OpenGL从1.0开始--曲线图形

这一节我们继续来实现一些有趣的高级图形，例如蜗形线limacon、心形线cardioid、三叶草threeLeaf、四叶草fourLeaf和螺旋线spiral等漂亮的曲线图形，如下面这些图形所示。

#include <gl/glut.h>#include <stdlib.h>#include <math.h>#include <iostream>using namespace std;const GLdouble twoPi = 6.283185;class screenPt{public:    GLint x, y;};typedef enum{limacon=1,cardioid,threeLeaf,fourLeaf,spiral}curveName;//五种图形的枚举GLsizei winWidth = 600, winHeight = 500;void init(void){    glClearColor(1.0, 1.0, 1.0, 1.0);    glMatrixMode(GL_PROJECTION);    gluOrtho2D(0.0, 200.0, 0.0, 150.0);}void lineSegment(screenPt pt1, screenPt pt2)//线段绘制函数，本节也是用曲线细分的方法绘制图形{    glBegin(GL_LINES);    glVertex2i(pt1.x, pt1.y);    glVertex2i(pt2.x, pt2.y);    glEnd();}void drawCurve(GLint curveNum)//核心绘制函数{    const GLint a = 175, b = 60;//任意的两个曲线参数    GLfloat r, theta, dtheta = 1.0 / float(a);    GLint x0 = 200, y0 = 250;//设置一个任意的屏幕初始坐标    screenPt curvePt[2];    glColor3f(0.0, 0.0, 0.0);    curvePt[0].x = x0;//初始化曲线位置    curvePt[0].y = y0;    switch (curveNum)    {    case  limacon:curvePt[0].x += a + b; break;    case cardioid:curvePt[0].x += a + a; break;    case threeLeaf : curvePt[0].x += a; break;    case fourLeaf:curvePt[0].x += a; break;    case spiral:break;    default:        break;    }    theta = dtheta;    while (theta<twoPi)//曲线细分    {        switch (curveNum)//不同的曲线适用不同的极函数        {        case limacon:            r = a*cos(theta) + b; break;        case cardioid:            r = a*(1 + cos(theta)); break;        case threeLeaf:            r = a*cos(3 * theta); break;        case fourLeaf:            r = a*cos(2 * theta);break;        case  spiral:            r = (a / 4.0)*theta; break;        default:            break;        }        curvePt[1].x = x0 + r*cos(theta);//绘制细分线段的终点        curvePt[1].y = y0 + r*sin(theta);        lineSegment(curvePt[0], curvePt[1]);//绘制该细分线段        curvePt[0].x = curvePt[1].x;//细分线段的起点坐标更新为终点坐标        curvePt[0].y = curvePt[1].y;        theta += dtheta;//曲线往前绘制    }}void displayFcn(void){    GLint curveNum;    glClear(GL_COLOR_BUFFER_BIT);    cout << "\nEnter the integer value corresponding to\n";    cout <<"one of the following curve names.\n";    cout << "\Press any other key to exit.\n";    cout << "\n1-limacon,2-cardioid,3-threeLeaf,4-fourLeaf,5-spiral:";    cin >> curveNum;//选择要绘制的曲线类型    if (curveNum == 1 || curveNum == 2 || curveNum == 3 || curveNum == 4 || curveNum == 5)    {        drawCurve(curveNum);//调用曲线绘制函数    }    else    {        exit(0);    }    glFlush();}void winReshapeFcn(GLint newWidth, GLint newHeight){    glMatrixMode(GL_PROJECTION);    glLoadIdentity();    gluOrtho2D(0.0, GLdouble(newWidth), 0.0, GLdouble(newHeight));    glClear(GL_COLOR_BUFFER_BIT);}void main(int argc, char**argv){    glutInit(&argc, argv);    glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB);    glutInitWindowPosition(100, 100);    glutInitWindowSize(winWidth, winHeight);    glutCreateWindow("Draw Curves");    init();    glutDisplayFunc(displayFcn);    glutReshapeFunc(winReshapeFcn);    glutMainLoop();}