brdf

Pros of Graphics

• More comprehensive graphics framework with broader functionality
• Active development and regular updates
• Larger community and ecosystem for support and resources

Cons of Graphics

• Steeper learning curve due to complexity
• Potentially heavier resource requirements
• Tied to Unity engine, less flexible for standalone use

Code Comparison

BRDF (Disney BRDF implementation):

float3 BRDF( float3 L, float3 V, float3 N, float3 X, float3 Y )
{
    float NdotL = dot(N, L);
    float NdotV = dot(N, V);
    if (NdotL < 0 || NdotV < 0) return float3(0,0,0);
    // ... (additional calculations)
}

Graphics (Unity's Standard BRDF):

half4 BRDF1_Unity_PBS (half3 diffColor, half3 specColor, half oneMinusReflectivity, half smoothness,
    float3 normal, float3 viewDir,
    UnityLight light, UnityIndirect gi)
{
    float perceptualRoughness = SmoothnessToPerceptualRoughness (smoothness);
    float3 halfDir = Unity_SafeNormalize (float3(light.dir) + viewDir);
    // ... (additional calculations)
}

Both repositories focus on BRDF implementations, but Graphics offers a more extensive framework for various graphics-related tasks within the Unity ecosystem. BRDF is more specialized and lightweight, focusing specifically on Disney's BRDF model.

Pros of Filament

• More comprehensive rendering engine with broader functionality
• Active development and regular updates
• Extensive documentation and examples

Cons of Filament

• Larger codebase and steeper learning curve
• May be overkill for simple BRDF implementations
• Potentially higher resource requirements

Code Comparison

BRDF:

float D_GGX(float roughness, float NdotH) {
    float alpha = roughness * roughness;
    float alpha2 = alpha * alpha;
    float denom = NdotH * NdotH * (alpha2 - 1.0) + 1.0;
    return alpha2 / (M_PI * denom * denom);
}

Filament:

float D_GGX(float NoH, float roughness) {
    float a = NoH * roughness;
    float k = roughness / (1.0 - NoH * NoH + a * a);
    return k * k * (1.0 / PI);
}

Summary

BRDF focuses specifically on Bidirectional Reflectance Distribution Functions, while Filament is a full-featured physically-based rendering engine. BRDF is simpler and more specialized, making it easier to understand and implement for specific BRDF-related tasks. Filament offers a more complete rendering solution but requires more time to learn and integrate. The choice between them depends on the project's scope and requirements.

Pros of glTF-Sample-Viewer

• Focuses on rendering and visualizing 3D models in glTF format
• Provides a comprehensive viewer with various rendering options and features
• Actively maintained with regular updates and community support

Cons of glTF-Sample-Viewer

• Limited to glTF format, not as versatile for general BRDF analysis
• More complex setup and usage compared to the simpler BRDF viewer
• Larger codebase and dependencies, potentially harder to integrate into other projects

Code Comparison

glTF-Sample-Viewer (JavaScript):

const viewer = new GltfView(canvas, options);
viewer.loadGltf(gltfFile).then(() => {
    viewer.renderFrame();
});

BRDF (Python):

brdf = BRDF(theta_h, theta_d, phi_d)
brdf.load_merl(filename)
brdf.plot()

The glTF-Sample-Viewer code demonstrates loading and rendering a 3D model, while the BRDF code shows loading and plotting BRDF data. glTF-Sample-Viewer is more focused on interactive 3D visualization, whereas BRDF is tailored for analyzing and visualizing BRDF data specifically.

Pros of pbrt-v3

• Comprehensive physically-based rendering system with extensive documentation
• Supports a wide range of rendering techniques and algorithms
• Active development and community support

Cons of pbrt-v3

• Steeper learning curve due to its complexity
• Larger codebase, which may be overwhelming for beginners
• Focused on offline rendering, not real-time applications

Code Comparison

BRDF (C++):

vec3 BRDF::eval(const vec3& V, const vec3& L, const vec3& N) const {
    vec3 H = normalize(V + L);
    float NdotL = max(dot(N, L), 0.0f);
    float NdotV = max(dot(N, V), 0.0f);
    float NdotH = max(dot(N, H), 0.0f);
    return diffuse + specular * (m_a + m_b * pow(NdotH, m_c)) / (NdotL * NdotV);
}

pbrt-v3 (C++):

Spectrum MicrofacetReflection::f(const Vector3f &wo, const Vector3f &wi) const {
    float cosThetaO = AbsCosTheta(wo), cosThetaI = AbsCosTheta(wi);
    Vector3f wh = wi + wo;
    if (cosThetaI == 0 || cosThetaO == 0) return Spectrum(0.);
    if (wh.x == 0 && wh.y == 0 && wh.z == 0) return Spectrum(0.);
    wh = Normalize(wh);
    Spectrum F = fresnel->Evaluate(Dot(wi, wh));
    return R * distribution->D(wh) * distribution->G(wo, wi) * F /
           (4 * cosThetaI * cosThetaO);
}

Pros of Falcor

• More comprehensive rendering framework with extensive features
• Active development and regular updates
• Supports modern graphics APIs like DirectX 12 and Vulkan

Cons of Falcor

• Steeper learning curve due to its complexity
• Larger codebase and potentially higher resource requirements
• Primarily focused on real-time rendering, which may not be suitable for all use cases

Code Comparison

BRDF (Python):

def beckmann(m, cos_theta):
    cos2 = cos_theta * cos_theta
    sin2 = 1.0 - cos2
    tan2 = sin2 / cos2
    return math.exp(-tan2 / (m * m)) / (math.pi * m * m * cos2 * cos2)

Falcor (C++):

float4 evalBRDF(ShadingData sd, float3 wo, float3 wi)
{
    float3 h = normalize(wo + wi);
    float NoH = dot(sd.N, h);
    float NoV = dot(sd.N, wo);
    float NoL = dot(sd.N, wi);
    return evalMicrofacetBRDF(sd, NoV, NoL, NoH, h);
}

The BRDF repository focuses on a specific BRDF implementation, while Falcor provides a more comprehensive rendering framework with various BRDF models and additional features. BRDF is simpler and easier to understand, while Falcor offers more flexibility and advanced rendering capabilities at the cost of increased complexity.

Pros of MaterialX

• Broader scope, covering material definitions beyond just BRDF
• More active development and community support
• Designed for cross-platform compatibility and integration with various DCC tools

Cons of MaterialX

• More complex and potentially steeper learning curve
• Larger codebase, which may be overkill for simple BRDF implementations
• Requires more setup and configuration for basic usage

Code Comparison

MaterialX example (defining a simple material):

<?xml version="1.0"?>
<materialx version="1.38">
  <standard_surface name="example_material" type="material">
    <input name="base_color" type="color3" value="0.8, 0.2, 0.2" />
    <input name="specular_roughness" type="float" value="0.3" />
  </standard_surface>
</materialx>

BRDF example (using the library):

#include "brdf/brdf.h"

BRDF::Params params;
params.roughness = 0.3f;
params.baseColor = Vec3f(0.8f, 0.2f, 0.2f);
float result = BRDF::eval(params, incomingLight, outgoingLight);

The MaterialX example demonstrates its XML-based material definition, while the BRDF example shows direct C++ usage for BRDF evaluation.