Week16,圓圈圈 圈圈圓

hw1:貼圖背景

要放背景圖，我們在display函式中修改成如下:
void display()
{   glEnable(GL_DEPTH_TEST); ///要啟動 Detph Test 深度值的測試,3D顯示才正確
    glClear(GL_COLOR_BUFFER_BIT  | GL_DEPTH_BUFFER_BIT);
    glPushMatrix();
        glBegin(GL_POLYGON);///多邊形  開始畫
            glTexCoord2f(0,0); glVertex3f(-1,+1,0);
            glTexCoord2f(1,0); glVertex3f(+1,+1,0);
            glTexCoord2f(1,1); glVertex3f(+1,-1,0);
            glTexCoord2f(0,1); glVertex3f(-1,-1,0);
        glEnd();///結束畫
    glPopMatrix();
    glFlush();
}

其中，

            glTexCoord2f(0,0); glVertex3f(-1,+1,0);            glTexCoord2f(1,0); glVertex3f(+1,+1,0);
            glTexCoord2f(1,1); glVertex3f(+1,-1,0);
            glTexCoord2f(0,1); glVertex3f(-1,-1,0);

前面代表貼圖座標，後面代表3D頂點

然後按下執行，貼圖就變成2D的了