c++ - 我怎样才能用osg api在osgearth上画一个三角形

Question

我想在地球上画三角形。 如果我通过类 osgEarth::Features::Feature 绘制三角形，则没有问题。

例如:

void DrawGeometryByFeature(ListVec3d& vecList, std::vector<unsigned int>& lstIndices)
{
        osgEarth::Symbology::Style shapeStyle;

        shapeStyle.getOrCreate<osgEarth::Symbology::PolygonSymbol>()->fill()->color() = osgEarth::Symbology::Color::Green;

        _polyFeature = new osgEarth::Features::Feature(new osgEarth::Symbology::MultiGeometry, s_mapNode->getMapSRS(), shapeStyle);
        _polyNode = new osgEarth::Annotation::FeatureNode(s_mapNode, _polyFeature);
        osgEarth::Symbology::MultiGeometry* pGeometry = (MultiGeometry*)_polyNode->getFeature()->getGeometry();

        pGeometry->clear();
        _polyNode->setStyle(shapeStyle);
        int index = 0;
        for (std::vector<unsigned int>::iterator iit = lstIndices.begin();
                iit != lstIndices.end(); iit++) {
                index++;
                if ((index + 1) % 3 == 0) {
                        osgEarth::Symbology::Geometry* polygen = new osgEarth::Symbology::Geometry();
                        polygen->push_back(vecList[lstIndices[index - 2]]);
                        polygen->push_back(vecList[lstIndices[index - 1]]);
                        polygen->push_back(vecList[lstIndices[index]]);
                        pGeometry->add(polygen);
                }
        }
        _polyNode->init();

        BBoxNodes.push_back(_polyNode);
        s_mapNode->addChild(_polyNode);
}

但我想更高效地绘制它，所以我尝试通过osg API绘制它

例如:

void DrawGeometryByOsg(std::vector<osg::Vec3d> vecList, std::vector<unsigned int>& lstIndices, int color, long type)
{
        // create Geometry object to store all the vertices and lines primitive.
        osg::Geometry* polyGeom = new osg::Geometry();

        // note, first coord at top, second at bottom, reverse to that buggy OpenGL image..
        const size_t numCoords  = lstIndices.size();
        osg::Vec3* myCoords = new osg::Vec3[numCoords];
        unsigned int index = 0;

        osg::Vec3Array* normals = new osg::Vec3Array(/*numCoords/3*/);
        for (std::vector<unsigned int>::iterator it = lstIndices.begin(); it != lstIndices.end(); it++){
                myCoords[index++] = vecList[*it];
                if(index%3 == 2){
                        //
                        osg::Vec3d kEdge1 = myCoords[index-1] - myCoords[index-2];
                        osg::Vec3d kEdge2 = myCoords[index] - myCoords[index - 2];
                        osg::Vec3d normal = kEdge1^kEdge2;
                        //normal.normalize();
                        normals->push_back(normal);
                        //
                }
        }
        osg::Vec3Array* vertices = new osg::Vec3Array(numCoords, myCoords);
        polyGeom->setVertexArray(vertices);

        osg::Vec4Array* colors = new osg::Vec4Array;

        colors->push_back(osg::Vec4(0.0f, 0.8f, 0.0f, 1.0f));


        polyGeom->setColorArray(colors, osg::Array::BIND_OVERALL);
        polyGeom->addPrimitiveSet(new osg::DrawArrays(osg::PrimitiveSet::TRIANGLES, 0, numCoords));

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

        geode->addDrawable(polyGeom);

        s_mapNode->addChild(geode);
}

但是我用Osg API画的gemotry一直在抖....(￣﹏￣；)

你能告诉我我的代码哪里有错误吗？

Answer 1

任何时候你有“抖动”的几何体，你都可能遇到浮点精度问题。 OpenGL 处理 32 位浮点坐标。因此，如果您的几何体使用较大的坐标值(就像在像 osgEarth 这样的地心 map 中那样)，这些值在发送到 GPU 时会被裁剪，并且当相机移动时您会摇晃/抖动。

要解决此问题，请表达相对于本地原点的数据。在某处选择一个 double 点——几何体的质心通常是一个好地方——并将其设为本地原点。然后翻译所有 double 坐标，使它们相对于原点。最后，使用将本地化数据转换为实际 double 位置的 MatrixTransform 作为几何体的父级。

希望这对您有所帮助!