Book 3, Chapter 10.2 Sampling Directions towards a Hittable - Updates to Hittable List Missing

[davidfrogley]

Code listings in chapter 10.2 do not include changes to the hittable_list class, which should include an override of the pdf_value and generate methods from the hittable base class. Without these, the rendered image uses the default value for both of these (0 for pdf_value, and vec3(1,0.0) for generate). This results in a completely black image, except for the light on the ceiling.

[hollasch]

For things that look like bugs or errors on our part, please create issues. I've spawned #1267 from this.

[davidfrogley]

OK, will do. Thanks.