Using QImage with OpenGL

Question

I\'ve very recently picked up Qt and am using it with OpenGL The thing though is that when moving my SDL code to Qt and changing the texture code to use QImage it stops work

Answer 1

I have similar code that works but uses 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);
}

And a few perfomance tweaks in the ctor

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

It looks like your problem is not here, as I have no problem with the following code. You should check your GL init and display setup.

Have you a glEnable(GL_TEXTURE_2D) somewhere ?

Also note glTexCoord2f must be before glVertex2f.

#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;
}

Answer 3

This is my solution for conversion from Qt to GL This also can work in reverse with little changes; Cheers -- Daimon

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++;
    }
}