47.使用帧缓存对象生成叠加

main.cpp

#include <QApplication>
#include <iostream>

#include "teapots.h"

int main(int argc, char *argv[])
{
    QApplication app(argc, argv);

    if (!QGLFormat::hasOpenGL()) {
        std::cerr << "This system has no OpenGL support" << std::endl;
        return 1;
    }

    if (!QGLFramebufferObject::hasOpenGLFramebufferObjects()) {
        std::cerr << "This system has no framebuffer object support"
                  << std::endl;
        return 1;
    }

    Teapots teapots;
    teapots.setWindowTitle(QObject::tr("Teapots"));
    teapots.resize(400, 400);
    teapots.show();

    return app.exec();
}

teapots.h

#ifndef TEAPOTS_H
#define TEAPOTS_H

#include <QGLFramebufferObject>
#include <QGLWidget>

class Teapots : public QGLWidget
{
    Q_OBJECT

public:
    Teapots(QWidget *parent = 0);
    ~Teapots();

protected:
    //实现了OpenGL的高级处理函数:
    void initializeGL();
    void resizeGL(int width, int height);
    void paintGL();

    //以便用户绘制一个橡皮筋选择框
    void mousePressEvent(QMouseEvent *event);
    void mouseMoveEvent(QMouseEvent *event);
    void mouseReleaseEvent(QMouseEvent *event);

    //私有函数负责创建茶壶对象以及茶壶的绘制.
private:
    void createGLTeapotObject();
    void drawTeapot(GLfloat x, GLfloat y, GLfloat ambientR,
                    GLfloat ambientG, GLfloat ambientB,
                    GLfloat diffuseR, GLfloat diffuseG,
                    GLfloat diffuseB, GLfloat specularR,
                    GLfloat specularG, GLfloat specularB,
                    GLfloat shininess);
    void drawTeapots();

    //私有变量可以保存framebuffer对象,茶壶对象
    QGLFramebufferObject *fbObject;
    GLuint glTeapotObject;
    //橡皮筋选择框的各个角
    QPoint rubberBandCorner1;
    QPoint rubberBandCorner2;
    //橡皮筋框的可见属性
    bool rubberBandIsShown;
};

#endif

teapots.cpp

#include <QtGui>
#include <QtOpenGL>

#include "teapots.h"

Teapots::Teapots(QWidget *parent)
    : QGLWidget(parent)
{
    //初始化rubberBandIsShown私有变量
    rubberBandIsShown = false;


    makeCurrent();
    //创建framebuffer对象
    fbObject = new QGLFramebufferObject(1024, 1024,
                                        QGLFramebufferObject::Depth);
    //创建茶壶对象
    createGLTeapotObject();
}

//释放与framebuffer对象和茶壶相关的资源
Teapots::~Teapots()
{
    makeCurrent();
    delete fbObject;
    glDeleteLists(glTeapotObject, 1);
}

//设置光照模式,打开OpenGL特性
void Teapots::initializeGL()
{
    static const GLfloat ambient[] = { 0.0, 0.0, 0.0, 1.0 };
    static const GLfloat diffuse[] = { 1.0, 1.0, 1.0, 1.0 };
    static const GLfloat position[] = { 0.0, 3.0, 3.0, 0.0 };
    static const GLfloat lmodelAmbient[] = { 0.2, 0.2, 0.2, 1.0 };
    static const GLfloat localView[] = { 0.0 };

    glLightfv(GL_LIGHT0, GL_AMBIENT, ambient);
    glLightfv(GL_LIGHT0, GL_DIFFUSE, diffuse);
    glLightfv(GL_LIGHT0, GL_POSITION, position);
    glLightModelfv(GL_LIGHT_MODEL_AMBIENT, lmodelAmbient);
    glLightModelfv(GL_LIGHT_MODEL_LOCAL_VIEWER, localView);

    glFrontFace(GL_CW);
    glEnable(GL_LIGHTING);
    glEnable(GL_LIGHT0);
    glEnable(GL_AUTO_NORMAL);
    glEnable(GL_NORMALIZE);
    glEnable(GL_DEPTH_TEST);
    glDepthFunc(GL_LESS);
}

//在Teapot窗口改变大小时重绘茶壶场景.
void Teapots::resizeGL(int width, int height)
{
    //为了在framebuffer对象上绘制茶壶
    fbObject->bind();

    //设置一些OpenGL特性,以及投影和模式视图矩阵
    glDisable(GL_TEXTURE_2D);
    glEnable(GL_LIGHTING);
    glEnable(GL_DEPTH_TEST);

    glViewport(0, 0, width, height);
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    if (width <= height) {
        glOrtho(0.0, 20.0, 0.0, 20.0 * GLfloat(height) / GLfloat(width),
                -10.0, 10.0);
    } else {
        glOrtho(0.0, 20.0 * GLfloat(width) / GLfloat(height), 0.0, 20.0,
                -10.0, 10.0);
    }
    glMatrixMode(GL_MODELVIEW);
    //在framebuffer对象上绘制茶壶
    drawTeapots();

    //释放framebuffer对象,确保随后的OpenGL绘制操作不会发生
    //在framebuffer对象上
    fbObject->release();
}

//先重新设置投影和模式视图矩阵
//然后把framebuffer对象绑定到纹理上,绘制一个带有该纹理的矩形覆盖
//整个窗口部件
void Teapots::paintGL()
{
    glDisable(GL_LIGHTING);
    glViewport(0, 0, width(), height());
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();
    glDisable(GL_DEPTH_TEST);

    glClear(GL_COLOR_BUFFER_BIT);
    glEnable(GL_TEXTURE_2D);
    glBindTexture(GL_TEXTURE_2D, fbObject->texture());
    glColor3f(1.0, 1.0, 1.0);
    GLfloat s = width() / GLfloat(fbObject->size().width());
    GLfloat t = height() / GLfloat(fbObject->size().height());

    glBegin(GL_QUADS);
    glTexCoord2f(0.0, 0.0);
    glVertex2f(-1.0, -1.0);
    glTexCoord2f(s, 0.0);
    glVertex2f(1.0, -1.0);
    glTexCoord2f(s, t);
    glVertex2f(1.0, 1.0);
    glTexCoord2f(0.0, t);
    glVertex2f(-1.0, 1.0);
    glEnd();

    //如果橡皮筋框是可见的,我们可以把它绘制在矩形 上
    if (rubberBandIsShown) {
        glMatrixMode(GL_PROJECTION);
        glOrtho(0, width(), height(), 0, 0, 100);
        glMatrixMode(GL_MODELVIEW);

        glDisable(GL_TEXTURE_2D);
        glEnable(GL_BLEND);
        glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
        glLineWidth(4.0);
        glColor4f(1.0, 1.0, 1.0, 0.2);
        glRecti(rubberBandCorner1.x(), rubberBandCorner1.y(),
                rubberBandCorner2.x(), rubberBandCorner2.y());
        glColor4f(1.0, 1.0, 0.0, 0.5);
        glLineStipple(3, 0xAAAA);
        glEnable(GL_LINE_STIPPLE);

        glBegin(GL_LINE_LOOP);
        glVertex2i(rubberBandCorner1.x(), rubberBandCorner1.y());
        glVertex2i(rubberBandCorner2.x(), rubberBandCorner1.y());
        glVertex2i(rubberBandCorner2.x(), rubberBandCorner2.y());
        glVertex2i(rubberBandCorner1.x(), rubberBandCorner2.y());
        glEnd();

        glLineWidth(1.0);
        glDisable(GL_LINE_STIPPLE);
        glDisable(GL_BLEND);
    }
}

//鼠标事件处理器负责更新用来绘制橡皮筋框的rubberBandCorner1,
//rubberBandCorner2和rubberBandIsShown变量,并且调用updateGL()
//重绘场景.绘制场景的速度很快,因为paintGL()仅绘制一个纹理矩形
//以及其上的橡皮筋选择框.只有当用户改变窗口大小时,场景才在
//resizeGL()中重新绘制
void Teapots::mousePressEvent(QMouseEvent *event)
{
    rubberBandCorner1 = event->pos();
    rubberBandCorner2 = event->pos();
    rubberBandIsShown = true;
}

void Teapots::mouseMoveEvent(QMouseEvent *event)
{
    if (rubberBandIsShown) {
        rubberBandCorner2 = event->pos();
        updateGL();
    }
}

void Teapots::mouseReleaseEvent(QMouseEvent * /* event */)
{
    if (rubberBandIsShown) {
        rubberBandIsShown = false;
        updateGL();
    }
}

void Teapots::createGLTeapotObject()
{
    static const int patch[][16] = {
        { 102, 103, 104, 105, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14,
          15 },
        { 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26,
          27 },
        { 24, 25, 26, 27, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39,
          40 },
        { 96, 96, 96, 96, 97, 98, 99, 100, 101, 101, 101, 101, 0, 1, 2,
          3 },
        { 0, 1, 2, 3, 106, 107, 108, 109, 110, 111, 112, 113, 114, 115,
          116, 117 },
        { 118, 118, 118, 118, 124, 122, 119, 121, 123, 126, 125, 120,
          40, 39, 38, 37 },
        { 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55,
          56 },
        { 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 28, 65, 66,
          67 },
        { 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82,
          83 },
        { 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94,
          95 }
    };
    static const GLfloat cp[][3] = {
        { 0.2, 0, 2.7 }, { 0.2, -0.112, 2.7 }, { 0.112, -0.2, 2.7 },
        { 0, -0.2, 2.7 }, { 1.3375, 0, 2.53125 },
        { 1.3375, -0.749, 2.53125 }, { 0.749, -1.3375, 2.53125 },
        { 0, -1.3375, 2.53125 }, { 1.4375, 0, 2.53125 },
        { 1.4375, -0.805, 2.53125 }, { 0.805, -1.4375, 2.53125 },

        { 0, -1.4375, 2.53125 }, { 1.5, 0, 2.4 }, { 1.5, -0.84, 2.4 },
        { 0.84, -1.5, 2.4 }, { 0, -1.5, 2.4 }, { 1.75, 0, 1.875 },
        { 1.75, -0.98, 1.875 }, { 0.98, -1.75, 1.875 },
        { 0, -1.75, 1.875 }, { 2, 0, 1.35 }, { 2, -1.12, 1.35 },
        { 1.12, -2, 1.35 }, { 0, -2, 1.35 }, { 2, 0, 0.9 },

        { 2, -1.12, 0.9 }, { 1.12, -2, 0.9 }, { 0, -2, 0.9 },
        { -2, 0, 0.9 }, { 2, 0, 0.45 }, { 2, -1.12, 0.45 },
        { 1.12, -2, 0.45 }, { 0, -2, 0.45 }, { 1.5, 0, 0.225 },
        { 1.5, -0.84, 0.225 }, { 0.84, -1.5, 0.225 },
        { 0, -1.5, 0.225 }, { 1.5, 0, 0.15 }, { 1.5, -0.84, 0.15 },

        { 0.84, -1.5, 0.15 }, { 0, -1.5, 0.15 }, { -1.6, 0, 2.025 },
        { -1.6, -0.3, 2.025 }, { -1.5, -0.3, 2.25 }, { -1.5, 0, 2.25 },
        { -2.3, 0, 2.025 }, { -2.3, -0.3, 2.025 }, { -2.5, -0.3, 2.25 },
        { -2.5, 0, 2.25 }, { -2.7, 0, 2.025 }, { -2.7, -0.3, 2.025 },
        { -3, -0.3, 2.25 }, { -3, 0, 2.25 }, { -2.7, 0, 1.8 },
        { -2.7, -0.3, 1.8 }, { -3, -0.3, 1.8 }, { -3, 0, 1.8 },

        { -2.7, 0, 1.575 }, { -2.7, -0.3, 1.575 }, { -3, -0.3, 1.35 },
        { -3, 0, 1.35 }, { -2.5, 0, 1.125 }, { -2.5, -0.3, 1.125 },
        { -2.65, -0.3, 0.9375 }, { -2.65, 0, 0.9375 },
        { -2, -0.3, 0.9 }, { -1.9, -0.3, 0.6 }, { -1.9, 0, 0.6 },
        { 1.7, 0, 1.425 }, { 1.7, -0.66, 1.425 }, { 1.7, -0.66, 0.6 },

        { 1.7, 0, 0.6 }, { 2.6, 0, 1.425 }, { 2.6, -0.66, 1.425 },
        { 3.1, -0.66, 0.825 }, { 3.1, 0, 0.825 }, { 2.3, 0, 2.1 },
        { 2.3, -0.25, 2.1 }, { 2.4, -0.25, 2.025 }, { 2.4, 0, 2.025 },
        { 2.7, 0, 2.4 }, { 2.7, -0.25, 2.4 }, { 3.3, -0.25, 2.4 },
        { 3.3, 0, 2.4 }, { 2.8, 0, 2.475 }, { 2.8, -0.25, 2.475 },

        { 3.525, -0.25, 2.49375 }, { 3.525, 0, 2.49375 },
        { 2.9, 0, 2.475 }, { 2.9, -0.15, 2.475 },
        { 3.45, -0.15, 2.5125 }, { 3.45, 0, 2.5125 }, { 2.8, 0, 2.4 },
        { 2.8, -0.15, 2.4 }, { 3.2, -0.15, 2.4 }, { 3.2, 0, 2.4 },
        { 0, 0, 3.15 }, { 0.8, 0, 3.15 }, { 0.8, -0.45, 3.15 },

        { 0.45, -0.8, 3.15 }, { 0, -0.8, 3.15 }, { 0, 0, 2.85 },
        { 1.4, 0, 2.4 }, { 1.4, -0.784, 2.4 }, { 0.784, -1.4, 2.4 },
        { 0, -1.4, 2.4 }, { 0.4, 0, 2.55 }, { 0.4, -0.224, 2.55 },
        { 0.224, -0.4, 2.55 }, { 0, -0.4, 2.55 }, { 1.3, 0, 2.55 },
        { 1.3, -0.728, 2.55 }, { 0.728, -1.3, 2.55 }, { 0, -1.3, 2.55 },

        { 1.3, 0, 2.4 }, { 1.3, -0.728, 2.4 }, { 0.728, -1.3, 2.4 },
        { 0, -1.3, 2.4 }, { 0, 0, 0 }, { 1.425, -0.798, 0 },
        { 1.5, 0, 0.075 }, { 1.425, 0, 0 }, { 0.798, -1.425, 0 },
        { 0, -1.5, 0.075 }, { 0, -1.425, 0 }, { 1.5, -0.84, 0.075 },
        { 0.84, -1.5, 0.075 }
    };
    static const GLfloat tex[2][2][2] = {
        { { 0, 0 }, { 1, 0 } }, { { 0, 1 }, { 1, 1 } }
    };

    GLfloat p[4][4][3];
    GLfloat q[4][4][3];
    GLfloat r[4][4][3];
    GLfloat s[4][4][3];
    int grid = 14;

    makeCurrent();

    glTeapotObject = glGenLists(1);

    glNewList(glTeapotObject, GL_COMPILE);
    glPushMatrix();
    glRotatef(270.0, 1.0, 0.0, 0.0);
    glScalef(0.5, 0.5, 0.5);
    glTranslatef(0.0, 0.0, -1.5);

    for (int i = 0; i < 10; i++) {
        for (int j = 0; j < 4; j++) {
            for (int k = 0; k < 4; k++) {
                for (int l = 0; l < 3; l++) {
                    p[j][k][l] = cp[patch[i][(j * 4) + k]][l];
                    q[j][k][l] = cp[patch[i][(j * 4) + (3 - k)]][l];
                    if (l == 1)
                        q[j][k][l] *= -1.0;
                    if (i < 6) {
                        r[j][k][l] = cp[patch[i][(j * 4) + (3 - k)]][l];
                        if (l == 0)
                            r[j][k][l] *= -1.0;
                        s[j][k][l] = cp[patch[i][(j * 4) + k]][l];
                        if (l <= 1)
                            s[j][k][l] *= -1.0;
                    }
                }
            }
        }
        glMap2f(GL_MAP2_TEXTURE_COORD_2, 0, 1, 2, 2, 0, 1, 4, 2,
                &tex[0][0][0]);
        glMap2f(GL_MAP2_VERTEX_3, 0, 1, 3, 4, 0, 1, 12, 4, &p[0][0][0]);
        glEnable(GL_MAP2_VERTEX_3);
        glEnable(GL_MAP2_TEXTURE_COORD_2);
        glMapGrid2f(grid, 0.0, 1.0, grid, 0.0, 1.0);
        glEvalMesh2(GL_LINE, 0, grid, 0, grid);
        glMap2f(GL_MAP2_VERTEX_3, 0, 1, 3, 4, 0, 1, 12, 4, &q[0][0][0]);
        glEvalMesh2(GL_LINE, 0, grid, 0, grid);
        if (i < 6) {
            glMap2f(GL_MAP2_VERTEX_3, 0, 1, 3, 4, 0, 1, 12, 4,
                    &r[0][0][0]);
            glEvalMesh2(GL_LINE, 0, grid, 0, grid);
            glMap2f(GL_MAP2_VERTEX_3, 0, 1, 3, 4, 0, 1, 12, 4,
                    &s[0][0][0]);
            glEvalMesh2(GL_LINE, 0, grid, 0, grid);
        }
    }
    glDisable(GL_MAP2_VERTEX_3);
    glDisable(GL_MAP2_TEXTURE_COORD_2);
    glPopMatrix();
    glEndList();
}

void Teapots::drawTeapot(GLfloat x, GLfloat y, GLfloat ambientR,
                         GLfloat ambientG, GLfloat ambientB,
                         GLfloat diffuseR, GLfloat diffuseG,
                         GLfloat diffuseB, GLfloat specularR,
                         GLfloat specularG, GLfloat specularB,
                         GLfloat shininess)
{
    GLfloat matrix[4];
    matrix[3] = 1.0;

    glPushMatrix();

    glTranslatef(x, y, 0.0);

    matrix[0] = ambientR;
    matrix[1] = ambientG;
    matrix[2] = ambientB;
    glMaterialfv(GL_FRONT, GL_AMBIENT, matrix);

    matrix[0] = diffuseR;
    matrix[1] = diffuseG;
    matrix[2] = diffuseB;
    glMaterialfv(GL_FRONT, GL_DIFFUSE, matrix);

    matrix[0] = specularR;
    matrix[1] = specularG;
    matrix[2] = specularB;
    glMaterialfv(GL_FRONT, GL_SPECULAR, matrix);

    glMaterialf(GL_FRONT, GL_SHININESS, shininess * 128.0);

    glCallList(glTeapotObject);

    glPopMatrix();
}

void Teapots::drawTeapots()
{
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

    drawTeapot(2.0, 17.0, 0.0215, 0.1745, 0.0215, 0.07568, 0.61424,
               0.07568, 0.633, 0.727811, 0.633, 0.6);
    drawTeapot(2.0, 14.0, 0.135, 0.2225, 0.1575, 0.54, 0.89, 0.63,
               0.316228, 0.316228, 0.316228, 0.1);
    drawTeapot(2.0, 11.0, 0.05375, 0.05, 0.06625, 0.18275, 0.17,
               0.22525, 0.332741, 0.328634, 0.346435, 0.3);
    drawTeapot(2.0, 8.0, 0.25, 0.20725, 0.20725, 1, 0.829, 0.829,
               0.296648, 0.296648, 0.296648, 0.088);
    drawTeapot(2.0, 5.0, 0.1745, 0.01175, 0.01175, 0.61424, 0.04136,
               0.04136, 0.727811, 0.626959, 0.626959, 0.6);
    drawTeapot(2.0, 2.0, 0.1, 0.18725, 0.1745, 0.396, 0.74151, 0.69102,
               0.297254, 0.30829, 0.306678, 0.1);

    drawTeapot(6.0, 17.0, 0.329412, 0.223529, 0.027451, 0.780392,
               0.568627, 0.113725, 0.992157, 0.941176, 0.807843,
               0.21794872);
    drawTeapot(6.0, 14.0, 0.2125, 0.1275, 0.054, 0.714, 0.4284, 0.18144,
               0.393548, 0.271906, 0.166721, 0.2);
    drawTeapot(6.0, 11.0, 0.25, 0.25, 0.25, 0.4, 0.4, 0.4, 0.774597,
               0.774597, 0.774597, 0.6);
    drawTeapot(6.0, 8.0, 0.19125, 0.0735, 0.0225, 0.7038, 0.27048,
               0.0828, 0.256777, 0.137622, 0.086014, 0.1);
    drawTeapot(6.0, 5.0, 0.24725, 0.1995, 0.0745, 0.75164, 0.60648,
               0.22648, 0.628281, 0.555802, 0.366065, 0.4);
    drawTeapot(6.0, 2.0, 0.19225, 0.19225, 0.19225, 0.50754, 0.50754,
               0.50754, 0.508273, 0.508273, 0.508273, 0.4);

    drawTeapot(10.0, 17.0, 0.0, 0.0, 0.0, 0.01, 0.01, 0.01, 0.50, 0.50,
               0.50, 0.25);
    drawTeapot(10.0, 14.0, 0.0, 0.1, 0.06, 0.0, 0.50980392, 0.50980392,
               0.50196078, 0.50196078, 0.50196078, 0.25);
    drawTeapot(10.0, 11.0, 0.0, 0.0, 0.0, 0.1, 0.35, 0.1, 0.45, 0.55,
               0.45, 0.25);
    drawTeapot(10.0, 8.0, 0.0, 0.0, 0.0, 0.5, 0.0, 0.0, 0.7, 0.6, 0.6,
               0.25);
    drawTeapot(10.0, 5.0, 0.0, 0.0, 0.0, 0.55, 0.55, 0.55, 0.70, 0.70,
               0.70, 0.25);
    drawTeapot(10.0, 2.0, 0.0, 0.0, 0.0, 0.5, 0.5, 0.0, 0.60, 0.60,
               0.50, 0.25);

    drawTeapot(14.0, 17.0, 0.02, 0.02, 0.02, 0.01, 0.01, 0.01, 0.4, 0.4,
               0.4, 0.078125);
    drawTeapot(14.0, 14.0, 0.0, 0.05, 0.05, 0.4, 0.5, 0.5, 0.04, 0.7,
               0.7, 0.078125);
    drawTeapot(14.0, 11.0, 0.0, 0.05, 0.0, 0.4, 0.5, 0.4, 0.04, 0.7,
               0.04, 0.078125);
    drawTeapot(14.0, 8.0, 0.05, 0.0, 0.0, 0.5, 0.4, 0.4, 0.7, 0.04,
               0.04, 0.078125);
    drawTeapot(14.0, 5.0, 0.05, 0.05, 0.05, 0.5, 0.5, 0.5, 0.7, 0.7,
               0.7, 0.078125);
    drawTeapot(14.0, 2.0, 0.05, 0.05, 0.0, 0.5, 0.5, 0.4, 0.7, 0.7,
               0.04, 0.078125);
}