GLUT GL 3/4 球体有问题

Question

我的图形课有任务要做。我必须只使用 GL_TRIANGLE_STRIP 构建 3/4。我已经完成了，但是有一个我不能接受的主要错误。

GLfloat radius = 3, alpha, beta, PI = 3.14314159;


//lHorizontal and lVertical im changing using keyboard it says how many 
 sphere divisions are 

for (alpha = 0.0; alpha < PI; alpha += PI / lVertical)
{

    glBegin(GL_TRIANGLE_STRIP);


    for (beta = 0.0; beta < 1.5075*PI; beta += PI / lHorizontal)
    {

        glColor3f(1, 1, 0);
        x = radius * cos(beta)*sin(alpha);
        y = radius * sin(beta)*sin(alpha);
        z = radius * cos(alpha);

        glNormal3f(x, y, z);
        glVertex3f(x, y, z);

        glColor3f(0, 1, 1);
        x = radius * cos(beta)*sin(alpha + PI / lVertical);
        y = radius * sin(beta)*sin(alpha + PI / lVertical);
        z = radius * cos(alpha + PI / lVertical);

        glNormal3f(x, y, z);
        glVertex3f(x, y, z);



    }
    glEnd();
}


glColor3f(1, 1, 0);
glBegin(GL_TRIANGLE_STRIP);

for (alpha = PI; alpha < 2.01*PI; alpha += PI / lVertical) {
    x = -radius * sin(alpha);
    y = 0;
    z = radius * cos(alpha);
    glNormal3f(x, y, z);
    glVertex3f(x, y, z);
    glNormal3f(0, 0, 0);
    glVertex3f(0, 0, 0);
}
glEnd();


glBegin(GL_TRIANGLE_STRIP);

for (alpha = PI; alpha < 2.01*PI; alpha += PI / lVertical) {
    x = 0;
    y = radius * sin(alpha);
    z = -radius * cos(alpha);
    glNormal3f(x, y, z);
    glVertex3f(x, y, z);
    glNormal3f(0, 0, 0);
    glVertex3f(0, 0, 0);
}
glEnd();

这段代码的结果是：

当我改变 lHorizontal 时，出现了不应该出现的部分（看图片）。我可以更改代码以避免此问题吗？

Answer 1

PI的值错误：

..., PI = 3.14314159; // 3.14159... ?

改正后，让我们在外循环中测试 alpha 的值，对于 lVertical = 8:

int lVertical = 8;
GLfloat radius = 3, alpha, beta, PI = 3.141592654;

for (alpha = 0.0; alpha < PI; alpha += PI / lVertical)
{
    printf("%f, %f\n", alpha, alpha + PI / lVertical);
}

输出：

0.000000, 0.392699
0.392699, 0.785398
0.785398, 1.178097
1.178097, 1.570796
1.570796, 1.963495
1.963495, 2.356194
2.356194, 2.748893
2.748893, 3.141593
3.141593, 3.534292 <<

3.534292 大于 PI，这意味着它是 alpha 的无效值。效果是最后一个多边形环"folds"周围，产生了不应该出现的部分。

最好直接从整数索引计算角度:

for (int i = 0; int i < lVertical; i++)
{
    GLfloat alpha1 = (PI / lVertical) * i;
    GLfloat alpha2 = (PI / lVertical) * (i + 1);

    glBegin(GL_TRIANGLE_STRIP);

    for (int j = 0; j < lHorizontal; j++)
    {
        GLfloat beta1 = (PI / lHorizontal) * j;
        GLfloat beta2 = (PI / lHorizontal) * (j + 1);

        glColor3f(1, 1, 0);
        x = radius * cos(beta1)*sin(alpha1);
        y = radius * sin(beta1)*sin(alpha1);
        z = radius * cos(alpha1);

        glNormal3f(x, y, z);
        glVertex3f(x, y, z);

        glColor3f(0, 1, 1);
        x = radius * cos(beta2)*sin(alpha2);
        y = radius * sin(beta2)*sin(alpha2);
        z = radius * cos(alpha2);

        glNormal3f(x, y, z);
        glVertex3f(x, y, z);
    }

    glEnd();
}

GLUT GL 3/4 球体有问题

GLUT GL 3/4 sphere something wrong

graphics

glut