I am trying to use a constant buffer in a program using SharpDX.Toolkit. I use the Toolkit because it has nice font support for writing on the screen.

The problem I face is in assigning data to the constant buffer.

In the screen below you may see a debug of my code. When it comes to the Draw event the buffer gets empty (obj:9 is active) and in Geometry Shader all values are 0.0f. On event 76 - GSSetShader the obj:16 is active, which contains the data I want to use, non-zero values. I have no idea why it gets overwritten/cleared. I tried assigning or updating buffer in numerous places in the draw method, but none of them helped. For sure it is not a problem of a slot, as in the debug window both (populated and empty) buffers are in slot 0.

NOTE: this way of loading data to constant buffer worked before I switched to using Toolkit, but then the device was explicitly created with SwapChain. I am not so experienced to tell if it may make any difference.

In my effect file I have defined the buffer as

cbuffer ConstantBuffer : register(b0)
{
    float slideX;
    float sinPi075;
    float cosPi075;
    float scaleK;
}

and in the main program

[StructLayout(LayoutKind.Explicit, Size = 16)]
struct GS_CONSTANT_BUF_DATA
{
    [FieldOffset(0)]
    public float slideX;
    [FieldOffset(4)]
    public float sinPi075;
    [FieldOffset(8)]
    public float cosPi075;
    [FieldOffset(12)]
    public float scaleK;
};

followed by

private SharpDX.Direct3D11.Buffer _constantBuffer;
private GS_CONSTANT_BUF_DATA constData;
private int sizeOfconstData;
private SharpDX.Direct3D11.Device _device;
private void InitializeConstantBuffer()
{
    System.Diagnostics.Debug.WriteLine("InitializeConstantBuffer");
    constData = new GS_CONSTANT_BUF_DATA
    {
        slideX = 0.0f,
        sinPi075 = (float)Math.Sin(Math.PI * 0.75),
        cosPi075 = (float)Math.Cos(Math.PI * 0.75),
        scaleK = 0.003f
    };
    _device = (SharpDX.Direct3D11.Device)GraphicsDevice.MainDevice;
    sizeOfconstData = Utilities.SizeOf<GS_CONSTANT_BUF_DATA>();
    _constantBuffer = new SharpDX.Direct3D11.Buffer(
                                       _device
                                     , sizeOfconstData
                                     , ResourceUsage.Default
                                     , BindFlags.ConstantBuffer
                                     , CpuAccessFlags.None
                                     , ResourceOptionFlags.None
                                     , 0);
    _device.ImmediateContext.GeometryShader.SetConstantBuffer(0, _constantBuffer);
    _device.ImmediateContext.UpdateSubresource(ref constData, _constantBuffer);
}

Draw method in the main program

  protected override void Draw(GameTime gameTime)
    {
 GraphicsDevice.Clear(Color.CornflowerBlue);
 for (int i = 0; i < technique.Passes.Count; ++i)
    {
     _device.ImmediateContext.GeometryShader.SetConstantBuffer(0, _constantBuffer);
    _chartGeometry.Draw(
                        GraphicsDevice
                      , SharpDX.Toolkit.Graphics.PrimitiveType.LineList
                      , technique.Passes[i]);
    }
}

And the Draw method associated with _chartGeometry

 public void Draw(GraphicsDevice graphicsDevice, PrimitiveType primitiveType, EffectPass pass)
    {
        if (pass != null)
            pass.Apply();
    
        // Setup the Vertex Buffer
        graphicsDevice.SetVertexBuffer(0, vertexBuffer);
    
        // Setup the Vertex Buffer Input layout
        graphicsDevice.SetVertexInputLayout(InputLayout);
    
        graphicsDevice.Draw(primitiveType, 4, 0);
    }