绘制像素点函数:在屏幕的P0（20,20）坐标位置处绘制一个绿色像素点，然后读出该像素点的颜色，水平平移100个像素绘制P1点。(The pixel function is plotted: a green pixel is drawn at the P0 (20,20) coordinates of the screen, and then the color of the pixel is read out. 100 pixels are horizontally shifted to draw the P1 point.)