综述：
这里只是简单记录了部分实现思想。该部分代码不具备实际使用功能。
考虑使用4把刀分别裁剪一个图形。核心思想是，有一个点在扫描整个图形的边界。在扫描过程中，如果从刀的内侧（需要自己定义）到刀的外侧那么就记录当前点p0，当再次从外侧进入内测时，将当前点和记录的p0连起来。对于“覆盖遮挡”的边界可以利用
(a^b)^b = a来实现“抹去还原”。
#include <GLUT/GLUT.h>
#include <iostream>
#include <cmath>
#include <algorithm>
using namespace std;
float wid = 400; //设置窗口的大小,约定窗口必须为正方形
float height = wid; //设置窗口的大小
int numbers = 40; //设置划分的网格的个数
float t = wid/numbers; //模拟像素下的单位1
int index_y; //记录下斜率为-1时的y的位置
int con[801][801]; //相当于我们的画布（其中的信息是有层次的）
int visited[801][801];
int flag = 0; //标定移动轨迹的位置
int x_pos,y_pos,x_1=2*wid,y_1=2*wid;
int pixel_size = 8; //统一设定所有的的pixel的大小；
/*
参数设置说明：
您应当确保参数范围在-400～400.且为整数。
由于使用的是模拟像素，应保持数据为单位模拟像素值的倍数。
*/
int x=0;
int y=0;
int a = 300;
int b = 200;
void draw_point(float x, float y,float x1,float y1);
void add(int x, int y ,int data){
con[x+400][y+400] = data ;
}
float translater(int x){
/*
函数说明：将像素坐标下的坐标转化为openGL坐标
参数说明：传入点像素坐标-wid-wid，返回-1～1坐标
*/
return x/wid;
}
void draw_point(float x , float y){
/*
函数说明：绘制像素的点，这里将点的大小设置为7。
颜色采用蓝色。利用圆八个部分的坐标对应关系进行绘图。
加x1与y1是为了进行圆的平移
参数说明：浮点数x，y是openGl坐标系。
*/
glPointSize(pixel_size);
glColor3f(1.0,0.0,0.0);
glBegin(GL_POINTS);
glVertex3f(x,y,0.0);
glVertex3f(-x,y,0.0); //关于y轴对称
glVertex3f(x,-y,0.0); //关于x轴对称
glVertex3f(-x,-y,0.0); //关于原点对称
glEnd();
glFlush();
}
bool out_of_index(int x,int y){
if(y>=801||x>=801||x<0||y<0){
return 0;
}else{
return 1;
}
}
void draw_inner(int x, int y){
glPointSize(pixel_size);
glColor3f(0.0,1.0,1.0);
glBegin(GL_POINTS);
glVertex3f(translater(x-400),translater(y-400),0.0);
glEnd();
glFlush();
}
void draw_inner2(int x, int y){
glPointSize(pixel_size);
glColor3f(0.0,0.0,1.0);
glBegin(GL_POINTS);
glVertex3f(translater(x-400),translater(y-400),0.0);
glEnd();
glFlush();
}
void draw_line(int x,int y , int xx , int yy){
for (int i = min(x,xx); i <= max(x,xx); i+=10) {
for(int j =min (y,yy);j<=max(y,yy);j+=10){
if(con[i][j]!=1){
int res= con[i][j]^1111;
if(res == -1){
glPointSize(pixel_size);
glColor3f(1.0,0.0,0.0);
glBegin(GL_POINTS);
glVertex3f(translater(i-400),translater(j-400),0.0);
glEnd();
glFlush();
}else{
draw_inner(i, j);
}
if(con[i][j] ==0){
con[i][j] = 1;
visited[i][j] =1;
}else{
con[i][j] = res;
}
}
}
}
}
void draw_line2(int x,int y , int xx , int yy){
for (int i = min(x,xx); i <= max(x,xx); i+=10) {
for(int j =min (y,yy);j<=max(y,yy);j+=10){
if(con[i][j]!=1){
int res= con[i][j]^1112;
if(res == -1&&res== ((-1)^1111)){
glPointSize(pixel_size);
glColor3f(1.0,0.0,0.0);
glBegin(GL_POINTS);
glVertex3f(translater(i-400),translater(j-400),0.0);
glEnd();
glFlush();
}else{
draw_inner2(i, j);
}
con[i][j] = res;
}
}
}
}
void search(int x,int y,int index){
cout << index << " - - "<<endl;
/*
函数说明：进行Dfs搜索并模拟四把刀当中的其中一把刀
可视化着色采用淡蓝色。
参数说明：x y是坐标，index是指明哪一把刀。
传入的xy是数组坐标！
*/
if (visited[x][y] ==1) {
return;
}
if(index == 1){
//讨论下方的情况
if(flag ==0){
//如果本来在外侧
if(y-400 >= -200){
//从外侧进入内侧
draw_inner(x, y);
y_1 = min(y_1,y);
x_1 = min(x_1,x);
flag =1;
x_pos= x;
y_pos = y;
}else{
glPointSize(8);
glColor3f(0.5,0.5,0.5);
glBegin(GL_POINTS);
glVertex3f(translater(x-400),translater(y-400),0.0);
glEnd();
glFlush();
flag =0;
con[x][y] = 0;
}
}else if(flag==1){
//如果本来在内侧进入了外侧
if(y-400 <= -200){
draw_inner(x, y);
//从内侧进入外侧
draw_line(x_pos, y_pos, x, y);
x_pos = 0;
y_pos =0;
flag =0;
}else{
flag=1;
draw_inner(x, y);
y_1 = min(y_1,y);
x_1 = min(x_1,x);
}
}
visited[x][y] = 1;
if(out_of_index(x+10, y)&&con[x+10][y]==1&&visited[x+10][y]==0){
search(x+10,y,index);
visited[x+10][y] =1;
}
if(out_of_index(x,y+10)&&con[x][y+10]==1&&visited[x][y+10]==0){
search(x,y+10,index);
visited[x][y+10] =1;
}
if(out_of_index(x+10,y+10)&&con[x+10][y+10]==1&&visited[x+10][y+10]==0){
search(x+10,y+10,index);
visited[x+10][y+10] =1;
}
if(out_of_index(x+10,y-10)&&con[x+10][y-10]==1&&visited[x+10][y-10]==0){
search(x+10,y-10,index);
visited[x+10][y-10] =1;
}
if(out_of_index(x,y-10)&&con[x][y-10]==1&&visited[x][y-10]==0){
search(x,y-10,index);
visited[x][y-10] =1;
}
if(out_of_index(x-10,y)&&con[x-10][y]==1&&visited[x-10][y]==0){
search(x-10,y,index);
visited[x-10][y] =1;
}
if(out_of_index(x-10,y+10)&&con[x-10][y+10]==1&&visited[x-10][y+10]==0){
search(x-10,y+10,index);
visited[x-10][y+10] =1;
}
if(out_of_index(x-10,y-10)&&con[x-10][y-10]==1&&visited[x-10][y-10]==0){
search(x-10,y-10,index);
visited[x-10][y-10] =1;
}
}else if(index ==2){
//讨论左侧的情况
if(flag ==0){
//如果本来在外侧
if(x-400 >= -300){
draw_inner2(x, y);
//从外侧进入内侧
flag =1;
x_pos= x;
y_pos = y;
}else{
glPointSize(8);
glColor3f(1.0,1.0,1.0);
glBegin(GL_POINTS);
glVertex3f(translater(x-400),translater(y-400),0.0);
glEnd();
glFlush();
flag =0;
}
}else if(flag==1){
//如果本来在内侧进入了外侧
if(x-400 <= -300){
draw_inner2(x, y);
//从内侧进入外侧
cout << "inner -> outer "<< endl;
cout << x_pos <<" == "<< y_pos <<endl;
cout << x <<" === " << y <<endl;
draw_line2(x_pos, y_pos, x, y);
cout << con[x-10][y] <<"here !! "<< endl;
x_pos = 0;
y_pos =0;
flag =0;
}else{
flag=1;
draw_inner2(x, y);
}
}
visited[x][y] = 1;
if(out_of_index(x+10, y)&&(con[x+10][y]==1||con[x+10][y]==(-1^1111))&&visited[x+10][y]==0){
search(x+10,y,index);
visited[x+10][y] =1;
}
if(out_of_index(x,y+10)&&(con[x][y+10]==1||con[x][y+10]==(-1^1111))&&visited[x][y+10]==0){
search(x,y+10,index);
visited[x][y+10] =1;
}
if(out_of_index(x+10,y+10)&&(con[x+10][y+10]==1||con[x+10][y+10]==(-1^1111))&&visited[x+10][y+10]==0){
search(x+10,y+10,index);
visited[x+10][y+10] =1;
}
if(out_of_index(x+10,y-10)&&(con[x+10][y-10]==1||con[x+10][y-10]==(-1^1111))&&visited[x+10][y-10]==0){
search(x+10,y-10,index);
visited[x+10][y-10] =1;
}
if(out_of_index(x,y-10)&&(con[x][y-10]==1||con[x][y-10]==(-1^1111))&&visited[x][y-10]==0){
search(x,y-10,index);
visited[x][y-10] =1;
}
if(out_of_index(x-10,y)&&(con[x-10][y]==1||con[x-10][y]==(-1^1111))&&visited[x-10][y]==0){
search(x-10,y,index);
visited[x-10][y] =1;
}
if(out_of_index(x-10,y+10)&&(con[x-10][y+10]==1||con[x-10][y+10]==(-1^1111))&&visited[x-10][y+10]==0){
search(x-10,y+10,index);
visited[x-10][y+10] =1;
}
if(out_of_index(x-10,y-10)&&(con[x-10][y-10]==1||con[x-10][y-10]==(-1^1111))&&visited[x-10][y-10]==0){
search(x-10,y-10,index);
visited[x-10][y-10] =1;
}
}
}
void cutter(int x, int y){
/*
函数说明：这里包含四把刀
参数说明：传入我们的起始坐标
*/
//首先判断点的位置：框内？框外？
for (int i = 0; i <801; i++) {
for (int j =0; j < 801; j++) {
visited[i][j] = 0;
}
}
if(y < -200){
//在下方
flag =0; //在下方外侧
search(x+400,y+400,1);
}
if(x < -300){
//在左侧！
flag = 0;
for (int i = 0; i <801; i++) {
for (int j =0; j < 801; j++) {
visited[i][j] = 0;
}
}
glPointSize(pixel_size);
glColor3f(0.9,0.89,0.1);
glBegin(GL_POINTS);
glVertex3f(translater(x_1-400),translater(y_1-400),0.0);
glEnd();
glFlush();
cout << "xx "<< x_1 -400 <<" " << y_1-400 <<endl;
search(x_1,y_1,2);
}
}
void p(float x , float y,float x1,float y1){
/*
函数说明：绘制像素的点，这里将点的大小设置为7。
颜色采用蓝色。利用圆八个部分的坐标对应关系进行绘图。
加x1与y1是为了进行圆的平移
参数说明：浮点数x，y是openGl坐标系。
*/
glPointSize(pixel_size);
glColor3f(1.0,1.0,0.0);
glBegin(GL_POINTS);
glVertex3f(x+x1,y+y1,0.0);
glEnd();
glFlush();
}
void paint(int x ,int y ){
add(x,y, 1);
p(translater(x), translater(y), 0, 0);
}
void grid(){
/*
函数说明：绘制网格为了便于将真实的像素pixel转化为我们模拟的像素
*/
glClearColor(0, 0, 0, 0);//这是设置背景色,必须要在glclear之前调用
glClear(GL_COLOR_BUFFER_BIT);
int hei_number = numbers;
float delta_hei = height / hei_number;
glColor3f(0.0,1.0,0);
for (int i = 1; i < numbers *2; i ++ ) { //利用循环绘制网格
glBegin(GL_LINES);
glVertex2f(-1+i*delta_hei/height, -1);
glVertex2f(-1+i*delta_hei/height, 1);
glVertex2f(-1,-1+i*delta_hei/height);
glVertex2f(1,-1+i*delta_hei/height);
glEnd();
glFlush();}
glColor3f(1.0,0,0);
glBegin(GL_LINES); //绘制坐标系，便于观察
glVertex2f(-1,0);
glVertex2f(1,0);
glVertex2f(0,-1);
glVertex2f(0,1);
glEnd();
glFlush();
//绘制我们的框图
for (int i = 0; i <= 300; i+=t) {
draw_point(translater( i),translater(200));
add(i, 200, -1);
add(-i, 200, -1);
add(i, -200, -1);
add(-i, -200, -1);
}
for (int i = 0; i <= 200; i+=t) {
draw_point(translater(300),translater( i));
add(300,i, -1);
add(-300,i, -1);
add(300,-i, -1);
add(-300,-i, -1);
}
//绘制多边形
int dm = -370;
//设置偏移量
for (int i = 140; i<=240; i+=10) {
paint(i, i+dm);
}
for(int i =240; i <=340 ; i+=10 ){
paint(240, i+dm);
//绘制横线
}
for(int i = 240;i>=-200;i-=10 ){
paint(i, 340+dm);
}
for(int i = -200;i>=-380;i-=10){
paint(i, 540+i+dm);
}
for(int i = -200;i>=-380;i-=10){
paint(i, 540+i+dm);
}
for(int i = 160; i >= -20 ; i-=10){
paint(-380, i+dm);
}
for (int i = 1;i <=30; i++) {
paint(-380+i*10, -20+i*10+dm);
}
for (int i = 1;i <=14; i++) {
paint(-80+i*10, 280-i*10+dm);
}
for(int i =60; i <=140 ; i+=10 ){
paint(i, 140+dm);
}
cutter(-380, -390);
//刷新缓冲，保证绘图命令能被执行
}
int main(int argc, char *argv[]) {
//初始化GLUT library
glutInit(&argc, argv);
//对窗口的大小进行初始化
glutInitWindowSize(700,700);
glutInitWindowPosition(300,200);
// 设置窗口出现的位置
//glutInitWindowPosition(int x, int y);
glutInitDisplayMode(GLUT_RGBA);
glutCreateWindow("hw_多边形裁剪");
glutDisplayFunc(&grid);
glutMainLoop();
return 0;
}