OpenGL根據極坐標參數方程繪制心形線、螺旋線等圖形

本代碼參考自《計算機圖形學》第4版，根據極坐標參數方程繪制曲線：蝸形線、心形線、三葉曲線、四葉曲線、螺旋線共5種圖形。

生成定點坐標的程序如下所示，該函數將需要繪制的頂點按順序添加到入參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;
    }
}

繪制時調用glDrawArrays(GL_LINES, 0, vert_num);

（vert_num等於verts.size()）