The Phong Shading technique creates a smooth shading effect by interpolating the normal vectors at the vertices of your vector graphics. Each corner has a direction vector pointing to where the surface is facing, and by interpolating these directions, the surface appears "smooth" even if made up of quads or triangles.
For more information on Phong shading, visit this link.
If you are manually constructing geometry, remember to calculate Face Normals for Phong shading using:
geometry.computeFaceNormals();
When building meshes manually, you can also specify normals in the face constructor like:
var face = new THREE.Face3( 0, 1, 2, normal, color, 0 );
To achieve a metallic look with specular reflection, add point lights close to the surface. Learn more about lighting options here:
PointLight,
SpotLight,
DirectionalLight.
Experiment with different parameters such as shininess, metal, and wraparound to control how light interacts with the surface material. Adjusting these values can create various effects on the rendered object.
If you want to dive deeper into the implementation details, check out the source code of the Fragment shader used by WebGL in Three.js:
lights_phong_fragment.glsl.
While the documentation focuses on PointLight, SpotLight, and DirectionalLight affecting MeshPhongMaterial, keep in mind that Diffuse and Ambient lights also play a role in determining the final appearance of the surface.