Render Paths & Frame Composer

Before diving into the internals of the Render Graph, understanding Myth's render paths and frame composer helps you build a global picture: which stages assemble a frame, and in what order.

1. Two Render Paths

The engine selects a render path via RendererSettings when creating an App:

App::new()
    .with_title("My App")
    .with_settings(RendererSettings {
        path: RenderPath::HighFidelity,
        ..Default::default()
    })
    .run::<MyApp>()

Render Path	Role	Use Case
RenderPath::HighFidelity	Full PBR + post-processing + screen-space FX + 3DGS pipeline	Desktop / high-end devices needing Bloom, SSAO, SSR, SSGI, TAA, 3DGS, etc.
RenderPath::BasicForward	Minimal forward rendering	Low-end devices, mobile, basic shading only

Feature Dependencies

Most advanced features (Bloom, SSAO, SSR, SSGI, SSSS, TAA, 3DGS) depend on the HighFidelity path. If a post-processing effect "doesn't work," first confirm the render path is set correctly.

2. High-Fidelity Frame Composition Order

On the HighFidelity path, the FrameComposer assembles each stage in the following topological order. Each stage declares its resource dependencies to the Render Graph, which schedules them uniformly:

Key points per stage:

• Shadow Pass: Generates Cascaded Shadow Maps (CSM) for shadow-casting directional lights, and separate shadows for spot lights.
• Pre Pass: Writes scene depth, normals, and velocity buffers ahead of time, reused by screen-space effects like SSAO, SSSS, and TAA.
• Opaque Pass: The main shading stage for PBR opaque geometry, where clustered light lookups happen.
• SSSS: Screen-space subsurface scattering, depending on Pre Pass normals and Feature ID.
• 3DGS: Gaussian splatting reads the opaque depth buffer for correct occlusion against traditional geometry (present only when the 3dgs feature is enabled).
• Bloom → Tone Mapping → FXAA: The HDR post-processing chain, finally output to screen.

Automatic Culling

Not all of these stages run every frame. If an effect is disabled (e.g. SSAO), the compiler automatically culls it and any predecessor nodes that exist solely to serve it (dead-pass elimination), with zero configuration. See Render Graph.

3. Injecting Custom Stages

The frame composer provides a hook system that lets you insert custom Render Graph nodes between standard stages without modifying engine source:

// Insert a custom full-screen effect before post-processing
composer.add_hook(HookStage::BeforePostProcess, move |ctx| {
    // Declare and return your custom pass on ctx.graph
});

This mechanism lets custom post-processing, debug visualization, and GPU data generation embed into the main loop with zero side effects. See Custom Shaders & Post FX.

Next Steps

• Go deep into the compiler internals → Render Graph
• Configure post-processing effects → Post-Processing & Screen-Space FX