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Lights in the Phong Model

Lights in the Phong Model. 1. How to compute these?. 2. What are these?. Light source direction: . Look around you … The light in Seattle: Indirect background, … ambient Sun light: Direct, very far away coming from a constant direction (independent of where you are)

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Lights in the Phong Model

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  1. Lights in the Phong Model 1. How to compute these? 2. What are these?

  2. Light source direction: • Look around you … • The light in Seattle: Indirect • background, … ambient • Sun light: Direct, very far away • coming from a constant direction(independent of where you are) • Light bulb at home: Direct • closer, shines from a fixed point • Light from the projector/desk lamp • How would you describe this? credit: http://mynasadata.larc.nasa.gov/Radiation_Explanation.html credit: http://www.truebeyonddesign.com/products-page/ http://www.apartmenttherapy.com/ny/lighting/best-product-tolomeo-desk-lamp-001066

  3. What is Ambient Light? • Not in the real world! • Implementation dependent! • constant color added to illumination results • Maya scene file Rendered image Ambient light Material Property

  4. What about the Sun? • How would you describe the incoming light source for this scene? http://www.planetware.com/picture/kansas-cottonwood-falls-tallgrass-prairie-national-preserve-flint-hills-national-prairie-us-ks108.htm

  5. Directional Light • Direction is: • No position!! (where is the Sun?) • Light has no geometry and does not show up in final rendered image • Planes looks … flat  • Maya Scene Rendered image Directional Light

  6. What about the Light Bulb? • How would you describe the light source of these scenes? http://companyofburninghearts.wordpress.com/2010/03/18/mystic-clusters/ http://home.cogeco.ca/~richardastro2/

  7. Point Light • Position () • For every visible position () • is unique! • Illumination is a function of relative position to lights! • Maya Scene Different vector for each visible point Point Lights Rendered image

  8. Now, my desk lamp • How would you describe the light source of these scenes? http://www.how-to-refinish-hardwood-floors.wirze.com/ http://agreenliving.org/tag/concept-design/ http://www.mackayphotography.co.uk/light_pollution.htm http://0.tqn.com/d/drawsketch/1/0/N/J/eggsetup.jpg

  9. Spot Light • Direction + Position: • Pointing direction • As in point light, for each visible point is unique! • Cone angle (θ) defines illumination range θ Different vector for each visible point

  10. Maya Scene Cone boundaries Rendered image

  11. Spotlight bounds Illumination at this point is • Position: • Main direction • : cone angle • θ: regions of full illumination • angle to position for illumination • If θ< < Illumination drops off according to: θ Region: fully illuminated Penumbra Region: gradual drop off

  12. Drop off behavior P<1 p=0.1 P>1 p=0.2 Drop off p=1 p=20 p=30

  13. scene No drop off Penumbra region

  14. Implement Penumbra Region • For a visible position: • cos( If (cos( > cos( // < Full illumination else if (cos() < cos()) // > no illumination else Penumbra region θ A visibleposition

  15. Distance Attenuation • Illumination is a function of • d = distance between light and visible position!! • Physics tells us • Did not follow physics in the rest of the model! • WAY too dark!! • Generally: d

  16. How about ? • Let user specify each of thecomponents! OpenGL: Maya: Our ToyRayTracer:

  17. General form of Phong Our Ray Tracer implements:

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