Shader Story

Lighting Models : Image-Based Lighting (IBL)

Image-Based Lighting (IBL) simulates real-world reflections and ambient lighting using environment maps rather than relying solely on direct lights.

Instead of computing lighting only from light sources, IBL samples a cubemap texture representing the surrounding environment, capturing diffuse and specular reflections from it.

IBL is a foundational technique for modern physically based rendering (PBR) pipelines and is often combined with Blinn-Phong or GGX specular terms for more control.

Perfect for metals, glossy plastics, lookdev.

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Visual demo

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// Pseudo-code (Complete per-vertex and per-pixel implementations, with detailed comments, are available in the related Patreon post)
// Link: https://www.patreon.com/posts/shader-story-142344957


// Blinn-Phong diffuse
NdotL = max(0, dot(N, lightDir))
diffuse = diffuseFactor x NdotL x lightColor

// Blinn-Phong specular
H = normalize(V + lightDir)
NdotH = max(0, dot(N, H))
specular = pow(NdotH, specularGloss) x specularPower x specularColor

// Compute reflection direction for IBL
R = reflect(-V, N)
envColor = sampleCube(IBL_Map, R)

// Blend regular specular with environment reflection
specular = lerp(specular, envColor x specular, IBL_Influence)

// Combine diffuse + specular terms
return diffuse + specular

Complete per-vertex and per-pixel implementations, with detailed comments, are available on Patreon.

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Basic idea

Light doesn’t only come from direct light sources, the world around emits ambient light as well.

With IBL, surrounding light is captured using a cubemap (like a panoramic HDR image) and use it to light the surface.

• The shading method first calculates standard Blinn-Phong lighting for base diffuse and specular terms.
• Then, reflection vector is computed based on the view and surface normal.
• That reflection vector is used to sample the environment cubemap, fetching a color that represents what the object “sees” in that direction.
• Finally, it blends this reflection with the Blinn-Phong specular result based on an IBL influence factor.

Image-Based Lighting Equation

C_output = (N*L × D x L_i) + lerp(S, T(R) × S, I)

Where:

• N·L - diffuse light contribution
• D - diffuse factor
• L_i - light color
• S - Blinn-Phong specular contribution
• R - reflection vector (reflect(-V, N))
• T(R) - cubemap texture sample using reflection direction
• I - IBL influence factor (0 → classic Blinn-Phong, 1 → fully IBL-driven)

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🔗 Related Functions

Lerp • Dot • Saturate

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