What am I looking at?

In Project 0, we place pieces on the game grid. These pieces are represented as another grid in which some cells are "filled".

A Piece's grid is represented internally using a 2D boolean array, called _positions. If the cell at that row and column inside the Piece's grid is filled, then positions[row][col] is true.

Piece, which are small grids, are placed on the larger game grid. How do we know which cells on the grid to check against cells on the Piece?

We mark the upper-left cell in the piece as its reference point, which may not necessarily be filled. The reference point in the Piece above is outlined in red. For a specific cell on the game grid, we align the Piece's reference point with that cell. The other cells in the Piece are positioned relative to the reference point.