[Interest] How to pass data to\from GLSL compute shaders in Qt5?

[Gleb "Crazy Sage" Igumnov]

Hello. I'm trying to port my program that is using GL compute shaders to Qt and I can't understand, what is correct way to work with buffers.
I initialize and use buffers with following code:

>    QOpenGLBuffer cull_ray_buffer;
>    QOpenGLBuffer cull_face_buffer;
>    QOpenGLBuffer cull_out_buffer;
>
>    if(!cull_ray_buffer.create())
>    {
>        qDebug()<<"Can't create cull ray buffer";
>        return false;
>    }
>    cull_ray_buffer.allocate(border_rays.size()*sizeof(QVector4D));//border_rays_ is QVector of QVector4D
>
>    if(!cull_face_buffer.create())
>    {
>        qDebug()<<"Can't create cull face buffer";
>        return false;
>    }
>    cull_face_buffer.allocate(faces_.data(), faces_.size()*sizeof(QVector4D));//faces_ is QVector of QVector4D
>
>    if(!cull_out_buffer.create())
>    {
>        qDebug()<<"Can't create cull out buffer";
>        return false;
>    }
>    cull_out_buffer.allocate(tmp_out.data(), tmp_out.size()*sizeof(int));//tmp_out_ is QVector of int
>
>    ogl->glBindBufferBase(GL_SHADER_STORAGE_BUFFER, 0, cull_ray_buffer.bufferId());//ogl is an instance of QOpenGLFunctions_4_4_Core
>    ogl->glBindBufferBase(GL_SHADER_STORAGE_BUFFER, 1, cull_face_buffer.bufferId());
>    ogl->glBindBufferBase(GL_SHADER_STORAGE_BUFFER, 2, cull_out_buffer.bufferId());

In my shader I have buffers declared like this:

>    layout(std430, binding=0) buffer rays{
>        vec4 r[];
>    };
>
>    layout(std430, binding=1) buffer faces{
>        vec4 f[];
>    };
>
>    layout(std430, binding=2) buffer outputs{
>        int o[];
>    };

I link shader before creating and binding buffers and then try to get output data by doing one of following things:

>    int* b = static_cast<int*>(cull_out_buffer.map(QOpenGLBuffer::ReadOnly));

or

>    cull_out_buffer.read(0,tmp_out.data(), tmp_out.size()*sizeof(int))

in first case I'm getting NULL pointer, in second - function returns false.
Also I'm not even sure that shader receives input data correctly (and I don't see any way to check it, because it is console gpu-computing project without any actual rendering).

Can  someone please explain to me, what is correct way of passing data
to compute shaders using QOpenGLBuffer (if there is any)?

-- 
With best regards,
 Gleb "Crazy Sage" Igumnov                          mailto:crazy.sage at gmail.com


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