How exactly does the block traverse the triangle? For example, how to determine the block size, the starting point of the block, the direction in which the block travels?
I think it may help to think of the block as a single sample in a low fidelity pass of the image, then the it should be much the same as in the previous slide.
@BryceSummers. I like your analogy as it's true a simple traversal order over blocks would be row-major. However, I want to clarify that it would not be appropriate to think about tile traversal as point-in-sample tests on a much sparser sample grid.
When traversing tiles, the tile cannot be trivially rejected if the triangle overlaps any part of the box. So a triangle-box intersection test must be employed, not a point-sample test.
We didn't directly address the math of triangle-box intersection tests in this lecture. One good example is given in this article: Rasterization on Larrabee by Michael Abrash. Note that this article also describes a hierarchical method of tile traversal as opposed to a flat row-major version. I'd use the article for a good reference on triangle/box tests, as in most situations you won't find the hierarchical approach as useful.