放大中心点是(0.0,0.0,0.0)。如果你画了再放大,那么对画的没影响,必须放大了再画。这个函数只有在调用后才对后边的绘图有影响。你这个只有glVertex3f(0.0f, 0.0f, 0.0f)这个点还在屏幕中心,其他点应该都超出屏幕范围。
glScalef(0.5,0.5,1);//缩小0.5
glBegin(GL_LINES);
glColor3f(0.0f,0.0f,0.0f);
glVertex3f(m_x1,m_y1,0.0 );
glVertex3f(m_x2,m_y2,0.0 );
glEnd();
glScalef(2,2,1);//缩放完后把坐标系还原