TD Grid Placement Help

[Saidon]

Hi, I'm trying to make a tower defense game not unlike the one at www.handdrawngames.com (Desktop Tower Defense). All was going well until I had to figure out how to build the towers so that they "lock" to a grid. My towers are 40px by 40px and I want to build them on a grid that is made up of 20px by 20px squares so that they can be built with more variety.

A quick break down of where I need help:

1. How to select the tower I want to build and then place it by clicking on the grid

2. How to have the towers lock to a grid half the size of the towers themselves



Any advice would be greatly appreciated, I've been googling this for hours and wasn't able to figure it out.

[Sirisian]

Locking to a grid is really easy actually
pos = Math.floor((mousePos+towerSize/2)/gridSize)*GridSize

[nathan99]

made a class a while back
http://www.kirupa.com/forum/showpost.php?p=2091137&postcount=47

[Saidon]

Thanks guys, that's exactly what I was looking for.