175 lines
4.5 KiB
C++
175 lines
4.5 KiB
C++
#include <GL/glut.h>
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#include <iostream>
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// --- 定义区域编码 ---
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#define INSIDE 0 // 0000
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#define LEFT 1 // 0001
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#define RIGHT 2 // 0010
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#define BOTTOM 4 // 0100
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#define TOP 8 // 1000
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// --- 定义裁剪窗口结构 ---
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struct ClipWindow {
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float xmin, xmax, ymin, ymax;
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};
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// --- 全局变量设置 ---
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ClipWindow rect;
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int x_0, y_0, x_1, y_1; // 线段端点
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/**
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* 计算点 (x, y) 的区域编码
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*/
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int computeCode(float x, float y, ClipWindow rect) {
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int code = INSIDE;
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if (x < rect.xmin) code |= LEFT;
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else if (x > rect.xmax) code |= RIGHT;
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if (y < rect.ymin) code |= BOTTOM;
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else if (y > rect.ymax) code |= TOP;
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return code;
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}
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/**
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* Cohen-Sutherland 算法核心
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* 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
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*/
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void cohenSutherlandClip(float& x_0, float& y_0, float& x_1, float& y_1, ClipWindow rect) {
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int code1 = computeCode(x_0, y_0, rect);
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int code2 = computeCode(x_1, y_1, rect);
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bool accept = false;
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while (true) {
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// 如果两端点都在窗口内 (0000 | 0000 == 0)
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if (!(code1 | code2)) {
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accept = true;
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break;
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}
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// 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
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else if (code1 & code2) {
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break; // 直接舍弃
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}
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// 3. 线段部分在窗口内，需要求交点
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else {
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int code_out;
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float x, y;
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// 选择窗口外的一个端点
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if (code1 != 0)
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code_out = code1;
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else
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code_out = code2;
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// 计算交点
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if (code_out & TOP) {
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x = x_0 + (x_1 - x_0) * (rect.ymax - y_0) / (y_1 - y_0);
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y = rect.ymax;
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}
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else if (code_out & BOTTOM) {
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x = x_0 + (x_1 - x_0) * (rect.ymin - y_0) / (y_1 - y_0);
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y = rect.ymin;
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}
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else if (code_out & RIGHT) {
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y = y_0 + (y_1 - y_0) * (rect.xmax - x_0) / (x_1 - x_0);
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x = rect.xmax;
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}
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else if (code_out & LEFT) {
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y = y_0 + (y_1 - y_0) * (rect.xmin - x_0) / (x_1 - x_0);
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x = rect.xmin;
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}
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// 用交点替换原来的外部端点
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if (code_out == code1) {
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x_0 = x; y_0 = y;
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code1 = computeCode(x_0, y_0, rect);
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}
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else {
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x_1 = x; y_1 = y;
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code2 = computeCode(x_1, y_1, rect);
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}
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}
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}
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// 如果接受，则绘制裁剪后的线段（蓝色）
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if (accept) {
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glBegin(GL_LINES);
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glColor3f(0.0f, 0.0f, 1.0f); // 蓝色
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glVertex2f(x_0, y_0);
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glVertex2f(x_1, y_1);
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glEnd();
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}
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}
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// --- 显示回调函数 ---
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void myDisplay() {
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glClear(GL_COLOR_BUFFER_BIT);
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// 1. 绘制裁剪窗口 (红色线框)
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glColor3f(1.0f, 0.0f, 0.0f); // 红色
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glBegin(GL_LINE_LOOP);
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glVertex2f(rect.xmin, rect.ymin);
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glVertex2f(rect.xmax, rect.ymin);
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glVertex2f(rect.xmax, rect.ymax);
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glVertex2f(rect.xmin, rect.ymax);
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glEnd();
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// 2. 绘制原始线段 (绿色)
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// 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，
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// 或者在这里直接用初始值绘制。这里我们使用初始值绘制。
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int orig_x_0 = 50, orig_y_0 = 350;
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int orig_x_1 = 550, orig_y_1 = 50;
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glBegin(GL_LINES);
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glColor3f(0.0f, 1.0f, 0.0f); // 绿色
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glVertex2f(orig_x_0, orig_y_0);
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glVertex2f(orig_x_1, orig_y_1);
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glEnd();
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// 3. 执行裁剪并绘制结果 (蓝色)
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// 使用 float 变量传入，因为算法内部会修改它们
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float cx_0 = orig_x_0, cy_0 = orig_y_0;
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float cx_1 = orig_x_1, cy_1 = orig_y_1;
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// 加粗蓝色线条以便区分
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glLineWidth(3.0);
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cohenSutherlandClip(cx_0, cy_0, cx_1, cy_1, rect);
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glLineWidth(1.0); // 恢复线宽
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glFlush();
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}
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// --- 初始化设置 ---
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void Init() {
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glShadeModel(GL_FLAT);
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rect.xmin = 100;
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rect.xmax = 400;
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rect.ymin = 100;
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rect.ymax = 300;
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}
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// --- 窗口大小调整 ---
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void myReshape(int w, int h) {
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glViewport(0, 0, (GLsizei)w, (GLsizei)h);
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glMatrixMode(GL_PROJECTION);
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glLoadIdentity();
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// 设置二维投影范围，与坐标数值对应
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gluOrtho2D(0.0, (GLdouble)w, 0.0, (GLdouble)h);
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glMatrixMode(GL_MODELVIEW);
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}
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// --- 主函数 ---
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int main(int argc, char* argv[]) {
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glutInit(&argc, argv);
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glutInitDisplayMode(GLUT_RGB | GLUT_SINGLE);
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glutInitWindowPosition(100, 100);
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glutInitWindowSize(600, 400);
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glutCreateWindow("实验2_03毕爽爽 Cohen-Sutherland 算法");
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Init();
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glutDisplayFunc(myDisplay);
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glutReshapeFunc(myReshape);
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glutMainLoop();
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return 0;
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} |