Convert a GL texture (GLuint) to QImage or QOpenGLTexture

**miyoku157** · 9th June 2017, 15:27

Hi,

I find a lot of way to pass a QImage to GL but in fact i retrieve a gl texture from an API. So i'm trying to convert it either in a QImage or in a QOpenGLTexture to display it. I didn't see any function that could do it. I'm still trying by retrieving the data with glteximage and trying to fill a QImage but i don't know if it will work.

This is my code to display :

Qt Code:

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void GLWidget::paintGL()
{
    glClearColor(clearColor.redF(), clearColor.greenF(), clearColor.blueF(), clearColor.alphaF());
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
 
    QMatrix4x4 m;
    m.ortho(-1, 1, +1.f, -01.f, 1.0f, 20.0f);
    m.translate(0.0f, 0.0f, -10.0f);
    nv.StartCapture();
    program->setUniformValue("matrix", m);
    program->enableAttributeArray(PROGRAM_VERTEX_ATTRIBUTE);
    program->enableAttributeArray(PROGRAM_TEXCOORD_ATTRIBUTE);
    program->setAttributeBuffer(PROGRAM_VERTEX_ATTRIBUTE, GL_FLOAT, 0, 3, 5 * sizeof(GLfloat));
    program->setAttributeBuffer(PROGRAM_TEXCOORD_ATTRIBUTE, GL_FLOAT, 3 * sizeof(GLfloat), 2, 5 * sizeof(GLfloat));
    textures[0]->bind();
    glDrawArrays(GL_TRIANGLE_FAN, 0 * 4, 4);
}

void GLWidget::paintGL()
{
    glClearColor(clearColor.redF(), clearColor.greenF(), clearColor.blueF(), clearColor.alphaF());
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

    QMatrix4x4 m;
    m.ortho(-1, 1, +1.f, -01.f, 1.0f, 20.0f);
    m.translate(0.0f, 0.0f, -10.0f);
    nv.StartCapture();
    program->setUniformValue("matrix", m);
    program->enableAttributeArray(PROGRAM_VERTEX_ATTRIBUTE);
    program->enableAttributeArray(PROGRAM_TEXCOORD_ATTRIBUTE);
    program->setAttributeBuffer(PROGRAM_VERTEX_ATTRIBUTE, GL_FLOAT, 0, 3, 5 * sizeof(GLfloat));
    program->setAttributeBuffer(PROGRAM_TEXCOORD_ATTRIBUTE, GL_FLOAT, 3 * sizeof(GLfloat), 2, 5 * sizeof(GLfloat));
    textures[0]->bind();
    glDrawArrays(GL_TRIANGLE_FAN, 0 * 4, 4);
}

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If you have any idea.
Thanks

**wysota** · 12th June 2017, 07:16

There is no direct way to do it since the texture resides in your graphics card's memory. The most direct way I can think of is to render a rectangle with the texture to a frame buffer object and that can easily be converted to a QImage. As for QOpenGLTexture I see nothing in its API that could be used to bind it to an externally defined texture.

**miyoku157** · 12th June 2017, 09:54

Hi,
Thanks for your answer
Currently, i retrieve the Gltexture from an opengl extension and i was thinking that the best way to draw it was to convert it in QImage. but if i can directly draw it in my glwidget, that's better. I've tried to set the GLTexture in uniform param but i have a black screen for the moment. I'm going to look at the framebuffer.

Qt Code:

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void GLWidget::initializeGL()
{
    initializeOpenGLFunctions();
    GLenum te=glewInit();
    glGenFramebuffers(1, &frameBuffer);
    glBindFramebuffer(GL_FRAMEBUFFER, frameBuffer);
 
 
    nvc = NVConfig();
    nvc.GlobalInit();
    nv= NVGL(nvc.l_vioConfig,GetDC((HWND)this->winId()));
    makeObject();
 
    glEnable(GL_DEPTH_TEST);
    glEnable(GL_CULL_FACE);
 
#define PROGRAM_VERTEX_ATTRIBUTE 0
#define PROGRAM_TEXCOORD_ATTRIBUTE 1
 
    QOpenGLShader *vshader = new QOpenGLShader(QOpenGLShader::Vertex, this);
    const char *vsrc =
        "attribute highp vec4 vertex;\n"
        "attribute mediump vec4 texCoord;\n"
        "varying mediump vec4 texc;\n"
        "uniform mediump mat4 matrix;\n"
        "void main(void)\n"
        "{\n"
        "    gl_Position = matrix * vertex;\n"
        "    texc = texCoord;\n"
        "}\n";
    vshader->compileSourceCode(vsrc);
 
    QOpenGLShader *fshader = new QOpenGLShader(QOpenGLShader::Fragment, this);
    const char *fsrc =
        "uniform sampler2D texture;\n"
        "varying mediump vec4 texc;\n"
        "void main(void)\n"
        "{\n"
        "    gl_FragColor = texture2D(texture, texc.st);\n"
        "}\n";
    fshader->compileSourceCode(fsrc);
 
    program = new QOpenGLShaderProgram;
    program->addShader(vshader);
    program->addShader(fshader);
    program->bindAttributeLocation("vertex", PROGRAM_VERTEX_ATTRIBUTE);
    program->bindAttributeLocation("texCoord", PROGRAM_TEXCOORD_ATTRIBUTE);
    program->link();
    program->bind();
    program->setUniformValue("texture", nv.m_videoTexture);
}
 
void GLWidget::paintGL()
{
    glClearColor(clearColor.redF(), clearColor.greenF(), clearColor.blueF(), clearColor.alphaF());
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
 
    QMatrix4x4 m;
    m.ortho(-1, 1, +1.f, -01.f, 1.0f, 20.0f);
    m.translate(0.0f, 0.0f, -10.0f);
    nv.StartCapture(); //This  function retrieve the GLTexture
    program->setUniformValue("matrix", m);
    program->enableAttributeArray(PROGRAM_VERTEX_ATTRIBUTE);
    program->enableAttributeArray(PROGRAM_TEXCOORD_ATTRIBUTE);
    program->setAttributeBuffer(PROGRAM_VERTEX_ATTRIBUTE, GL_FLOAT, 0, 3, 5 * sizeof(GLfloat));
    program->setAttributeBuffer(PROGRAM_TEXCOORD_ATTRIBUTE, GL_FLOAT, 3 * sizeof(GLfloat), 2, 5 * sizeof(GLfloat));
    glDrawArrays(GL_TRIANGLE_FAN, 0 * 4, 4);
}

void GLWidget::initializeGL()
{
    initializeOpenGLFunctions();
    GLenum te=glewInit();
    glGenFramebuffers(1, &frameBuffer);
    glBindFramebuffer(GL_FRAMEBUFFER, frameBuffer);


    nvc = NVConfig();
    nvc.GlobalInit();
    nv= NVGL(nvc.l_vioConfig,GetDC((HWND)this->winId()));
    makeObject();

    glEnable(GL_DEPTH_TEST);
    glEnable(GL_CULL_FACE);

#define PROGRAM_VERTEX_ATTRIBUTE 0
#define PROGRAM_TEXCOORD_ATTRIBUTE 1

    QOpenGLShader *vshader = new QOpenGLShader(QOpenGLShader::Vertex, this);
    const char *vsrc =
        "attribute highp vec4 vertex;\n"
        "attribute mediump vec4 texCoord;\n"
        "varying mediump vec4 texc;\n"
        "uniform mediump mat4 matrix;\n"
        "void main(void)\n"
        "{\n"
        "    gl_Position = matrix * vertex;\n"
        "    texc = texCoord;\n"
        "}\n";
    vshader->compileSourceCode(vsrc);

    QOpenGLShader *fshader = new QOpenGLShader(QOpenGLShader::Fragment, this);
    const char *fsrc =
        "uniform sampler2D texture;\n"
        "varying mediump vec4 texc;\n"
        "void main(void)\n"
        "{\n"
        "    gl_FragColor = texture2D(texture, texc.st);\n"
        "}\n";
    fshader->compileSourceCode(fsrc);

    program = new QOpenGLShaderProgram;
    program->addShader(vshader);
    program->addShader(fshader);
    program->bindAttributeLocation("vertex", PROGRAM_VERTEX_ATTRIBUTE);
    program->bindAttributeLocation("texCoord", PROGRAM_TEXCOORD_ATTRIBUTE);
    program->link();
    program->bind();
    program->setUniformValue("texture", nv.m_videoTexture);
}

void GLWidget::paintGL()
{
    glClearColor(clearColor.redF(), clearColor.greenF(), clearColor.blueF(), clearColor.alphaF());
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

    QMatrix4x4 m;
    m.ortho(-1, 1, +1.f, -01.f, 1.0f, 20.0f);
    m.translate(0.0f, 0.0f, -10.0f);
    nv.StartCapture(); //This  function retrieve the GLTexture
    program->setUniformValue("matrix", m);
    program->enableAttributeArray(PROGRAM_VERTEX_ATTRIBUTE);
    program->enableAttributeArray(PROGRAM_TEXCOORD_ATTRIBUTE);
    program->setAttributeBuffer(PROGRAM_VERTEX_ATTRIBUTE, GL_FLOAT, 0, 3, 5 * sizeof(GLfloat));
    program->setAttributeBuffer(PROGRAM_TEXCOORD_ATTRIBUTE, GL_FLOAT, 3 * sizeof(GLfloat), 2, 5 * sizeof(GLfloat));
    glDrawArrays(GL_TRIANGLE_FAN, 0 * 4, 4);
}

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EDIT***
I still have a black screen, so to be sure i have a correct texture, i saved my texture in .tiff file. And i got a correct result. So my problem is really to draw my texture on the widget