在看一些画图形的书当画一个正方体时，只要确定顶点和画的要求就可以画出一个正方体了，使我不明白的是，在画八个顶点时，比如说
glBegin(GL_POLYGON);
glNormal3d(0.0,0.0,1.0);
glTexCoord2f(0.0, 1.0); glVertex3d(-x, x, x);
glTexCoord2f(1.0, 1.0); glVertex3d(-x, -x, x);
glTexCoord2f(1.0, 0.0); glVertex3d( x, -x, x);
glTexCoord2f(0.0, 0.0); glVertex3d( x, x, x);
glEnd();
glBegin(GL_POLYGON);
glNormal3d(0.0,0.0,-1.0);
glTexCoord2f(0.0, 1.0); glVertex3d( x, x, -x);
glTexCoord2f(0.0, 0.0); glVertex3d( x, -x, -x);
glTexCoord2f(1.0, 0.0); glVertex3d( -x, -x, -x);
glTexCoord2f(1.0, 1.0); glVertex3d( -x, x, -x);
glEnd();
glBegin(GL_POLYGON);
glNormal3d(1.0,0.0,0.0);
glTexCoord2f(0.0, 0.0); glVertex3d( x, x, x);
glTexCoord2f(1.0, 0.0); glVertex3d( x, -x, x);
glTexCoord2f(1.0, 1.0); glVertex3d( x, -x, -x);
glTexCoord2f(0.0, 1.0); glVertex3d( x, x, -x);
glEnd();
glBegin(GL_POLYGON);
glNormal3d(-1.0,0.0,0.0);
glTexCoord2f(0.0, 0.0); glVertex3d( -x, x, x);
glTexCoord2f(1.0, 0.0); glVertex3d( -x, x, -x);
glTexCoord2f(1.0, 1.0); glVertex3d( -x, -x, -x);
glTexCoord2f(0.0, 1.0); glVertex3d( -x, -x, x);
glEnd();
glBegin(GL_POLYGON);
glNormal3d(0.0,-1.0,0.0);
glTexCoord2f(0.0, 0.0); glVertex3d( -x, -x, x);
glTexCoord2f(1.0, 0.0); glVertex3d( -x, -x, -x);
glTexCoord2f(1.0, 1.0); glVertex3d( x, -x, -x);
glTexCoord2f(0.0, 1.0); glVertex3d( x, -x, x);
glEnd();
glBegin(GL_POLYGON);
glNormal3d(0.0,1.0,0.0);
glTexCoord2f(0.0, 0.0); glVertex3d( -x, x, x);
glTexCoord2f(1.0, 0.0); glVertex3d( x, x, x);
glTexCoord2f(1.0, 1.0); glVertex3d( x, x, -x);
glTexCoord2f(0.0, 1.0); glVertex3d( -x, x, -x);
glEnd();就可以实现了，但是它的坐标是怎么来的，怎样建立坐标啊，坐标不确定的话，那些顶点怎么知道画在哪里，说的有点糊涂
总之，就是怎么建立坐标，点画在对应的三维坐标上，谢谢
