DeferredRenderer

The DeferredRenderer is the default rendering technique used in the Grindstone Engine. It is designed for flexibility and efficiency, particularly in scenes with many dynamic lights.

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What is Deferred Rendering?

In traditional forward rendering, each object is rendered and lit in a single pass. This means each light has to be considered for every object, which becomes inefficient with many lights.

Deferred rendering separates rendering into two main stages:

1. Geometry Pass – Renders scene geometry into a set of G-buffers (geometry buffers)
2. Lighting Pass – Applies lighting using the data from the G-buffers

This approach means geometry is only drawn once, and lights are processed independently, making it ideal for scenes with high light counts.

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Summary of Render Stages

1. Opaque Geometry Pass
   
   • Writes Diffuse, Normal, SpecularRoughness, and Depth attachments.
   • Uses GeometryOpaque
2. Screen Space Ambient Occlusion Pass
   
   • Detects for geometry that is close to each other from the opaque pass, in order to increase the shadow around contact areas.
3. Lighting Pass
   
   • Per-light fullscreen passes of point lights, spot lights, and directional lights.
   • Image-based lighting pass that uses light probes to add ambient detail and reflections (using spherical harmonics for ambient and cubemaps for reflections).
4. Unlit Geometry Pass
   
   • Uses GeometryUnlit
     
   • Unlit geometry on top.
5. Sky Geometry Pass
   
   • Uses GeometrySky
     
   • Forward-rendered skies, which appear at the back of the scene.
6. Transparent Geometry Pass
   
   • Uses GeometryTransparent
     
   • Forward-rendered transparent objects, which are blended on top (glass, particles, etc).
7. Post-Processing
   
   • Enhances the look of the scene after geometry and lighting.

Opaque Geometry Pass

The renderer writes material and surface data to several textures, known as attachments or G-buffers:

• Diffuse – stores surface diffuse color
• SpecularRoughness – stores surface specular color and roughness
• Normals – stores surface normal directions in view space
• Depth – stores pixel depth (also used to reconstruct world positions)

These are written using calls to assetRendererManager->RenderQueue(commandBuffer, registry, "GeometryOpaque"), which asks each registered AssetRenderer (such as Mesh3dRenderer) to render all opaque objects.

Lighting Pass

Once geometry is captured, lighting is applied:

• Per-light passes: Each light (point, directional, spot) is rendered as a full-screen quad, using shaders that read from the G-buffers to compute lighting at each pixel.
• Image-Based Lighting (IBL): The renderer applies global lighting using an environment cubemap (for specular reflections) and spherical harmonics (for diffuse lighting). This simulates ambient lighting from the surrounding world.

Unlit, Sky, and Transparent Passes

After lighting, unlit, sky, and transparent transparent objects are rendered separately using:

assetRendererManager->RenderQueue(commandBuffer, registry, "GeometryUnlit");
assetRendererManager->RenderQueue(commandBuffer, registry, "GeometrySky");
assetRendererManager->RenderQueue(commandBuffer, registry, "GeometryTransparent");

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Post-Processing

Following the lighting stage, the DeferredRenderer runs a post-processing pipeline, which includes:

• Screen Space Ambient Occlusion (SSAO) - This calculates how much the ambient lighting will be able to reach certain areas, where less lighting can reach corners and areas with high detail.
• Screen Space Reflections (SSR) (Work In Progress) - Reflect rays on the geometry as it has been already rendered, to be able to render reflections. This only works if the reflection results in a position that is on the screen.
• Depth of Field (DOF) (Work In Progress) - Breaks the geometry into slices - near, far, and mid-distance, where near and far places may be blurred differently.
• Bloom - Takes extremely bright pixels and blurs them.
• Composite - This does many operations in one go:
  • Chromatic Abberation - shifts colors slightly by channel (red, green, and blue channels).
  • Compositing Bloom - takes the result of the Bloom process and combines it with the regular image.
  • Vignette - darkens the edges of the image.
  • Grain - applies static noise to the image.
  • Tonemapping - takes a high dynamic range color (0-Infinity colors) and tones it down to standard dynamic range (0-255 colors).
  • Linear to SRGB - applies gamma correction to the image.

These effects refine the final image for realism and mood.

Final Output

The final image, as with any Renderer, is redirected to one of two places - the swapchain (monitor), or another render target to be used elsewhere (like the editor viewport).

Future Work

• Screen Space Reflections for higher fidelity reflections
• Depth of Field for blurring very close or very far geometry, like a real lens does
• Improved light culling using meshes (spheres for point lights, and cones for spot lights), and tiled or clustered light culling. This reduces the pixels which are lit for each light.