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 dr