忧郁的空间

微软应用商店里面有个有趣的镜像绘图程序 Mirror Paint，以下代码模拟了这个镜像绘图程序的基本功能，效果如下：

完整代码如下：

///////////////////////////////////////////////////////////
// 程序名称：迷盘(mirror_paint)
// 编译环境：Visual Studio 2017 / EasyX_20180727(beta)
// 程序编写：忧郁 506688268@qq.com
// 最后更新：2018-08-09
////////////////////////////////////////////////////////////

#include <graphics.h>
#include <iostream>
const int Width = 1280;               // 客户区宽
const int Height = 720;               // 客户区高
const int hWidth = Width / 2;         // 客户区半宽
const int hHeight = Height / 2;       // 客户区半高
const int block_count = 16;           // 块数量
const double PI = 3.141592653589793;  // π
const double PI_2 = PI * 2;           // 2倍π

									  // 定义平面向量
class vector2_t
{
public:
	double x, y;
	vector2_t(double _x = 0, double _y = 0) : x(_x), y(_y) {}
};

// 平面向量的旋转(绕某个点旋转多少弧度)
void rotate(vector2_t& self, const vector2_t& axis, double radians)
{
	double sinRadians = std::sin(radians);
	double cosRadians = std::cos(radians);

	double tmp_x = self.x - axis.x;
	double tmp_y = self.y - axis.y;
	self.x = tmp_x * cosRadians - tmp_y * sinRadians + axis.x;
	self.y = tmp_x * sinRadians + tmp_y * cosRadians + axis.y;
}

// 屏幕坐标系转画图坐标系
inline void screen_to_paint(vector2_t& pos)
{
	pos.x -= hWidth;
	pos.y -= hHeight;
}


int main()
{
	initgraph(Width, Height);

	// 设置原点到中心
	setorigin(hWidth, hHeight);
	BeginBatchDraw();
	setbkcolor(WHITE);
	cleardevice();
	FlushBatchDraw();

	// 绘制参考虚线
	setlinecolor(BLACK);
	const int Radius = Width > Height ? Width : Height;  // 半径
	for (int i = 0; i < block_count; ++i)
	{
		vector2_t p(0, -Radius);
		rotate(p, vector2_t(0, 0), PI_2 * i / block_count);
		line((int)p.x, (int)p.y, 0, 0);
	}
	FlushBatchDraw();
	setlinestyle(PS_SOLID, 3);

	setlinecolor(RED);

	vector2_t pts[block_count] = {};
	bool press_down = false;
	while (true)
	{
		MOUSEMSG msg = GetMouseMsg();
		switch (msg.uMsg)
		{
			case WM_LBUTTONDOWN:
			{
				vector2_t pos(msg.x, msg.y);
				screen_to_paint(pos);
				// 记录起点
				for (int i = 0; i < block_count; ++i)
				{
					pts[i] = pos;
					rotate(pts[i], vector2_t(0, 0), PI_2 * i / block_count);
				}
				press_down = true;
			} break;

			case WM_MOUSEMOVE:
			{
				if (press_down)
				{
					vector2_t pos(msg.x, msg.y);
					screen_to_paint(pos);
					for (int i = 0; i < block_count; ++i)
					{
						vector2_t tmp = pos;
						rotate(tmp, vector2_t(0, 0), PI_2 * i / block_count);
						line((int)(pts[i].x + 0.5), (int)(pts[i].y + 0.5),
							(int)(tmp.x + 0.5), (int)(tmp.y + 0.5));
						pts[i] = tmp;
					}
					FlushBatchDraw();
				}
			} break;

			case WM_LBUTTONUP:
			{
				press_down = false;
			} break;
		}
	}

	EndBatchDraw();
	closegraph();
	return 0;
}