feat: Step 4 load .obj and glTF models into ECS

- Add Vertex struct and Mesh ECS component (vertices + indices).
- Add Vulkan IndexBuffer for indexed draws.
- Add MeshRenderer that draws Mesh + Transform entities with vkCmdDrawIndexed.
- Add minimal .obj loader (positions, faces) and glTF/glTF-binary loader via SharpGLTF.Core.
- Rewrite shaders to 3D position + color; recompile to SPIR-V.
- Update VulkanPipeline for new vertex format.
- Ship a sample Content/cube.obj and wire Program.cs to load it.
- Remove TriangleRenderer (replaced by MeshRenderer).

src/Engine.Graphics/Engine.Graphics.csproj

@@ -22,6 +22,7 @@
     <PackageReference Include="Silk.NET.Vulkan.Extensions.KHR" Version="2.21.0" />
     <PackageReference Include="Flecs.NET.Debug" Version="4.0.4-build.546" Condition="'$(Configuration)' == 'Debug'" />
     <PackageReference Include="Flecs.NET.Release" Version="4.0.4-build.546" Condition="'$(Configuration)' == 'Release'" />
+    <PackageReference Include="SharpGLTF.Core" Version="1.0.6" />
   </ItemGroup>
 
   <ItemGroup>

src/Engine.Graphics/IndexBuffer.cs

@@ -0,0 +1,113 @@
+using System;
+using Silk.NET.Core;
+using Silk.NET.Vulkan;
+
+namespace Engine.Graphics;
+
+/// <summary>
+/// GPU index buffer for indexed draws.
+/// Uses 32-bit indices.
+/// </summary>
+public sealed unsafe class IndexBuffer : IDisposable
+{
+    private readonly VulkanContext _context;
+    public Silk.NET.Vulkan.Buffer Buffer { get; }
+    public DeviceMemory Memory { get; }
+    public ulong Size { get; }
+    public uint Count { get; }
+
+    public IndexBuffer(VulkanContext context, ReadOnlySpan<byte> data, uint count)
+    {
+        _context = context;
+        Size = (ulong)data.Length;
+        Count = count;
+
+        Buffer = CreateBuffer(Size, BufferUsageFlags.IndexBufferBit);
+        var memoryRequirements = GetMemoryRequirements(Buffer);
+        Memory = AllocateMemory(memoryRequirements, MemoryPropertyFlags.HostVisibleBit | MemoryPropertyFlags.HostCoherentBit);
+
+        var result = _context.Vk.BindBufferMemory(_context.Device, Buffer, Memory, 0);
+        if (result != Result.Success)
+            throw new InvalidOperationException($"vkBindBufferMemory failed: {result}");
+
+        CopyData(data);
+    }
+
+    private Silk.NET.Vulkan.Buffer CreateBuffer(ulong size, BufferUsageFlags usage)
+    {
+        var createInfo = new BufferCreateInfo
+        {
+            SType = StructureType.BufferCreateInfo,
+            Size = size,
+            Usage = usage,
+            SharingMode = SharingMode.Exclusive
+        };
+
+        Silk.NET.Vulkan.Buffer buffer;
+        var result = _context.Vk.CreateBuffer(_context.Device, &createInfo, null, &buffer);
+        if (result != Result.Success)
+            throw new InvalidOperationException($"vkCreateBuffer failed: {result}");
+        return buffer;
+    }
+
+    private MemoryRequirements GetMemoryRequirements(Silk.NET.Vulkan.Buffer buffer)
+    {
+        MemoryRequirements requirements;
+        _context.Vk.GetBufferMemoryRequirements(_context.Device, buffer, &requirements);
+        return requirements;
+    }
+
+    private DeviceMemory AllocateMemory(MemoryRequirements requirements, MemoryPropertyFlags properties)
+    {
+        var memoryTypeIndex = FindMemoryType(requirements.MemoryTypeBits, properties);
+        var allocateInfo = new MemoryAllocateInfo
+        {
+            SType = StructureType.MemoryAllocateInfo,
+            AllocationSize = requirements.Size,
+            MemoryTypeIndex = memoryTypeIndex
+        };
+
+        DeviceMemory memory;
+        var result = _context.Vk.AllocateMemory(_context.Device, &allocateInfo, null, &memory);
+        if (result != Result.Success)
+            throw new InvalidOperationException($"vkAllocateMemory failed: {result}");
+        return memory;
+    }
+
+    private uint FindMemoryType(uint typeFilter, MemoryPropertyFlags properties)
+    {
+        PhysicalDeviceMemoryProperties memoryProperties;
+        _context.Vk.GetPhysicalDeviceMemoryProperties(_context.PhysicalDevice, &memoryProperties);
+        for (var i = 0; i < memoryProperties.MemoryTypeCount; i++)
+        {
+            if ((typeFilter & (1u << i)) != 0 &&
+                (memoryProperties.MemoryTypes[i].PropertyFlags & properties) == properties)
+            {
+                return (uint)i;
+            }
+        }
+        throw new InvalidOperationException("Failed to find suitable memory type.");
+    }
+
+    private void CopyData(ReadOnlySpan<byte> data)
+    {
+        void* mappedData;
+        var result = _context.Vk.MapMemory(_context.Device, Memory, 0, Size, MemoryMapFlags.None, &mappedData);
+        if (result != Result.Success)
+            throw new InvalidOperationException($"vkMapMemory failed: {result}");
+
+        fixed (byte* src = data)
+        {
+            global::System.Buffer.MemoryCopy(src, mappedData, (long)Size, data.Length);
+        }
+
+        _context.Vk.UnmapMemory(_context.Device, Memory);
+    }
+
+    public void Dispose()
+    {
+        _context.Vk.DeviceWaitIdle(_context.Device);
+        _context.Vk.DestroyBuffer(_context.Device, Buffer, null);
+        _context.Vk.FreeMemory(_context.Device, Memory, null);
+    }
+}

src/Engine.Graphics/Loaders/GltfLoader.cs

@@ -0,0 +1,58 @@
+using System;
+using System.Collections.Generic;
+using System.Numerics;
+using Engine.Core;
+using Engine.Core.Components;
+using SharpGLTF.Schema2;
+
+namespace Engine.Graphics.Loaders;
+
+/// <summary>
+/// glTF/glTF binary loader using SharpGLTF.Core.
+/// Loads the first primitive of the first mesh and converts it to a colored Mesh component.
+/// </summary>
+public static class GltfLoader
+{
+    public static Engine.Core.Components.Mesh Load(string path, Vector3? defaultColor = null)
+    {
+        var color = defaultColor ?? new Vector3(0.7f, 0.7f, 0.7f);
+
+        var model = ModelRoot.Load(path);
+        if (model.LogicalMeshes.Count == 0)
+            throw new InvalidOperationException($"glTF file has no meshes: {path}");
+
+        var mesh = model.LogicalMeshes[0];
+        if (mesh.Primitives.Count == 0)
+            throw new InvalidOperationException($"glTF mesh has no primitives: {path}");
+
+        var primitive = mesh.Primitives[0];
+
+        if (!primitive.VertexAccessors.TryGetValue("POSITION", out var positionAccessor))
+            throw new InvalidOperationException($"glTF primitive has no POSITION accessor: {path}");
+
+        var positions = positionAccessor.AsVector3Array();
+        var vertices = new Vertex[positions.Count];
+        for (var i = 0; i < positions.Count; i++)
+        {
+            vertices[i] = new Vertex(positions[i], color);
+        }
+
+        uint[] indices;
+        if (primitive.IndexAccessor != null)
+        {
+            var idx = primitive.IndexAccessor.AsIndexArray();
+            indices = new uint[idx.Count];
+            for (var i = 0; i < idx.Count; i++)
+                indices[i] = idx[i];
+        }
+        else
+        {
+            // Non-indexed primitive
+            indices = new uint[positions.Count];
+            for (var i = 0; i < positions.Count; i++)
+                indices[i] = (uint)i;
+        }
+
+        return new Engine.Core.Components.Mesh(vertices, indices);
+    }
+}

src/Engine.Graphics/Loaders/ObjLoader.cs

@@ -0,0 +1,76 @@
+using System;
+using System.Collections.Generic;
+using System.IO;
+using System.Numerics;
+using Engine.Core;
+using Engine.Core.Components;
+
+namespace Engine.Graphics.Loaders;
+
+/// <summary>
+/// Minimal .obj loader.
+/// Supports vertices (v) and faces (f). Ignores normals/UVs for now.
+/// Produces a colored Mesh component.
+/// </summary>
+public static class ObjLoader
+{
+    public static Mesh Load(string path, Vector3? defaultColor = null)
+    {
+        var color = defaultColor ?? new Vector3(0.7f, 0.7f, 0.7f);
+
+        var positions = new List<Vector3>();
+        var indices = new List<uint>();
+
+        foreach (var rawLine in File.ReadLines(path))
+        {
+            var line = rawLine.Trim();
+            if (string.IsNullOrEmpty(line) || line.StartsWith("#"))
+                continue;
+
+            var parts = line.Split((char[]?)null, StringSplitOptions.RemoveEmptyEntries);
+            if (parts.Length == 0)
+                continue;
+
+            switch (parts[0])
+            {
+                case "v" when parts.Length >= 4:
+                    positions.Add(new Vector3(
+                        float.Parse(parts[1]),
+                        float.Parse(parts[2]),
+                        float.Parse(parts[3])));
+                    break;
+
+                case "f" when parts.Length >= 4:
+                    // Triangulate the face as a fan. Only the position index is used.
+                    var baseIndex = ParseFaceIndex(parts[1]);
+                    for (var i = 2; i < parts.Length - 1; i++)
+                    {
+                        indices.Add(baseIndex);
+                        indices.Add(ParseFaceIndex(parts[i]));
+                        indices.Add(ParseFaceIndex(parts[i + 1]));
+                    }
+                    break;
+            }
+        }
+
+        if (positions.Count == 0)
+            throw new InvalidOperationException($"OBJ file has no vertices: {path}");
+
+        var vertices = new Vertex[positions.Count];
+        for (var i = 0; i < positions.Count; i++)
+        {
+            vertices[i] = new Vertex(positions[i], color);
+        }
+
+        return new Mesh(vertices, indices.ToArray());
+    }
+
+    private static uint ParseFaceIndex(string part)
+    {
+        // Formats: v, v/vt, v/vt/vn, v//vn
+        var slashIndex = part.IndexOf('/');
+        var indexStr = slashIndex == -1 ? part : part.Substring(0, slashIndex);
+        var index = int.Parse(indexStr);
+        return (uint)(index - 1); // OBJ indices are 1-based
+    }
+}

src/Engine.Graphics/MeshRenderer.cs

@@ -1,22 +1,24 @@
 using System;
+using System.Collections.Generic;
 using System.Numerics;
 using Flecs.NET.Core;
 using Silk.NET.Core;
 using Silk.NET.Vulkan;
+using Engine.Core;
 using Engine.Core.Components;
 
 namespace Engine.Graphics;
 
 /// <summary>
-/// Renders a colored triangle using a vertex buffer and a simple graphics pipeline.
-/// Uses Silk.NET.Vulkan and reads entity transforms from the ECS world.
+/// Renders indexed meshes attached to ECS entities.
+/// Uses Silk.NET.Vulkan and reads Mesh + Transform components from the ECS world.
 /// </summary>
-public sealed unsafe class TriangleRenderer : IDisposable
+public sealed unsafe class MeshRenderer : IDisposable
 {
     private readonly VulkanContext _context;
     private readonly Swapchain _swapchain;
     private readonly VulkanPipeline _pipeline;
-    private readonly VertexBuffer _vertexBuffer;
+    private readonly Dictionary<Entity, MeshBuffers> _buffers = new();
     private CommandPool _commandPool;
     private CommandBuffer[] _commandBuffers = null!;
     private Silk.NET.Vulkan.Semaphore[] _imageAvailableSemaphores = null!;
@@ -24,37 +26,35 @@ public sealed unsafe class TriangleRenderer : IDisposable
     private Silk.NET.Vulkan.Fence[] _inFlightFences = null!;
     private int _currentFrame;
 
-    public TriangleRenderer(VulkanContext context, Swapchain swapchain)
+    private sealed class MeshBuffers : IDisposable
+    {
+        public VertexBuffer VertexBuffer;
+        public IndexBuffer IndexBuffer;
+
+        public MeshBuffers(VertexBuffer vertexBuffer, IndexBuffer indexBuffer)
+        {
+            VertexBuffer = vertexBuffer;
+            IndexBuffer = indexBuffer;
+        }
+
+        public void Dispose()
+        {
+            VertexBuffer.Dispose();
+            IndexBuffer.Dispose();
+        }
+    }
+
+    public MeshRenderer(VulkanContext context, Swapchain swapchain)
     {
         _context = context;
         _swapchain = swapchain;
 
         _pipeline = new VulkanPipeline(context, swapchain);
-        _vertexBuffer = CreateTriangleBuffer();
         CreateCommandPool();
         CreateCommandBuffers();
         CreateSyncObjects();
     }
 
-    private VertexBuffer CreateTriangleBuffer()
-    {
-        var vertices = new[]
-        {
-             0.0f, -0.5f,  1.0f, 0.0f, 0.0f,
-             0.5f,  0.5f,  0.0f, 1.0f, 0.0f,
-            -0.5f,  0.5f,  0.0f, 0.0f, 1.0f
-        };
-
-        var bytes = new byte[vertices.Length * sizeof(float)];
-        fixed (byte* p = bytes)
-        fixed (float* v = vertices)
-        {
-            global::System.Buffer.MemoryCopy(v, p, bytes.Length, vertices.Length * sizeof(float));
-        }
-
-        return new VertexBuffer(_context, bytes);
-    }
-
     private void CreateCommandPool()
     {
         var createInfo = new CommandPoolCreateInfo
@@ -160,16 +160,23 @@ public sealed unsafe class TriangleRenderer : IDisposable
         _context.Vk.CmdSetViewport(cmd, 0, 1, &viewport);
         _context.Vk.CmdSetScissor(cmd, 0, 1, &scissor);
 
-        var vertexBuffer = _vertexBuffer.Buffer;
-        var offset = 0ul;
-        _context.Vk.CmdBindVertexBuffers(cmd, 0, 1, &vertexBuffer, &offset);
-
         var drawCmd = cmd;
-        world.Each((Entity e, ref Transform transform) =>
+        world.Each((Entity e, ref Mesh mesh, ref Transform transform) =>
         {
-            var bytes = BuildTriangleVertices(transform);
-            _vertexBuffer.Update(bytes);
-            _context.Vk.CmdDraw(drawCmd, 3, 1, 0, 0);
+            if (!_buffers.TryGetValue(e, out var buffers))
+            {
+                buffers = CreateMeshBuffers(mesh);
+                _buffers[e] = buffers;
+            }
+
+            var bytes = BuildMeshVertices(mesh, transform);
+            buffers.VertexBuffer.Update(bytes);
+
+            var vertexBuffer = buffers.VertexBuffer.Buffer;
+            var offset = 0ul;
+            _context.Vk.CmdBindVertexBuffers(drawCmd, 0, 1, &vertexBuffer, &offset);
+            _context.Vk.CmdBindIndexBuffer(drawCmd, buffers.IndexBuffer.Buffer, 0, IndexType.Uint32);
+            _context.Vk.CmdDrawIndexed(drawCmd, buffers.IndexBuffer.Count, 1, 0, 0, 0);
         });
 
         _context.Vk.CmdEndRenderPass(cmd);
@@ -207,34 +214,52 @@ public sealed unsafe class TriangleRenderer : IDisposable
         _currentFrame++;
     }
 
-    private byte[] BuildTriangleVertices(Transform transform)
+    private MeshBuffers CreateMeshBuffers(Mesh mesh)
+    {
+        var vertexBytes = new byte[mesh.Vertices.Length * 6 * sizeof(float)];
+        fixed (byte* p = vertexBytes)
+        {
+            var dst = (float*)p;
+            for (var i = 0; i < mesh.Vertices.Length; i++)
+            {
+                var v = mesh.Vertices[i];
+                dst[i * 6 + 0] = v.Position.X;
+                dst[i * 6 + 1] = v.Position.Y;
+                dst[i * 6 + 2] = v.Position.Z;
+                dst[i * 6 + 3] = v.Color.X;
+                dst[i * 6 + 4] = v.Color.Y;
+                dst[i * 6 + 5] = v.Color.Z;
+            }
+        }
+
+        var indexBytes = new byte[mesh.Indices.Length * sizeof(uint)];
+        fixed (byte* p = indexBytes)
+        fixed (uint* src = mesh.Indices)
+        {
+            global::System.Buffer.MemoryCopy(src, p, indexBytes.Length, mesh.Indices.Length * sizeof(uint));
+        }
+
+        return new MeshBuffers(
+            new VertexBuffer(_context, vertexBytes),
+            new IndexBuffer(_context, indexBytes, (uint)mesh.Indices.Length));
+    }
+
+    private byte[] BuildMeshVertices(Mesh mesh, Transform transform)
     {
         var matrix = transform.GetMatrix();
-        var positions = new Vector3[]
-        {
-            new Vector3(0.0f, -0.5f, 0.0f),
-            new Vector3(0.5f, 0.5f, 0.0f),
-            new Vector3(-0.5f, 0.5f, 0.0f)
-        };
-        var colors = new[]
-        {
-            new Vector3(1.0f, 0.0f, 0.0f),
-            new Vector3(0.0f, 1.0f, 0.0f),
-            new Vector3(0.0f, 0.0f, 1.0f)
-        };
-
-        var bytes = new byte[3 * 5 * sizeof(float)];
+        var bytes = new byte[mesh.Vertices.Length * 6 * sizeof(float)];
         fixed (byte* p = bytes)
         {
             var dst = (float*)p;
-            for (var i = 0; i < 3; i++)
+            for (var i = 0; i < mesh.Vertices.Length; i++)
             {
-                var transformed = Vector3.Transform(positions[i], matrix);
-                dst[i * 5 + 0] = transformed.X;
-                dst[i * 5 + 1] = transformed.Y;
-                dst[i * 5 + 2] = colors[i].X;
-                dst[i * 5 + 3] = colors[i].Y;
-                dst[i * 5 + 4] = colors[i].Z;
+                var transformed = Vector3.Transform(mesh.Vertices[i].Position, matrix);
+                dst[i * 6 + 0] = transformed.X;
+                dst[i * 6 + 1] = transformed.Y;
+                dst[i * 6 + 2] = transformed.Z;
+                dst[i * 6 + 3] = mesh.Vertices[i].Color.X;
+                dst[i * 6 + 4] = mesh.Vertices[i].Color.Y;
+                dst[i * 6 + 5] = mesh.Vertices[i].Color.Z;
             }
         }
         return bytes;
@@ -244,6 +269,10 @@ public sealed unsafe class TriangleRenderer : IDisposable
     {
         _context.Vk.DeviceWaitIdle(_context.Device);
 
+        foreach (var buffers in _buffers.Values)
+            buffers.Dispose();
+        _buffers.Clear();
+
         for (var i = 0; i < 2; i++)
         {
             _context.Vk.DestroySemaphore(_context.Device, _renderFinishedSemaphores[i], null);
@@ -253,7 +282,6 @@ public sealed unsafe class TriangleRenderer : IDisposable
 
         _context.Vk.DestroyCommandPool(_context.Device, _commandPool, null);
 
-        _vertexBuffer.Dispose();
         _pipeline.Dispose();
     }
 }

src/Engine.Graphics/Shaders/fragment.frag

@@ -0,0 +1,10 @@
+#version 450
+
+layout(location = 0) in vec3 fragColor;
+
+layout(location = 0) out vec4 outColor;
+
+void main()
+{
+    outColor = vec4(fragColor, 1.0);
+}

src/Engine.Graphics/Shaders/vertex.vert

@@ -0,0 +1,12 @@
+#version 450
+
+layout(location = 0) in vec3 inPosition;
+layout(location = 1) in vec3 inColor;
+
+layout(location = 0) out vec3 fragColor;
+
+void main()
+{
+    gl_Position = vec4(inPosition, 1.0);
+    fragColor = inColor;
+}

src/Engine.Graphics/VulkanPipeline.cs

@@ -5,7 +5,7 @@ using Silk.NET.Vulkan;
 namespace Engine.Graphics;
 
 /// <summary>
-/// Simple graphics pipeline for a triangle with vec2 position + vec3 color.
+/// Simple graphics pipeline for indexed meshes with vec3 position + vec3 color.
 /// Uses Silk.NET.Vulkan.
 /// </summary>
 public sealed unsafe class VulkanPipeline : IDisposable
@@ -93,7 +93,7 @@ public sealed unsafe class VulkanPipeline : IDisposable
         var bindingDescription = new VertexInputBindingDescription
         {
             Binding = 0,
-            Stride = (uint)(5 * sizeof(float)),
+            Stride = (uint)(6 * sizeof(float)),
             InputRate = VertexInputRate.Vertex
         };
 
@@ -103,7 +103,7 @@ public sealed unsafe class VulkanPipeline : IDisposable
             {
                 Binding = 0,
                 Location = 0,
-                Format = Format.R32G32Sfloat,
+                Format = Format.R32G32B32Sfloat,
                 Offset = 0
             },
             new VertexInputAttributeDescription
@@ -111,7 +111,7 @@ public sealed unsafe class VulkanPipeline : IDisposable
                 Binding = 0,
                 Location = 1,
                 Format = Format.R32G32B32Sfloat,
-                Offset = (uint)(2 * sizeof(float))
+                Offset = (uint)(3 * sizeof(float))
             }
         };