Attempted to implement Cel-Shading. Need more work !!!

Function combines Cook–Torrance BRDF using:GGX NDF,Schlick–Smith geometry term,Schlick Fresnel,Lambert diffuse only for dielectrics,Metallic/roughness workflow with F0 from IORReference : real shading in unreal engine 4

Recreation of Sample from OpenGL Programming Guide 1.1. Lighted, smooth-shaded spheres drawn with different material properties that approximate real materials. The first column has materials that resemble from top to bottom emerald, jade, obsidian, pearl, ruby, and turquoise. The second column resembles brass, bronze, chrome, copper, gold, and silver. The third column represents various colors of plastic: black, cyan, green, red, white, and yellow. The fourth column is drawn with similar colors of rubber. link: https://book.huihoo.com/opengl-programming-guide-version-1.1/appendixi.html

Final Result Blin-Phong Scene

Fixed the specular but now third sphere is blue for some reason...

First Try at Blin Phong Shading. I dont know why third sphere specular is wrong !!!