QOpenGLShaderProgram example not working in QGraphicsItem

bigred9678

I am trying to use QOpenGLShaderProgram in a QGraphicsItem. I have a custom QGraphicsView where I have changed the viewport to a QGLWidget. My shader is getting compiled, linked and bound and is even drawing a triangle on the screen. But the color being passed to the fragment shader is being ignored. The triangle is always white. The shader example works if I use it in a QGLWidget, but not if it is part of a QGraphicsItem in a QGraphicsView. I am using Qt 5.2.

Am I missing something in OpenGL? Or is this a bug?

Here is some code: (though it is mostly copied from the example in the docs)

@
void MyGraphicsItem::paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget)
{
if (mShaderProgram.bind())
{
static GLfloat const triangleVertices[] = {
10.0f, 110.0f, 0.0f,
110.0f, 110.0f, 0.0f,
60.0f, 10.0f, 0.0f
};

    QColor color(0, 255, 0, 255);

    QMatrix4x4 pmvMatrix;

    painter->beginNativePainting();

        pmvMatrix.ortho(mBoundingRect);

        mShaderProgram.enableAttributeArray("vertex");
        mShaderProgram.setAttributeArray("vertex", triangleVertices, 3);
        mShaderProgram.setUniformValue("matrix", pmvMatrix);
        mShaderProgram.setUniformValue("color", color);

        glDrawArrays(GL_TRIANGLES, 0, 3);

        mShaderProgram.disableAttributeArray("vertex");

    painter->beginNativePainting();

    mShaderProgram.release();
}

}
@

@
void MyGraphicsItem::InitializeShaders()
{
if (!mShaderProgram.addShaderFromSourceCode(QOpenGLShader::Vertex,
"attribute highp vec4 vertex;\n"
"uniform highp mat4 matrix;\n"
"void main(void)\n"
"{\n"
" gl_Position = matrix * vertex;\n"
"}"))
{
qDebug() << "could not add vertex shader";
}

if (!mShaderProgram.addShaderFromSourceCode(QOpenGLShader::Fragment,
    "uniform mediump vec4 color;\n"
    "void main(void)\n"
    "{\n"
    "   gl_FragColor = color;\n"
    "}"))
{
    qDebug() << "could not add fragment shader";
}

if (!mShaderProgram.link())
{
    qDebug() << "could not link shader program";
}
if (!mShaderProgram.bind())
{
    qDebug() << "could not bind shader program";
}

}
@