Display graphics results in autograder output

[sravanareddy]

(in case we don't develop perfect graphics-grading functionality...)

Define a class of test cases where there is no expected result -- the autograder simply displays the resulting picture (take the cs1graphics output and save it as a png), and the expected image. Use the quilt task as an example.

[sravanareddy]

To allow displayPic calls without the second argument, for backwards compatibility of other functions that may be calling it, define a default value

def displayPic(pic, filename=None)

and have it save to file only when filename is not None.

[sravanareddy]

Need to look into why saveToFile is not halting the program...

[sravanareddy]

On investigation, it appears the quilt is too large (892 primitive objects, going 9 levels deep). The method works fine on simpler objects.

Some preliminary testing suggests that 500 objects is its breaking point.

[dkreimer]

So that's not something we can fix, is it?

[sravanareddy]

Not easily, but I'm going to look into it.

Worst case, we can simplify the quilt a little bit without sacrificing its aesthetics/difficulty. Or, we can test an intermediate function -- for example, each quadrant is only 223 objects/8 levels, and going from there to the final step is straightforward.

[sravanareddy]

Update for our records: waiting on LTS to install PIL on Canopy so we can test this.