Render Backends

Buffer Layout

MeshRenderData2D stores vertices as tightly packed floats:

x, y, u, v

Each vertex uses MeshRenderData2D.FloatsPerVertex, which is currently 4.

var data = new MeshRenderData2D();
MeshRenderExtractor.Extract(mesh, deformer: null, data);

ReadOnlySpan<float> vertices = data.Vertices;
ReadOnlySpan<int> indices = data.Indices;

The index buffer contains triangle indices from Mesh2D.Faces, three indices per face.

Dirty Flags

MeshRenderData2D tracks independent flags:

Flag	Meaning
VerticesDirty	Vertex buffer contents changed.
IndicesDirty	Index buffer contents changed.

After uploading buffers to your renderer, clear the flags:

if (data.VerticesDirty)
{
    // upload vertex buffer
}

if (data.IndicesDirty)
{
    // upload index buffer
}

data.ClearDirtyFlags();

Non-Indexed Triangle Lists

Some APIs or debug paths are simpler with expanded triangle vertices.

float[] triangles = data.ExpandIndexedTriangles();

ExpandIndexedTriangles() returns a new float array where every triangle index has been resolved into x, y, u, v vertex data.

Backend Contract

Implement IMeshRenderBackend2D when integrating with an engine or graphics API.

public interface IMeshRenderBackend2D : IDisposable
{
    RenderResourceHandle CreateResource(MeshRenderData2D data);
    void UpdateResource(RenderResourceHandle handle, MeshRenderData2D data);
    void BindTexture(RenderResourceHandle handle, Texture2D? texture);
    void Draw(RenderResourceHandle handle, in RenderTransform2D transform);
    void DestroyResource(RenderResourceHandle handle);
}

The core library does not own GPU resources. Your backend maps RenderResourceHandle to API-specific objects such as buffers, vertex arrays, descriptor sets, or textures.

You do not have to use the reference backend classes. If your application already uses Veldrid or another renderer, keep Vergeo2D.Mesh as the mesh/deformation layer and map MeshRenderData2D.Vertices plus MeshRenderData2D.Indices into that renderer’s own vertex and index buffers.

RenderResourceHandle

RenderResourceHandle mirrors the generation-checked handle pattern used by MeshHandle.

if (handle.IsValid)
{
    backend.Draw(handle, RenderTransform2D.Identity);
}

Use the generation value to detect stale GPU resource references after a backend resource is destroyed and a slot is reused.

RenderTransform2D

RenderTransform2D stores:

• Position
• RotationRadians
• Scale

var transform = new RenderTransform2D(
    position: new Vector2(100, 80),
    rotationRadians: 0f,
    scale: Vector2.One);

var matrix = transform.ToMatrix();

ToMatrix() applies scale, then rotation, then translation.

Optional Backends

Reference backend implementations are opt-in and guarded by compilation symbols.

Backend	NuGet package	Define constant
OpenGLMeshRenderBackend2D	Silk.NET.OpenGL	VERGEO_OPENGL
Direct3D11MeshRenderBackend2D	Vortice.Direct3D11	VERGEO_DIRECTX
VulkanMeshRenderBackend2D	Silk.NET.Vulkan	VERGEO_VULKAN

<PropertyGroup>
  <DefineConstants>$(DefineConstants);VERGEO_OPENGL</DefineConstants>
</PropertyGroup>

<ItemGroup>
  <PackageReference Include="Silk.NET.OpenGL" Version="x.x.x" />
</ItemGroup>

Without the matching define constant, that backend class is not compiled into the package.

Constructors

Each reference backend expects the native API objects owned by your application:

var backend = new OpenGLMeshRenderBackend2D(gl);

var backend = new Direct3D11MeshRenderBackend2D(device, context);

var backend = new VulkanMeshRenderBackend2D(vk, physicalDevice, device, commandBuffer);

The backend does not create a window, swapchain, command loop, shader program, or pipeline state for you.

Texture Binding Notes

Reference texture binding is intentionally small:

• OpenGL tracks a texture ID on the resource, but BindTexture(handle, null) only clears it.
• Direct3D11 and Vulkan currently leave BindTexture() empty.

In a real renderer, use Texture2D.Path, Texture2D.Width, and Texture2D.Height to load or look up your engine texture, then bind your own shader resource, descriptor set, or API texture object before drawing.

Shader Expectations

The extracted vertex layout is:

Attribute	Components	Offset
Position	float2	0
UV	float2	2 * sizeof(float)

Reference OpenGL backend enables attribute 0 for position and attribute 1 for UV.