1

我一直在阅读有关采摘的教程，而颜色采摘是迄今为止最流行和最简单的形式。

以雪人为例尝试了一些教程，但它对我不起作用。当我运行该程序时，它只给我一个黑色的画面，没有任何绘画。当我单击几次时，除了关闭窗口时，什么都没有发生，然后它说“你还没有点击雪人”。

不知道有什么问题可以帮助我吗？

void GLWidget::paintGL() {
    glEnable(GL_DEPTH_TEST);
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

    glLoadIdentity();

    gluLookAt(camPosx ,camPosy ,camPosz,
              camPosx + camViewx,camViewy,camPosz + camViewz,
              camUpx, camUpy, camUpz );

    draw(); //draw the normal scene

    if (mode == SELECT)
        drawPickingMode();
    else
        drawPickingMode();

    if (mode == SELECT) {
        processPick();
        mode = RENDER;
    }
    else
        QGLWidget::swapBuffers();

    // restore current matrix
    glMatrixMode( GL_MODELVIEW );
    glPopMatrix( );

}

void GLWidget::mousePressEvent(QMouseEvent * e)
{
    if(e->button() == Qt::LeftButton)
    {
        qDebug("mouse");
        qDebug("%d %d",QCursor::pos().x(),QCursor::pos().y());
        this->cursorX = QCursor::pos().x(); // set x and y cord from mouse
        this->cursorY = QCursor::pos().y();
        mode = SELECT; // set the mode to select
    }
}

void GLWidget::draw() {

// Draw ground
    glColor3f(0.9f, 0.9f, 0.9f);
    glBegin(GL_QUADS);
        glVertex3f(-100.0f, 0.0f, -100.0f);
        glVertex3f(-100.0f, 0.0f,  100.0f);
        glVertex3f( 100.0f, 0.0f,  100.0f);
        glVertex3f( 100.0f, 0.0f, -100.0f);
    glEnd();

// Draw 4 Snowmen

    glColor3f(1.0f, 1.0f, 1.0f);

    for(int i = 0; i < 2; i++)
        for(int j = 0; j < 2; j++) {
            glPushMatrix();
            glTranslatef(i*3.0,0,-j * 3.0);
            glColor3f(1.0f, 1.0f, 1.0f);
            glCallList(snowman_display_list);
            glPopMatrix();
        }

}

void GLWidget::processPick ()
{
    GLint viewport[4];
    GLubyte pixel[3];

    glGetIntegerv(GL_VIEWPORT,viewport);

    glReadPixels(cursorX,viewport[3]-cursorY,1,1,
        GL_RGB,GL_UNSIGNED_BYTE,(void *)pixel);

    printf("%d %d %d\n",pixel[0],pixel[1],pixel[2]);
    if (pixel[0] == 255)
      printf ("You picked the 1st snowman on the 1st row");
    else if (pixel[1] == 255)
      printf ("You picked the 1st snowman on the 2nd row");
    else if (pixel[2] == 255)
      printf ("You picked the 2nd snowman on the 1st row");
    else if (pixel[0] == 250)
      printf ("You picked the 2nd snowman on the 2nd row");
    else
       printf("You didn't click a snowman!");
  printf ("\n");

}

void GLWidget::drawPickingMode() {

// Draw 4 SnowMen


    glDisable(GL_DITHER);
    for(int i = 0; i < 2; i++)
           for(int j = 0; j < 2; j++) {
        glPushMatrix();

// A different color for each snowman

        switch (i*2+j) {
            case 0: glColor3ub(255,0,0);break;
            case 1: glColor3ub(0,255,0);break;
            case 2: glColor3ub(0,0,255);break;
            case 3: glColor3ub(250,0,250);break;
        }

        glTranslatef(i*3.0,0,-j * 3.0);
        glCallList(snowman_display_list);
        glPopMatrix();
       }
    glEnable(GL_DITHER);
}

void GLWidget::initializeGL() {

    loadGLTextures();
    //LoadXml();
    glEnable(GL_TEXTURE_2D);       // Enable Texture Mapping
    glShadeModel(GL_SMOOTH);       // Enable Smooth Shading
    glClearColor(0.0f, 0.0f, 0.0f, 0.5f);    // Black Background
    glClearDepth(1.0f);         // Depth Buffer Setup
    glEnable(GL_DEPTH_TEST);       // Enables Depth Testing
    glDepthFunc(GL_LEQUAL);        // The Type Of Depth Testing To Do
    glEnable(GL_LIGHT0);        // Quick And Dirty Lighting (Assumes Light0 Is Set Up)
    glEnable(GL_LIGHTING);        // Enable Lighting
    glEnable(GL_COLOR_MATERIAL);      // Enable Material Coloring
    glHint(GL_PERSPECTIVE_CORRECTION_HINT, GL_NICEST); // Perspective Calculations
   // buildLists(2);                                      // Creating displaylist #
    glLoadIdentity();

    timer->start(50);
    qDebug("Init");
}

投影矩阵设置如下：

void GLWidget::resizeGL(int width, int height) {

    //set viewport
    glViewport(0,0,width,height);

    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();

    //set persepective
    //change the next line order to have a different perspective
    aspect_ratio=(GLdouble)width/(GLdouble)height;
    gluPerspective(45.0f, aspect_ratio, 0.1 , 100.0);

    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();
}
4

2 回答 2

0

Although you're not specifying it explicitly, you're probably rendering to the back buffer double buffered window. Hence you should prepend calls to glReadPixels with a call to glReadBuffer to set which buffer to read the color from. Also remember that on-screen windows are subject to pixel ownership tests and other things that may interfere with your method of choice.

于 2012-05-26T08:51:05.743 回答
-1

我没有看到冲洗。这可能会导致一个空白屏幕，因为它正在加载以前的数据（通常是无意义的，因此是空白的）

于 2012-05-25T14:55:26.527 回答