Using QImage with OpenGL - qt

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 working.
The image does load correctly, as shown through the error checking code.
Thanks!
P.S: Please don't suggest I use glDrawPixels, I need to fix the problem at hand. Some of the reasons for that being 1. slow 2. android (which this code may be running on eventually) is OpenGL ES and does not support glDrawPixels
Here's the code:
//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();
Here's the original texture loading function with SDL:
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

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

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++;
}
}

Answer 3

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;
}