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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