Lighting

1. Lighting Jeff Chastine

2. What is Light? • A very complex process • Find a dark area – how is it being lit? • Light bounces (mirrors, shiny objects) • Light refracts through other media (water, heat) • Light comes from everywhere (Global Illumination) • Light bounces off of lakes in weird ways (Fresnel effect) • THUS • We’re forced to make approximations • Tradeoff between time and realism • “If it looks good, it is good” – Michael Abrash http://en.wikipedia.org/wiki/File:Global_illumination.JPG http://darrentakenaga.com/3d.html Jeff Chastine

3. A Basic Lighting Concept • How can we determine how much light should be cast onto a triangle from a directional light? Directional light - position doesn’t matter - triangle is almost fully lit P0 P1 P2 Jeff Chastine

4. A Basic Lighting Concept • How can we determine how much light should be cast onto a triangle from a directional light? P0 (Triangle less lit) P1 P2 Jeff Chastine

5. A Basic Lighting Concept • How can we determine how much light should be cast onto a triangle from a directional light? P0 P1 P2 (Little to no light hits the surface) Jeff Chastine

6. A Basic Lighting Concept • How can we determine how much light should be cast onto a triangle from a directional light? P0 (Directional light) P1 P2 Jeff Chastine

7. A Basic Lighting Concept • How can we determine how much light should be cast onto a triangle from a directional light? P0 (Directional light) P1 P2 Jeff Chastine

8. A Basic Lighting Concept • How can we determine how much light should be cast onto a triangle from a directional light? Lesson learned: Lighting depends on angles between vectors! P0 (Directional light) P1 P2 Jeff Chastine

9. A Basic Lighting Concept • How can we determine how much light should be cast onto a triangle from a directional light? P0 (Directional light) P1 P2 Assuming N and L are normalized, and N∙L isn’t negative Jeff Chastine

10. Basic Lighting • Four independent components: • Diffuse – the way light “falls off” of an object • Specular – the “shininess” of the object • Ambient – a minimum amount of light used to simulate “global illumination” • Emit – a “glowing” effect Only diffuse Jeff Chastine

11. Basic Lighting • Four independent components: • Diffuse – the way light “falls off” of an object • Specular – the “shininess” of the object • Ambient – a minimum amount of light used to simulate “global illumination” • Emit – a “glowing” effect Diffuse+Specular Jeff Chastine

12. Basic Lighting • Four independent components: • Diffuse – the way light “falls off” of an object • Specular – the “shininess” of the object • Ambient – a minimum amount of light used to simulate “global illumination” • Emit – a “glowing” effect Diffuse+Specular+Ambient Ambient Jeff Chastine

13. Basic Lighting • Four independent components: • Diffuse – the way light “falls off” of an object • Specular – the “shininess” of the object • Ambient – a minimum amount of light used to simulate “global illumination” • Emit – a “glowing” effect D+S+A+Emit Note: emit does not produce light! Jeff Chastine

14. Interaction between Material and Lights • Final color of an object is comprised of many things: • The base object color (called a “material”) • The light color • Example: a purple light on a white surface • Any textures we apply (later) • Materials and lights have four individual components • Diffuse color (cdand ld) • Specular color (csand ls) • Ambient color (caand la) • Emit color (ceand le) • cd* ld = [cd.r*ld.r, cd.g*ld.g, cd.b*ld.b] // R, G, B Jeff Chastine

15. General Lighting • Primary vectors • l – the incoming light vector • n – the normal of the plane/vertex • r – the reflection vector • v – the viewpoint (camera) v n l r θ θ Jeff Chastine

16. LambertianReFlectance(diffuse Component) • Light falling on an object is the same regardless of the observer’s viewpoint • Good for rough surfaces without specular highlights • where and are normalized n l θ Jeff Chastine

17. LambertianReFlectance(diffuse Component) • Light falling on an object is the same regardless of the observer’s viewpoint • Good for rough surfaces without specular highlights • where and are normalized 3 parts (R, G, B) scalar n l θ Note: final_colordiffusehas R, G, B Jeff Chastine

18. LambertianReFlectance(diffuse Component) • Technically, it should be: n l θ Jeff Chastine

19. BLINN-PHONG Reflection(Specular Component) • Describes the specular highlight and is dependent on viewpoint v • Also describes a “half-vector” h that is halfway between v and l h v n r l θ θ Jeff Chastine

20. BLINN-PHONG Reflection(Specular Component) • - which is really Blinn’s contribution to the original Phong model h v n r l θ θ Note: vectors should be normalized Jeff Chastine

21. BLINN-PHONG Reflection(Specular Component) • Our final specular equation is: h v n r l θ θ Jeff Chastine

22. Determining • Realize that will always be < 1.0, so raising it to a power will make it smaller • is the “shininess” factor • It relates to the size of the specular highlight s = ~1 s = ~30 s = ~255 Jeff Chastine

23. Ambient and Emit Components • Ambient: • Used to simulate light bouncing around the environment (global illumination) • Real world is far too complex for real time, so just add a little light! • Emit: • Used to make the object “glow” • Does not emit light!!! • Both: • Independent of viewpoint • Super easy to calculate Jeff Chastine

24. Final Color • To determine the final color (excluding textures) we sum up all components: final_colordiffuse final_colorspecular final_colorambient final_coloremit final_color + http://en.wikipedia.org/wiki/Phong_reflection_model Jeff Chastine

25. What about Multiple lights? • Calculate final colors and sum them all together • Assuming results are in f [ ] and there are count number of lights Jeff Chastine

26. Common Kinds of Lights • Point light • Directional Light • Spot Light • Area Light • Interesting fact: • Lights cannot be seen! • Only their effects • We can light per vertex (fast) or per fragment (slower) Jeff Chastine

27. Point Lights • These lights have a position in 3D space • Sometimes called a “Lamp” • Light emanates from the light in all directions • Distance d determines brightness (“attenuation”): Here, per fragment lighting used Jeff Chastine

28. Point Lights • These lights have a position in 3D space • Sometimes called a “Lamp” • Light emanates from the light in all directions • Distance d determines brightness (“attenuation”): Here, per vertex lighting used Jeff Chastine

29. Directional Lights • Are infinitely far away • position in NO WAY matters • Have only direction • All objects are lit evenly • Sometimes called a “Sun” Jeff Chastine

30. Spotlights • Point light source • Conical in shape Jeff Chastine

31. Spotlights • Point light source • Conical in shape • Have: • An inner and outer cone angle • Umbra – areas that are fully in shadow • Penumbra – areas that are in partial shadow • Note: There’s an ambient light Jeff Chastine

32. Area Lights • A “surface” lights objects • Has a position and direction • Provides for a smoother drop off than point • Larger surface == smoother shadows • Expensive to calculate Jeff Chastine

33. What you’ll see if you don’t glEnable(GL_LIGHTING) The End!