OpenGL根据极坐标参数方程绘制心形线、螺旋线等图形

本代码参考自《计算机图形学》第4版，根据极坐标参数方程绘制曲线：蜗形线、心形线、三叶曲线、四叶曲线、螺旋线共5种图形。

生成定点坐标的程序如下所示，该函数将需要绘制的顶点按顺序添加到入参verts的最后

typedef enum { LIMACON = 1,
                CARDIOID,
                THREELEAF,
                FOURLEAF,
                SPIRAL  } curveName;

void GLApp::genVertices(std::vector<glm::vec2> &verts, GLint curveNum, const GLint x0, const GLint y0)
{
    const GLdouble twoPi = 6.283185;
    const GLint a = 175, b = 60;

    GLfloat r, theta, dtheta = 1.0 / float(a);
    glm::vec2 curvePt[2];

    curvePt[0].x = x0;
    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)
    {
        switch (curveNum) {
        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);
        curvePt[1].y = y0 + r * sin(theta);
        verts.push_back(curvePt[0]);
        verts.push_back(curvePt[1]);

        curvePt[0].x = curvePt[1].x;
        curvePt[0].y = curvePt[1].y;
        theta += dtheta;
    }
}

绘制时调用glDrawArrays(GL_LINES, 0, vert_num);

（vert_num等于verts.size()）