GL.GenBuffer() gets 0

[shlykovarseny]

Hi there. If I define buffers inside the OpenTkInit() method like in tutorials, it work OK. But if I do same in some other method after the OpenTK is already initialized, GL.GenBuffer() gets zero. How to solve it? I need to add buffered data during the runtime. For example, add some surface from the file or remove it.

[NogginBops]

What is the OpenTkInit() function and where in the code is it? What version of OpenTK are you using? Are you running code on different threads?

[shlykovarseny]

First of all, I'm using OpenTK in the Avalonia project. Avalonia's version is 0.10.14 and OpenTK's version is 4.7.7

All my code is single thread for now.

I took this code as reference OpenTKAvalonia.

Here is the "original" OpentTkInit method:

protected override void OpenTkInit()
        {
            //Compile shaders
            _shader = new("Shaders/shader.vert", "Shaders/shader.frag");

            //Load textures
            _brickTexture = new();
            _brickTexture.Use();
            _brickTexture.LoadFromFile("Textures/wall.jpg");

            //Set textures in shaders
            _shader.Use();
            _shader.SetInt("texture0", 2);

            //Create vertex and buffer objects
            _vertexArrayObject = GL.GenVertexArray();
            _vertexBufferObject = GL.GenBuffer();

            //Set bg colour to a dark forest green
            GL.ClearColor(0.2f, 0.3f, 0.3f, 1.0f);

            //Bind to the VAO
            GL.BindVertexArray(_vertexArrayObject);

            //Set up the buffer for the triangle
            GL.BindBuffer(BufferTarget.ArrayBuffer, _vertexBufferObject);

            //Copy triangle vertices to the buffer
            GL.BufferData(BufferTarget.ArrayBuffer, _vertices.Length * sizeof(float), _vertices, BufferUsageHint.StaticDraw);

            //Configure structure of the vertices
            //                    (position parameter in vertex shader, 3 points, data is stored as floats, non-normalized, 5 floats/point, first point at offset 0 in data array)
            GL.VertexAttribPointer(_shader.GetAttribLocation("aPosition"), 3, VertexAttribPointerType.Float, false, 5 * sizeof(float), 0);
            GL.EnableVertexAttribArray(_shader.GetAttribLocation("aPosition"));

            //Configure texture coordinate structure
            var texCoordLocation = _shader.GetAttribLocation("aTexCoord");
            GL.VertexAttribPointer(texCoordLocation, 2, VertexAttribPointerType.Float, false, 5 * sizeof(float), 3 * sizeof(float));
            GL.EnableVertexAttribArray(texCoordLocation);

            //Set up the EBO
            _elementBufferObject = GL.GenBuffer();

            //Set up its buffer
            GL.BindBuffer(BufferTarget.ElementArrayBuffer, _elementBufferObject);

            //Copy data to the buffer
            GL.BufferData(BufferTarget.ElementArrayBuffer, _indices.Length * sizeof(uint), _indices, BufferUsageHint.StaticDraw);
        }

From the base class BaseTkOpenGlControl inherited from the Avalonia.OpenGL.Controls.OpenGlControlBase:

protected sealed override void OnOpenGlInit(GlInterface gl, int fb)
    {
        //Initialize the OpenTK<->Avalonia Bridge
        _avaloniaTkContext = new(gl);
        GL.LoadBindings(_avaloniaTkContext);

        //Invoke the subclass' init function
        OpenTkInit();
    }

    //Simply call the subclass' teardown function
    protected sealed override void OnOpenGlDeinit(GlInterface gl, int fb)
    {
        OpenTkTeardown();

        //Workaround an avalonia issue where the depth buffer ID is not cleared
        //which causes depth problems (see issue #1 on this repo)
        _depthBufferField.SetValue(this, 0);
    }

That works ok. My issue is about moving all job with buffers to the other method whith runs in the app's runtime. Absolutely same code but in the other place.

[NogginBops]

You need to make sure that you have an opengl context current on the thread. Is it possible that the "runtime" function doesn't have a context current?