CSC418: Computer Graphics DAVID LEVIN Todays Topics 1. Texture - - PowerPoint PPT Presentation

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CSC418: Computer Graphics DAVID LEVIN Todays Topics 1. Texture - - PowerPoint PPT Presentation

Mar 30, 2023 208 likes •1.23k views

CSC418: Computer Graphics DAVID LEVIN Todays Topics 1. Texture mapping 2. Ray Tracing Some slides and figures courtesy of Wolfgang Hurst, Patricio Simari Some figures courtesy of Peter Shirley, Fundamentals of Computer Graphics,

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DAVID LEVIN

CSC418: Computer Graphics

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Today’s Topics

  • 1. Texture mapping
  • 2. Ray Tracing

Some slides and figures courtesy of Wolfgang Hürst, Patricio Simari Some figures courtesy of Peter Shirley, “Fundamentals of Computer Graphics”, 3rd Ed.

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Showtime

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But First … Logistical Things

  • You should all have your Assignment 1 and Midterm Grades
  • Assignment 2 is due this Friday
  • If you are still having troubles email the TAs
  • csc418tas@cs.toronto.edu
  • Karan is still away so email me if you have any issues
  • diwlevin@cs.toronto.edu (usually requires two emails)
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Phong Shading: Comparisons

Phong shading: 1. Interpolate to get at 2. Compute

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Phong Shading: Comparisons

Phong shading: 1. Interpolate to get at 2. Compute

Comparison to Gouraud shading + Smooth intensity variations as in Gouraud shading + Handles specular highlights correctly even for large triangles (Why?)

  • Computationally less efficient (but okay in today's

hardware!) (Must interpolate 3 vectors & evaluate Phong reflection model at each triangle pixel)

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Topic 1: Texture Mapping

  • Motivation
  • Sources of texture
  • Texture coordinates
  • {Bump, MIP, displacement, environmental}

mapping

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Motivation

  • Adding lots of detail to our models to realistically depict skin,

grass, bark, stone, etc., would increase rendering times dramatically, even for hardware-supported projective methods.

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Motivation

  • Adding lots of detail to our models to realistically depict skin,

grass, bark, stone, etc., would increase rendering times dramatically, even for hardware-supported projective methods.

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Motivation

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Motivation

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Topic 1: Texture Mapping

  • Motivation
  • Sources of texture
  • Texture coordinates
  • {Bump, MIP, displacement, environmental}

mapping

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Texture sources: Photographs

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Texture sources: Solid textures

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Texture sources: Procedural

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Texture sources: Synthesized

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Original Synthesized Original Synthesized

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Topic 1: Texture Mapping

  • Motivation
  • Sources of texture
  • Texture coordinates
  • {Bump, MIP, displacement, environmental}

mapping

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Texture coordinates

How does one establish correspondence? (UV mapping)

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Texture coordinates

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Texture coordinates

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Texture coordinates

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Texture coordinates

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Texture coordinates

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Texture coordinates

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Texture coordinates

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Texture coordinates

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Texture coordinates

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Topic 1: Texture Mapping

  • Motivation
  • Sources of texture
  • Texture coordinates
  • {Bump, MIP, displacement, environmental}

mapping

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Mipmapping

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MIP-Mapping: Basic Idea

Given a polygon, use the texture image, where the projected polygon best matches the size of the polygon on screen.

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Mipmapping

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Mipmapping

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Environment mapping

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Environment mapping

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Environment mapping

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Environment mapping

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Bump mapping

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Bump mapping

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Bump mapping

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SLIDE 42
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Displacement mapping

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Displacement mapping

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Topic 2: Basic Ray Tracing

  • Introduction to ray tracing
  • Computing rays
  • Computing intersections
  • ray-triangle
  • ray-polygon
  • ray-quadric
  • the scene signature
  • Computing normals
  • Evaluating shading model
  • Spawning rays
  • Incorporating transmission
  • refraction
  • ray-spawning & refraction
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Local vs. Global Illumination

Local Illumination Models e.g. Phong

  • Model source from a light reflected once off a surface

towards the eye

  • Indirect light is included with an ad hoc “ambient” term

which is normally constant across the scene Global Illumination Models e.g. ray tracing or radiosity (both are incomplete)

  • Try to measure light propagation in the scene
  • Model interaction between objects and other objects,
  • bjects and their environment
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All surfaces are not created equal

Specular surfaces

  • e.g. mirrors, glass balls
  • An idealized model provides ‘perfect’ reflection

Incident ray is reflected back as a ray in a single direction Diffuse surfaces

  • e.g. flat paint, chalk
  • Lambertian surfaces
  • Incident light is scattered equally in all directions

General reflectance model: BRDF

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Categories of light transport

Specular-Specular Specular-Diffuse Diffuse-Diffuse Diffuse-Specular

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Ray Tracing

Traces path of specularly reflected or transmitted (refracted) rays through environment Rays are infinitely thin Don’t disperse Signature: shiny objects exhibiting sharp, multiple reflections Transport E - S – S – S – D – L.

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Ray Tracing

Unifies in one framework

  • Hidden surface removal
  • Shadow computation
  • Reflection of light
  • Refraction of light
  • Global specular interaction
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Rasterization vs. Ray Tracing

Rasterization:

  • project geometry onto image.
  • pixel color computed by local illumination

(direct lighting). Ray-Tracing:

  • project image pixels (backwards) onto scene.
  • pixel color determined based on direct light

as well indirectly by recursively following promising lights path of the ray.

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Projective methods

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Ray tracing / ray casting

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Ray tracing / ray casting

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Ray tracing / ray casting

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Ray tracing

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Ray tracing

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Ray tracing

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Ray tracing

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Ray tracing

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Projective methods vs. ray tracing

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Projective methods vs. ray tracing

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A basic ray tracing algorithm

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Lines and rays

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Lines and rays

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Lines and rays

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Coordinate system

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Coordinate system

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Coordinate system

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Coordinate system

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Coordinate system

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Viewing window

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Viewing window

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Viewing window

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Viewing rays

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Viewing rays

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Viewing rays compared

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A basic ray tracing algorithm

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Ray-object intersection (implicit surface)

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Spheres

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Intersections between rays and spheres

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Intersections between rays and spheres

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Intersections between rays and planes

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Ray-object intersection (parametric surface)

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Ray-object intersection (parametric surface)

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Ray-triangle intersection

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Plane specification

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Ray-plane specification

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Ray-plane specification

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Ray-plane specification

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Rays: parametric representation

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Computing Ray-Poly Intersections: Step b

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Computing Ray-Poly Intersections: Step b

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Computing Ray-Quadric Intersections

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Computing Ray-Quadric Intersections

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Computing Ray-Quadric Intersections: 3 Cases

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Ray-Quadric Intersections: Sub-cases for D>0

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Intersecting Rays & Composite Objects

  • Intersect ray with component objects
  • Process the intersections ordered by depth

to return intersection pairs with the object.

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Ray Intersection: Efficiency Considerations

Speed-up the intersection process.

  • Ignore object that clearly don’t intersect.
  • Use proxy geometry.
  • Subdivide and structure space hierarchically.
  • Project volume onto image to ignore entire

Sets of rays.