I am still in the think-ahead-and-plan stage of a project where I'll want the player to be able to drag-out blocks - tiles but a minecraft-like 3D block-world.
So my question is: how can you determine where the user wants to place a block?
Here's a random minecraft screenshot I found on the internet:
My game will not be first-person camera; the user will be able to click anywhere to place a block.
If the user clicks on the centre of that green cross I've marked, which just misses the stonework to its right, where should the block be placed?
Technically determining the ray under the mouse cursor is trivial.
Given a ray and computing its distance / intersection with all existing block faces, and knowing the blocks that have previously been placed e.g. the last placed block, how can you 'do the right thing' with regards ambiguous movement? What rule set can you use?