openGL实现图形学扫描线种子填充算法

---

title: "openGL实现图形学扫描线种子填充算法"
date: 2018-06-11T19:41:30+08:00
tags: ["图形学"]
categories: ["C++"]

---

先上效果图

白色的起始种子点

代码

#include <GL/glut.h>
#include <cmath>
#include <set>
#include <vector>
#include <unistd.h> //sleep函数
#include <iostream>
#include <algorithm> //find函数，查找vector中元素
#include <stack>


using namespace std;

//规格化为0.05的倍数
inline GLdouble normal(GLdouble x)
{
    return (round(x * 20) / 20);
}

typedef struct Point {
    GLdouble x, y;

    Point(GLdouble a = 0, GLdouble b = 0)
    {
        x = a, y = b;
    }

    // set会对插入的元素自动排序，需要重载运算符.定义排序规则
    //
    //
    // 重载运算符的要求
    // 1. 若A<B为真,则B<A为假
    // 2. 若A<B,B<C --> A<C
    // 3. A<A永远为假
    // set中判断元素是否相等
    // if(!(A<B||B<A)) --> A=B
    bool operator<(const Point &a) const
    {
        return ((x - a.x) < -0.01 || ((x - a.x) < 0.01 && (y - a.y) < -0.01));
    }

    bool operator==(const Point &a) const
    {
        return (abs(x - a.x) < 0.01 && abs(y - a.y) < 0.01);
    }
} point;

void drawGrid();

void initGraphBorder();

void drawGraphices();

void myDisplay();

void DDA(point A, point B);

void initGraphBorder();


point first_seed;
unsigned long m;
static int n = 40;
static GLfloat pointSize = 12.5;
set<point> graphBorder; // 图形边界数组<set>可以快速查找
//set虽然可以快速查找，但却会打乱顺序，不方便实现填充动画
vector<point> graphFill;   // 要填充的数组
vector<point> graphVertex;  //存储图形定点数组，按顺序
stack<point> seed;  //存储种子

GLdouble p = float(2.0 / n); // 每个格子的大小

//画网格坐标
void drawGrid()
{
    glColor3d(1, 1, 1); //网格用白色表示
    glLineWidth(1);
    glBegin(GL_LINES);

    for (int i = 0; i <= n; i++) {
        //画竖线
        glVertex2d(-1 + 1.0 / n + i * 2.0 / n, -1);
        glVertex2d(-1 + 1.0 / n + i * 2.0 / n, 1);
        //画横线
        glVertex2d(-1, -1 + 1.0 / n + i * 2.0 / n);
        glVertex2d(1, -1 + 1.0 / n + i * 2.0 / n);
    }

    glEnd();
}


//DDA算法
void DDA(point A, point B)
{
    cout << "连接(" << A.x << ',' << A.y << ") 到 (" << B.x << ',' << B.y << ")\n";

    if (A.x > B.x) {
        swap(A, B);
    }

    A.x = normal(A.x);
    A.y = normal(A.y);
    B.x = normal(B.x);
    B.y = normal(B.y);
    double delta_x = B.x - A.x;
    double delta_y = B.y - A.y;
    double k = delta_y / delta_x;
    double x = A.x, y = A.y;

    if (k > -1 && k < 1) {
        //x是最大位移
        //cout << k << endl;
        while (true) {
            if ((x - B.x) > 0.01)break;

            graphBorder.insert(point(normal(x), normal(y)));
            x += p;
            y += (p * k);
        }
    }
    else if (k >= 1) {
        //Y是最大位移
        while (true) {
            if ((y - B.y) > 0.01) break;

            graphBorder.insert(point(normal(x), normal(y)));
            y += p;
            x += (p / k);
        }
    }
    else {
        while (true) {
            if ((B.y - y) > 0.01) break;

            graphBorder.insert(point(normal(x), normal(y)));
            y -= p;
            x -= (p / k);
        }
    }
}


//初始化图形边界数组
void initGraphBorder()
{
    //    graphVertex存储图形的顶点
    for (auto it = graphVertex.begin(); it != graphVertex.end(); it++) {
        if (it == graphVertex.end() - 1) {
            //最后一个点连接第一个点
            DDA(*it, *graphVertex.begin());
        }
        else {
            //连接it1和it2xr
            DDA(*it, *(it + 1));
        }
    }
}

/*********************************
 * 1. 初始化：堆栈置空,将种子seed(x,y)入栈
 * 2. 出栈: 若栈空则结束，否则将栈顶元素出栈，以y作为当前扫描线
 * 3. 填充并确定新种子点所在区域：从当前种子点出发，沿y扫描线向左右方向填充
 *    直到遇到边界像素。标记当前区段的左右端点坐标为Xl, Xr.
 * 4. 确定新种子点：检查[Xl-1,Xr]和[Xl+1,Xr]区域，若存在非边界，未填充的
 *    像素，则把每一区间的最右像素作为种子点压栈。返回第2步
**********************************/

// 沿扫描线的区域填充
// 从种子堆栈<stack>seed中取出种子点
// 把要填充的点加入<vector>graphFill
void floodFillSet()
{
    while (!seed.empty()) {
        point s = seed.top();   //当前种子点
        seed.pop();
        cout << "当前种子点  " << s.x << "  " << s.y << endl;
        //填充种子点及左右连续区域
        point t = s, xl, xr;

        //填充左侧连续区域,并找到区域最左边界
        while (true) {
            //到达边界退出
            if (t.x < -1)break;
            graphFill.push_back(t);
            t.x -= p;
            //查找是否已填充
            auto it1 = find(graphFill.begin(), graphFill.end(), t);
            //查找是否是边界
            auto it2 = graphBorder.find(t);

            if (it1 != graphFill.end() || it2 != graphBorder.end()) { //已填充或已达边界
                xl = t;
                xl.x += p;
                break;
            }
        }

        t = s;

        //填充右侧区域
        while (true) {
            if (t.x > 1)break;

            graphFill.push_back(t);
            t.x += p;
            //查找是否已填充
            auto it1 = find(graphFill.begin(), graphFill.end(), t);
            //查找是否是边界
            auto it2 = graphBorder.find(t);

            if (it1 != graphFill.end() || it2 != graphBorder.end()) { //已填充或已达边界
                xr = t;
                xr.x -= p;
                break;
            }
        }

        //在下一行找种子点
        for (int d : { 1, -1 }) {//先上再下
            bool status = false; //标记一段空白区域的开始
            t = xl;
            t.y += (p * d);   //移到下一行或上一行

            while ((t.x - xr.x) < 0.07) {
                auto it1 = find(graphFill.begin(), graphFill.end(), t);
                auto it2 = graphBorder.find(t);

                //找空白区域开始点
                //如果当前点是空白区域,且空白区域未开始 则s=true
                if (!status && it1 == graphFill.end() && it2 == graphBorder.end()) {
                    status = true;
                }

                //区域开始且遇到边界或填充区域
                if (status && (it1 != graphFill.end() || it2 != graphBorder.end())) { //到达边界或已填充颜色，且左侧有空白区域
                    status = false;
                    //添加左侧一点为种子点
                    seed.push(point(t.x - p, t.y));
                }

                // 到达最右区间xr，即便不是边界,只要s=true也应标注最右种子点
                if (status && abs(t.x - xr.x) < 0.01) {   //注意浮点数比较大小
                    status = false;
                    seed.push(t);
                }

                t.x += p;
            }
        }
    }
}


//画待填充的图形边界
void drawGraphices()
{
    glColor3f(0.5, 0.5, 0.2);
    glBegin(GL_POINTS);

    //C++11的新特性，可以遍历vector map list or {1,2,3}
    for (auto it : graphBorder) {
        glVertex2d(it.x, it.y);
    }

    glEnd();
}

//画填充像素
void drawFloodFill(unsigned long m)
{
    glColor3f(0.4, 0.8, 0.1);
    glBegin(GL_POINTS);

    for (unsigned long i = 0; i < m && i < graphFill.size(); i++) {
        glVertex2d(graphFill[i].x, graphFill[i].y);
        //myDisplay();
    }

    glEnd();
}

//绘图
void myDisplay()
{
    glClearColor(0.1f, 0.3f, 0.33f, 0.0f);
    glClear(GL_COLOR_BUFFER_BIT);
    //画图形边界
    drawGraphices();
    //画m个填充像素
    drawFloodFill(m);
    glColor3d(1, 0, 0);
    glPointSize(pointSize);
    //加个白点,起始种子点
    glColor3d(1, 1, 1);
    glBegin(GL_POINTS);
    glVertex2d(first_seed.x, first_seed.y);
    glEnd();
    //画网格
    drawGrid();
    glFlush();
}


int main(int argc, char *argv[])
{
    //存入要填充的图形顶点 8
    //(-0.7,0.6) (0.7,0.6) (0.7,0) (0.3,0) (0.3,-0.5) (-0.3,-0.5)
    // (-0.3,0) (-0.7,0)
    cout << "请输入顶点坐标,(-1,1) 输入>1 结束 \n";
    double x, y;

    while (cin >> x) {
        if (x > 1)
            break;
        else
            cin >> y;

        graphVertex.emplace_back(point(x, y));
    }

    cout << "输入初始种子点\n";
    cin >> x >> y;
    first_seed.x = x;
    first_seed.y = y;
    glutInit(&argc, argv);
    glutInitDisplayMode(GLUT_RGB | GLUT_SINGLE);
    glutInitWindowSize(500, 500);
    glutInitWindowPosition(100, 100);
    //初始化边界集
    initGraphBorder();
    //扫描线种子填充
    seed.push(first_seed);
    floodFillSet();
    glutCreateWindow("扫描线种子填充");
    glutDisplayFunc(&myDisplay);

    for (m = 0; m < graphFill.size(); m++) {
        usleep(10000);
        myDisplay();
    }

    glutMainLoop();
    return 0;
}

输入样例

-0.7 0.7
-0.35 0.7
-0.35 0
0.35 0
0.35 0.7
0.7 0.7
0.7 -0.7
-0.7 -0.7
2 
0 -0.2