Basic Lighting and Shading

The Important Properties of Light

• It can Reflect, bend, spread and scatter

Most Common Light Sources

• Global Illumination• Light Located at Infinity (Distant Light)• Light Located Locally– Uniform Light (Ambient)– Point Source • Intensity is L(p,P0) = (1 / |p-p0|2 ) L(P0)

– Spotlights (Directional Lights)

OpenGL Light Types

PointSpotlightAmbientDistant

Point

home.elka.pw.edu.pl/.../general/General.html

Spot

home.elka.pw.edu.pl/.../general/General.html

Ambient (Area)

home.elka.pw.edu.pl/.../general/General.html

Distant (Sun / Moon)

home.elka.pw.edu.pl/.../general/General.html

Physical Light

Bidirectional Reflection Distribution Function– (BRDF)

This is based on 5 Variables:– Frequency– Source Vector (x,y)– Output Vector (x,y)

• It also requires a ‘real’ surface

This is a hugely expensive calculation

• Most light consists of a large frequency Range

• In games we have many fast ways of creating the effects of light

Firslty we need to get rid of the ‘spectrum’

• The human Eye recognises colours through 3 types of cones– We can exploit this behaviour by directly

addressing the cones

http://www.unenergy.org/index.php?p=1_180_CPV---Concentrated-PVhttp://www.atmos.ucla.edu/~fovell/AS3/theory_of_color.html

By exploiting this behaviour we can define the colour of light as

• RGB• Varying the levels of Red, Green and Blue can

make the eye ‘see’ every colour of the spectrum.

• The downside to this simplification is that our model of light looses the ability to separate during reflections/refractions.

• As a solution to this we can either use multiple lights, or use explicit functions to ‘create’ light separation

• For offline rendering you may even consider doing a BRDF Rendering using a more complex Lighting method

http://www.tufts.edu/as/tampl/projects/micro_rs/theory.html

Using Basic Lighting in OpenGL

http://www.cs.virginia.edu/~gfx/Courses/2002/RealTime.fall.02/Cg/CG%20Effects%20Explained/Cg%20Effects%20Explained.htm

Enabling Lighting

Enable Lighting in OpenGLglEnable(GL_LIGHTING)

Enable Each Individual LightglEnable(GL_LIGHTi)i <= GL_MAX_LIGHTS

All implementations support at least 8 lights

The 3 Functions to set you lights

• glLightfv(…)• glLightf(…)• glLightModelfv(…)

Specular Reflection

• Specular– The more specular a surface, the move light is

reflected very closely to the angle of reflection– A mirror is a near perfect Specular Surface

http://www.indigorenderer.com/joomla/forum/files/specular_material_test_01_168.jpg

Diffuse Reflection(Lambertian reflection)

http://torcode.com/http://www.glenspectra.co.uk/SiteResources/Data/Templates/1product.asp?DocID=389&v1ID=

Emissive

• It Glows!

http://www.gennetten-concreteartist.com/d-network.html

Translucent Surfaces

http://www.trinity3d.com/product.php?productid=1572&cat=293&page=2http://www.nondot.org/sabre/Projects/Raytracer/

The End (for now)