gl viewport

NResUI/Rendering/Viewport/Meshes/GpuMesh.cs

@@ -0,0 +1,36 @@
+using Silk.NET.OpenGL;
+
+namespace NResUI.Rendering.Viewport.Meshes;
+
+public sealed class GpuMesh
+{
+    private readonly GL _gl;
+
+    public uint VertexArrayObject { get; }
+    public uint VertexBufferObject { get; }
+    public uint ElementBufferObject { get; }
+    public uint IndexCount { get; }
+    public PrimitiveType PrimitiveType { get; }
+
+    public GpuMesh(
+        GL gl,
+        uint vertexArrayObject,
+        uint vertexBufferObject,
+        uint elementBufferObject,
+        uint indexCount,
+        PrimitiveType primitiveType = PrimitiveType.Triangles)
+    {
+        _gl = gl;
+        VertexArrayObject = vertexArrayObject;
+        VertexBufferObject = vertexBufferObject;
+        ElementBufferObject = elementBufferObject;
+        IndexCount = indexCount;
+        PrimitiveType = primitiveType;
+    }
+
+    public void Draw()
+    {
+        _gl.BindVertexArray(VertexArrayObject);
+        _gl.DrawElements(PrimitiveType, IndexCount, DrawElementsType.UnsignedInt, null);
+    }
+}

NResUI/Rendering/Viewport/Meshes/PrimitiveMeshes.cs

@@ -0,0 +1,191 @@
+using System;
+using System.Collections.Generic;
+using Silk.NET.OpenGL;
+
+namespace NResUI.Rendering.Viewport.Meshes;
+
+public static unsafe class PrimitiveMeshes
+{
+    public static GpuMesh CreateCube(GL gl)
+    {
+        // position.xyz, color.rgb
+        float[] vertices =
+        {
+            // front
+            -1, -1,  1,  1, 0, 0,
+             1, -1,  1,  0, 1, 0,
+             1,  1,  1,  0, 0, 1,
+            -1,  1,  1,  1, 1, 0,
+
+            // back
+            -1, -1, -1,  1, 0, 1,
+             1, -1, -1,  0, 1, 1,
+             1,  1, -1,  1, 1, 1,
+            -1,  1, -1,  0.5f, 0.5f, 0.5f,
+        };
+
+        uint[] indices =
+        {
+            // front
+            0, 1, 2,
+            2, 3, 0,
+
+            // right
+            1, 5, 6,
+            6, 2, 1,
+
+            // back
+            5, 4, 7,
+            7, 6, 5,
+
+            // left
+            4, 0, 3,
+            3, 7, 4,
+
+            // top
+            3, 2, 6,
+            6, 7, 3,
+
+            // bottom
+            4, 5, 1,
+            1, 0, 4,
+        };
+
+        return CreateIndexedMesh(gl, vertices, indices, PrimitiveType.Triangles);
+    }
+
+    public static GpuMesh CreateWorldGrid(
+        GL gl,
+        int halfExtent = 20,
+        int minorStep = 1,
+        int majorStep = 5)
+    {
+        if (halfExtent <= 0)
+            throw new ArgumentOutOfRangeException(nameof(halfExtent));
+
+        if (minorStep <= 0)
+            throw new ArgumentOutOfRangeException(nameof(minorStep));
+
+        if (majorStep <= 0)
+            throw new ArgumentOutOfRangeException(nameof(majorStep));
+
+        var vertices = new List<float>();
+        var indices = new List<uint>();
+
+        void AddVertex(float x, float y, float z, float r, float g, float b)
+        {
+            vertices.Add(x);
+            vertices.Add(y);
+            vertices.Add(z);
+            vertices.Add(r);
+            vertices.Add(g);
+            vertices.Add(b);
+        }
+
+        void AddLine(
+            float x0, float y0, float z0,
+            float x1, float y1, float z1,
+            float r, float g, float b)
+        {
+            var startIndex = (uint)(vertices.Count / 6);
+
+            AddVertex(x0, y0, z0, r, g, b);
+            AddVertex(x1, y1, z1, r, g, b);
+
+            indices.Add(startIndex);
+            indices.Add(startIndex + 1);
+        }
+
+        const float y = 0.0f;
+
+        for (var i = -halfExtent; i <= halfExtent; i += minorStep)
+        {
+            var isAxis = i == 0;
+            var isMajor = i % majorStep == 0;
+
+            var brightness = isMajor ? 0.38f : 0.24f;
+            var r = brightness;
+            var g = brightness;
+            var b = brightness;
+
+            // Lines parallel to X. The Z axis itself is blue.
+            if (isAxis)
+            {
+                AddLine(-halfExtent, y, i, halfExtent, y, i, 0.25f, 0.45f, 1.0f);
+            }
+            else
+            {
+                AddLine(-halfExtent, y, i, halfExtent, y, i, r, g, b);
+            }
+
+            // Lines parallel to Z. The X axis itself is red.
+            if (isAxis)
+            {
+                AddLine(i, y, -halfExtent, i, y, halfExtent, 1.0f, 0.25f, 0.25f);
+            }
+            else
+            {
+                AddLine(i, y, -halfExtent, i, y, halfExtent, r, g, b);
+            }
+        }
+
+        return CreateIndexedMesh(gl, vertices.ToArray(), indices.ToArray(), PrimitiveType.Lines);
+    }
+
+    private static GpuMesh CreateIndexedMesh(
+        GL gl,
+        float[] vertices,
+        uint[] indices,
+        PrimitiveType primitiveType)
+    {
+        var vao = gl.GenVertexArray();
+        var vbo = gl.GenBuffer();
+        var ebo = gl.GenBuffer();
+
+        gl.BindVertexArray(vao);
+
+        gl.BindBuffer(BufferTargetARB.ArrayBuffer, vbo);
+        fixed (float* vertexPtr = vertices)
+        {
+            gl.BufferData(
+                BufferTargetARB.ArrayBuffer,
+                (nuint)(vertices.Length * sizeof(float)),
+                vertexPtr,
+                BufferUsageARB.StaticDraw);
+        }
+
+        gl.BindBuffer(BufferTargetARB.ElementArrayBuffer, ebo);
+        fixed (uint* indexPtr = indices)
+        {
+            gl.BufferData(
+                BufferTargetARB.ElementArrayBuffer,
+                (nuint)(indices.Length * sizeof(uint)),
+                indexPtr,
+                BufferUsageARB.StaticDraw);
+        }
+
+        const uint stride = 6 * sizeof(float);
+
+        gl.EnableVertexAttribArray(0);
+        gl.VertexAttribPointer(
+            0,
+            3,
+            VertexAttribPointerType.Float,
+            false,
+            stride,
+            null);
+
+        gl.EnableVertexAttribArray(1);
+        gl.VertexAttribPointer(
+            1,
+            3,
+            VertexAttribPointerType.Float,
+            false,
+            stride,
+            (void*)(3 * sizeof(float)));
+
+        gl.BindVertexArray(0);
+
+        return new GpuMesh(gl, vao, vbo, ebo, (uint)indices.Length, primitiveType);
+    }
+}

NResUI/Rendering/Viewport/OpenGL/MsaaFramebuffer.cs

@@ -0,0 +1,150 @@
+using Silk.NET.OpenGL;
+
+namespace NResUI.Rendering.Viewport.OpenGL;
+
+public sealed class MsaaFramebuffer
+{
+    private readonly GL _gl;
+    private readonly uint _samples;
+
+    private uint _msaaFramebuffer;
+    private uint _msaaColorRenderbuffer;
+    private uint _msaaDepthStencilRenderbuffer;
+
+    private uint _resolveFramebuffer;
+    private uint _resolveColorTexture;
+
+    private int _width;
+    private int _height;
+
+    public uint ColorTexture => _resolveColorTexture;
+
+    public MsaaFramebuffer(GL gl, uint samples = 4)
+    {
+        _gl = gl;
+        _samples = samples;
+    }
+
+    public void EnsureSize(int width, int height)
+    {
+        width = Math.Max(1, width);
+        height = Math.Max(1, height);
+
+        if (_msaaFramebuffer != 0 && _width == width && _height == height)
+            return;
+
+        _width = width;
+        _height = height;
+
+        if (_msaaFramebuffer == 0)
+        {
+            _msaaFramebuffer = _gl.GenFramebuffer();
+            _msaaColorRenderbuffer = _gl.GenRenderbuffer();
+            _msaaDepthStencilRenderbuffer = _gl.GenRenderbuffer();
+
+            _resolveFramebuffer = _gl.GenFramebuffer();
+            _resolveColorTexture = _gl.GenTexture();
+        }
+
+        _gl.BindRenderbuffer(RenderbufferTarget.Renderbuffer, _msaaColorRenderbuffer);
+        _gl.RenderbufferStorageMultisample(
+            RenderbufferTarget.Renderbuffer,
+            _samples,
+            InternalFormat.Rgba8,
+            (uint)width,
+            (uint)height);
+
+        _gl.BindRenderbuffer(RenderbufferTarget.Renderbuffer, _msaaDepthStencilRenderbuffer);
+        _gl.RenderbufferStorageMultisample(
+            RenderbufferTarget.Renderbuffer,
+            _samples,
+            InternalFormat.Depth24Stencil8,
+            (uint)width,
+            (uint)height);
+
+        _gl.BindFramebuffer(FramebufferTarget.Framebuffer, _msaaFramebuffer);
+
+        _gl.FramebufferRenderbuffer(
+            FramebufferTarget.Framebuffer,
+            FramebufferAttachment.ColorAttachment0,
+            RenderbufferTarget.Renderbuffer,
+            _msaaColorRenderbuffer);
+
+        _gl.FramebufferRenderbuffer(
+            FramebufferTarget.Framebuffer,
+            FramebufferAttachment.DepthStencilAttachment,
+            RenderbufferTarget.Renderbuffer,
+            _msaaDepthStencilRenderbuffer);
+
+        var msaaStatus = _gl.CheckFramebufferStatus(FramebufferTarget.Framebuffer);
+        if (msaaStatus != GLEnum.FramebufferComplete)
+            throw new InvalidOperationException($"MSAA viewport framebuffer is incomplete: {msaaStatus}");
+
+        _gl.BindTexture(TextureTarget.Texture2D, _resolveColorTexture);
+        _gl.TexImage2D(
+            TextureTarget.Texture2D,
+            0,
+            InternalFormat.Rgba8,
+            (uint)width,
+            (uint)height,
+            0,
+            PixelFormat.Rgba,
+            PixelType.UnsignedByte,
+            null);
+
+        _gl.TexParameter(
+            TextureTarget.Texture2D,
+            TextureParameterName.TextureMinFilter,
+            (int)TextureMinFilter.Linear);
+
+        _gl.TexParameter(
+            TextureTarget.Texture2D,
+            TextureParameterName.TextureMagFilter,
+            (int)TextureMagFilter.Linear);
+
+        _gl.TexParameter(
+            TextureTarget.Texture2D,
+            TextureParameterName.TextureWrapS,
+            (int)TextureWrapMode.ClampToEdge);
+
+        _gl.TexParameter(
+            TextureTarget.Texture2D,
+            TextureParameterName.TextureWrapT,
+            (int)TextureWrapMode.ClampToEdge);
+
+        _gl.BindFramebuffer(FramebufferTarget.Framebuffer, _resolveFramebuffer);
+
+        _gl.FramebufferTexture2D(
+            FramebufferTarget.Framebuffer,
+            FramebufferAttachment.ColorAttachment0,
+            TextureTarget.Texture2D,
+            _resolveColorTexture,
+            0);
+
+        var resolveStatus = _gl.CheckFramebufferStatus(FramebufferTarget.Framebuffer);
+        if (resolveStatus != GLEnum.FramebufferComplete)
+            throw new InvalidOperationException($"Resolve viewport framebuffer is incomplete: {resolveStatus}");
+
+        _gl.BindFramebuffer(FramebufferTarget.Framebuffer, 0);
+        _gl.BindTexture(TextureTarget.Texture2D, 0);
+        _gl.BindRenderbuffer(RenderbufferTarget.Renderbuffer, 0);
+    }
+
+    public void BindForRender()
+    {
+        _gl.BindFramebuffer(FramebufferTarget.Framebuffer, _msaaFramebuffer);
+        _gl.Viewport(0, 0, (uint)_width, (uint)_height);
+    }
+
+    public void Resolve()
+    {
+        _gl.BindFramebuffer(FramebufferTarget.ReadFramebuffer, _msaaFramebuffer);
+        _gl.BindFramebuffer(FramebufferTarget.DrawFramebuffer, _resolveFramebuffer);
+
+        _gl.BlitFramebuffer(
+            0, 0, _width, _height,
+            0, 0, _width, _height,
+            ClearBufferMask.ColorBufferBit,
+            BlitFramebufferFilter.Nearest);
+    }
+}

NResUI/Rendering/Viewport/OpenGL/ShaderProgram.cs

@@ -0,0 +1,72 @@
+using System.Numerics;
+using Silk.NET.OpenGL;
+
+namespace NResUI.Rendering.Viewport.OpenGL;
+
+public sealed unsafe class ShaderProgram
+{
+    private readonly GL _gl;
+
+    public uint Handle { get; }
+
+    public ShaderProgram(GL gl, string vertexShaderSource, string fragmentShaderSource, string debugName)
+    {
+        _gl = gl;
+
+        var vertexShader = CompileShader(ShaderType.VertexShader, vertexShaderSource, debugName);
+        var fragmentShader = CompileShader(ShaderType.FragmentShader, fragmentShaderSource, debugName);
+
+        Handle = _gl.CreateProgram();
+        _gl.AttachShader(Handle, vertexShader);
+        _gl.AttachShader(Handle, fragmentShader);
+        _gl.LinkProgram(Handle);
+
+        _gl.GetProgram(Handle, ProgramPropertyARB.LinkStatus, out var linked);
+        if (linked == 0)
+        {
+            var log = _gl.GetProgramInfoLog(Handle);
+            throw new InvalidOperationException($"{debugName} shader link failed: {log}");
+        }
+
+        _gl.DetachShader(Handle, vertexShader);
+        _gl.DetachShader(Handle, fragmentShader);
+        _gl.DeleteShader(vertexShader);
+        _gl.DeleteShader(fragmentShader);
+    }
+
+    public void Use()
+    {
+        _gl.UseProgram(Handle);
+    }
+
+    public int GetUniformLocation(string name)
+    {
+        return _gl.GetUniformLocation(Handle, name);
+    }
+
+    public void SetMatrix4(int location, Matrix4x4 matrix)
+    {
+        _gl.UniformMatrix4(location, 1, false, (float*)&matrix);
+    }
+
+    public void SetVector4(int location, Vector4 value)
+    {
+        _gl.Uniform4(location, value.X, value.Y, value.Z, value.W);
+    }
+
+    private uint CompileShader(ShaderType type, string source, string debugName)
+    {
+        var shader = _gl.CreateShader(type);
+        _gl.ShaderSource(shader, source);
+        _gl.CompileShader(shader);
+
+        _gl.GetShader(shader, ShaderParameterName.CompileStatus, out var compiled);
+        if (compiled == 0)
+        {
+            var log = _gl.GetShaderInfoLog(shader);
+            throw new InvalidOperationException($"{debugName} {type} compile failed: {log}");
+        }
+
+        return shader;
+    }
+}

NResUI/Rendering/Viewport/ViewportCamera.cs

@@ -0,0 +1,38 @@
+using System.Numerics;
+
+namespace NResUI.Rendering.Viewport;
+
+public sealed class ViewportCamera
+{
+    public float YawDegrees { get; set; } = 35.0f;
+    public float PitchDegrees { get; set; } = 25.0f;
+    public float Distance { get; set; } = 4.0f;
+
+    public Matrix4x4 GetSceneRotationMatrix()
+    {
+        return Matrix4x4.CreateRotationY(ToRadians(YawDegrees)) *
+               Matrix4x4.CreateRotationX(ToRadians(PitchDegrees));
+    }
+
+    public Matrix4x4 GetViewMatrix()
+    {
+        return Matrix4x4.CreateLookAt(
+            new Vector3(0.0f, 0.0f, Distance),
+            Vector3.Zero,
+            Vector3.UnitY);
+    }
+
+    public Matrix4x4 GetProjectionMatrix(float aspectRatio)
+    {
+        return Matrix4x4.CreatePerspectiveFieldOfView(
+            ToRadians(60.0f),
+            aspectRatio,
+            0.01f,
+            100.0f);
+    }
+
+    public static float ToRadians(float degrees)
+    {
+        return degrees * MathF.PI / 180.0f;
+    }
+}

NResUI/Rendering/Viewport/ViewportGrid.cs

@@ -0,0 +1,16 @@
+using System.Numerics;
+using NResUI.Rendering.Viewport.Meshes;
+
+namespace NResUI.Rendering.Viewport;
+
+public sealed class ViewportGrid
+{
+    public GpuMesh Mesh { get; }
+    public bool IsVisible { get; set; } = true;
+    public Matrix4x4 LocalTransform { get; set; } = Matrix4x4.Identity;
+
+    public ViewportGrid(GpuMesh mesh)
+    {
+        Mesh = mesh;
+    }
+}

NResUI/Rendering/Viewport/ViewportInputController.cs

@@ -0,0 +1,53 @@
+using System.Numerics;
+using ImGuiNET;
+
+namespace NResUI.Rendering.Viewport;
+
+public sealed class ViewportInputController
+{
+    private const float MouseRotationSpeed = 0.25f;
+    private const float MouseZoomSpeed = 0.35f;
+
+    private bool _isRotatingViewport;
+
+    public void Handle(
+        ViewportScene scene,
+        ViewportCamera camera,
+        bool viewportHovered,
+        Vector2 imageMin,
+        Vector2 imageSize)
+    {
+        var io = ImGui.GetIO();
+
+        if (viewportHovered && ImGui.IsMouseClicked(ImGuiMouseButton.Middle))
+            _isRotatingViewport = true;
+
+        if (!ImGui.IsMouseDown(ImGuiMouseButton.Middle))
+            _isRotatingViewport = false;
+
+        if (_isRotatingViewport)
+        {
+            camera.YawDegrees += io.MouseDelta.X * MouseRotationSpeed;
+            camera.PitchDegrees += io.MouseDelta.Y * MouseRotationSpeed;
+            camera.PitchDegrees = Math.Clamp(camera.PitchDegrees, -89.0f, 89.0f);
+        }
+
+        if (viewportHovered && Math.Abs(io.MouseWheel) > float.Epsilon)
+        {
+            camera.Distance -= io.MouseWheel * MouseZoomSpeed;
+            camera.Distance = Math.Clamp(camera.Distance, 1.5f, 40.0f);
+        }
+
+        if (viewportHovered && ImGui.IsMouseClicked(ImGuiMouseButton.Left))
+        {
+            var mouse = ImGui.GetMousePos();
+            var localMouse = mouse - imageMin;
+
+            scene.SelectedPieceId = ViewportSelection.PickPiece(
+                scene,
+                camera,
+                localMouse,
+                imageSize);
+        }
+    }
+}

NResUI/Rendering/Viewport/ViewportPiece.cs

@@ -0,0 +1,43 @@
+using System.Numerics;
+using NResUI.Rendering.Viewport.Meshes;
+
+namespace NResUI.Rendering.Viewport;
+
+public sealed class ViewportPiece
+{
+    public int Id { get; }
+    public string Name { get; }
+    public GpuMesh Mesh { get; }
+
+    public Matrix4x4 LocalTransform { get; set; }
+
+    public Vector3 BoundsMin { get; }
+    public Vector3 BoundsMax { get; }
+
+    public ViewportPiece(
+        int id,
+        string name,
+        GpuMesh mesh,
+        Matrix4x4 localTransform,
+        Vector3 boundsMin,
+        Vector3 boundsMax)
+    {
+        Id = id;
+        Name = name;
+        Mesh = mesh;
+        LocalTransform = localTransform;
+        BoundsMin = boundsMin;
+        BoundsMax = boundsMax;
+    }
+
+    public static ViewportPiece CreateUnitCube(int id, string name, GpuMesh mesh)
+    {
+        return new ViewportPiece(
+            id,
+            name,
+            mesh,
+            Matrix4x4.Identity,
+            new Vector3(-1.0f, -1.0f, -1.0f),
+            new Vector3(1.0f, 1.0f, 1.0f));
+    }
+}

NResUI/Rendering/Viewport/ViewportRenderer.cs

@@ -0,0 +1,254 @@
+using System.Numerics;
+using NResUI.Rendering.Viewport.OpenGL;
+using Silk.NET.OpenGL;
+using Silk.NET.Windowing;
+
+namespace NResUI.Rendering.Viewport;
+
+public sealed class ViewportRenderer
+{
+    private readonly GL _gl;
+    private readonly IWindow _window;
+    private readonly MsaaFramebuffer _framebuffer;
+
+    private ShaderProgram? _meshShader;
+    private ShaderProgram? _outlineShader;
+
+    private int _meshMvpLocation;
+    private int _outlineMvpLocation;
+    private int _outlineColorLocation;
+
+    private bool _initialized;
+
+    public ViewportRenderer(GL gl, IWindow window)
+    {
+        _gl = gl;
+        _window = window;
+        _framebuffer = new MsaaFramebuffer(gl, samples: 4);
+    }
+
+    public uint Render(int width, int height, ViewportScene scene, ViewportCamera camera)
+    {
+        EnsureInitialized();
+
+        width = Math.Max(1, width);
+        height = Math.Max(1, height);
+
+        _framebuffer.EnsureSize(width, height);
+        _framebuffer.BindForRender();
+
+        _gl.Enable(EnableCap.DepthTest);
+        _gl.Enable(EnableCap.CullFace);
+        _gl.CullFace(TriangleFace.Back);
+
+        _gl.ClearColor(0.12f, 0.13f, 0.15f, 1.0f);
+        _gl.ClearStencil(0);
+        _gl.Clear((uint)(
+            ClearBufferMask.ColorBufferBit |
+            ClearBufferMask.DepthBufferBit |
+            ClearBufferMask.StencilBufferBit));
+
+        var aspect = width / (float)Math.Max(1, height);
+        var sceneRotation = camera.GetSceneRotationMatrix();
+        var view = camera.GetViewMatrix();
+        var projection = camera.GetProjectionMatrix(aspect);
+
+        DrawGrid(scene, sceneRotation, view, projection);
+        DrawScene(scene, sceneRotation, view, projection);
+
+        _framebuffer.Resolve();
+
+        _gl.Disable(EnableCap.CullFace);
+        _gl.Disable(EnableCap.DepthTest);
+        _gl.Disable(EnableCap.StencilTest);
+        _gl.UseProgram(0);
+        _gl.BindVertexArray(0);
+        _gl.BindFramebuffer(FramebufferTarget.Framebuffer, 0);
+
+        var framebufferSize = _window.FramebufferSize;
+        _gl.Viewport(0, 0, (uint)framebufferSize.X, (uint)framebufferSize.Y);
+
+        return _framebuffer.ColorTexture;
+    }
+
+
+    private void DrawGrid(
+        ViewportScene scene,
+        Matrix4x4 sceneRotation,
+        Matrix4x4 view,
+        Matrix4x4 projection)
+    {
+        if (_meshShader == null)
+            throw new InvalidOperationException("Viewport mesh shader is not initialized.");
+
+        var grid = scene.Grid;
+        if (grid == null || !grid.IsVisible)
+            return;
+
+        var model = grid.LocalTransform * sceneRotation;
+        var mvp = model * view * projection;
+
+        _gl.Disable(EnableCap.StencilTest);
+        _gl.Disable(EnableCap.CullFace);
+
+        _meshShader.Use();
+        _meshShader.SetMatrix4(_meshMvpLocation, mvp);
+        grid.Mesh.Draw();
+
+        _gl.Enable(EnableCap.CullFace);
+    }
+
+    private void DrawScene(
+        ViewportScene scene,
+        Matrix4x4 sceneRotation,
+        Matrix4x4 view,
+        Matrix4x4 projection)
+    {
+        if (_meshShader == null || _outlineShader == null)
+            throw new InvalidOperationException("Viewport renderer is not initialized.");
+
+        _gl.Disable(EnableCap.StencilTest);
+        _meshShader.Use();
+
+        foreach (var piece in scene.Pieces)
+        {
+            if (piece.Id == scene.SelectedPieceId)
+                continue;
+
+            DrawPiece(piece, sceneRotation, view, projection);
+        }
+
+        var selectedPiece = scene.SelectedPiece;
+        if (selectedPiece == null)
+            return;
+
+        _gl.Enable(EnableCap.StencilTest);
+        _gl.StencilMask(0xFF);
+        _gl.StencilFunc(StencilFunction.Always, 1, 0xFF);
+        _gl.StencilOp(StencilOp.Keep, StencilOp.Keep, StencilOp.Replace);
+
+        _meshShader.Use();
+        DrawPiece(selectedPiece, sceneRotation, view, projection);
+
+        _gl.StencilFunc(StencilFunction.Notequal, 1, 0xFF);
+        _gl.StencilMask(0x00);
+        _gl.Disable(EnableCap.DepthTest);
+
+        DrawPieceOutline(selectedPiece, sceneRotation, view, projection);
+
+        _gl.Enable(EnableCap.DepthTest);
+        _gl.StencilMask(0xFF);
+        _gl.Disable(EnableCap.StencilTest);
+    }
+
+    private void DrawPiece(
+        ViewportPiece piece,
+        Matrix4x4 sceneRotation,
+        Matrix4x4 view,
+        Matrix4x4 projection)
+    {
+        if (_meshShader == null)
+            throw new InvalidOperationException("Viewport mesh shader is not initialized.");
+
+        var model = piece.LocalTransform * sceneRotation;
+        var mvp = model * view * projection;
+
+        _meshShader.Use();
+        _meshShader.SetMatrix4(_meshMvpLocation, mvp);
+        piece.Mesh.Draw();
+    }
+
+    private void DrawPieceOutline(
+        ViewportPiece piece,
+        Matrix4x4 sceneRotation,
+        Matrix4x4 view,
+        Matrix4x4 projection)
+    {
+        if (_outlineShader == null)
+            throw new InvalidOperationException("Viewport outline shader is not initialized.");
+
+        const float outlineScale = 1.06f;
+
+        var model = Matrix4x4.CreateScale(outlineScale) * piece.LocalTransform * sceneRotation;
+        var mvp = model * view * projection;
+
+        _outlineShader.Use();
+        _outlineShader.SetMatrix4(_outlineMvpLocation, mvp);
+        _outlineShader.SetVector4(_outlineColorLocation, new Vector4(1.0f, 0.82f, 0.15f, 1.0f));
+
+        piece.Mesh.Draw();
+    }
+
+    private void EnsureInitialized()
+    {
+        if (_initialized)
+            return;
+
+        CreateShaders();
+        _initialized = true;
+    }
+
+    private void CreateShaders()
+    {
+        const string meshVertexShaderSource = """
+        #version 330 core
+
+        layout (location = 0) in vec3 aPosition;
+        layout (location = 1) in vec3 aColor;
+
+        uniform mat4 uMvp;
+
+        out vec3 vColor;
+
+        void main()
+        {
+            vColor = aColor;
+            gl_Position = uMvp * vec4(aPosition, 1.0);
+        }
+        """;
+
+        const string meshFragmentShaderSource = """
+        #version 330 core
+
+        in vec3 vColor;
+        out vec4 FragColor;
+
+        void main()
+        {
+            FragColor = vec4(vColor, 1.0);
+        }
+        """;
+
+        const string outlineVertexShaderSource = """
+        #version 330 core
+
+        layout (location = 0) in vec3 aPosition;
+
+        uniform mat4 uMvp;
+
+        void main()
+        {
+            gl_Position = uMvp * vec4(aPosition, 1.0);
+        }
+        """;
+
+        const string outlineFragmentShaderSource = """
+        #version 330 core
+
+        uniform vec4 uColor;
+        out vec4 FragColor;
+
+        void main()
+        {
+            FragColor = uColor;
+        }
+        """;
+
+        _meshShader = new ShaderProgram(_gl, meshVertexShaderSource, meshFragmentShaderSource, "Viewport mesh");
+        _outlineShader = new ShaderProgram(_gl, outlineVertexShaderSource, outlineFragmentShaderSource, "Viewport outline");
+
+        _meshMvpLocation = _meshShader.GetUniformLocation("uMvp");
+        _outlineMvpLocation = _outlineShader.GetUniformLocation("uMvp");
+        _outlineColorLocation = _outlineShader.GetUniformLocation("uColor");
+    }
+}

NResUI/Rendering/Viewport/ViewportScene.cs

@@ -0,0 +1,53 @@
+using NResUI.Rendering.Viewport.Meshes;
+
+namespace NResUI.Rendering.Viewport;
+
+public sealed class ViewportScene
+{
+    private readonly List<ViewportPiece> _pieces = new();
+
+    public IReadOnlyList<ViewportPiece> Pieces => _pieces;
+
+    public ViewportGrid? Grid { get; set; }
+
+    public int SelectedPieceId { get; set; } = -1;
+
+    public ViewportPiece? SelectedPiece
+    {
+        get
+        {
+            if (SelectedPieceId < 0)
+                return null;
+
+            foreach (var piece in _pieces)
+            {
+                if (piece.Id == SelectedPieceId)
+                    return piece;
+            }
+
+            return null;
+        }
+    }
+
+    public void AddPiece(ViewportPiece piece)
+    {
+        _pieces.Add(piece);
+    }
+
+    public void ClearSelection()
+    {
+        SelectedPieceId = -1;
+    }
+
+    public static ViewportScene CreateDefaultCubeScene(GpuMesh cubeMesh, GpuMesh gridMesh)
+    {
+        var scene = new ViewportScene
+        {
+            Grid = new ViewportGrid(gridMesh)
+        };
+
+        scene.AddPiece(ViewportPiece.CreateUnitCube(0, "Cube", cubeMesh));
+
+        return scene;
+    }
+}

NResUI/Rendering/Viewport/ViewportSelection.cs

@@ -0,0 +1,109 @@
+using System.Numerics;
+
+namespace NResUI.Rendering.Viewport;
+
+public static class ViewportSelection
+{
+    public static int PickPiece(
+        ViewportScene scene,
+        ViewportCamera camera,
+        Vector2 localMouse,
+        Vector2 viewportSize)
+    {
+        if (viewportSize.X <= 1.0f || viewportSize.Y <= 1.0f)
+            return -1;
+
+        var aspect = viewportSize.X / viewportSize.Y;
+        var fovRadians = ViewportCamera.ToRadians(60.0f);
+        var tanHalfFov = MathF.Tan(fovRadians * 0.5f);
+
+        var ndcX = (2.0f * localMouse.X / viewportSize.X) - 1.0f;
+        var ndcY = 1.0f - (2.0f * localMouse.Y / viewportSize.Y);
+
+        var rayOriginWorld = new Vector3(0.0f, 0.0f, camera.Distance);
+        var rayDirectionWorld = Vector3.Normalize(new Vector3(
+            ndcX * aspect * tanHalfFov,
+            ndcY * tanHalfFov,
+            -1.0f));
+
+        var sceneRotation = camera.GetSceneRotationMatrix();
+
+        var bestPieceId = -1;
+        var bestDistance = float.PositiveInfinity;
+
+        foreach (var piece in scene.Pieces)
+        {
+            var model = piece.LocalTransform * sceneRotation;
+
+            if (!Matrix4x4.Invert(model, out var inverseModel))
+                continue;
+
+            var rayOriginLocal = Vector3.Transform(rayOriginWorld, inverseModel);
+            var rayDirectionLocal = Vector3.Normalize(
+                Vector3.TransformNormal(rayDirectionWorld, inverseModel));
+
+            if (IntersectRayAabb(
+                    rayOriginLocal,
+                    rayDirectionLocal,
+                    piece.BoundsMin,
+                    piece.BoundsMax,
+                    out var hitDistance) &&
+                hitDistance < bestDistance)
+            {
+                bestDistance = hitDistance;
+                bestPieceId = piece.Id;
+            }
+        }
+
+        return bestPieceId;
+    }
+
+    private static bool IntersectRayAabb(
+        Vector3 rayOrigin,
+        Vector3 rayDirection,
+        Vector3 boundsMin,
+        Vector3 boundsMax,
+        out float hitDistance)
+    {
+        hitDistance = 0.0f;
+
+        var tMin = 0.0f;
+        var tMax = float.PositiveInfinity;
+
+        if (!IntersectSlab(rayOrigin.X, rayDirection.X, boundsMin.X, boundsMax.X, ref tMin, ref tMax) ||
+            !IntersectSlab(rayOrigin.Y, rayDirection.Y, boundsMin.Y, boundsMax.Y, ref tMin, ref tMax) ||
+            !IntersectSlab(rayOrigin.Z, rayDirection.Z, boundsMin.Z, boundsMax.Z, ref tMin, ref tMax))
+        {
+            return false;
+        }
+
+        hitDistance = tMin;
+        return true;
+    }
+
+    private static bool IntersectSlab(
+        float origin,
+        float direction,
+        float min,
+        float max,
+        ref float tMin,
+        ref float tMax)
+    {
+        const float epsilon = 1e-6f;
+
+        if (MathF.Abs(direction) < epsilon)
+            return origin >= min && origin <= max;
+
+        var invDirection = 1.0f / direction;
+        var t1 = (min - origin) * invDirection;
+        var t2 = (max - origin) * invDirection;
+
+        if (t1 > t2)
+            (t1, t2) = (t2, t1);
+
+        tMin = MathF.Max(tMin, t1);
+        tMax = MathF.Min(tMax, t2);
+
+        return tMin <= tMax;
+    }
+}