osg绘图的形式

enum Mode
{
    POINTS = GL_POINTS,  //点
    LINES = GL_LINES,    //线
    LINE_STRIP = GL_LINE_STRIP,
    LINE_LOOP = GL_LINE_LOOP,   //封闭轮廓
    TRIANGLES = GL_TRIANGLES,    //三角形
    TRIANGLE_STRIP = GL_TRIANGLE_STRIP,   //三角面
    TRIANGLE_FAN = GL_TRIANGLE_FAN,  //三角面
    QUADS = GL_QUADS,   //四边形
    QUAD_STRIP = GL_QUAD_STRIP,   //四边面
    POLYGON = GL_POLYGON,    //多边形
    LINES_ADJACENCY = GL_LINES_ADJACENCY,
    LINE_STRIP_ADJACENCY = GL_LINE_STRIP_ADJACENCY,
    TRIANGLES_ADJACENCY = GL_TRIANGLES_ADJACENCY,
    TRIANGLE_STRIP_ADJACENCY = GL_TRIANGLE_STRIP_ADJACENCY,
    PATCHES = GL_PATCHES
};
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