Using multiple QGLWidgets (QT) to display (same) 3D Texture? - c++

Question

I have a question about OpenGL and Qt. I haven’t worked with OpenGL so far and got the code from somebody else. Unfortunately I can't ask him.
I create multiple CTAGLWidgets (ref. Constructor) to display CT image data from different perspectives (sagittal, axial, coronal). Therefore I want all OpenGL widgets to load the created 3D texture (see last part of source code). So far only the last widget loads the texture and the other widgets keep showing a black screen.
I can provide additional code if necessary (shader, ...), but I think I added all relevant parts.
What do I need to change? Or can you provide a link that could help me solve the problem? Anything will help!
Code snippet of the .cpp file:
CTAGLWidget::CTAGLWidget(QWidget* parent ) : QGLWidget (parent) {
}
void CTAGLWidget::initShaders() {
setlocale(LC_NUMERIC, "C");
if (!program.addShaderFromSourceFile(QGLShader::Vertex, ":/vshader.glsl"))
close();
if (!program.addShaderFromSourceFile(QGLShader::Fragment, ":/fshader.glsl"))
close();
if (!program.link())
close();
if (!program.bind())
close();
setlocale(LC_ALL, "");
}
void CTAGLWidget::initializeGL() {
initializeGLFunctions();
initShaders();
qglClearColor(Qt::black);
zoom = 1.0;
qNow = QQuaternion(1,0,0,0);
min = QVector3D( 1.0, 1.0, 1.0);
max = QVector3D(-1.0,-1.0,-1.0);
center = QVector3D(0,0,0);
glGenBuffers(1,&vboQuadId);
std::vector<QVector3D> vertex;
vertex.push_back(QVector3D(-2,-2, 0));
vertex.push_back(QVector3D( 0, 0, 0));
vertex.push_back(QVector3D( 2,-2, 0));
vertex.push_back(QVector3D( 1, 0, 0));
vertex.push_back(QVector3D( 2, 2, 0));
vertex.push_back(QVector3D( 1, 1, 0));
vertex.push_back(QVector3D(-2, 2, 0));
vertex.push_back(QVector3D( 0, 1, 0));
glBindBuffer(GL_ARRAY_BUFFER,vboQuadId);
glBufferData(GL_ARRAY_BUFFER,vertex.size()*sizeof(QVector3D),vertex.data(),GL_STATIC_DRAW);
}
void CTAGLWidget::paintGL() {
glClear(GL_COLOR_BUFFER_BIT);
QMatrix4x4 P(projection);
P.scale(zoom,zoom,zoom);
modelView.setToIdentity();
modelView.rotate(qNow.conjugate());
modelView.translate(-center);
program.bind();
program.setUniformValue("uPMat", P);
program.setUniformValue("uMVMat", modelView);
program.setUniformValue("uColor", QVector4D(1.0,0.0,0.0,1.0));
glBindBuffer(GL_ARRAY_BUFFER, vboQuadId);
int vertexLocation = program.attributeLocation("a_position");
program.enableAttributeArray(vertexLocation);
glVertexAttribPointer(vertexLocation, 3, GL_FLOAT, GL_FALSE,
2*sizeof(QVector3D), 0);
int texAttribLoc = program.attributeLocation("aTexCoord");
program.enableAttributeArray(texAttribLoc);
glVertexAttribPointer(texAttribLoc, 3, GL_FLOAT, GL_FALSE,
2*sizeof(QVector3D), (const void*) sizeof(QVector3D));
glDrawArrays(GL_QUADS,0,4);
}
Here the 3D texture is created from the QByteArray "texture":
void CTScanMain::setTexture() {
...
glTexParameteri(GL_TEXTURE_3D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
glTexImage3D(GL_TEXTURE_3D, 0, GL_RGB8,
ctAnalyser->x(), ctAnalyser->y(), ctAnalyser->z(),
0, GL_RGB, GL_UNSIGNED_BYTE, texture);
...
}
There are no further OpenGL calls in the program.

Answer 1

One possible solution can be found looking at the constructor of the QGLWidget:
QGLWidget ( QWidget * parent = 0, const QGLWidget * shareWidget = 0, Qt::WindowFlags f = 0 )
Passing the first opengl widget object as "shareWidget" makes further widgets share the same texture.
Qt documentation:
"If shareWidget is a valid QGLWidget, this widget will share OpenGL display lists and texture objects with shareWidget."
A similar question has been asked at:
http://qt-project.org/forums/viewthread/8265