Initial villager spawning

Question

On the initial generation (before any player interactions, and not repopulation) of a village, what determines where the villagers will spawn? Will they spawn inside houses within a radius of the center? Or outside on the gravel paths/farms?.

Answer 1

During generation, a structure has the option to run the following function:

protected void spawnVillagers(World worldIn, StructureBoundingBox sbb, int X, int Y, int Z, int maxVillagers)
{
    if (this.villagersSpawned < maxVillagers)
    {
        for (int i = this.villagersSpawned; i < maxVillagers; ++i)
        {
            int xOffset = this.getXWithOffset(X + i, Z);
            int yOffset = this.getYWithOffset(Y);
            int zOffset = this.getZWithOffset(X + i, Z);

            if (!sbb.isVecInside(new BlockPos(xOffset, yOffset, zOffset)))
            {
                break;
            }

            ++this.villagersSpawned;
            EntityVillager entityvillager = new EntityVillager(worldIn);
            entityvillager.setLocationAndAngles(xOffset + 0.5D, yOffset, zOffset + 0.5D, 0.0F, 0.0F);
            entityvillager.onInitialSpawn(worldIn.getDifficultyForLocation(new BlockPos(entityvillager)), (IEntityLivingData)null);
            entityvillager.setProfession(this.func_180779_c(i, entityvillager.getProfession()));
            worldIn.spawnEntityInWorld(entityvillager);
        }
    }
}

As long as the number villagers spawned for this individual structure is less than the maximum input, it will attempt to spawn a villager at the specified coordinates (which are initially relative to the corner of the structure's bounding box) provided it's not inside a block. To reiterate: the villagersSpawned is not for the entire village, but for this individually-spawned structure.

An example of the function being called, which is used by the "church" structure:

this.spawnVillagers(worldIn, structureBoundingBoxIn, 2, 1, 2, 1);

The maximum number of villagers to spawn inside a church is 1 and will always spawn at the provided offset coordinates.

Out of all the structures available, only large and small farms do not use this function.

Here are images where villagers will always spawn, represented by armor stands (though rotation of the structure may cause them to be mirrored on the other side).

Overview

Here is an example village where villager spawns are highlighted (armor stands with the Glowing effect):

Church

Wood Hut

Large House

Butcher's Shop

Library

Small House

Blacksmith

Answer 2

The Wiki says,

"Villagers spawn along with naturally-generated villages, inside various buildings."

So we can assume that they are in fact spawned inside the surrounding buildings of the village, and then exit.

Again hitting up the Wiki it says that,

"There is evidence that villagers are prone to overcrowding certain areas of a village while leaving other areas completely empty. When moving inside, the AI prefers doors within 16 blocks (Euclidean distance). It also attempts to prefer doors with fewer villagers nearby, however "nearby" in this case is only 1.5 blocks and, when moving inside, villagers prefer to move 2.5 blocks inside when the inside is to the south or east and therefore will be out of range of this check. During the day, it has been observed that villagers will tend to cluster near a trapped villager or any existing large cluster of villagers, likely due to the "socialize" AI routine overriding their inclination to wander".

Seeing as the AI clump together within a shorter radius, they likely spawn as a group, and then spread out initially during the day, moving to different areas as they travel throughout the day, and return to their various homes come nightfall.