Qt5.12+OpenGL 计算机图形学（第四版）第4章 例子1

因为使用的是Qt框架，没有使用GLUT，所以改写了书中部分代码：

1. 文本用QString数组保存。

2. 绘制字符没有使用GLUT函数，直接使用QPainter进行绘制，Qt绘图坐标是以左上角为原点（0，0），因此，坐标也需要进行变换。

关键部分源代码，其它可以参照前面章节的例子。

a. 绘制折线图

QString label[12] = {
    "Jan", "Feb", "Mar", "May", "Jun", "Jul", "Aug", "Sep", "Oct", "Nov", "Dec"
};

GLint dataValue[12] = {
    420, 342, 324, 310, 262, 185, 190, 196, 217, 240, 312, 438
};

void OpenGLWidget::lineGraph()
{
    GLint month, k;
    GLint xRaster = 20;
    GLint yRaster = 150;
    GLint x = 30;

    int h = this->height();

    glClear(GL_COLOR_BUFFER_BIT);
    glColor3f(0.0, 0.0, 1.0);

    glBegin(GL_LINE_STRIP);
        for(k=0; k< 12; k++)
            glVertex2i(x+k*50, dataValue[k]);
    glEnd();

    QPainter painter(this);
    painter.setPen(Qt::red);
    painter.setFont(QFont("Arial", 10));
    for(k=0; k<12; k++) {
        painter.drawText(x+k*50-5, h-dataValue[k]+10, "*");
    }

    painter.setPen(Qt::black);
    painter.setFont(QFont("Helvecica", 12));
    for(month=0; month<12; month++) {
        for(k=3*month; k<3*month+3; k++)
            painter.drawText(xRaster, h - yRaster, label[month]);
        xRaster += 50;
    }

    glFlush();
}

效果图：

b. 绘制直方图

void OpenGLWidget::barChart()
{
    GLint month, k;
    GLint xRaster = 20;
    GLint yRaster = 150;
    int h = this->height();

    glClear(GL_COLOR_BUFFER_BIT);

    glColor3f(1.0, 0.0, 0.0);
    for(k=0; k<12; k++)
        glRecti(20+k*50, 165, 40+k*50, dataValue[k]);

    QPainter painter(this);
    painter.setPen(Qt::black);
    painter.setFont(QFont("Helvecica", 12));
    for(month=0; month<12; month++) {
        for(k=3*month; k<3*month+3; k++)
            painter.drawText(xRaster, h - yRaster, label[month]);
        xRaster += 50;
    }
}

效果图：

c. 绘制饼图

关于中点画圆的算法可以参考https://www.cnblogs.com/clairvoyant/p/5528067.html这篇文章，讲得还是比较清楚的。

GLsizei winWidth = 400, winHeight = 300;

const GLdouble twoPi = 6.283185;

void OpenGLWidget::pieChart()
{
    QPoint circCtr, piePt;
    GLint radius = winWidth / 4;

    GLdouble sliceAngle, previousSliceAngle = 0.0;

    GLint k, nSlices = 12;

    GLfloat dataValues[12] = {
        10.0, 7.0, 13.0, 5.0, 13.0, 14.0, 3.0, 16.0, 5.0, 3.0, 17.0, 8.0
    };
    GLfloat dataSum = 0.0;

    circCtr.setX(winWidth / 2);
    circCtr.setY(winHeight / 2);
    circleMidpoint(circCtr, radius);

    for(k=0; k<nSlices; k++) {
        dataSum += dataValues[k];
    }

    for(k=0; k<nSlices; k++) {
        sliceAngle = twoPi * dataValues[k] / dataSum + previousSliceAngle;
        piePt.setX(circCtr.x() + radius * cos(sliceAngle));
        piePt.setY(circCtr.y() + radius * sin(sliceAngle));

        glBegin(GL_LINES);
            glVertex2i(circCtr.x(), circCtr.y());
            glVertex2i(piePt.x(), piePt.y());
        glEnd();
        previousSliceAngle = sliceAngle;
    }
}

void putpixel(int x0, int y0, int x, int y)
{
    glBegin(GL_POINTS);
        glVertex2f(x0 + x, y0 + y);
        glVertex2f(x0 + x, y0 - y);
        glVertex2f(x0 - x, y0 + y);
        glVertex2f(x0 - x, y0 - y);
        glVertex2f(x0 + y, y0 + x);
        glVertex2f(x0 + y, y0 - x);
        glVertex2f(x0 - y, y0 + x);
        glVertex2f(x0 - y, y0 - x);
    glEnd();
}

/*
 * 通过中点和半径画圆
 */
void OpenGLWidget::circleMidpoint(QPoint c, int r)
{
    int x, y, p;
    x = 0; y = r; p = 1 - r;
    while(x <= y) {
        putpixel(c.x(), c.y(), x, y);
        if ( p < 0 ) {
            p += 2 * x + 1;
        } else {
            p += 2 * (x - y) + 1;
            y--;
        }
        x++;
    }
}

效果图：