osgearth 体绘制之面片方法

liyihongcug

体数据 ： 不好用点线面表达的大范围采样数据。
面片方式渲染体数据 ：
优点：可以在任意性能的机器和平台上进行高速渲染
缺点：对其做复杂的运算和效果相对低效
代码说明：
1、使用Geometry建立切片，设置好3D纹理坐标是关键。
2、将Raw读取到3D纹理当中
3、渲染即可


#include <osgViewer/viewer>
#include <osgDB/ReadFile>
#include <osg/Texture3D>
#include <osgDB/FileUtils>

#ifdef _DEBUG
#pragma comment(lib, "osgViewerd.lib")
#pragma comment(lib, "osgDBd.lib")
#pragma comment(lib, "osgd.lib")
#else
#pragma comment(lib, "osgViewer.lib")
#pragma comment(lib, "osgDB.lib")
#pragma comment(lib, "osg.lib")
#endif

#define VSIZE 128
//从raw文件中创建3D纹理
osg::Texture3D* Create3DTextureFromRaw()
{
    osg::Texture3D* t3d = new osg::Texture3D;
    osg::Image* image = new osg::Image;
    image->allocateImage(VSIZE, VSIZE, VSIZE, GL_RGBA, GL_UNSIGNED_BYTE);
    t3d->setImage(image);

    osgDB::ifstream fin("buckball.raw", osgDB::ifstream::binary);

    for (int s = 0; s < VSIZE; s++)
    {
        for (int t = 0; t < VSIZE; t++)
        {
            for (int r = 0; r < VSIZE; r++)
            {
                unsigned char* datePtr = image->data(s, t, r);
                unsigned char dataTemp;
                fin.read((char*)(&dataTemp), 1);
                datePtr[0] = dataTemp;
                datePtr[1] = 0;
                datePtr[2] = 0;
                if (dataTemp < 100)
                {
                    dataTemp = 0;
                }
                datePtr[3] = dataTemp;

            }
        }
    }

    fin.close();

    t3d->setFilter(osg::Texture::MIN_FILTER, osg::Texture::NEAREST);
    t3d->setFilter(osg::Texture::MAG_FILTER, osg::Texture::NEAREST);
    t3d->setWrap(osg::Texture::WRAP_R, osg::Texture3D::CLAMP_TO_EDGE);
    t3d->setWrap(osg::Texture::WRAP_T, osg::Texture3D::CLAMP_TO_EDGE);
    t3d->setWrap(osg::Texture::WRAP_S, osg::Texture3D::CLAMP_TO_EDGE);

    return t3d;
}

//创建切片
osg::Node* CreateCube()
{
    osg::Geode* gnode = new osg::Geode;
    osg::Geometry* geom = new osg::Geometry;
    gnode->addDrawable(geom);

    osg::Vec3Array* vertex = new osg::Vec3Array;
    osg::Vec3Array* texCoord = new osg::Vec3Array;
    geom->setVertexArray(vertex);
    geom->setTexCoordArray(0, texCoord);

    //
    for (int y = VSIZE - 1; y >= 0; y--)
    {
        //压入顶点
        vertex->push_back(osg::Vec3f(-0.5, y*1.0 / VSIZE,-0.5));
        vertex->push_back(osg::Vec3f(-0.5, y*1.0 / VSIZE, 0.5));
        vertex->push_back(osg::Vec3f(0.5, y*1.0 / VSIZE, 0.5));
        vertex->push_back(osg::Vec3f(0.5, y*1.0 / VSIZE, -0.5));

        texCoord->push_back(osg::Vec3f(0.0, y*1.0 / VSIZE, 0.0));
        texCoord->push_back(osg::Vec3f(0.0, y*1.0 / VSIZE, 1.0));
        texCoord->push_back(osg::Vec3f(1.0, y*1.0 / VSIZE, 1.0));
        texCoord->push_back(osg::Vec3f(1.0, y*1.0 / VSIZE, 0.0));
    }

    geom->addPrimitiveSet(new osg:rawArrays(GL_QUADS, 0, vertex->size()));

    osg::StateSet* ss = gnode->getOrCreateStateSet();
    ss->setTextureAttributeAndModes(0, Create3DTextureFromRaw(), osg::StateAttribute::ON);
    ss->setMode(GL_BLEND, osg::StateAttribute::ON);
    ss->setMode(GL_LIGHTING, osg::StateAttribute::OFF);

    return gnode;
}

int main()
{
    osgViewer::Viewer viewer;
    viewer.setSceneData(CreateCube());
    return viewer.run();
}

liyihongcug

配色
billboard解决切片一拖角度就改变的问题
实时的生成纹理坐标
osg::TexGen::Mode::EYE_LINEAR
公式：coordTex=p1’xe+p2’ye+p3’ze+p4’we
其中(p1’,p2’,p3’,p4’)=(p1,p2,p3,p4)M-1
pn是设置的参数
clipNode解决冗余数据问题

#include <osgViewer/viewer>
#include <osgDB/ReadFile>
#include <osg/Texture3D>
#include <osgDB/FileUtils>
#include <osg/Billboard>
#include <osg/TexGenNode>
#include <osg/ClipNode>


#ifdef _DEBUG
#pragma comment(lib, "osgViewerd.lib")
#pragma comment(lib, "osgDBd.lib")
#pragma comment(lib, "osgd.lib")
#else
#pragma comment(lib, "osgViewer.lib")
#pragma comment(lib, "osgDB.lib")
#pragma comment(lib, "osg.lib")
#endif

#define VSIZE 128
//从raw文件中创建3D纹理
osg::Texture3D* Create3DTextureFromRaw()
{
    osg::Texture3D* t3d = new osg::Texture3D;
    osg::Image* image = new osg::Image;
    image->allocateImage(VSIZE, VSIZE, VSIZE, GL_RGBA, GL_UNSIGNED_BYTE);
    t3d->setImage(image);

    osgDB::ifstream fin("buckball.raw", osgDB::ifstream::binary);

    for (int s = 0; s < VSIZE; s++)
    {
        for (int t = 0; t < VSIZE; t++)
        {
            for (int r = 0; r < VSIZE; r++)
            {
                unsigned char* datePtr = image->data(s, t, r);
                unsigned char dataTemp;
                fin.read((char*)(&dataTemp), 1);

                if (dataTemp < 10)
                {
                    datePtr[0] = 0;
                    datePtr[1] = 255;
                    datePtr[2] = dataTemp;
                    datePtr[3] = 0;
                }
                else if (dataTemp < 30)
                {
                    datePtr[0] = dataTemp;
                    datePtr[1] = 255;
                    datePtr[2] = dataTemp;
                    datePtr[3] = 10;
                }
                else if (dataTemp >= 150)
                {
                    datePtr[0] = 255;
                    datePtr[1] = 255;
                    datePtr[2] = dataTemp;
                    datePtr[3] = 100;
                }
                else
                {
                    datePtr[0] = 0;
                    datePtr[1] = 0;
                    datePtr[2] = 0;
                    datePtr[3] = 0;
                }


            }
        }
    }

    fin.close();

    t3d->setFilter(osg::Texture::MIN_FILTER, osg::Texture::NEAREST);
    t3d->setFilter(osg::Texture::MAG_FILTER, osg::Texture::NEAREST);
    t3d->setWrap(osg::Texture::WRAP_R, osg::Texture3D::CLAMP_TO_EDGE);
    t3d->setWrap(osg::Texture::WRAP_T, osg::Texture3D::CLAMP_TO_EDGE);
    t3d->setWrap(osg::Texture::WRAP_S, osg::Texture3D::CLAMP_TO_EDGE);

    return t3d;
}

//创建切片
osg::Node* CreateCube()
{
    osg::Billboard* bd = new osg::Billboard;
    bd->setMode(osg::Billboard::Mode:OINT_ROT_WORLD);
   
   
    osg::Geometry* geom = new osg::Geometry;
    bd->addDrawable(geom);
    bd->setPosition(0, osg::Vec3(0.5, 0.5, 0.5));


    osg::Vec3Array* vertex = new osg::Vec3Array;
    geom->setVertexArray(vertex);

    //
    float scalef = 1.75;
    for (int y = VSIZE - 1; y >= 0; y--)
    {
        //压入顶点
        vertex->push_back(osg::Vec3f(-0.5, y*1.0 / (VSIZE-1)-0.5,-0.5)*scalef);
        vertex->push_back(osg::Vec3f(-0.5, y*1.0 / (VSIZE-1)-0.5, 0.5)*scalef);
        vertex->push_back(osg::Vec3f(0.5, y*1.0 / (VSIZE-1)-0.5, 0.5)*scalef);
        vertex->push_back(osg::Vec3f(0.5, y*1.0 / (VSIZE-1)-0.5, -0.5)*scalef);

    }

    geom->addPrimitiveSet(new osg:rawArrays(GL_QUADS, 0, vertex->size()));


    osg::TexGenNode* tn = new osg::TexGenNode();
    tn->addChild(bd);
    tn->setTextureUnit(0);
    tn->getTexGen()->setPlanesFromMatrix(osg::Matrix::identity());
    tn->getTexGen()->setMode(osg::TexGen::Mode::EYE_LINEAR);

    osg::StateSet* ss = tn->getOrCreateStateSet();
    ss->setTextureAttributeAndModes(0, Create3DTextureFromRaw(), osg::StateAttribute::ON);
    ss->setMode(GL_BLEND, osg::StateAttribute::ON);
    ss->setMode(GL_LIGHTING, osg::StateAttribute::OFF);

    ss->setTextureMode(0, GL_TEXTURE_GEN_S, osg::StateAttribute::ON);
    ss->setTextureMode(0, GL_TEXTURE_GEN_T, osg::StateAttribute::ON);
    ss->setTextureMode(0, GL_TEXTURE_GEN_R, osg::StateAttribute::ON);

    osg::ClipNode* cn = new osg::ClipNode;
    cn->addChild(tn);

    osg::Vec3d v000 = osg::Vec3d(0.0, 0.0, 0.0);
    osg::Vec3d v100 = osg::Vec3d(1.0, 0.0, 0.0);
    osg::Vec3d v010 = osg::Vec3d(0.0, 1.0, 0.0);
    osg::Vec3d v110 = osg::Vec3d(1.0, 1.0, 0.0);

    osg::Vec3d v001 = osg::Vec3d(0.0, 0.0, 1.0);
    osg::Vec3d v101 = osg::Vec3d(1.0, 0.0, 1.0);
    osg::Vec3d v011 = osg::Vec3d(0.0, 1.0, 1.0);
    osg::Vec3d v111 = osg::Vec3d(1.0, 1.0, 1.0);

    cn->addClipPlane(new osg::ClipPlane(0, osg::Plane(v000, v011, v001)));
    cn->addClipPlane(new osg::ClipPlane(1, osg::Plane(v100, v111, v110)));
    cn->addClipPlane(new osg::ClipPlane(2, osg::Plane(v000, v101, v100)));
    cn->addClipPlane(new osg::ClipPlane(3, osg::Plane(v110, v011, v010)));
    cn->addClipPlane(new osg::ClipPlane(4, osg::Plane(v000, v110, v010)));
    cn->addClipPlane(new osg::ClipPlane(5, osg::Plane(v001, v111, v101)));

    return cn;
}

int main()
{
    osgViewer::Viewer viewer;
    viewer.setSceneData(CreateCube());
    return viewer.run();
}

liyihongcug

目标是：视点可见的蓝色边框的显示颜色

眼睛的位置cameraPos：在顶点着色器中通过
gl_ModelViewMatrixInverse * vec4(0,0,0,1);获取

fn:是顶点着色器中的顶点，也是纹理坐标值

fn-cameraPos得到光线的方向direction

以fn为为起点direction为方向，1/切片数量为为步进长度，判断纹理坐标是否在[0,1]范围内为判断光线是否在体内的条件

1、将配色表表达成纹理传入GPU
2、从原始体数据中查询到标量数据
3、拿查到的标量数据到本色表中查询
到最终颜色。


1、体渲染清晰可见的轮廓是等值面
2、当前点的梯度表示这个点沿方向的最大变化率，垂直于等值面
3、根据梯度的定义来求标量场中的梯度