diff --git a/src/shaders/pbr.fs b/src/shaders/pbr.fs
new file mode 100644
index 0000000..cb930aa
--- /dev/null
+++ b/src/shaders/pbr.fs
@@ -0,0 +1,126 @@
+#version 410 core
+
+// Output color
+out vec4 FragColor;
+
+in vec3 vertexPos;
+in vec3 vertexNormal;
+in vec2 TexCoords;
+
+uniform vec3 lightPos;
+uniform vec3 viewPos;
+
+// From Object Renderer
+uniform vec3 ambientColor;
+uniform vec3 diffuseColor;
+uniform vec3 specularColor;   // used as F0 (base reflectance)
+
+uniform float ambientStrength;
+uniform float specularStrength; 
+uniform float shininess;      // mapped to roughness
+uniform bool useSpecular;
+
+uniform float opacity;
+
+uniform sampler2D diffuseTex;
+uniform bool useTexture;
+
+#define LIGHT_COLOR vec3(1.0, 1.0, 1.0)
+
+// ----------------------------------------------------------------------------
+// Helper functions for Cook-Torrance BRDF
+// ----------------------------------------------------------------------------
+
+// Normal Distribution Function (GGX/Trowbridge-Reitz)
+float DistributionGGX(vec3 N, vec3 H, float roughness)
+{
+    float a      = roughness * roughness;
+    float a2     = a * a;
+    float NdotH  = max(dot(N, H), 0.0);
+    float NdotH2 = NdotH * NdotH;
+
+    float num   = a2;
+    float denom = (NdotH2 * (a2 - 1.0) + 1.0);
+    denom = 3.14159265 * denom * denom;
+
+    return num / denom;
+}
+
+// Geometry function (Schlick-GGX)
+float GeometrySchlickGGX(float NdotV, float roughness)
+{
+    float r = (roughness + 1.0);
+    float k = (r * r) / 8.0; // remapped for direct lighting
+
+    float num   = NdotV;
+    float denom = NdotV * (1.0 - k) + k;
+
+    return num / denom;
+}
+
+// Smith's geometry function
+float GeometrySmith(vec3 N, vec3 V, vec3 L, float roughness)
+{
+    float NdotV = max(dot(N, V), 0.0);
+    float NdotL = max(dot(N, L), 0.0);
+    float ggx1 = GeometrySchlickGGX(NdotV, roughness);
+    float ggx2 = GeometrySchlickGGX(NdotL, roughness);
+    return ggx1 * ggx2;
+}
+
+// Fresnel term (Schlick's approximation)
+vec3 FresnelSchlick(float cosTheta, vec3 F0)
+{
+    return F0 + (1.0 - F0) * pow(1.0 - cosTheta, 5.0);
+}
+
+// ----------------------------------------------------------------------------
+void main()
+{
+    vec3 N = normalize(vertexNormal);
+    vec3 V = normalize(viewPos - vertexPos);
+    vec3 L = normalize(lightPos - vertexPos);
+    vec3 H = normalize(V + L);
+
+    // Texture or uniform color
+    vec3 albedo = (useTexture)
+        ? texture(diffuseTex, TexCoords).rgb
+        : diffuseColor;
+
+    // Map shininess to roughness (inverse relationship)
+    float roughness = clamp(1.0 - (shininess / 256.0), 0.05, 1.0);
+
+    // Base reflectivity (F0)
+    vec3 F0 = mix(vec3(0.04), specularColor, specularStrength);
+
+    // Cook-Torrance BRDF
+    float NDF = DistributionGGX(N, H, roughness);
+    float G   = GeometrySmith(N, V, L, roughness);
+    vec3  F   = FresnelSchlick(max(dot(H, V), 0.0), F0);
+
+    vec3 numerator    = NDF * G * F;
+    float denominator = 4.0 * max(dot(N, V), 0.0) * max(dot(N, L), 0.0) + 0.001;
+    vec3 specular     = numerator / denominator;
+
+    // Energy conservation
+    vec3 kS = F;
+    vec3 kD = vec3(1.0) - kS;
+    kD *= (useSpecular ? 1.0 : 1.0); // keep diffuse always unless specular is off
+
+    float NdotL = max(dot(N, L), 0.0);
+
+    vec3 diffuse = kD * albedo / 3.14159265;
+    vec3 radiance = LIGHT_COLOR;
+
+    vec3 Lo = (diffuse + specular) * radiance * NdotL;
+
+    // Ambient (simple, not IBL)
+    vec3 ambient = ambientStrength * ambientColor * albedo;
+
+    vec3 result = ambient + Lo;
+
+    // Gamma correction
+    result = pow(result, vec3(1.0/2.2));
+
+    FragColor = vec4(result, opacity);
+}