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GLSL · 19 Specular Lighting and View Vectors
Series contents · Technology map
Stage: Lighting and Procedural Surfaces · Editable example · Storage ID: glsl-step-19
Goals and learning outcomes
- Implement view-dependent specular lighting.
- Explain the limits of an educational lighting model.
Prerequisites
Continue using the output and records from Unit 18. Before experimenting with Specular Lighting and View Vectors, preserve the previous inputs and reference outputs.
Key concepts and explanations
View Direction
Specular lighting depends on camera direction as well as the light. If highlights stay fixed when the camera moves, check spaces and direction signs.
Model Limitations
A simple Blinn-Phong term is an educational reflection model. Do not call it a complete energy-conserving PBR implementation.
Practice setup
First check the execution scope guidance on the example screen. The following describes the environment needed to extend the assignment in a separate project. This document-guided exercise requires your own implementation using WebGL2 and GLSL ES 3.00 in a separate localhost project. First check the GLSL version of existing examples and avoid mixing in 1.00 syntax.
The linked example is a starting point. It does not implement every task below. Complete work beyond its supported scope in a separate project.
Practice tasks
- Write normalize(L+V) and pow(max(dot(N,H),0),shininess) in specular.glsl.
- Keep the light fixed and move the camera to two positions.
- Compare highlight width at the same time point with shininess 8 and 64.
Variables to observe
| Variable | Baseline | Change | Expected change / hypothesis |
|---|---|---|---|
| shininess | 8 | 64 | Expect narrower highlights, while recognizing that this does not describe every physical property of the material. |
Predictions in this table are not measured results. Change one condition at a time and record why the actual result differs.
Completion criteria
- Check highlight movement at both camera positions.
- Record highlight widths in pixels for both shininess values.
Self-check
- What happens to the normalize input when L and V are nearly opposite?
- Can roughness and shininess be treated as the same value?
Official references
Linked example and execution scope
Example source · Runtime environments and limits
Runs WebGL ShaderMaterial in the browser. Comparisons use a fixed 640×360 size; frame intervals are different from GPU time.
Source code and records are not overwritten automatically. Resetting an existing example also preserves your notes.
Next learning
Previous: Normals and Diffuse Lighting · Next: Normals on Deformed Surfaces