Hi!
Im doing a top-down tilebased game in c++. Players can enter houses in which case roofs should be hidden (so you can see the enterior of the house. Right now i simply do:

if player is standing on a ground-tile that has a roof (player is inside a house) skip drawing ALL roof tiles.

I would like to only skip drawing the roof of that SPECIFIC building (not skip ALL roofs). Any clever way to do this? I need to find all "touching" roof-tiles and mark these for "hide"?

I could mark all those tiles with an unique ID when I place the building and hide/show based on that, but i would prefer a more flexible solution (if there are any).

Thanks!
Erik

Put a sensor, that is a rectangle of a tile size if you want. Place this sensor near the door, since the player can only enter from there. When the player passes over the sensor, the sensor will act like a light switch, turn on / off light, but in this case, turn on / off the roof.

if ( sensor.detect == true ) {
    building.roof.visible = !building.roof.visible;
}

but the problem is how do i find all roof-tiles belonging to that building? Buildings are not classes, they are just a section of the map that happens to have roof painted on those tiles.

I need like a spreading search to find all adjacent roof-tiles which are not 0 (meaning no roof for that tile).

Generally speaking, you will eventually want a bit more information about the world than just inside/outside. What I suggest may be a bit overkill for the specific question, but a subset could do what you are looking for.

I start by determining rules that I can use to make general categorization of the area. For instance, I might start by saying that any tile which is roofed and can be entered from a tile that is not roofed constitutes a transition between indoors and outdoors. Then I may say any roofed tile which connects to another roofed tile is considered part of the same indoor area. By running a relatively simple flood fill style algorithm I can uniquely identify various groups of tiles which are joined together to form a single indoor area.

Starting with something this simple, you can now find which tiles are connected interiors and only disable drawing of the roofs for those tiles. Expand on these rules and you can do things such as identifying special 'types' of rooms based on contents, internal divisions such as doors between room areas etc. The nice thing is that a fairly simple set of rules can categorize a relatively large number of things so if you have AI involved they can do relatively intelligent looking things when wandering around.

I haven't yet implemented this in my game, but I intend to solve this by using rectangles to define a building's region, and using the rectangles to mask out anything from layers above the player, and then inverting the mask to darken areas outside the building.

Mine's not art heavy (no new art needs to be created), it is "developer heavy", in that the developer has to decide what locations to mark, but it'd be very little effort (depending on your map editing tools), and take very little memory. You'd store a few rects (four ints), I would guess it'd be about 4 to 20 bytes per house - less than a single KB for a large village. Virtually nothing. You could compact it further with short ints if necessary. Honestly not an area I'd focus memory optimization on, it's small enough with too little gains already.

From the rects you'd:

A) Detect if the player is within one set of rects (one building) vs another set

B) Generate a stencil mask or screen-space alpha mask from the

C) Use the mask to prevent (roof/whatever) overdraw of the building (or just a single room, if you prefer) that you are in.

D) Use the inverse of the mask to darken everything outside of the building - not entirely black, but say, 50% darker.

As mentioned, I haven't implemented this in my game yet, but I don't seen any reason why it'd be an excessive memory hog or performance bottleneck, other than the costs of the mask buffer.

I would suggest to find all roof tiles adjacent to the roof tile above the player via a simple flood fill style algorithm. Easy to implement and will only hide all tiles which touch other roof tiles which are connected to the roof tile above the player. If you want to separate roofs which have no spacing in between you would need to add additional criteria for the neighborhood check (e.g. same roof tile set or something similar).

But the easiest to do would be to ensure a space of at least one non-roof covered tile between two houses..

See here for the algorithm: https://en.wikipedia.org/wiki/Flood_fill