Photorealistic Rendering vs' Interactive 3D Graphics

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Photorealistic Rendering vs. Interactive 3D
Graphics

• (An Introduction to Digital Image Synthesis)

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Short Film Festival

• I will show a short film at the beginning of each
  class, so dont be late!

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How Do You Draw a Picture (Without a Computer)?

• What is your subject?
• Viewing Parameters
• Camera, Picture Frames, Resolutions
• Many ways to specify it
• eye, focus length, image plane
• eye, direction, FOV, up vector

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(No Transcript)
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3D to 2D Projection

• OK, so we can map a 3D point (or vertex) to 2D
  image.
• But what about a 3D surface?
• Polygons are made from points.
• Actually, we only need triangles!

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Scan Conversion

• Also called rasterization.
• The 3D to 2D Projection gives us 2D vertices
  (points).
• We need to fill in the interior.

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Shading
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An Overview of 3D Pipeline

• The above can be implemented in hardware.
• Z Buffer to detect hidden surfaces.
• Other transformations not mentioned here
  Modeling and Viewing.
• Browse Chapters 5 6 of Watts book if youre
  not familiar with it.

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But They Dont Look Real.

• Most things are not flat or simple geometry like
  spheres andcones.
• We need correct surface colors and shapes (and
  more) 

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• We also need correct lighting.
• Textures help, but not enough.
• Even simple things like CD can be challenging.   

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Real-time Graphics

• Theyre becoming darn good!

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But

• Some effects are hard to do in hardware, such as
  the caustics

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A Different View Ray Tracing
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• Actually inverse ray tracing.

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Ray Tracing

• Writing a Very Simple Version

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What Makes a Good Picture?

• Contents (3D models).
• Lighting.
• Reflection.
• Shadow.
• Surface textures.

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Ray Tracing Algorithm

• An overview in Pharrs 1.2
• More detail in Watts 10.3.1 (pp.284-286) and
  12.2-12.4 (pp.342-354)

Transmitted
Reflected
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Creating a Ray

• Parameters
• Image Plane (position, size, and resolution)
• Viewpoint
• Which ray (x, y)?

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Ray-Object Intersection

• For example sphere
• (x-x0)2(y-y0)2(z-z0)2r2
• Ray (x,y,z)(x1,y1,z1)t(xd,yd,zd)
• Find t that satisfy
• (x-x0)2(y-y0)2(z-z0)2r2
• Normal vector?
• Also easy for planes, cones, etc.

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Shading Models

• Pixel color ambient diffuse specular
  reflected transmitted
• The weight of each is determined by the surface
  properties.
• We will discuss each of them within the next a
  few lectures.

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Light Source Shadow

• Point light is easy to implement, but does not
  look real.
• How to determine a surface point is in the
  shadow?
• In real world area light with soft shadow.

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Reflection and Refraction

• Reflected ray is determined by
• incoming ray and normal vector.
• Refracted ray is determined by
• Incoming ray
• Normal vector
• And density
• Snells law
• ?I sin ?i ?t sin ?t

?i
?t
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Recursive Algorithm

• The reflected ray and refracted ray are traced
  recursively.
• Termination condition
• Depth of trace
• Weight (to the final pixel color) of ray

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Advantage

• We get all the following automatically
• Hidden surface removal
• Shadow
• Reflection
• Transparency and refraction

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Disadvantage

• Slow. Many rays are spawned.
• Slow. Ray-object intersection for every ray and
  every object. (We will discuss how to avoid this
  in the next lecture).
• The lighting is still not completely right!

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Assignment 1 A Ray Tracer

• Split into two parts.
• Part A due October 8.
• Camera module
• Object module (sphere only)
• No recursive ray tracing
• Simple output (in text mode)
• The rest (Part B) are due October 22.

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Required Modules

• Camera Module
• Object Module
• Ray Tracer Module (main program)
• Display (Output) Module

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Camera Module

• Definition of eye position and image plane.
• Generating a ray if given (x, y)
• Note that x and y may be real numbers (not
  integers).

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Object Module

• Sphere type only (for now).
• Ray-object intersection.
• Light.
• Read from files.
• Camera is sometimes defined in the object file
  for convenience.

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Ray Tracer Module

• Integration of other modules.
• Shading.
• Spawn reflected and refracted rays.

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Display (Output) Module

• Output to a text file for now.
• Example output 0 if no intersection and 1 if
  intersecting an object.
• May create PPM, TIFF, or JPEG files later.

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Part A due October 8

• Camera module
• Object module
• Read from a file
• Sphere and Light only
• Ray tracer module
• No shading. No reflection and refraction.
• Display module (in text mode)

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Part B due October 22

• Object module
• Add at least a plane type.
• Ray tracer module
• Add shading, reflection, and refraction.
• Display module
• PPM, TIFF, or JPEG library will be provided.
• Add a demo scene of your own.