CMPS 160 -- Lab 2

Early if time stamp is before midnight Oct 21, 2017.
On time if time stamp is before midnight Oct 22, 2017.
Late submissions will not be accepted/graded.

Objectives:

Description:

Assume that each polygon in the GC has the same material information:
Ka 0 0 0
Kd 0 1 0
Ks 0 0 0
Also assume that the light source is pure white (1, 1, 1) and is coming from the direction [1, 1, 1]. The viewer is still at (0,0,∞). Render the GC but this time with flat shading and lit by the single light source.

Details:

Here are the major new things you need to do for this assignment:
• Calculate the color of each polygon. The appearance (color that we observe) of a polygon depends on its material property (intrinsic to the polygon) and its relationship with the light source (and later with the viewer as well). For the latter, we will be using Lambertian reflectance. Meaning we will need to know the surface normal and the light color and direction (both are given). So, the first step is given the vertex coordinates, you will need to calculate a surface normal for each polygon (if you did not do the bonus in prog1).

  For this task, we shall assume that all our polygons are planar. And that the vertices are specified in a counter-clockwise order as viewed from the outside. You will need to form 2 vectors and calculate their cross product. Make sure you are using the right sequence of points for the vectors, and the right sequence of vectors for the cross product.

  Add a toggle button to turn the display of surface normals on/off. Display surface normals in red.

• Apply Lambert's reflectance function. Calculate the perceived color for each polygon.
• Pass information to shaders. There are a few ways to do this problem. What we would like you to do is the following:
  • Calculate the surface normals on the CPU side (javascript code).
  • Calculate the color of each polygon on the CPU side.
  • Pass the vertices (and colors) of the polygons to the GPU to render.
  • Apply view transformation on the vertices of the polygons on the GPU prior to rendering.
  The last step requires setting up the transformation matrix on the CPU side and passing that to the GPU. The view specification is an orthographic projection onto the xy-plane. Converting from a 3D world point to a 2D projected point involves multiplying a vertex in world coordinates by a transformation matrix. The transformation matrix in this case is an orthographic projection.

  The transformation task is done in the vertex shader. For this, you need to pass the vertex information to the vertex shader to work on. You will also need to tell the vertex shader the transformation matrix to apply to each vertex.

  Since the color of a polygon is determined on the CPU side, the vertex shader does not need to do anything with regards to colors. On the other hand, the fragment shader takes the color that was calculated in the CPU and uses that to fill (or paint) each pixel of the projected polygon.

Resources:

Directional lighting tutorial

The followind examples from the Matsuda Lea book are relevant to this assignment:

• ColoredCube for how to fill in a polygon with a single color,
• OrthoView for how to set up an orthographic view, and
• LightedCube for how to do lighting calculations.

Grading:

• Rubric:

  You start off with 100 points.  You earn additional credit by turning in your assignment
  early and/or implementing additional features.  You lose credit for missing functionality,
  incorrect results, poorly documented or formatted code, or not following instructions.
  
  Below is a partial list:
  
  - up to 10 points off for poor features.html file
  - up to 10 points off for inadequate comments or hard-to-read code
  - up to 10 points off for not following instructions
  - up to 10 points off for special handling to grade your homework (usually
    because you did not check that it runs on the computers in the lab first).
  - functionality points depending on importance
  
  Make sure you:
  a.  submit the right files you want us to grade,
  b.  have tested your code on the browsers in the lab.
  c.  follow the general instructions described in overview.html
  
  

• Who graded your assignment based on your login name:

  hugh:	a - k
  cole:	l - z
  

Submission:

Put materials in a folder named lab2 and zip it up. Submission must be done using the "submit" command from unix.ucsc.edu

• submit cmps160-ap.f17 lab2 lab2.zip

Last modified Tuesday, 22-Jan-2019 09:42:16 PST.