Dragging objects on a grid

Often, games require objects to be in specific locations in order to be used, such as buildings in a real-time strategy game. When placing your building, you'll need to drop it on a specific grid. There are different ways to demonstrate this, but the most common way is simply to lock the building to the said grid in order to keep it from being placed in an undesired location. If real life worked this way, then construction planning would be a breeze. Since real life does not work like this, let's at least make it happen in GameMaker so that we can enjoy some form of worry-free construction.

Getting ready

This recipe assumes the completion of the previous recipe, Dragging onscreen objects, so you'll need to get it done and open your GameMaker file. Go ahead and do it now, if you haven't; I'll wait. All set? Good. Now before you begin, there are certain things you need to check. Make sure the length and width of the room you're using...