Qt、Opencv环境下，演示ptr、at（）函数遍历图像示例，在该示例中显示了简单圆和线的绘制。仅仅用于教学演示，没有采用Bresenham等快速算法。-Under Qt, Opencv environment, demonstrate ptr, at () function to traverse a sample image showing the draw simple circles and lines in this example. Only for teaching demonstration, we did not use the other fast Bresenham algorithm.