OpenGL 4 multisampling with FBO - FBO incomplete

Question

I'm making 2D games in OpenTK (a C# wrapper for OpenGL 4), and all was well except for jagged edges of polygons and things jumping and stuttering instead of moving smoothly - so I'm trying to add in multisampling to antialias my textures.

My setup has several Cameras which render all their scene objects onto a FrameBufferObject texture (I would like this to be MSAA), which are then all drawn to the screen (no multisampling needed), one on top of the other.

Without multisampling, it worked fine, but now I tried to change all my Texture2D calls to Texture2DMultisample etc but now I get FBO Not Complete errors and it draws wrong. I believe I need to change my shaders too, but I want to solve this first.

The code below references a few classes like Texture that I've made, but I don't think that should impact this, and I don't want to clutter the post - will give mroe details if needed.

I set up the FBO for each camera with:

 private void SetUpFBOTex()
    {
        _frameBufferTexture = new Texture(GL.GenTexture(), Window.W, Window.H);
        GL.BindTexture(TextureTarget.Texture2DMultisample, _frameBufferTexture.ID);           
        GL.TexImage2DMultisample(TextureTargetMultisample.Texture2DMultisample, 0, PixelInternalFormat.Rgba8, Window.W, Window.H, true);

        _frameBufferID = GL.GenFramebuffer();
    }

and draw with:

public void Render(Matrix4 matrix)
    {
        GL.Enable(EnableCap.Multisample);
        //Bind FBO to be the draw destination and clear it
        GL.BindFramebuffer(FramebufferTarget.Framebuffer, _frameBufferID);
        GL.FramebufferTexture2D(FramebufferTarget.Framebuffer, FramebufferAttachment.ColorAttachment0, TextureTarget.Texture2DMultisample, _frameBufferTexture.ID, 0);
        GL.ClearColor(new Color4(0,0,0,0));
        GL.Clear(ClearBufferMask.ColorBufferBit | ClearBufferMask.DepthBufferBit);

        //draw stuff here 
        foreach (Layer l in Layers)
            l.Render(Matrix);


        GL.BindFramebuffer(FramebufferTarget.Framebuffer, 0);

        //Bind the FBO to be drawn
        _frameBufferTexture.Bind();

        //Translate to camera window position
        Matrix4 fbomatrix = matrix * Matrix4.CreateTranslation(_window.x, _window.y, 0) * FBOMatrix;            

        //Bind shader 
        shader.Bind(ref fbomatrix, DrawType);

        //Some OpenGL setup nonsense, binding vertices and index buffer and telling OpenGL where in the vertex struct things are, pointers &c
        GL.BindBuffer(BufferTarget.ArrayBuffer, vertexBuffer);
        GL.EnableVertexAttribArray(shader.LocationPosition);
        GL.VertexAttribPointer(shader.LocationPosition, 2, VertexAttribPointerType.Float, false, Stride, 0);
        if (shader.LocationTexture != -1)
        {
            GL.EnableVertexAttribArray(shader.LocationTexture);
            GL.VertexAttribPointer(shader.LocationTexture, 2, VertexAttribPointerType.Float, false, Stride, 8);
        }
        GL.EnableVertexAttribArray(shader.LocationColour);
        GL.VertexAttribPointer(shader.LocationColour, 4, VertexAttribPointerType.UnsignedByte, true, Stride, 16);
        GL.BindBuffer(BufferTarget.ElementArrayBuffer, indexBuffer);

        //Draw the damn quad
        GL.DrawArrays(DrawType, 0, Vertices.Length);

        //Cleanup
        GL.DisableVertexAttribArray(shader.LocationPosition);
        if (shader.LocationTexture != -1)
            GL.DisableVertexAttribArray(shader.LocationTexture);
        GL.DisableVertexAttribArray(shader.LocationColour);
    }

Answer 1

Ok @Andon gets credit for this - if you write it as an answer I'll mark that as the solution. I was indeed doing antialiasing with 0 samples!

I'm posting the working antialiased drawing to multiple FBOS code for future OpenTK googlers.

private void SetUpFBOTex()
    {
        _frameBufferTexture = new Texture(GL.GenTexture(), Window.W, Window.H);
        GL.BindTexture(TextureTarget.Texture2DMultisample, _frameBufferTexture.ID);
        GL.TexImage2DMultisample(TextureTargetMultisample.Texture2DMultisample, 8, PixelInternalFormat.Rgba8, Window.W, Window.H, false);

        _frameBufferID = GL.GenFramebuffer();
    }

public void Render(Matrix4 matrix)
    {
        //Bind FBO to be the draw destination and clear it
        GL.BindFramebuffer(FramebufferTarget.Framebuffer, _frameBufferID);
        GL.FramebufferTexture2D(FramebufferTarget.Framebuffer, FramebufferAttachment.ColorAttachment0, TextureTarget.Texture2DMultisample, _frameBufferTexture.ID, 0);
        GL.ClearColor(new Color4(0,0,0,0));
        GL.Clear(ClearBufferMask.ColorBufferBit);

        //draw stuff here 
        foreach (Layer l in Layers)
            l.Render(Matrix);

        //unbind FBO to allow drawing to screen again
        GL.BindFramebuffer(FramebufferTarget.Framebuffer, 0);


        //Bind the FBO to be drawn
        GL.BindTexture(TextureTarget.Texture2DMultisample, _frameBufferTexture.ID);

        //Translate to camera window position
        Matrix4 fbomatrix = matrix * Matrix4.CreateTranslation(_window.x, _window.y, 0) * FBOMatrix;

        //Rotate camera FBO texture
        if (_rotationAngle != 0f)
        {
            fbomatrix = Matrix4.CreateTranslation(RotationCentre.x, RotationCentre.y, 0) * fbomatrix;
            fbomatrix = Matrix4.CreateRotationZ(_rotationAngle) * fbomatrix;
            fbomatrix = Matrix4.CreateTranslation(-RotationCentre.x, -RotationCentre.y, 0) * fbomatrix;
        }


        shader.Bind(ref fbomatrix, DrawType);

        //Some OpenGL setup nonsense, binding vertices and index buffer and telling OpenGL where in the vertex struct things are, pointers &c
        GL.BindBuffer(BufferTarget.ArrayBuffer, vertexBuffer);
        GL.EnableVertexAttribArray(shader.LocationPosition);
        GL.VertexAttribPointer(shader.LocationPosition, 2, VertexAttribPointerType.Float, false, Stride, 0);
        if (shader.LocationTexture != -1)
        {
            GL.EnableVertexAttribArray(shader.LocationTexture);
            GL.VertexAttribPointer(shader.LocationTexture, 2, VertexAttribPointerType.Float, false, Stride, 8);
        }
        GL.EnableVertexAttribArray(shader.LocationColour);
        GL.VertexAttribPointer(shader.LocationColour, 4, VertexAttribPointerType.UnsignedByte, true, Stride, 16);
        GL.BindBuffer(BufferTarget.ElementArrayBuffer, indexBuffer);

        //Draw the damn quad
        GL.DrawArrays(DrawType, 0, Vertices.Length);

        //Cleanup
        GL.DisableVertexAttribArray(shader.LocationPosition);
        if (shader.LocationTexture != -1)
            GL.DisableVertexAttribArray(shader.LocationTexture);
        GL.DisableVertexAttribArray(shader.LocationColour);

    }

I have a wrapper class to control Shader code, here's the bind call:

internal void Bind(ref Matrix4 matrixMVP)
        {
            //Set this shader as active shader
            GL.UseProgram(programID);

            //Load position matrix into vertex shaders
            GL.UniformMatrix4(LocationMVPMatrix, false, ref matrixMVP);

            //Load active texture into fragment shaders
            GL.Uniform1(LocationSampler, 0);
        }

Fragment shader:

/// <summary>
    /// Test for a Multisampled fragment shader - http://www.opentk.com/node/2251
    /// </summary>
    public const string fragmentShaderTestSrc =
    @"
    #version 330

    uniform sampler2DMS Sampler;

    in vec2 InTexture;
    in vec4 OutColour;

    out vec4 OutFragColor;

    int samples = 16;
    float div= 1.0/samples;

    void main()
    {
        OutFragColor = vec4(0.0);
        ivec2 texcoord = ivec2(textureSize(Sampler) * InTexture); // used to fetch msaa texel location
        for (int i=0;i<samples;i++)
        {
            OutFragColor += texelFetch(Sampler, texcoord, i) * OutColour;  // add  color samples together
        }

        OutFragColor*= div; //devide by num of samples to get color avg.
    }
    ";

Vertex shader:

/// <summary>
    /// Default vertex shader that only applies specified matrix transformation
    /// </summary>
    public const string vertexShaderDefaultSrc =
        @"
        #version 330

        uniform mat4 MVPMatrix;

        layout (location = 0) in vec2 Position;
        layout (location = 1) in vec2 Texture;
        layout (location = 2) in vec4 Colour;

        out vec2 InVTexture;
        out vec4 vFragColorVs;

        void main()
        {
            gl_Position = MVPMatrix * vec4(Position, 0, 1);
            InVTexture = Texture;
            vFragColorVs = Colour;
        }";