2D Rendering

The 2D rendering pipeline is a deferred command system: each frame, your view function populates a RenderBuffer2D with Command2D values, and the Renderer2D<'Model> sorts them by layer and executes them in order.

What and Why

A deferred renderer means you describe what to draw without worrying about when to draw it. The renderer handles:

• Layer ordering — Commands are sorted by int<RenderLayer> so backgrounds draw before foregrounds.
• Camera transforms — .beginCamera() / .endCamera() bracket world-space content.
• Shader modes — .beginShader() / .endShader() enable per-section effects.
• Post-processing — Screen-space shader passes applied after the scene renders.
• GPU batching — the backend auto-batches standard draw calls; the renderer never interferes.

This is especially useful for:

• 2D lighting — Light commands and sprites are interleaved in the same buffer and processed together.
• UI overlays — Draw UI on a higher layer (and optionally a separate camera) above your game world.
• Debug visualization — Toggle debug shapes on/off by adding or removing commands.
• Portability — The same view function works with any renderer configuration.

When to use deferred vs immediate

Situation	Approach
Sprites, text, shapes, tiles	Use the fluent Draw members (deferred)
Custom GPU work (e.g. raw rlgl meshes, instancing)	Use .drawImmediate(...) (escape hatch)
One-off GPU operations	Prefer deferred; use immediate only when the backend lacks the API

How it works

Program.mkProgram init update
|> Program.withRenderer (fun () -> Renderer2D.create myView)

Each frame, the runtime calls myView ctx model buffer. Your view adds commands, the renderer sorts and executes:

1. buffer.Clear() — wipe previous frame's commands
2. myView ctx model buffer — populate with this frame's draw commands
3. buffer.Sort() — sort by layer (ascending)
4. Execute in order, managing camera/shader state transitions

Adding commands

Everyday view code chains members of the fluent Draw DSL on the buffer — see Draw DSL for the full surface.

Lighting

The 2D lighting system (Mibo.Elmish.Graphics2D.Lighting) provides point lights, directional lights, ambient light, and SDF soft shadows — all GPU-driven with no extra render passes.

buffer
  .setAmbient(lightingCtx, gray, layer = 5<RenderLayer>)
  .addDirectionalLight(lightingCtx, sunDir, sunColor, intensity = 1.5f, layer = 6<RenderLayer>)
  .addPointLight(lightingCtx, torchLight, layer = 7<RenderLayer>)
  .litSprite(lightingCtx, playerSprite)
  .endLighting(lightingCtx, layer = 999<RenderLayer>)
  .drop()

See Lighting & Shadows for details.

Multi-camera rendering

Use Camera2DConfig for viewport-based rendering, split-screen, or picture-in-picture cameras:

// Split-screen left/right
let left = Camera2D.splitScreenLeft cam1 Color.CornflowerBlue
let right = Camera2D.splitScreenRight cam2 Color.DarkGreen

buffer
  .beginCameraWith(left)
  // ... left viewport ...
  .endCamera(layer = 100<RenderLayer>)
  .beginCameraWith(right, layer = 200<RenderLayer>)
  // ... right viewport ...
  .endCamera(layer = 300<RenderLayer>)
  .drop()

Camera2DConfig controls viewport (normalized 0–1 coordinates) and clear color. See Camera for the full API.

Next steps

• Draw DSL — The fluent, backend-neutral draw surface (2D and 3D)
• Buffer & Commands — How to build every type of draw command
• Lighting & Shadows — Point, directional, ambient lights + SDF shadows
• Particles — Batched textured quads
• Custom Commands — Custom rendering with DrawImmediate
• Performance — Writing efficient rendering code
• Camera — Cameras and coordinate transforms