[求助]怎么才能不默认填充

lzhlzz

比如
glBegin(GL_TRIANGLES);
glVertex3f(2.0f,0.0f,0.0f);
glVertex3f(0.0f,2.0f,0.0f);
glVertex3f(0.0f,0.0f,2.0f);
glEnd();

默认是自动填充成白色的，我怎么才能修改成不填充，而只看到边框，也就是达到效果：

glBegin(GL_LINES);
glVertex3f(2.0f,0.0f,0.0f);
glVertex3f(0.0f,2.0f,0.0f);

glVertex3f(0.0f,2.0f,0.0f);
glVertex3f(0.0f,0.0f,2.0f);

glVertex3f(0.0f,0.0f,2.0f);
glVertex3f(2.0f,0.0f,0.0f);
glEnd();