[abenedik]

I recommend that you store the VertexColorArray to the mesh, by using:

Code:

mesh.SetDataChannel(MeshDataChannelTypes.VertexColors, vertexColors);

Then in your effect class use the following code (all taken from VertexColorEffect):

in OnInitializeDeviceResources override (prepare effect's resources):

Code:

_positionNormalTexture0Color1_vertexBufferDescription = gpuDevice.VertexBufferDescriptionsManager.GetPositionNormalTexture0Color1VertexBufferDescription();

_standardTechnique = new StandardEffectTechnique(Scene, "VertexColorEffect-StandardTechnique")  {
    VertexInputStatePtr = _positionNormalTexture0Color1_vertexBufferDescription.PipelineVertexInputStateCreateInfoPtr,
    ShaderStages = _pipelineShaderStages,
    PipelineLayout = _pipelineLayout,
    ColorBlendAttachmentState = CommonStatesManager.OpaqueAttachmentStat
};

in ApplyRenderingItemMaterial override:

Code:

if (renderingItem.ParentSceneNode is ModelNode modelNode)
{
    var sceneNodeMesh = modelNode.GetMesh();

    // Check if mesh provides PixelColors or PixelSizes data channels
    if (sceneNodeMesh != null)
    {
        vertexColorsBuffer = GetVertexColorBufferFromMesh(sceneNodeMesh, renderingContext.GpuDevice, out var hasTransparentColors);
       
        if (hasTransparentColors.HasValue)
            hasTransparency = hasTransparentColors.Value;
    }
}

if (vertexColorsBuffer != null)
{
    if (vertexColorsBuffer.ItemsCount < renderingItem.VertexCount)
        Log.Warn?.Write(LogArea, "VertexColorEffect warning: vertexColorsBuffer has less colors defined ({0}) then the number of vertices ({1}) in the RenderingItem (ParentSceneNode.Id: {2})", vertexColorsBuffer.ItemsCount, renderingItem.VertexCount, renderingItem.ParentSceneNode?.Id.ToString() ?? "<null>");
   
    renderingItem.AdditionalVertexBuffers = new Buffer[] { vertexColorsBuffer.Buffer };


    // Add Color vertex buffer to binding 1
    renderingItem.VertexBufferDescription = _positionNormalTexture0Color1_vertexBufferDescription;
}

The following method was used in the previous code block:

Code:

internal static GpuBuffer? GetVertexColorBufferFromMesh(Mesh mesh, VulkanDevice gpuDevice, out bool? hasTransparentColors)
{
    hasTransparentColors = null;

    GpuBuffer? vertexColorsBuffer = mesh.GetDataChannelGpuBuffer(MeshDataChannelTypes.VertexColors);

    if (vertexColorsBuffer == null)
    {
        mesh.GetDataChannelArray<Color4>(MeshDataChannelTypes.VertexColors)

        var pixelColorsObject = mesh.GetDataChannel(MeshDataChannelTypes.VertexColors);
        if (pixelColorsObject != null)
        {
            Color4[]? positionColorsArray;

            if (pixelColorsObject is Color4[] positionColors4)
            {
                positionColorsArray = positionColors4;
            }
            else if (pixelColorsObject is Color3[] positionColors3)
            {
                // Convert Color3 to Color4
                positionColorsArray = new Color4[positionColors3.Length];
                for (int i = 0; i < positionColors3.Length; i++)
                    positionColorsArray[i] = positionColors3[i].ToColor4();
            }
            else
            {
                Log.Warn?.Write(LogArea, $"Unknown VertexColors or PixelColors data format: {pixelColorsObject.GetType().Name}. VertexColorEffect and PixelEffect support only Color4[] and Color3[] formats.");
                positionColorsArray = null;
            }

            if (positionColorsArray != null)
            {
                Log.Trace?.Write(LogArea, "VertexColorBuffer from VertexColors mesh data");

                vertexColorsBuffer = gpuDevice.CreateBuffer(positionColorsArray, BufferUsageFlags.VertexBuffer, isDeviceLocal: true);

                // Set GpuBuffer for next VertexColors usage
                mesh.SetDataChannelGpuBuffer(MeshDataChannelTypes.PixelColors, vertexColorsBuffer);
            }
        }
    }

    if (vertexColorsBuffer != null)
    {
        // Try to get the HasTransparentColors metadata if it was set
        hasTransparentColors = mesh.GetMetadata(VertexColorEffect.HasTransparentColorsMetadataKey) as bool?;
    }

    return vertexColorsBuffer;
}

In vertex shader you define the following layouts:

Code:

layout (location = 0) in vec3 inPosition;
layout (location = 1) in vec3 inNormal;
layout (location = 2) in vec2 inUV;
layout (location = 3) in vec4 inColor;

layout (location = 0) out vec3 outNormal;
layout (location = 1) out vec2 outUV;
layout (location = 2) out vec4 outColor;

// Set the outColor = inColor;

Fragment shader is then simply:

Code:

layout (location = 0) in vec3 inNormal;
layout (location = 1) in vec2 inUV;
layout (location = 2) in vec4 inColor;

layout(location = 0) out vec4 outColor;

void main()
{
    outColor = inColor;
}

I hope you got enough information to create your own version of the VertexColorEffect.