求助：Qt 5.7.0关于Opengl 的一个全程 hellogl2之中关于画图代码的解释

[小宇不内向]

#include "logo.h"
#include <qmath.h>

Logo::Logo()
: m_count(0)
{
m_data.resize(2500 * 6);

const GLfloat x1 = +0.06f;
const GLfloat y1 = -0.14f;
const GLfloat x2 = +0.14f;
const GLfloat y2 = -0.06f;
const GLfloat x3 = +0.08f;
const GLfloat y3 = +0.00f;
const GLfloat x4 = +0.30f;
const GLfloat y4 = +0.22f;

quad(x1, y1, x2, y2, y2, x2, y1, x1);
quad(x3, y3, x4, y4, y4, x4, y3, x3);

extrude(x1, y1, x2, y2);
extrude(x2, y2, y2, x2);
extrude(y2, x2, y1, x1);
extrude(y1, x1, x1, y1);
extrude(x3, y3, x4, y4);
extrude(x4, y4, y4, x4);
extrude(y4, x4, y3, x3);

const int NumSectors = 100;

for (int i = 0; i < NumSectors; ++i) {
GLfloat angle = (i * 2 * M_PI) / NumSectors;
GLfloat angleSin = qSin(angle);
GLfloat angleCos = qCos(angle);
const GLfloat x5 = 0.30f * angleSin;
const GLfloat y5 = 0.30f * angleCos;
const GLfloat x6 = 0.20f * angleSin;
const GLfloat y6 = 0.20f * angleCos;

angle = ((i + 1) * 2 * M_PI) / NumSectors;
angleSin = qSin(angle);
angleCos = qCos(angle);
const GLfloat x7 = 0.20f * angleSin;
const GLfloat y7 = 0.20f * angleCos;
const GLfloat x8 = 0.30f * angleSin;
const GLfloat y8 = 0.30f * angleCos;

quad(x5, y5, x6, y6, x7, y7, x8, y8);

extrude(x6, y6, x7, y7);
extrude(x8, y8, x5, y5);
}
}

void Logo::add(const QVector3D &v, const QVector3D &n)
{
GLfloat *p = m_data.data() + m_count;
*p++ = v.x(); //赋值，指针自增1
*p++ = v.y();
*p++ = v.z();
*p++ = n.x();
*p++ = n.y();
*p++ = n.z();
m_count += 6;
}

void Logo::quad(GLfloat x1, GLfloat y1, GLfloat x2, GLfloat y2, GLfloat x3, GLfloat y3, GLfloat x4, GLfloat y4)
{
QVector3D n = QVector3D::normal(QVector3D(x4 - x1, y4 - y1, 0.0f), QVector3D(x2 - x1, y2 - y1, 0.0f));

add(QVector3D(x1, y1, -0.05f), n);
add(QVector3D(x4, y4, -0.05f), n);
add(QVector3D(x2, y2, -0.05f), n);

add(QVector3D(x3, y3, -0.05f), n);
add(QVector3D(x2, y2, -0.05f), n);
add(QVector3D(x4, y4, -0.05f), n);

n = QVector3D::normal(QVector3D(x1 - x4, y1 - y4, 0.0f), QVector3D(x2 - x4, y2 - y4, 0.0f));

add(QVector3D(x4, y4, 0.05f), n);
add(QVector3D(x1, y1, 0.05f), n);
add(QVector3D(x2, y2, 0.05f), n);

add(QVector3D(x2, y2, 0.05f), n);
add(QVector3D(x3, y3, 0.05f), n);
add(QVector3D(x4, y4, 0.05f), n);
}

void Logo::extrude(GLfloat x1, GLfloat y1, GLfloat x2, GLfloat y2)
{
QVector3D n = QVector3D::normal(QVector3D(0.0f, 0.0f, -0.1f), QVector3D(x2 - x1, y2 - y1, 0.0f));

add(QVector3D(x1, y1, +0.05f), n);
add(QVector3D(x1, y1, -0.05f), n);
add(QVector3D(x2, y2, +0.05f), n);

add(QVector3D(x2, y2, -0.05f), n);
add(QVector3D(x2, y2, +0.05f), n);
add(QVector3D(x1, y1, -0.05f), n);
}

以上代码，是画出如图所示3D图形的代码 。
主要是：add(const QVector3D &v, const QVector3D &n);quad();和extrude(GLfloat x1, GLfloat y1, GLfloat x2, GLfloat y2)这三个函数，请大神帮助解释一下。

[赵4老师]

VS IDE中，在不明白的符号上点鼠标右键，选转到定义。

[小宇不内向]

但是，这是Qt的示例啊~