CS 457/557 -- Winter Quarter 2025

Test #1 Review

This page was last updated: December 28, 2024

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Test dates and times:

Test #1 will go live at 12:01 AM PT on Wednesday, February 5. It will close at 23:59 PT on Saturday, February 8.

Test Information:

• This will be a multiple choice test cast as a Canvas "Quiz".
• There will be 40 questions, worth 2.5 points each.
• You will have 60 minutes to complete it. Once you start, you need to finish. Canvas does not allow you to pause, leave, then come back and resume.
• The test is open notes and closed friends.
  Warning! "Open Notes" is not the same as "I don't need to study for it"! You will run out of time if you have to look up in the notes every one of the questions.
• Clearly, I cannot stop you from accessing information on the Internet. However, the test has been written against our class notes. If you miss a particular question, any protest of the form "But somethingsomething.com said that..." will be ignored.
• You are responsible for
  1. what is in the handouts
  2. what was said in class and the videos, including the Live Lectures
  3. what was covered on the quizzes
  4. what you have done in the projects

The test can cover any of the following topics:

• Course Infrastructure:
  Project Turn-in procedures
  Bonus Days
  [ History of Shaders won't be on the test ]

• Homogeneous coordinates
  What that means
  What are they good for?
  What the projection matrices to besides projection

• Coordinate systems: Model Coordinates (MC), World/Eye Coordinates (EC), Screen Coordinates (SC)

• GLSL:
  GLSL vertex and fragment shaders. How they work. Where they fit into the overall OpenGL pipeline.
  What the vertex shader replaces. What it doesn't.
  What the fragment shader replaces. What it doesn't.
  Where the GLSL shader compiler lives (for us, in the driver)
  Uniform, Out/In, and Per-vertex Attribute variables. What they do. In what circumstances they are used.
  Built-in GLSL variables
  Built-in GLSL functions.
  [ You don't need to know all of them -- just the major ones we've been using in class and are used in the projects. ]

• GLSL coordinates:
  Model: gl_Vertex
  Eye/World: gl_ModelViewMatrix * gl_Vertex
  What effects you can get with each (stripes example)
  Clip: gl_ModelViewProjectionMatrix * gl_Vertex
  NDC: ( gl_ModelViewProjectionMatrix * gl_Vertex ) divided by the resulting w
  Sent down to the rest of the pipeline: gl_Position

• Normal vector transformation: gl_NormalMatrix * gl_Normal

• Shader patterns:
  Deciding what to key off of
  Stripes: keying off Cartesian (x,y,z) coordinates vs. keying off texture (s,t) coordinates
  Stripes: keying off a quantity in Model Coordinates vs. a quantity in World/Eye Coordinates

• The GLSL discard operator
  What happens if you use gl_FragColor.a = 0. instead?

• The GLSL API for using shaders:
  Reading, creating, compiling, attaching, linking
  Passing in uniform and attribute variables
  Enabling (Use'ing) a shader program
  UnUse'ing shader programs (and thus returning to Fixed-Function OpenGL)
  The fact that OpenGL-ES (mobile, web) has no fixed-function pipeline
  [You don't need to know the names of the OpenGL functions that are used to create the shader program.]
  Our glslprogram C++ class

• Mixing / Blending:
  The step( ) and smoothstep( ) functions
  Creating our own smoothpulse( ) from two smoothstep( ) functions
  The mix( ) function
  How to blur the ellipse boundaries,

• Fun With One: different ways to manipulate the path from 0. to 1.
  [ The exact equations won't be on the test. ]

• Morphing:
  cow-to-sphere, cow-to-cube, sphere-to-disk
  Why not cow-to-dino?

• Stripes, Rings, Dots:
  Getting stripes
  Applying a sine wave to the stripes
  Getting rings
  Getting circles
  Getting ellipses

• GLSL Textures:
  Types (1D, 2D, 3D, Cube)
  One overloaded texture( ) function
  All types return a vec4. They are "typed" by what gets passed in to index into the texture.
  Texture units
  Sampler variables (e.g., sampler2D, sampler3D, samplerCube)

• Displaceent textures:
  Yes, you can read a texture from a vertex shader in order to displace vertices

• Noise:
  What does it mean that noise needs to be coherent?
  What does it mean that noise needs to be repeatable?
  Why it can't really be random
  What's wrong with Positional noise?
  How Gradient noise (also called Perlin noise) is produced
  Noise amplitude, Noise frequency
  Octaves (twice the frequency, half the amplitude)
  "Turbulence"
  How to use noise and why
  glman's noise: "baked" into a look-up texture
  [ The noise equations won't be on the test. ]

• Noise terrain:
  Using noise to create a terrain surface

• Bump-mapping:
  General idea
  Advantages of bump-mapping over displacement-mapping
  Advantages of displacement-mapping over bump-mapping

• Height Field Bump-Mapping (e.g., Oregon terrain):
  What is a height field? (≈ A pin box.)
  Storing and accessing the height field data
  Tangent Vectors
  Computing the normal

• Equation-based Bump-Mapping (e.g., ripples)
  The calculus of Tangent Vectors (dzdx, dzdy)
  Computing the normal

• Nonlinear uses for the vertex shader:
  Dome projection [you are not responsible for the equations]
  Hyperbolic Geometry [you are not responsible for the equations]

• Lighting: Ambient, Diffuse, Specular
  Per-vertex vs. Per-fragment lighting -- what gets interpolated in each
  Flat vs. Smooth lighting -- what each looks like
  The flat GLSL keyword for in and out variables
  How the disco ball lighting works and the fact that it only uses one light source

• Cube-mapping:
  Cube-mapping texture consists of 6 images in one "texture"
  How an (s,t,p) vec3 gets turned into an (r,g,b) from a cube map
  Reflection. (reflect function)
  How the cube-mapped version differs from "real" reflection (2 things)
  Refraction. (refract function)
  How the cube-mapped version differs from "real" refraction (3 things)

The test can cover any of the following Projects:

• Project 1: Elliptical Dots: ellipse equations, finding out what checker you are in, smoothstep( ) function, mix( ) function

• Project 2: Noisy Displaced Elliptical Dots: use of noise, glman's way of giving you noise, how apply noise to ellipse boundaries

• Project 3: Displacement Mapping, Bump-Mapping, and Lighting: computing derivatives, tangent vectors, computing the normal, perturbing the normal