Drafting
Drafting is the process by which drawn floorplans become physical rooms. The process of drafting a floorplan, from interacting with a door to manifesting the physical room, is called a draft. Drafting is a central gameplay mechanic, and arguably the most important mechanic, of Blue Prince.
At the start of each day, the house is empty aside from permanent rooms such as the Entrance Hall. All other rooms must be drafted at an existing door in the house. Newly drafted rooms contain their own doors which allow for further drafting, thus allowing rooms to be drafted throughout the house. At the end of each day, all drafted rooms other than permanent rooms reset, vanishing from the estate. This process is subject to a large number of drafting effects that may come from rooms such as Drafting Rooms, items, and other sources.
The Mount Holly Blueprint, found on the central table in the Entrance Hall, is required to draft.
Initiating a draft
All drafts begin by interacting with a drafting door. If the door is unlocked, the drafting process begins immediately. If the door is locked, the player is given an opportunity to either use keys or other tools at their disposal to unlock the door, or to leave and explore elsewhere.
Once the drafting process has begun, it cannot be exited without choosing a room.
Drawing floorplans
After choosing a door, three different floorplans are randomly drawn from the draft pool. There are a large number of potential drafting effects that can alter the drawing process in several ways, such as:
- Make certain floorplans more likely to be drawn
- Prevent certain floorplans from being drawn
- Force certain floorplans to be drawn
- Alter how frequently floorplans of each rarity are chosen
Additionally, some drafting effects alter the draft pool itself, changing which floorplans the drawing process has access to.
Orientation is not considered while drawing floorplans, unless a floorplan has no valid orientation as described in the room shape section below. A floorplan with multiple valid orientations is not more likely to be drawn than a floorplan with just one.
Duplicate floorplans are never drawn outside of bugs.
Rarity
Floorplans of a lower rarity are generally more likely to be drawn than rooms of a higher rarity. The likelihood of a particular rarity being drawn is believed to depend on a number of factors, including the rank of the planned room, the slot, and even the current day.
Gem cost
Floorplans with a gem cost are known as special floorplans. When floorplans are being drawn, there will always be a "free" floorplan in the first slot, if possible. In the rare event that a special floorplan is drawn in the first slot, its cost is bypassed and treated as 0 for the sake of this draw.
Room shape
It is ordinarily impossible to draft a floorplan that would cause a doorway to lead outside of the house. Because of this, the planned location of the drafted room, or the tile, has a significant impact on which general room shapes may be drawn.
- While drafting into a central tile, floorplans of any shape may be drawn.
- While drafting into an edge tile, 4-way floorplans cannot be drawn. While drafting into an edge tile from the center rather than along the edge, Straight floorplans cannot be drawn.
- While drafting into a corner tile, only L-shape floorplans and Dead Ends can be drawn.
Additionally, the three floorplans will never be all Dead Ends outside of very specific interactions.
Orientation
Once a floorplan is drawn, it is randomly assigned a valid orientation, i.e. an orientation that does not result in a doorway leading outside of the house. Only L-shape and T-shape floorplans can have more than one orientation; although Straight and 4-way floorplans have multiple doorways, their rotations are identical in terms of shape due to symmetry and so those additional orientations are excluded.
Orientations determine which of the floorplan's doorways is connected to the drafting door. For example, the Parlor has two doors, one by the desk and one by the couch. The Parlor may be drafted from either of them depending on whether the floorplan appears pointing leftwards or rightwards on the drafting interface.
- While drafting into a central tile, both L-shape and T-shape floorplans may drafted from any of their doors.
- While drafting into an edge tile from the center, L-shape rooms may point either way, but T-shape floorplans are fixed, drafted only from their middle doors.
- While drafting into an edge tile from another edge or corner, or drafting into a corner, all orientations are fixed.
Some floorplans have additional restrictions on how they are orientated or which of their doorways can be drafted from.
Floorplans are slightly more likely to be oriented so that they have a south door, and less likely to have a north door. The Compass significantly increases the likelihood of floorplans being oriented with a doorway pointing north.
[Datamined Information] For more detailed info, see Drafting/Advanced#Rotation.
Choosing a floorplan
Once the three floorplans are drawn, the player must choose one of them to draft. The drafting interface cannot be exited except by drafting a room.
While choosing a floorplan, players may have access to one or more drafting options, which may be used before or instead of choosing a floorplan. One common drafting option is to redraw floorplans - or discard the three shown floorplans and draw three new ones - which can be provided by a number of effects such as ivory dice or the Drawing Room.
Special floorplans
Special floorplans are displayed with their 
gem cost. A free floorplan can always be chosen, but a special floorplan can only be chosen if the player is able to pay the displayed gem cost. If they cannot, the special floorplan cannot be drafted. Some effects alter, remove or otherwise interact with gem costs.
Drafting a room
Finally, after one of the three floorplans has been chosen, it is drafted. The drafting interface vanishes, the player regains control, and the drafting door opens up to reveal the newly drafted room. At this point, any effects which trigger when a room is drafted will trigger. This includes effects from the new room itself, meaning that, for instance, drafting a Nursery will trigger its own effect and provide 5
.
Newly drafted rooms are also populated with random items. The range and quantity of items spawned differ significantly from room to room and depend on both in-game luck and random chance. Items are spawned after room effects are applied; for instance, a newly drafted Veranda will benefit from the increased luck it provides.
In-drafting
When a room is drafted, all of its doorways, other than the doorway connected to the room it was drafted from, are checked to see if they can spawn a drafting door. Doorways that lead into empty space in the house gain a door, but doorways that lead into an existing room in the house do not. When this happens, one of two things usually happens:
- If the doorway leads into an existing doorway, the existing door opens and becomes uninteractable. This happens even if that door was locked or security locked. Since the door technically belongs to the attached room rather than the room that was just drafted, it appears to open inwards rather than outwards.
- If the doorway leads into the wall side of an existing room, the doorway appears barricaded and inaccessible.
- Drafting a room that leads nowhere due to all of its doorways being barricaded does not cause it to be considered a Dead End.
In-drafting also occurs when a room is drafted so that one of its wall sides blocks off an existing doorway, which will cause that doorway to become barricaded and the existing door to be deleted.
This is usually undesirable, as it reduces the number of accessible doors in the house. However in-drafting may still be beneficial for a few reasons:
- The permanent Foundation and Antechamber can usually only be accessed by drafting in to their doorways. In particular, since the existing Foundation doors open automatically while drafting into them, rooms that are drafted into the Foundation gain a Corridor-like property.
- Drafting into existing doorways may be useful to create shortcuts and save steps.
- Several rooms have unique interactions when accessed from doorways other than those that they were drafted from.
Spoilers Within
This section contains spoilers for all rooms with special in-drafting interactions, including late-game rooms.
- The Foundation: Accessing the Foundation from its sole non-doorway side will reveal a crank in place of the usual boarded up wall. When the crank is turned, a cutscene shows the Foundation elevator being lowered to ground level, permanently providing access to the lower Foundation.
- Chamber of Mirrors: Accessing the Chamber of Mirrors from any of its other sides leads to buttons that lower glass panes in the room and provide further access. In-drafting at once is required to reach any of the other subchambers, including the corners which contain items. Entering the Chamber of Mirrors from behind is required to access the center, which leads to the upper floor.
- Security: Security has a unique early-game drafting restriction which only allows it to be drafted from its middle door until its cinematic has been seen. This cinematic only plays when entering through the middle door, but it is still possible to draft it, then draft another room into one of its other doors and enter that way. Doing this prevents the cinematic from playing and causes the restriction to continue to subsequent days, until Security is entered normally.
- Secret Passage: Accessing the Secret Passage from behind before pulling any of the colored books reveals a cryptic note etched into the back of the bookcase.
- Closed Exhibit: TODO
An Entrance Hall doorway that has been blocked off by another room to the north
A Corridor drafted into a security locked door shortly before it opens; note the backwards texture and lack of any control panel
Out-drafting
The rules restricting the placement of specific room shapes usually prevent rooms from being drafted in a way that results in doorways leading outside of the house. In rare circumstances however, it is possible to use certain drafting effects to force a floorplan to be drawn in a place where it usually should not, resulting in a doorway that leads into the house boundary. These doorways appear boarded up, the same as they appear when leading in the walls of other rooms, though they sometimes have additional texture glitches. This mainly happens during color-selective drafts using the Prism Key or Secret Passage.
Additional information
- For most rooms, drafting that room at least once is required to view its entry in the Room Directory. The entries show the total number of times that particular room has been drafted.
- The Mount Holly Records and Mount Holly Scrapbook, found upstairs in the Library contain several permanent records of various drafts:
- The Draft Records page of Mount Holly Records shows the total number of rooms drafted for the current game file, plus the total numbers of Bedrooms, Hallways, Green Rooms, Shops, and Red Rooms.
- The Puzzle Records page of Mount Holly Records shows the total number of times the Parlor and Billiard Room have been drafted, and the number of times their respective puzzles have been solved.
- The Mount Holly Scrapbook shows the three floorplans which have been drafted the most; the three special floorplans on which the most gems have been spent; the player's "favorite" floorplan, i.e. the floorplan that has been drafted the most considering how often it has been drawn; and the three most avoided floorplans, which are rarely drafted when drawn.