Lecture Cameras and lights 1Elias Holmlid

 First part  Cameras  Lights ▪ Light types ▪ Light models ▪ How light is computed  Second part  We’ll implement an effect for phong shading & cel shading Elias Holmlid2

 Fixed perspective  First person  Third person Elias Holmlid3

 Example: Alone in the Dark (1992) Elias Holmlid4

 Example: Bioshock (2007) Elias Holmlid5

 Example: Tomb Raider something Elias Holmlid6

 Problems with geometry hiding the players  Might be solved with transparency Elias Holmlid7

 Dizziness... Elias Holmlid8

 Different follow behavior + giving the player some camera control Elias Holmlid9

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 A game might use several different cameras  Use a manager for handling all the cameras Elias Holmlid11

 Directional  Sunlight (on Earth)  Spotlight  Point light (ominidirectional)  Emitting light from one point in all directions  Sunlight (on a deadly distance) Elias Holmlid12

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 Global illumination model Elias Holmlid14

 Local illumination model Elias Holmlid15

 Light may be precomputed and stored  Global illumination models might be used (!) Elias Holmlid16

Elias Holmlid17 Gouraud: Per vertex Phong: Per pixel Color interpolated during rasterization Normal interpolated during rasterization

 Can be accomplished in different ways; one technique is called hard shading Elias Holmlid18

Elias Holmlid19 LightMaterial (object) (Ambient) Diffuse: i d Diffuse: m d Specular: i s Specular: m s SpecularPower: s (Emissive)

 In the real world, light bounces around:  Therefore, all points are hit by light in some way  Ambient light makes up for our non-global illumination model  Ambient component might be just a global color (and not part of each light/object) Elias Holmlid20

 Simulates how light bounces off a rough surface (it scatters in all directions) Elias Holmlid21

Elias Holmlid22  We want to find a scaling factor depending on how a point is hit by the light...

Elias Holmlid23 ...the dot product is ideal for this if clamped to the interval [0..1]. HLSL has a dot() function and [0..1] clamping can be done with s aturate()

 Takes the viewpoint into consideration  Light bounces off in a specific direction and might hit the eye (camera) Elias Holmlid24

 If objects are only rotated and translated, normals can be transformed with the same matix  If the above applies, but the object is also uniformely scaled, normals will have to be renormalized  However, if non-uniform scaling or shearing is applied, normals will no longer be normal to the surface  Then, the inverse-transpose of the transformation matrix does the job:  B = (A 1 ) t  In XNA: B = Matrix.Invert(A); B = Matrix.Transpose(B);  This is done automatically for you if you use BasicEffect! Elias Holmlid25

 BasicEffect supports a maximum of three directional lights  If you want point/spot-lights, more lights, or do stuff like toon-shading you have to implement your own effects Elias Holmlid26

 Stores all the lights  Might contain methods for finding the closest light to a point etc Elias Holmlid27