CS465 Homework 4

This homework has separate handouts for the written part:

• hw4a assignment handout (v. 4) | [old v. 3] [old v. 2] [old v. 1]
• FAQ
• HW4a Solutions

and the programming part:

• hw4b assignment handout | framework code
• A test file for your previous raytracer here
• And the result of said test file here
• Test set 1
• Results from test set 1

One more input file for your testing pleasure:

•  columns.txt

FAQ

Check here for any updates to the hw4b description

• 11/10/2003: Everything is working with transformations but my spheres!

  There is a bug in the framework code - changes need to be made on lines 64, 67, and 68 of Sphere.java. All of the lines of code make an assignment to the variable B, and the expression that is assigned to B has a "/2.0" at the end of it. This expression needs to be divided by "/(2.0*A)". Make sure to put in the parentheses!

• 11/9/2003: I'm confused about the difference between transformVector and transformPoint.

  Read the handout's section on helpful hints... see if that makes anything clearer.

• 11/9/2003: The handout says we should use the text "Transformation" in our scene files, but the Parser doesn't like this....what's the deal?

  Again, my apologies. The handout is wrong, and the parser is not. Use the "Transform" keyword, not "Transformation".

• 11/7/2003: So... are angles in radians or degrees?

  Ok, my apologies for this one. The numbers that get handed to Surface.rotateBy() will be exactly as they are in the file. The Parser doesn't do anything intelligent with numbers, it simply puts what it reads where it ought to go. The methods in Transformation should expect to receive angles in radians only. Thus, it is up to the person calling the Transformation methods to make sure that they use radians as angles. We will be specifying rotations in degrees in our input files - these are just infinitely more readable. You need to make sure that you account for this in Surface.rotateBy() then. Use the Math.PI constant in converting numbers. A quick reminder for those of you who get confused (as I do):

  • x radians = PI/180 * y degrees
  • y degrees = 180/PI * x radians

• 11/7/2003: I don't get it! Why the heck do you have up to 3 different versions of the same method? One should be enough!

  Instantiating objects in Java is a good deal more expensive than one might think. This is done for run time safety. When a programmer is potentially instantiating many objects per pixel, and is rendering from a few thousand to a few million pixels though, this can become very inefficient. The use of an output parameter can give the programmer using the Transformation class a way of specifying where the result of a matrix operation should be put. This is done in lieu of returning a newly instantiated object. If the output parameter is null, then it is often the case that the result should be returned. If there is no return value, and the output parameter is null, then this is an error.

  Take Transformation.leftProduct() as an example. There are three versions of this function:

  • Transformation leftProduct(Transformation input)
  • void leftProduct(Transformation input, Transformation output)
  • void leftCompose(Transformatoin input)

  The first version will take in a single Transformation as input. Let's call the matrix represented by the input Transformation B, and the matrix represented by this Transformation A. The first method should return a newly instantiated Transformation that represents the matrix equal to B*A.

  The second version will take in two Transformations. Use the same naming convention as above. This second method should store the Transformation object that represents B*A in the output parameter. This output parameter will not be null.

  The last version of this method will essentially perform the *= operation. After its execution, this=B*this.

  Another form of method calls exists in the Transformation class. This is where the output parameter can be null and a return value exists. In this case, the result is stored in output, and the result is returned. If output is null, the value is still returned.

• 11/7/2003: There was a mistake in the handout - you do NOT have to implement Transformation.new{Scale|Translate}(). The new handout has been corrected.

• 11/4/2003: There was a mistake in the handout - you do NOT have to implement Transformation.new{X|Y|Z}Rotation(). The new handout has been corrected.

• 10/31/2003: As before, we will be posting sample inputs/outputs later on.