WebGL shading: diffuse vs. specular
Above you see images of a decorative relief. Move the mouse cursor around: it controls the position of a light source. The relief on the left appears matte, while the relief on the right appears shiny.
The difference is in the shading model. Here are the key lines of the diffuse and specular models:
// Diffuse vec4 to_light_dir = normalize(light_pos-surface_pos); float intensity = dot(normal, to_light_dir);
// Specular vec4 from_light_dir = normalize(surface_pos-light_pos); vec4 reflection_dir = reflect(from_light_dir, normal); vec4 camera_dir = normalize(vec4(0.0, 0.0, 1.0, 0.0)); float intensity = dot(reflection_dir, camera_dir);
Both models use the surface normal and the light position to calculate the light intensity at a point on the surface. In the diffuse model, a point is lit to the extent that it faces the light source. In the specular model, a point is lit to the extent that it reflects the light source towards the camera.
The specular model uses the built-in function
vec4 reflect(vec4 I, vec4 N),
which reflects a vector across the normal of a surface.
It then uses the dot product to compare this reflection with the camera direction.
I don’t know what the formal name is for this shading model!
More by Jim
- The inception bar: a new phishing method
- The hacker hype cycle
- Project C-43: the lost origins of asymmetric crypto
- How Hacker News stays interesting
- My parents are Flat-Earthers
- The dots do matter: how to scam a Gmail user
- The sorry state of OpenSSL usability
- I hate telephones
- The Three Ts of Time, Thought and Typing: measuring cost on the web
- Granddad died today
- Your syntax highlighter is wrong
Tagged . All content copyright James Fisher 2017. This post is not associated with my employer. Found an error? Edit this page.