1. SET09115 Intro Graphics Programming
Lighting
SET09115 Intro Graphics Programming

2. Breakdown Working with Colour Basics of Lighting Surface Lighting
Why Lighting?
Ambient Light
Surface Lighting
Diffuse Light
Specular Light
Other Lighting Types

3. Recommended Reading Real Time Rendering Course Text
Chapter 5 – Visual Appearance
Course Text
Chapter 6 – Lighting and Shading

4. Colours

5. Colour Representation
Modern graphics work with 32 bit colour
Typically 4 values of 8 bits used
Red, green, blue, alpha (transparency)
Other formats exist
We could work with values
Better to work with floats 0.0f ..1.0f
0% to 100%

6. Working with Colour Treat colour as a value you can work with
Add colours together
Red + Green = Yellow
(1.0, 0.0, 0.0) + (0.0, 1.0, 0.0) = (1.0, 1.0, 0.0)
Multiply colours together
Magenta * Yellow = Red
(1.0, 0.0, 1.0) * (1.0, 1.0, 0.0) = (1.0, 0.0, 0.0)

7. Vertex Colours
Attaching colours to vertices is what we have been doing up until this point
Blending occurs over surfaces between colour points
OpenGL follows the RGBA format
Image formats may not be in RGBA
DirectX can support other formats
These colours can be used in lighting calculations
Typically, we use textured objects to provide more detail

8. Blending The ability to blend colours in this way is useful
Multi-texturing
Terrain
We will revisit blending colours when working with textures and terrain

9. Questions?
Working with colour

10. Basics of Lighting

11. Why Lighting? Lighting adds depth to a scene
Unlit objects are flat and lack detail
Lighting adds realism to objects
Specular detail
Light reflection

12. How Lighting Works Light works in rays from a graphics point of view
Light comes from a source
Light is reflected off of objects
Light eventually makes it into the eye

13. Materials Light rays are just one part of the equation
Light itself can have a colour
Objects also have a colour
The type of light they reflect into the eye rather than absorb
The light that an object reflects is commonly described in its material
Material may have other properties

14. Main Lighting Types
Generally, an object has three lighting effects affecting it at any time
Ambient
Diffuse
Specular
The colour of an object are these three lighting effects combined
Plus any other effectx

15. What is Ambient Light?
Ambient light is the light that affects everything equally in a scene
Has no direction
Has no distance
Doesn’t care about which part of the object is being calculated
Outside, daylight is an ambient light effect

16. Ambient Light Equation
Ambient light calculation is the simplest
The ambient light of a particular vertex is just the ambient material colour of the object multiplied by the ambient light colour of the scene

17. Example

18. Questions?
Why lighting?
Materials
Ambient light

19. Lighting Surfaces

20. Lighting a Surface
Ambient light is something affecting all geometry equally
Still gives a flat appearance to a scene
Objects reflect light based on how their surfaces are aligned with the light source
Occluded objects / surfaces get no light
Surfaces perpendicular to light source get full light

21. Working with Normals
We use surface normals to determine how light should be reflected off a surface
Andrew will go into the mathematics of lighting next week
Normals are very important for lighting

22. What is Diffuse Light?
Diffuse light is concerned with directionality of the light
Geometry facing a light source is lit
Geometry facing away from the light source unlit
Think sunlight outside

23. How does Diffuse Light Work?
Diffuse light is concerned with the light direction against the surface normal of the piece of geometry in question
If angle = 90 then full light
If angle 0 to 90, or 90 to 180, then shaded
If angle < 0 or > 180 then not lit
Think about how this would work if you shone a light on a table

24. Lambert’s Cosine Law
A simple way to calculate the diffuse light of an object is using Lambert’s Cosine Law
Cos(0) = 0
Cos(90) = 1
Cos(180) = 0
The cosine graph shows how this works

25. Diffuse Light Algorithm
Using Lambert’s Cosine Law, we can generate the diffuse lighting algorithm
Remember, dot product of two vectors is equal to the cosine of the angle between them
We would normally have to transform the surface normal if the model is transformed
Diffuse alpha should always be 1. We will have to set this

26. Example

27. What is Specular Light?
Specular light refers to the point on the object where the light strikes
Specular reflection
This provides a shiny look to objects
Also indicates where the light is coming from

28. How does Specular Light Work?
Specular light requires three pieces of information
Light direction
Surface normal
Eye position
Specular intensity is based on eye position

29. Specular Light Algorithm
Specular light is the most complicated algorithm

30. Example

31. Questions?
Surface lighting
Diffuse lighting
Specular lighting

32. Other Lighting Types

33. Other Lighting Types
Ambient, Diffuse, and Specular are considered the main environmental lighting types
Object materials usually deal with these three types
There are of course other lighting types which affect a scene
Dynamic lighting
Point lights
Spot lights

34. Point Lights
A point light is a light that emanates from a particular point in the scene
Use the same equations, but calculate light vector based on vertex position and light position
Distance to light affects the strength of the light

35. Spot Lights Spot lights also work using light position and distance
The direction of the light is also important
Objects behind the spot light aren’t lit
Light also has an angle associated with it
Beam width at distance

36. Phong Shading
Phong Shading is a popular per-pixel approach to performing lighting calculations
Normals are interpolated across the surface of a polygon
Provides a smoother shading look
Vertex lighting as discussed in this lecture is sometimes referred to as Gourand shading

37. Questions?
Point Lights
Spot Lights
Phong Shading

38. To do this week…
Investigate some of the different forms of light that can affect a scene
In particular, try and find their lighting values
Consider the type of lighting you may want in your coursework
OpenGL has light functionality built in without the use of shaders
Shaders provide more controllable lighting

39. Summary
Lighting is an important concept to provide depth and realism to your scene
Lighting is about the colour of the light, and how an object reflects this light
Three main types of lighting
Ambient
Diffuse
Specular
You should make yourself familiar with how to work these out