Phong Lighting

From paper: Illumination for computer generated pictures

Phong is a local illumination model , because it only considers the to-be-shaded geometry relative to the light and does not consider other objects that might block the light. Therefore also no shadows are cast in pure Phong Lighting.

Components #

Phong Lighting consists of 3 Components

Ambient #

Reflected light of the environment, that is present everywhere.

with

• , how much ambient light should influence the material
• material color
• component-wise multiply
• Ambient light color

Diffuse #

Reflected light of the light source. Diffuse light is dependent on the surface normal and light direction, but independent on the view direction.

with:

• , how diffuse the material should be (“roughness”)
• vector to the light source
• normal vector
• dot product
• light color
• material color

Specular #

Reflected specular highlights, dependent on the light position, surface normal and view direction.

with:

• , how shiny the material should be
• reflection vector
• view vector
• , of the angle between and
• how focussed the highlight is, bigger more focussed
• light color
• [Only for metals] Material color

Light Sources #

Non-Area lights can be modelled useing Phong Lighting

• Point lights
• Directional lights
• Spot lights
• Sun light

When dealing with multiple light sources in a scene, evaluate the Phong Lighting model for each light and add the resulting fragment colors (additive light mixing).

Blinn-Phong Lighting #

• After James F. Blinn.
• Paper : models of light reflection for computer synthesized pictures

Mostly same as Phong Lighting but for calculating specular instead of: do with:

• the “halfway vector” between the light and the view:

Then use the angle between and to determine how much light hits the eye

• if then
• does not need to be calculated

Shading Models using Phong Lighting #

Flat Shading

Compute vertex colors in the VS with Phong Lighing, for each face, choose one vertex color

Gouraud shading

Compute vertex colors in the VS with Phong Lighting, let the GPU interpolate the vertex colors over the faces

Phong Shading

Pass everything to the PS/FS and do per pixel/fragment Phong Lighting