Creating the grid

Let's take some time now to review the grid logic in the game. This grid is created inside the createStarGrid method in GameLayer.cpp. What the method does is determine all possible spots on the screen where we can place the _star particle system.

We use a C++ vector list called _grid to store the available spots:

std::vector<Point> _grid;

The createStarGrid method divides the screen into multiple cells of 32 x 32 pixels, ignoring the areas too close to the screen borders (gridFrame). Then we check the distance between each cell and the planet sprites stored inside the vector _planets. If the cell is far enough from the planets, we store it inside the _grid vector as Point.

In the following figure, you can get an idea of the result we're after. We want all the white cells not overlapping any of the planets.

We output a message to the console with Log stating how many cells we end up with:

CCLOG("POSSIBLE STARS: %i", _grid.size());

This vector list will...