned int numY = 512;
        double sizeX = 10.0;
        double sizeY = 10.0;
        grid->allocate(numX,numY);
        grid->setXInterval(sizeX/float(numX));
        grid->setYInterval(sizeY/float(numY));

        for(unsigned int r=0;r<numY;++r)
        {
            for(unsigned int c=0;c<numX;++c)
            {
                double rx = double(c)/double(numX-1);
                double ry = double(r)/double(numY-1);

                grid->setHeight(c, r, 2.0*sin(rx*ry*4.0*osg::PI));
            }
        }
    }
    else　　　　　　　　　　　　　　//小范围
    {
        grid->allocate(38,39);
        grid->setXInterval(0.28f);
        grid->setYInterval(0.28f);

        for(unsigned int r=0;r<39;++r)
        {
            for(unsigned int c=0;c<38;++c)
            {
                grid->setHeight(c,r,vertex[r+c*39][2]);
            }
        }
    }

    geode->addDrawable(new osg::ShapeDrawable(grid));

    return geode;
}

在以上代码中，首先建立了几何节点Geode，加载纹理图像，并将其设置为节点的材质。

之后向节点中加入各种Shape模型，设置它们的集合参数。之后建立了高程域模型osg::HeightField* grid,根据运行程序时提供的命令行参数，设置其为不同的点密度。若运行命令中提供有--large选项，则建立高密度高程集，两层for循环中嵌套的语句，即为计算高程网格中各点的高程值方程。对于large情形，其在点（x,y）处的高程值为2*sin(x*y*4π)。而在普通情况下，点的高程值取决与vertex向量的第三个分量，因为在文件的开始，包含了地形坐标数据：

#include "../osghangglide/terrain_coords.h"

最后，将定义的地形平面添加到节点中去。

在主函数中，调用上面定义的createShapes函数，在进行一些其他准备工作即可：

int main(int argc, char **argv)
{
    osg::ArgumentParser arguments(&argc,argv);

    // construct the viewer.
    osgViewer::Viewer viewer(arguments);

    // add model to viewer.
    viewer.setSceneData( createShapes(arguments) );

    // add the state manipulator
    viewer.addEventHandler( new osgGA::StateSetManipulator(viewer.getCamera()->getOrCreateStateSet()) );

    return viewer.run();
}

按不同模式运行程序，得到不同的效果：

--large模式：

正常模式：

由此程序受到启发，可利用osg高程域，建立DEM（数字高程模型）浏览或仿真、编辑工具，达到学以致用的目的。

Enjoy!