QuaternionEngine/docs/MultiLighting.md

Multi-Light System: Punctual Point Lights

Extends the rendering pipeline to support multiple dynamic point lights alongside the existing directional sun light. All lighting calculations use a shared PBR (Cook-Torrance) BRDF implementation.

• Files: src/scene/vk_scene.h/.cpp, src/core/types.h, shaders/lighting_common.glsl

Data Structures

CPU-side (C++)

// src/scene/vk_scene.h
struct PointLight {
    glm::vec3 position;
    float radius;       // falloff radius
    glm::vec3 color;
    float intensity;
};

GPU-side (GLSL)

// shaders/input_structures.glsl
#define MAX_PUNCTUAL_LIGHTS 64

struct GPUPunctualLight {
    vec4 position_radius;   // xyz: world position, w: radius
    vec4 color_intensity;   // rgb: color, a: intensity
};

The GPUSceneData uniform buffer includes:

• punctualLights[MAX_PUNCTUAL_LIGHTS]: array of packed light data
• lightCounts.x: number of active point lights

Scene API

SceneManager exposes a simple API to manage point lights at runtime:

Method	Description
addPointLight(const PointLight& light)	Appends a point light to the scene
clearPointLights()	Removes all point lights
getPointLights()	Returns const reference to current lights

Example usage:

SceneManager::PointLight light{};
light.position  = glm::vec3(5.0f, 3.0f, 0.0f);
light.radius    = 15.0f;
light.color     = glm::vec3(1.0f, 0.9f, 0.7f);
light.intensity = 20.0f;
sceneManager->addPointLight(light);

GPU Upload

During SceneManager::update_scene(), point lights are packed into GPUSceneData:

1. Iterate over pointLights vector (capped at kMaxPunctualLights = 64)
2. Pack each light into GPUPunctualLight format
3. Zero-fill unused array slots
4. Set lightCounts.x to active count

This data is uploaded to the per-frame UBO and bound via DescriptorManager::gpuSceneDataLayout() at set 0, binding 0.

Shader Implementation

lighting_common.glsl

Shared PBR functions extracted for reuse across all lighting passes:

Function	Purpose
fresnelSchlick()	Fresnel term (Schlick approximation)
DistributionGGX()	Normal distribution function (GGX/Trowbridge-Reitz)
GeometrySchlickGGX()	Geometry term (Schlick-GGX)
GeometrySmith()	Combined geometry attenuation
evaluate_brdf(N, V, L, albedo, roughness, metallic)	Full Cook-Torrance BRDF evaluation
eval_point_light(light, pos, N, V, albedo, roughness, metallic)	Point light contribution with falloff

Point Light Falloff

Uses smooth inverse-square attenuation with radius-based cutoff:

float att = 1.0 / max(dist * dist, 0.0001);
float x   = clamp(dist / radius, 0.0, 1.0);
float smth = (1.0 - x * x);
smth *= smth;
float falloff = att * smth;

This provides physically-based falloff that smoothly reaches zero at the specified radius.

Render Path Integration

Deferred Lighting (deferred_lighting.frag, deferred_lighting_nort.frag)

// Directional sun
vec3 Lsun = normalize(-sceneData.sunlightDirection.xyz);
float sunVis = calcShadowVisibility(pos, N, Lsun);
vec3 sunBRDF = evaluate_brdf(N, V, Lsun, albedo, roughness, metallic);
vec3 direct = sunBRDF * sceneData.sunlightColor.rgb * sceneData.sunlightColor.a * sunVis;

// Accumulate point lights
uint pointCount = sceneData.lightCounts.x;
for (uint i = 0u; i < pointCount; ++i) {
    direct += eval_point_light(sceneData.punctualLights[i], pos, N, V, albedo, roughness, metallic);
}

Forward Pass (mesh.frag)

Same accumulation loop, but without shadow visibility (used for transparent objects).

Ray-Traced Point Light Shadows

When ray tracing is enabled (hybrid mode), the first 4 point lights receive RT shadows:

if (sceneData.rtOptions.x == 1u && i < 4u) {
    // Cast shadow ray from surface toward light
    vec3 toL = light.position_radius.xyz - pos;
    // ... rayQueryInitializeEXT / rayQueryProceedEXT ...
    if (hit) contrib = vec3(0.0);
}

This provides accurate point light shadows without additional shadow maps.

Performance Considerations

• Light Count: Up to 64 point lights supported; practical limit depends on scene complexity
• Loop Unrolling: Shader compilers typically unroll small loops; consider dynamic branching for very high light counts
• Shadow Maps: Point light shadows use RT only; traditional cubemap shadows are not implemented
• Bandwidth: Each light adds 32 bytes to the UBO; full array is 2KB

Default Lights

SceneManager::init() creates two default point lights for testing:

Light	Position	Radius	Color	Intensity
Warm Key	(0, 0, 0)	25	(1.0, 0.95, 0.8)	15
Cool Fill	(-10, 4, 10)	20	(0.6, 0.7, 1.0)	10

Call clearPointLights() before adding your own lights to remove these defaults.

Future Extensions

• Spot lights (add cone angle to GPUPunctualLight)