使用OpenGL和QT进行纹理映射-C ++ [英] Texture mapping with OpenGL and QT - C++

问题描述

我无法使用OpenGL和Qt将纹理映射到四边形.我看过其他几个SO线程，但是我编译时必须使用很多函数调用(Qt Verison 4.8.6).这是我的相关代码，现在所发生的只是一个显示有黑色背景的窗口，但没有其他内容.

void LoadGLTextures( const char * name )
{
    QImage img;

    if(!img.load("resources/Green_Dragon.bmp")){
        std::cerr << "ERROR in loading image" << std::endl;
    }

    QImage t = QGLWidget::convertToGLFormat(img);

    glGenTextures(1, &texture[0]);
    glBindTexture(GL_TEXTURE_2D, texture[0]);
    glTexImage2D(GL_TEXTURE_2D, 0, 3, t.width(), t.height(), 0, GL_RGBA, GL_UNSIGNED_BYTE, t.bits());

    glTexParameteri( GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR );
    glTexParameteri( GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR );
    glBindTexture( GL_TEXTURE_2D, 0 );
}



void GLWidget::initializeGL()
{


    qglClearColor(qtBlack.dark());
    glEnable(GL_CULL_FACE);
    glShadeModel(GL_SMOOTH);
    glEnable(GL_LIGHTING);
    glEnable(GL_LIGHT0);
    glEnable(GL_MULTISAMPLE);
    static GLfloat lightPosition[4] = { 0.5, 5.0, 7.0, 1.0 };
    glLightfv(GL_LIGHT0, GL_POSITION, lightPosition);
    cameraPos = 0;
    glEnable(GL_TEXTURE_2D);
    LoadGLTextures("resources/Green_Dragon.jpeg");

}

void GLWidget::paintGL()
{
    glClearColor( 0.0f, 0.0f, 0.0f, 0.0f);
    glClear( GL_COLOR_BUFFER_BIT );


    glMatrixMode( GL_MODELVIEW );
    glLoadIdentity();

    glShadeModel( GL_FLAT );
    glEnable(GL_LIGHTING);
    glEnable(GL_LIGHT0);
    glEnable(GL_DEPTH_TEST);
    glEnable(GL_TEXTURE_2D);
    glColor3f(0.5, 0.5, 0);
    glBindTexture(GL_TEXTURE_2D, texture[0]);

    glBegin(GL_QUADS);
    glTexCoord2f(0.0f, 1.0f); glVertex2f(-0.5f, 0.5f);  // vertex 1
    glTexCoord2f(0.0f, 0.0f); glVertex2f(-0.5f, -0.5f); // vertex 2
    glTexCoord2f(1.0f, 0.0f); glVertex2f(0.5f, -0.5f); // vertex 3
    glTexCoord2f(1.0f, 1.0f); glVertex2f(0.5f, 0.5f); // vertex 4
    glEnd();
    glDisable(GL_TEXTURE_2D);

    glFlush();
}

解决方案

看着您的评论，答案现在已经很清楚了，很抱歉我在问题评论中没有找到它.

由于启用了深度测试，所以您看到黑屏，但是没有清除帧之间的深度缓冲区.因此，前一帧的深度缓冲区值保持不变，并且所有后续帧的深度测试均失败(请注意， glClear()

I'm having trouble getting my texture to map to a quad using OpenGL and Qt. I've looked at several other SO threads, but a lot of the function calls have to be used slightly differently for me to compile (Qt Verison 4.8.6). Here's my relevant code, right now all that happens is a window is displayed with a black background, but nothing else.

void LoadGLTextures( const char * name )
{
    QImage img;

    if(!img.load("resources/Green_Dragon.bmp")){
        std::cerr << "ERROR in loading image" << std::endl;
    }

    QImage t = QGLWidget::convertToGLFormat(img);

    glGenTextures(1, &texture[0]);
    glBindTexture(GL_TEXTURE_2D, texture[0]);
    glTexImage2D(GL_TEXTURE_2D, 0, 3, t.width(), t.height(), 0, GL_RGBA, GL_UNSIGNED_BYTE, t.bits());

    glTexParameteri( GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR );
    glTexParameteri( GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR );
    glBindTexture( GL_TEXTURE_2D, 0 );
}



void GLWidget::initializeGL()
{


    qglClearColor(qtBlack.dark());
    glEnable(GL_CULL_FACE);
    glShadeModel(GL_SMOOTH);
    glEnable(GL_LIGHTING);
    glEnable(GL_LIGHT0);
    glEnable(GL_MULTISAMPLE);
    static GLfloat lightPosition[4] = { 0.5, 5.0, 7.0, 1.0 };
    glLightfv(GL_LIGHT0, GL_POSITION, lightPosition);
    cameraPos = 0;
    glEnable(GL_TEXTURE_2D);
    LoadGLTextures("resources/Green_Dragon.jpeg");

}

void GLWidget::paintGL()
{
    glClearColor( 0.0f, 0.0f, 0.0f, 0.0f);
    glClear( GL_COLOR_BUFFER_BIT );


    glMatrixMode( GL_MODELVIEW );
    glLoadIdentity();

    glShadeModel( GL_FLAT );
    glEnable(GL_LIGHTING);
    glEnable(GL_LIGHT0);
    glEnable(GL_DEPTH_TEST);
    glEnable(GL_TEXTURE_2D);
    glColor3f(0.5, 0.5, 0);
    glBindTexture(GL_TEXTURE_2D, texture[0]);

    glBegin(GL_QUADS);
    glTexCoord2f(0.0f, 1.0f); glVertex2f(-0.5f, 0.5f);  // vertex 1
    glTexCoord2f(0.0f, 0.0f); glVertex2f(-0.5f, -0.5f); // vertex 2
    glTexCoord2f(1.0f, 0.0f); glVertex2f(0.5f, -0.5f); // vertex 3
    glTexCoord2f(1.0f, 1.0f); glVertex2f(0.5f, 0.5f); // vertex 4
    glEnd();
    glDisable(GL_TEXTURE_2D);

    glFlush();
}

解决方案

Looking at your comment, the answer is fairly clear now, sorry that I missed it in the question comments.

You are seeing a black screen because you are enabling depth testing, but you are not clearing the depth buffer between frames. Therefore, the previous frame's depth buffer values remain in place, and the depth tests fail for all subsequent frames (note that the default depth function is GL_LESS).

You may leave depth testing enabled. The correct solution is to clear your depth buffer in addition to your color buffer before each render. You have:

glClear( GL_COLOR_BUFFER_BIT );

But you need:

glClear( GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT );

See also: glClear()

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