Monogame backend

[MartelementAyy]

Hello, thanks you for your great bindings.
I managed to pull out an implementation of ImGuiRenderer (based on the "official" ImGuiRenderer from ImGui.NET)

I'm nowhere near an expert on this topic, but it might be interesting to maybe add it to your examples ?

I might drop the code here if anyone interested in making a pull request and/or optimize it.

Sadly, config flag for viewports enable doesn't seem to work, but dockspace yes.

[JunaMeinhold]

Hi, cool thing. But you might be able to use the native backends if you can get your hands on the internal device and hwnd of xna/fna/monogame.

(I really recommend using them, because sometimes ImGui introduces breaking changes/new features in backends and those are hard to maintain)

[MartelementAyy]

Thanks, that is a good suggestion
I will look into it and return here if I managed to find something

[Thraka]

This would be nice to have a modern implementation! I'm the author of ImGuiNET/ImGui.NET#364 which worked a bit on getting the internals exposed and also overhauling the command line generator. However, I'm not an expert in unmanaged code and I really struggled to get things working. But every time I want to check out something new and cool from ImGui I totally don't want to jump in and break everything I have working 😆

[JunaMeinhold]

@Thraka
Well, this wrapper here has internals build in accessible via ImGuiP.XXX

(PS: If you need any help with ImGui stuff feel free to just hop on my discord (readme) and ask me there)

[Thraka]

@MartelementAyy Please do provide your implementation.

[Thraka]

Thanks @JunaMeinhold With a MonoGame implementation of your library, I'll totally switch. Thanks!

[MartelementAyy]

@Thraka You want the implementation of the native ImGuiRenderer from ImGui.NET ?

DrawVertDeclaration

DrawVertDeclaration :

public static class DrawVertDeclaration
{
  public static readonly VertexDeclaration Declaration;

  public static readonly int Size;

  static DrawVertDeclaration()
  {
      unsafe { Size = sizeof(ImDrawVert); }

      Declaration = new VertexDeclaration(
          Size,

          // Position
          new VertexElement(0, VertexElementFormat.Vector2, VertexElementUsage.Position, 0),

          // UV
          new VertexElement(8, VertexElementFormat.Vector2, VertexElementUsage.TextureCoordinate, 0),

          // Color
          new VertexElement(16, VertexElementFormat.Color, VertexElementUsage.Color, 0)
      );
  }
}

ImGuiRenderer

    /// <summary>
    /// ImGui renderer for use with XNA-likes (FNA & MonoGame)
    /// </summary>
    public class ImGuiRenderer
    {
        private Game _game;

        // Graphics
        private GraphicsDevice _graphicsDevice;

        private BasicEffect _effect;
        private RasterizerState _rasterizerState;

        private byte[] _vertexData;
        private VertexBuffer _vertexBuffer;
        private int _vertexBufferSize;

        private byte[] _indexData;
        private IndexBuffer _indexBuffer;
        private int _indexBufferSize;

        // Textures
        private Dictionary<ImTextureID, Texture2D> _loadedTextures;

        private int _textureId;
        private ImTextureID? _fontTextureId;

        // Input
        private int _scrollWheelValue;
        private int _horizontalScrollWheelValue;
        private readonly float WHEEL_DELTA = 120;
        private Keys[] _allKeys = Enum.GetValues<Keys>();

        public ImGuiRenderer(Game game)
        {
            var context = ImGui.CreateContext();
            ImGui.SetCurrentContext(context);

            _game = game ?? throw new ArgumentNullException(nameof(game));
            _graphicsDevice = game.GraphicsDevice;

            _loadedTextures = new Dictionary<ImTextureID, Texture2D>();

            _rasterizerState = new RasterizerState()
            {
                CullMode = CullMode.None,
                DepthBias = 0,
                FillMode = FillMode.Solid,
                MultiSampleAntiAlias = false,
                ScissorTestEnable = true,
                SlopeScaleDepthBias = 0
            };

            SetupInput();
        }

        #region ImGuiRenderer

        /// <summary>
        /// Creates a texture and loads the font data from ImGui. Should be called when the <see cref="GraphicsDevice" /> is initialized but before any rendering is done
        /// </summary>
        public virtual unsafe void RebuildFontAtlas()
        {
            // Get font texture from ImGui
            var io = ImGui.GetIO();
            byte* pixelData = null;
            int width = 0;
            int height = 0;
            int bytesPerPixel = 0;

            io.Fonts.GetTexDataAsRGBA32(ref pixelData, ref width, ref height, ref bytesPerPixel);
            // Copy the data to a managed array
           
            var pixels = new byte[width * height * bytesPerPixel];
            unsafe { Marshal.Copy(new IntPtr(pixelData), pixels, 0, pixels.Length); }

            // Create and register the texture as an XNA texture
            var tex2d = new Texture2D(_graphicsDevice, width, height, false, SurfaceFormat.Color);
            tex2d.SetData(pixels);

            // Should a texture already have been build previously, unbind it first so it can be deallocated
            if (_fontTextureId.HasValue) UnbindTexture(_fontTextureId.Value);

            // Bind the new texture to an ImGui-friendly id
            _fontTextureId = BindTexture(tex2d);

            // Let ImGui know where to find the texture
            io.Fonts.SetTexID(_fontTextureId.Value);
            io.Fonts.ClearTexData(); // Clears CPU side texture data
        }

        /// <summary>
        /// Creates a pointer to a texture, which can be passed through ImGui calls such as <see cref="ImGui.Image" />. That pointer is then used by ImGui to let us know what texture to draw
        /// </summary>
        public virtual ImTextureID BindTexture(Texture2D texture)
        {
            var id = new ImTextureID(_textureId++);
            _loadedTextures.Add(id, texture);

            return id;
        }

        /// <summary>
        /// Removes a previously created texture pointer, releasing its reference and allowing it to be deallocated
        /// </summary>
        public virtual void UnbindTexture(ImTextureID textureId)
        {
            _loadedTextures.Remove(textureId);
        }

        /// <summary>
        /// Sets up ImGui for a new frame, should be called at frame start
        /// </summary>
        public virtual void BeforeLayout(GameTime gameTime)
        {
            ImGui.GetIO().DeltaTime = (float)gameTime.ElapsedGameTime.TotalSeconds;

            UpdateInput();

            ImGui.NewFrame();
        }

        /// <summary>
        /// Asks ImGui for the generated geometry data and sends it to the graphics pipeline, should be called after the UI is drawn using ImGui.** calls
        /// </summary>
        public virtual void AfterLayout()
        {
            ImGui.Render();

            unsafe { RenderDrawData(ImGui.GetDrawData()); }
        }

        #endregion ImGuiRenderer

        #region Setup & Update

        /// <summary>
        /// Setup key input event handler.
        /// </summary>
        protected virtual void SetupInput()
        {
            var io = ImGui.GetIO();

            // MonoGame-specific //////////////////////
            _game.Window.TextInput += (s, a) =>
            {
                if (a.Character == '\t') return;
                io.AddInputCharacter(a.Character);
            };

            ///////////////////////////////////////////

            // FNA-specific ///////////////////////////
            //TextInputEXT.TextInput += c =>
            //{
            //    if (c == '\t') return;

            //    ImGui.GetIO().AddInputCharacter(c);
            //};
            ///////////////////////////////////////////
        }

        /// <summary>
        /// Updates the <see cref="Effect" /> to the current matrices and texture
        /// </summary>
        protected virtual Effect UpdateEffect(Texture2D texture)
        {
            _effect = _effect ?? new BasicEffect(_graphicsDevice);

            var io = ImGui.GetIO();

            _effect.World = Matrix.Identity;
            _effect.View = Matrix.Identity;
            _effect.Projection = Matrix.CreateOrthographicOffCenter(0f, io.DisplaySize.X, io.DisplaySize.Y, 0f, -1f, 1f);
            _effect.TextureEnabled = true;
            _effect.Texture = texture;
            _effect.VertexColorEnabled = true;

            return _effect;
        }

        /// <summary>
        /// Sends XNA input state to ImGui
        /// </summary>
        protected virtual void UpdateInput()
        {
            if (!_game.IsActive) return;

            var io = ImGui.GetIO();

            var mouse = Mouse.GetState();
            var keyboard = Keyboard.GetState();
            io.AddMousePosEvent(mouse.X, mouse.Y);
            io.AddMouseButtonEvent(0, mouse.LeftButton == ButtonState.Pressed);
            io.AddMouseButtonEvent(1, mouse.RightButton == ButtonState.Pressed);
            io.AddMouseButtonEvent(2, mouse.MiddleButton == ButtonState.Pressed);
            io.AddMouseButtonEvent(3, mouse.XButton1 == ButtonState.Pressed);
            io.AddMouseButtonEvent(4, mouse.XButton2 == ButtonState.Pressed);

            io.AddMouseWheelEvent(
                (mouse.HorizontalScrollWheelValue - _horizontalScrollWheelValue) / WHEEL_DELTA,
                (mouse.ScrollWheelValue - _scrollWheelValue) / WHEEL_DELTA);
            _scrollWheelValue = mouse.ScrollWheelValue;
            _horizontalScrollWheelValue = mouse.HorizontalScrollWheelValue;

            foreach (var key in _allKeys)
            {
                if (TryMapKeys(key, out ImGuiKey imguikey))
                {
                    io.AddKeyEvent(imguikey, keyboard.IsKeyDown(key));
                }
            }

            io.DisplaySize = new System.Numerics.Vector2(_graphicsDevice.PresentationParameters.BackBufferWidth, _graphicsDevice.PresentationParameters.BackBufferHeight);
            io.DisplayFramebufferScale = new System.Numerics.Vector2(1f, 1f);
        }

        private bool TryMapKeys(Keys key, out ImGuiKey imguikey)
        {
            //Special case not handed in the switch...
            //If the actual key we put in is "None", return none and true. 
            //otherwise, return none and false.
            if (key == Keys.None)
            {
                imguikey = ImGuiKey.None;
                return true;
            }

            imguikey = key switch
            {
                Keys.Back => ImGuiKey.Backspace,
                Keys.Tab => ImGuiKey.Tab,
                Keys.Enter => ImGuiKey.Enter,
                Keys.CapsLock => ImGuiKey.CapsLock,
                Keys.Escape => ImGuiKey.Escape,
                Keys.Space => ImGuiKey.Space,
                Keys.PageUp => ImGuiKey.PageUp,
                Keys.PageDown => ImGuiKey.PageDown,
                Keys.End => ImGuiKey.End,
                Keys.Home => ImGuiKey.Home,
                Keys.Left => ImGuiKey.LeftArrow,
                Keys.Right => ImGuiKey.RightArrow,
                Keys.Up => ImGuiKey.UpArrow,
                Keys.Down => ImGuiKey.DownArrow,
                Keys.PrintScreen => ImGuiKey.PrintScreen,
                Keys.Insert => ImGuiKey.Insert,
                Keys.Delete => ImGuiKey.Delete,
                //>= Keys.D0 and <= Keys.D9 => ImGuiKey._0 + (key - Keys.D0),
                >= Keys.A and <= Keys.Z => ImGuiKey.A + (key - Keys.A),
                >= Keys.NumPad0 and <= Keys.NumPad9 => ImGuiKey.Keypad0 + (key - Keys.NumPad0),
                Keys.Multiply => ImGuiKey.KeypadMultiply,
                Keys.Add => ImGuiKey.KeypadAdd,
                Keys.Subtract => ImGuiKey.KeypadSubtract,
                Keys.Decimal => ImGuiKey.KeypadDecimal,
                Keys.Divide => ImGuiKey.KeypadDivide,
                >= Keys.F1 and <= Keys.F24 => ImGuiKey.F1 + (key - Keys.F1),
                Keys.NumLock => ImGuiKey.NumLock,
                Keys.Scroll => ImGuiKey.ScrollLock,
                Keys.LeftShift => ImGuiKey.ModShift,
                Keys.LeftControl => ImGuiKey.ModCtrl,
                Keys.LeftAlt => ImGuiKey.ModAlt,
                Keys.OemSemicolon => ImGuiKey.Semicolon,
                Keys.OemPlus => ImGuiKey.Equal,
                Keys.OemComma => ImGuiKey.Comma,
                Keys.OemMinus => ImGuiKey.Minus,
                Keys.OemPeriod => ImGuiKey.Period,
                Keys.OemQuestion => ImGuiKey.Slash,
                Keys.OemTilde => ImGuiKey.GraveAccent,
                Keys.OemOpenBrackets => ImGuiKey.LeftBracket,
                Keys.OemCloseBrackets => ImGuiKey.RightBracket,
                Keys.OemPipe => ImGuiKey.Backslash,
                Keys.OemQuotes => ImGuiKey.Apostrophe,
                Keys.BrowserBack => ImGuiKey.AppBack,
                Keys.BrowserForward => ImGuiKey.AppForward,
                _ => ImGuiKey.None,
            };

            return imguikey != ImGuiKey.None;
        }

        #endregion Setup & Update

        #region Internals

        /// <summary>
        /// Gets the geometry as set up by ImGui and sends it to the graphics device
        /// </summary>
        private void RenderDrawData(ImDrawDataPtr drawData)
        {
            // Setup render state: alpha-blending enabled, no face culling, no depth testing, scissor enabled, vertex/texcoord/color pointers
            var lastViewport = _graphicsDevice.Viewport;
            var lastScissorBox = _graphicsDevice.ScissorRectangle;
            var lastRasterizer = _graphicsDevice.RasterizerState;
            var lastDepthStencil = _graphicsDevice.DepthStencilState;
            var lastBlendFactor = _graphicsDevice.BlendFactor;
            var lastBlendState = _graphicsDevice.BlendState;

            _graphicsDevice.BlendFactor = Color.White;
            _graphicsDevice.BlendState = BlendState.NonPremultiplied;
            _graphicsDevice.RasterizerState = _rasterizerState;
            _graphicsDevice.DepthStencilState = DepthStencilState.DepthRead;

            // Handle cases of screen coordinates != from framebuffer coordinates (e.g. retina displays)
            drawData.ScaleClipRects(ImGui.GetIO().DisplayFramebufferScale);

            // Setup projection
            _graphicsDevice.Viewport = new Viewport(0, 0, _graphicsDevice.PresentationParameters.BackBufferWidth, _graphicsDevice.PresentationParameters.BackBufferHeight);

            UpdateBuffers(drawData);

            RenderCommandLists(drawData);

            // Restore modified state
            _graphicsDevice.Viewport = lastViewport;
            _graphicsDevice.ScissorRectangle = lastScissorBox;
            _graphicsDevice.RasterizerState = lastRasterizer;
            _graphicsDevice.DepthStencilState = lastDepthStencil;
            _graphicsDevice.BlendState = lastBlendState;
            _graphicsDevice.BlendFactor = lastBlendFactor;
        }

        private unsafe void UpdateBuffers(ImDrawDataPtr drawData)
        {
            if (drawData.TotalVtxCount == 0)
            {
                return;
            }

            // Expand buffers if we need more room
            if (drawData.TotalVtxCount > _vertexBufferSize)
            {
                _vertexBuffer?.Dispose();

                _vertexBufferSize = (int)(drawData.TotalVtxCount * 1.5f);
                _vertexBuffer = new VertexBuffer(_graphicsDevice, DrawVertDeclaration.Declaration, _vertexBufferSize, BufferUsage.None);
                _vertexData = new byte[_vertexBufferSize * DrawVertDeclaration.Size];
            }

            if (drawData.TotalIdxCount > _indexBufferSize)
            {
                _indexBuffer?.Dispose();

                _indexBufferSize = (int)(drawData.TotalIdxCount * 1.5f);
                _indexBuffer = new IndexBuffer(_graphicsDevice, IndexElementSize.SixteenBits, _indexBufferSize, BufferUsage.None);
                _indexData = new byte[_indexBufferSize * sizeof(ushort)];
            }

            // Copy ImGui's vertices and indices to a set of managed byte arrays
            int vtxOffset = 0;
            int idxOffset = 0;

            for (int n = 0; n < drawData.CmdListsCount; n++)
            {
                ImDrawListPtr cmdList = drawData.CmdLists[n];

                fixed (void* vtxDstPtr = &_vertexData[vtxOffset * DrawVertDeclaration.Size])
                fixed (void* idxDstPtr = &_indexData[idxOffset * sizeof(ushort)])
                {
                    Buffer.MemoryCopy(cmdList.VtxBuffer.Data, vtxDstPtr, _vertexData.Length, cmdList.VtxBuffer.Size * DrawVertDeclaration.Size);
                    Buffer.MemoryCopy(cmdList.IdxBuffer.Data, idxDstPtr, _indexData.Length, cmdList.IdxBuffer.Size * sizeof(ushort));
                }

                vtxOffset += cmdList.VtxBuffer.Size;
                idxOffset += cmdList.IdxBuffer.Size;
            }

            // Copy the managed byte arrays to the gpu vertex- and index buffers
            _vertexBuffer.SetData(_vertexData, 0, drawData.TotalVtxCount * DrawVertDeclaration.Size);
            _indexBuffer.SetData(_indexData, 0, drawData.TotalIdxCount * sizeof(ushort));
        }

        private unsafe void RenderCommandLists(ImDrawDataPtr drawData)
        {
            _graphicsDevice.SetVertexBuffer(_vertexBuffer);
            _graphicsDevice.Indices = _indexBuffer;

            int vtxOffset = 0;
            int idxOffset = 0;

            for (int n = 0; n < drawData.CmdListsCount; n++)
            {
                ImDrawListPtr cmdList = drawData.CmdLists[n];

                for (int cmdi = 0; cmdi < cmdList.CmdBuffer.Size; cmdi++)
                {
                    ImDrawCmd drawCmd = cmdList.CmdBuffer[cmdi];

                    if (drawCmd.ElemCount == 0)
                    {
                        continue;
                    }

                    if (!_loadedTextures.ContainsKey(drawCmd.TextureId))
                    {
                        throw new InvalidOperationException($"Could not find a texture with id '{drawCmd.TextureId}', please check your bindings");
                    }

                    _graphicsDevice.ScissorRectangle = new Rectangle(
                        (int)drawCmd.ClipRect.X,
                        (int)drawCmd.ClipRect.Y,
                        (int)(drawCmd.ClipRect.Z - drawCmd.ClipRect.X),
                        (int)(drawCmd.ClipRect.W - drawCmd.ClipRect.Y)
                    );

                    var effect = UpdateEffect(_loadedTextures[drawCmd.TextureId]);

                    foreach (var pass in effect.CurrentTechnique.Passes)
                    {
                        pass.Apply();

#pragma warning disable CS0618 // // FNA does not expose an alternative method.
                        _graphicsDevice.DrawIndexedPrimitives(
                            primitiveType: PrimitiveType.TriangleList,
                            baseVertex: (int)drawCmd.VtxOffset + vtxOffset,
                            minVertexIndex: 0,
                            numVertices: cmdList.VtxBuffer.Size,
                            startIndex: (int)drawCmd.IdxOffset + idxOffset,
                            primitiveCount: (int)drawCmd.ElemCount / 3
                        );
#pragma warning restore CS0618
                    }
                }

                vtxOffset += cmdList.VtxBuffer.Size;
                idxOffset += cmdList.IdxBuffer.Size;
            }
        }

        #endregion Internals
    }

Also there is one key I couldn't find which is ImGuiKey._0, might be ImGuiKey.Key0

In the Initialize method of your game :

protected override void Initialize()
{
    // TODO: Add your initialization logic here
    _imGuiRenderer = new ImGuiRenderer(this);
    _imGuiRenderer.RebuildFontAtlas();
    base.Initialize();
}

And in the Draw :

_imGuiRenderer.BeforeLayout(gameTime);
ImGui.ShowDemoWindow();
_imGuiRenderer.AfterLayout();

Or the one using internal device and hwnd of monogame? If it is the latest one, I don't have it yet.

[Thraka]

I didn't realize the ImGui.NET renderer would just sort of port straight over. I was thinking there was more work for the backend. Regardless, thanks!

[realcoloride]

@JunaMeinhold FNA and Hexa.NET does not seem to mix very well at all.

As of right now FNA uses SDL3 (SDL-CS) as its rendering backend. However, an incompatibility is present.
Using the OpenGL renderer and InitForOpenGL(), a strange non agnostic syntax where it uses Hexa.NET SDL3 classes and not pointers makes it impossible for it to be used.

Casting in the method results in the following exception:

System.AccessViolationException: 'Attempted to read or write protected memory. This is often an indication that other memory is corrupt.'

The way SDLWindow is defined is pretty strange and does not leave room to create SDLWindow instance to match the constraints of the method or find some kind of compatibility.
https://github.com/HexaEngine/Hexa.NET.ImGui/blob/master/Hexa.NET.ImGui.Backends.SDL3/Generated/Structs/SDLWindow.cs

Is this intentional? Hexa.Net's SDL3 implementation is not used in FNA3D (FNA's rendering backend).
Cheers