#include <GL/glut.h>
#include <iostream>

// --- 定义区域编码 ---
#define INSIDE 0 // 0000
#define LEFT   1 // 0001
#define RIGHT  2 // 0010
#define BOTTOM 4 // 0100
#define TOP    8 // 1000

// --- 定义裁剪窗口结构 ---
struct ClipWindow {
    float xmin, xmax, ymin, ymax;
};

// --- 全局变量设置 ---
ClipWindow rect;
int x_0, y_0, x_1, y_1; // 线段端点

/**
 * 计算点 (x, y) 的区域编码
 */
int computeCode(float x, float y, ClipWindow rect) {
    int code = INSIDE;
    if (x < rect.xmin)      code |= LEFT;
    else if (x > rect.xmax) code |= RIGHT;
    if (y < rect.ymin)      code |= BOTTOM;
    else if (y > rect.ymax) code |= TOP;
    return code;
}

/**
 * Cohen-Sutherland 算法核心
 * 注意：这里传入坐标的引用，直接修改坐标值以得到裁剪后的结果
 */
void cohenSutherlandClip(float& x_0, float& y_0, float& x_1, float& y_1, ClipWindow rect) {
    int code1 = computeCode(x_0, y_0, rect);
    int code2 = computeCode(x_1, y_1, rect);
    bool accept = false;

    while (true) {
        // 如果两端点都在窗口内 (0000 | 0000 == 0)
        if (!(code1 | code2)) {
            accept = true;
            break;
        }
        // 如果两端点都在窗口的同一侧外部 (例如都在左边：0001 & 0001 != 0) 按位与运算
        else if (code1 & code2) {
            break; // 直接舍弃
        }
        // 3. 线段部分在窗口内，需要求交点
        else {
            int code_out;
            float x, y;

            // 选择窗口外的一个端点
            if (code1 != 0)
                code_out = code1;
            else
                code_out = code2;

            // 计算交点
            if (code_out & TOP) {
                x = x_0 + (x_1 - x_0) * (rect.ymax - y_0) / (y_1 - y_0);
                y = rect.ymax;
            }
            else if (code_out & BOTTOM) {
                x = x_0 + (x_1 - x_0) * (rect.ymin - y_0) / (y_1 - y_0);
                y = rect.ymin;
            }
            else if (code_out & RIGHT) {
                y = y_0 + (y_1 - y_0) * (rect.xmax - x_0) / (x_1 - x_0);
                x = rect.xmax;
            }
            else if (code_out & LEFT) {
                y = y_0 + (y_1 - y_0) * (rect.xmin - x_0) / (x_1 - x_0);
                x = rect.xmin;
            }

            // 用交点替换原来的外部端点
            if (code_out == code1) {
                x_0 = x; y_0 = y;
                code1 = computeCode(x_0, y_0, rect);
            }
            else {
                x_1 = x; y_1 = y;
                code2 = computeCode(x_1, y_1, rect);
            }
        }
    }

    // 如果接受，则绘制裁剪后的线段（蓝色）
    if (accept) {
        glBegin(GL_LINES);
        glColor3f(0.0f, 0.0f, 1.0f); // 蓝色
        glVertex2f(x_0, y_0);
        glVertex2f(x_1, y_1);
        glEnd();
    }
}

// --- 显示回调函数 ---
void myDisplay() {
    glClear(GL_COLOR_BUFFER_BIT);

    // 1. 绘制裁剪窗口 (红色线框)
    glColor3f(1.0f, 0.0f, 0.0f); // 红色
    glBegin(GL_LINE_LOOP);
        glVertex2f(rect.xmin, rect.ymin);
        glVertex2f(rect.xmax, rect.ymin);
        glVertex2f(rect.xmax, rect.ymax);
        glVertex2f(rect.xmin, rect.ymax);
    glEnd();

    // 2. 绘制原始线段 (绿色)
    // 注意：为了演示效果，我们在调用裁剪函数前，先保存原始坐标，
    // 或者在这里直接用初始值绘制。这里我们使用初始值绘制。
    int orig_x_0 = 50, orig_y_0 = 350;
    int orig_x_1 = 550, orig_y_1 = 50;

    glBegin(GL_LINES);
    glColor3f(0.0f, 1.0f, 0.0f); // 绿色
    glVertex2f(orig_x_0, orig_y_0);
    glVertex2f(orig_x_1, orig_y_1);
    glEnd();

    // 3. 执行裁剪并绘制结果 (蓝色)
    // 使用 float 变量传入，因为算法内部会修改它们
    float cx_0 = orig_x_0, cy_0 = orig_y_0;
    float cx_1 = orig_x_1, cy_1 = orig_y_1;
    
    // 加粗蓝色线条以便区分
    glLineWidth(3.0); 
    cohenSutherlandClip(cx_0, cy_0, cx_1, cy_1, rect);
    glLineWidth(1.0); // 恢复线宽

    glFlush();
}

// --- 初始化设置 ---
void Init() {
    glShadeModel(GL_FLAT);

    rect.xmin = 100;
    rect.xmax = 400;
    rect.ymin = 100;
    rect.ymax = 300;
}

// --- 窗口大小调整 ---
void myReshape(int w, int h) {
    glViewport(0, 0, (GLsizei)w, (GLsizei)h);
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    // 设置二维投影范围，与坐标数值对应
    gluOrtho2D(0.0, (GLdouble)w, 0.0, (GLdouble)h);
    glMatrixMode(GL_MODELVIEW);
}

// --- 主函数 ---
int main(int argc, char* argv[]) {
    glutInit(&argc, argv);
    glutInitDisplayMode(GLUT_RGB | GLUT_SINGLE);
    glutInitWindowPosition(100, 100);
    glutInitWindowSize(600, 400);
    glutCreateWindow("实验2_03毕爽爽 Cohen-Sutherland 算法");

    Init();

    glutDisplayFunc(myDisplay);
    glutReshapeFunc(myReshape);

    glutMainLoop();
    return 0;
}