将 QImage 与 OpenGL 结合使用

Question

我最近开始使用 Qt 并将其与 OpenGL 一起使用 但问题是，当我将 SDL 代码移动到 Qt 并更改纹理代码以使用 QImage 时，它​​会停止工作。

图像确实加载正确，如错误检查代码所示。

谢谢！

PS：请不要建议我使用glDrawPixels，我需要解决手头的问题。部分原因是 1. 速度慢 2. android（此代码最终可能在其上运行）是 OpenGL ES 并且不支持 glDrawPixels

这是代码：

//original image
QImage img;
if(!img.load(":/star.png"))
{
    //loads correctly
    qWarning("ERROR LOADING IMAGE");
}

//array for holding texture ID
GLuint texture[1];

//get the OpenGL-friendly image
QImage GL_formatted_image;
GL_formatted_image = QGLWidget::convertToGLFormat(img);

//make sure its not null
if(GL_formatted_image.isNull())
    qWarning("IMAGE IS NULL");
else
    qWarning("IMAGE NOT NULL");

//generate the texture name
glGenTextures(1, texture);

//bind the texture ID
glBindTexture(GL_TEXTURE_2D, texture[0]);

//generate the texture
glTexImage2D( GL_TEXTURE_2D, 0, GL_RGBA, GL_formatted_image.width(),
              GL_formatted_image.height(),
              0, GL_RGBA, GL_UNSIGNED_BYTE, GL_formatted_image.bits() );

//texture parameters
glTexParameteri( GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR );
glTexParameteri( GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);



//draw the texture
glPushMatrix();
glTranslatef(-2.0f, 0.0f, 0.0f);
glColor3f(1.0f, 1.0f, 1.0f);
glBegin(GL_TRIANGLES);
    glVertex2f(1.0f, 0.0f);
 glTexCoord2f(1.0f, 0.0f);
    glVertex2f(0.0f, 1.0f);
 glTexCoord2f(0.0f, 1.0f);
    glVertex2f(0.0f, 0.0f);
 glTexCoord2f(0.0f, 0.0f);
glEnd();
glPopMatrix();

这是使用 SDL 的原始纹理加载函数：

GLuint loadTexturewithSDL(const char* FILE, GLenum texture_format)
{
    GLuint texture;         // This is a handle to our texture object
    SDL_Surface *surface;   // This surface will tell us the details of the image
    GLint  nOfColors;



    if ( (surface = SDL_LoadBMP(FILE)) ) {

    // Check that the image's width is a power of 2
    if ( (surface->w & (surface->w - 1)) != 0 ) {
        printf("warning: image's width is not a power of 2\n");
    }

    // Also check if the height is a power of 2
    if ( (surface->h & (surface->h - 1)) != 0 ) {
        printf("warning: image's height is not a power of 2\n");
    }

        // get the number of channels in the SDL surface
        nOfColors = surface->format->BytesPerPixel;
        if (nOfColors == 4)     // contains an alpha channel
        {
                if (surface->format->Rmask == 0x000000ff)
                        texture_format = GL_RGBA;
                else
                        texture_format = GL_BGRA;
        } else if (nOfColors == 3)     // no alpha channel
        {
                if (surface->format->Rmask == 0x000000ff)
                        texture_format = GL_RGB;
                else
                        texture_format = GL_BGR;
        } else {
                printf("warning: the image is not truecolor..  this will probably break\n");
                // this error should not go unhandled
        }

    // Have OpenGL generate a texture object handle for us
    glGenTextures( 1, &texture );

    // Bind the texture object
    glBindTexture( GL_TEXTURE_2D, texture );

    // Set the texture's stretching properties
        glTexParameteri( GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR );
        glTexParameteri( GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR );

    // Edit the texture object's image data using the information SDL_Surface gives us
    glTexImage2D( GL_TEXTURE_2D, 0, nOfColors, surface->w, surface->h, 0,
                      texture_format, GL_UNSIGNED_BYTE, surface->pixels );
}
else {
    printf("SDL could not load image %s\n", SDL_GetError());
    SDL_Quit();
    return 1;
}

// Free the SDL_Surface only if it was successfully created
if ( surface ) {
    SDL_FreeSurface( surface );
}

    return texture;
}

Answer 1

我有类似的代码，但使用 glTexSubImage2D ：

void Widget::paintGL() 
{
    glClear (GL_COLOR_BUFFER_BIT);       
    glDisable(GL_DEPTH_TEST);
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();        
    gluOrtho2D(0,win.width(),0,win.height());
    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();        
    glEnable(GL_TEXTURE_2D);

    glBindTexture(GL_TEXTURE_2D,texture); 
    glTexSubImage2D(GL_TEXTURE_2D, 0, 0,0 , image.width(), image.height(),  glFormat, glType, image.bits() );       
    glBegin(GL_QUADS);   // in theory triangles are better
    glTexCoord2i(0,0); glVertex2i(0,win.height());
    glTexCoord2i(0,1); glVertex2i(0,0);
    glTexCoord2i(1,1); glVertex2i(win.width(),0);
    glTexCoord2i(1,0); glVertex2i(win.width(),win.height());
    glEnd();             

    glFlush();
}


void Widget::initializeGL() 
{
    glClearColor (0.0,0.0,0.0,1.0);
    glDisable(GL_DEPTH_TEST);
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();        
    gluOrtho2D(0,win.width(),0,win.height());
    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();        

    glEnable(GL_TEXTURE_2D);
    glGenTextures(3,&texture);
    glBindTexture(GL_TEXTURE_2D,texture);       
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);          
    glBindTexture(GL_TEXTURE_2D,texture);               
    glTexImage2D(GL_TEXTURE_2D, 0, glFormat, image.width(), image.height(), 0, glFormat, glType, NULL );    

    glDisable(GL_TEXTURE_2D);
}

以及 ctor 中的一些性能调整

void Widget::setDisplayOptions()
{
    glFormat = GL_RGB;  //  QImage RGBA is BGRA
    glType = GL_UNSIGNED_BYTE;

    QGL::setPreferredPaintEngine(QPaintEngine::OpenGL2);

    QGLFormat glFmt;
    glFmt.setSwapInterval(1); // 1= vsync on 
    glFmt.setAlpha(GL_RGBA==glFormat);
    glFmt.setRgba(GL_RGBA==glFormat); 
    glFmt.setDoubleBuffer(true); // default
    glFmt.setOverlay(false);
    glFmt.setSampleBuffers(false);
    QGLFormat::setDefaultFormat(glFmt);

    setAttribute(Qt::WA_OpaquePaintEvent,true);
    setAttribute(Qt::WA_PaintOnScreen,true);        
}

Answer 2

这是我从 Qt 转换为 GL 的解决方案
这也可以反向工作，只需稍加改变即可；
干杯——戴蒙

void Image::Convert32bitARGBtoRGBA()
{
    if(!isQtImage()) return;
    QImage& q = *(m_data->image);
    U32 count=0, max=(U32)(q.height()*q.width());
    U32* p = (U32*)(q.bits());
    U32 n;
    while( count<max )
    {
        n = p[count];   //n = ARGB
        p[count] =  0x00000000 |
                ((n<<8)  & 0x0000ff00) |
                ((n<<8)  & 0x00ff0000) |
                ((n<<8)  & 0xff000000) |
                ((n>>24) & 0x000000ff);
                // p[count] = RGBA
        count++;
    }
}

void Image::Convert32bitRGBAtoARGB()
{
    if(!isQtImage()) return;
    QImage& q = *(m_data->image);
    U32 count=0, max=(U32)(q.height()*q.width());
    U32* p = (U32*)(q.bits());
    U32 n;
    while( count<max )
    {
        n = p[count];   //n = RGBA
        p[count] =  0x00000000 |
                ((n>>8)  & 0x000000ff) |
                ((n>>8)  & 0x0000ff00) |
                ((n>>8)  & 0x00ff0000) |
                ((n<<24) & 0xff000000);
                // p[count] = ARGB
        count++;
    }
}

Answer 3

看起来你的问题不在这里，因为我对以下代码没有问题。
您应该检查 GL 初始化和显示设置。

你在某处有 glEnable(GL_TEXTURE_2D) 吗？

另请注意，glTexCoord2f 必须位于 glVertex2f 之前。

#include <GL/glut.h>
#include <QtOpenGL/qgl.h>
#include <iostream>

GLuint texture[1] ;

void LoadGLTextures( const char * name )
{
    QImage img;
    if( ! img.load( name ) )
    {
        std::cerr << "error loading " << name << std::endl ;
        exit( 1 );
    }

    QImage GL_formatted_image;
    GL_formatted_image = QGLWidget::convertToGLFormat(img);
    if( GL_formatted_image.isNull() )
    {
        std::cerr << "error GL_formatted_image" << std::endl ;
        exit( 1 );
    }

    glGenTextures(1, texture);
    glBindTexture(GL_TEXTURE_2D, texture[0]);
    glTexImage2D( GL_TEXTURE_2D, 0, GL_RGBA,
            GL_formatted_image.width(), GL_formatted_image.height(),
            0, GL_RGBA, GL_UNSIGNED_BYTE, GL_formatted_image.bits() );
    glTexParameteri( GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR );
    glTexParameteri( GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR ); 
}

void resize(int Width, int Height)
{
    glViewport( 0 , 0 , Width , Height );
}

void draw()
{
    glClearColor( 0.0f, 0.0f, 0.0f, 0.0f);
    glClear( GL_COLOR_BUFFER_BIT );

    gluOrtho2D( -1 , 1 , -1 , 1 );

    glMatrixMode( GL_MODELVIEW );
    glLoadIdentity();

    glShadeModel( GL_FLAT );

    glEnable(GL_TEXTURE_2D);
    glBindTexture(GL_TEXTURE_2D, texture[0]);

    glBegin(GL_TRIANGLES);
    glTexCoord2f( 1.0f, 0.0f);
    glVertex2f( 1.0f, 0.0f);
    glTexCoord2f( 0.0f, 1.0f);
    glVertex2f( 0.0f, 1.0f);
    glTexCoord2f( 0.0f, 0.0f);
    glVertex2f( 0.0f, 0.0f);
    glEnd();

    glutSwapBuffers();
}

int main(int argc, char **argv) 
{  
    glutInit(&argc, argv);  
    glutInitDisplayMode( GLUT_RGBA | GLUT_DOUBLE | GLUT_ALPHA );  
    glutInitWindowSize(640, 480);

    glutCreateWindow("Texture"); 

    LoadGLTextures( "star.png" );

    glutDisplayFunc( & draw );  
    glutReshapeFunc( & resize );
    glutMainLoop();  

    return 1;
}