In the process function

Capture the current position of the mouse

from the viewport

Multiple by 100 to capture anything within 100m

We will now set the target position

of the ray to the projected local ray normal at the mouse position

Also force the ray to update so we get the current position

Now we need to check if we are colliding

then store what we are colliding with

If the collider is a GridMap 

then we want to access the cells

We don't have access yet so for now we pass

To gain access to the GridMap

Make it available as an export variable

Save your scene

Now that we have access to the GridMap

In the BaseLevel scene

We can find the point in the grid

at which we are colliding

and that corresponds to

a cell on the grid

To interact with the gridmap

add a new Input Action for

mouse clicks

name it click

set the action to left click

If the ray is colliding with something

change the cursor to a hand

check if the current cell is empty 

(line 20)

change the current cell to a red one

(line 21)

otherwise change cursor back to arrow

full code shown alongside

Turrets