osg指南针怎么绘制代码

以下是使用OpenGL绘制osg指南针的示例代码：

#include <osgViewer/Viewer>
#include <osg/Geode>
#include <osg/Geometry>
#include <osg/LineWidth>

osg::ref_ptr<osg::Geode> createCompass(const float& radius, const float& lineWidth)
{
    osg::ref_ptr<osg::Geode> compassGeode = new osg::Geode();

    // create the outer circle
    osg::ref_ptr<osg::Geometry> outerCircleGeometry = new osg::Geometry();
    osg::ref_ptr<osg::Vec3Array> outerCircleVertices = new osg::Vec3Array();
    osg::ref_ptr<osg::Vec4Array> outerCircleColors = new osg::Vec4Array();
    outerCircleGeometry->setVertexArray(outerCircleVertices);
    outerCircleGeometry->setColorArray(outerCircleColors, osg::Array::BIND_OVERALL);
    outerCircleGeometry->addPrimitiveSet(new osg::DrawArrays(GL_LINE_LOOP, 0, 360));
    compassGeode->addDrawable(outerCircleGeometry);

    // create the inner circle
    osg::ref_ptr<osg::Geometry> innerCircleGeometry = new osg::Geometry();
    osg::ref_ptr<osg::Vec3Array> innerCircleVertices = new osg::Vec3Array();
    osg::ref_ptr<osg::Vec4Array> innerCircleColors = new osg::Vec4Array();
    innerCircleGeometry->setVertexArray(innerCircleVertices);
    innerCircleGeometry->setColorArray(innerCircleColors, osg::Array::BIND_OVERALL);
    innerCircleGeometry->addPrimitiveSet(new osg::DrawArrays(GL_LINE_LOOP, 0, 360));
    compassGeode->addDrawable(innerCircleGeometry);

    // create the lines
    osg::ref_ptr<osg::Geometry> lineGeometry = new osg::Geometry();
    osg::ref_ptr<osg::Vec3Array> lineVertices = new osg::Vec3Array();
    osg::ref_ptr<osg::Vec4Array> lineColors = new osg::Vec4Array();
    lineGeometry->setVertexArray(lineVertices);
    lineGeometry->setColorArray(lineColors, osg::Array::BIND_OVERALL);
    lineGeometry->addPrimitiveSet(new osg::DrawArrays(GL_LINES, 0, 4));
    compassGeode->addDrawable(lineGeometry);

    // set the line width
    osg::ref_ptr<osg::LineWidth> lineWidthState = new osg::LineWidth();
    lineWidthState->setWidth(lineWidth);
    compassGeode->getOrCreateStateSet()->setAttribute(lineWidthState);

    // set the vertex and color data for the outer circle
    float angleStep = osg::PI / 180.0f;
    for (int i = 0; i < 360; ++i)
    {
        float angle = i * angleStep;
        float x = radius * cos(angle);
        float y = radius * sin(angle);
        outerCircleVertices->push_back(osg::Vec3(x, y, 0.0f));
        outerCircleColors->push_back(osg::Vec4(1.0f, 1.0f, 1.0f, 1.0f));
    }

    // set the vertex and color data for the inner circle
    float innerRadius = radius * 0.8f;
    for (int i = 0; i < 360; ++i)
    {
        float angle = i * angleStep;
        float x = innerRadius * cos(angle);
        float y = innerRadius * sin(angle);
        innerCircleVertices->push_back(osg::Vec3(x, y, 0.0f));
        innerCircleColors->push_back(osg::Vec4(1.0f, 1.0f, 1.0f, 1.0f));
    }

    // set the vertex and color data for the lines
    float lineLength = radius * 0.6f;
    lineVertices->push_back(osg::Vec3(0.0f, 0.0f, 0.0f));
    lineVertices->push_back(osg::Vec3(radius, 0.0f, 0.0f));
    lineVertices->push_back(osg::Vec3(0.0f, 0.0f, 0.0f));
    lineVertices->push_back(osg::Vec3(0.0f, radius, 0.0f));
    lineColors->push_back(osg::Vec4(1.0f, 1.0f, 1.0f, 1.0f));
    lineColors->push_back(osg::Vec4(1.0f, 1.0f, 1.0f, 1.0f));
    lineColors->push_back(osg::Vec4(1.0f, 1.0f, 1.0f, 1.0f));
    lineColors->push_back(osg::Vec4(1.0f, 1.0f, 1.0f, 1.0f));

    return compassGeode;
}

int main(int argc, char** argv)
{
    osgViewer::Viewer viewer;

    // create the compass geode
    osg::ref_ptr<osg::Geode> compassGeode = createCompass(100.0f, 2.0f);

    // add the compass geode to the scene graph
    osg::ref_ptr<osg::Group> root = new osg::Group();
    root->addChild(compassGeode);
    viewer.setSceneData(root);

    return viewer.run();
}

这个示例代码使用OpenGL和OpenSceneGraph（OSG）库来绘制osg指南针。它创建了一个osg::Geode对象，其中包含了一个外圆、一个内圆和四条线，然后将其添加到场景图中。您可以根据需要更改半径和线宽度来调整指南针的大小和外观。