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fairland: Prefer placing islands away from the edge of the sphere

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When an island gets placed too close to the edge of the sphere of
influence, its side facing the edge will likely be formed by the edge.
Looks unnatural, and can give a clue on the location of the other
continent.

Make place_island() prefer sectors away from the edge: instead of
picking one of the admissible sectors with equal probability, reduce
the probability as we get closer to the edge.

Signed-off-by: Markus Armbruster <armbru@pond.sub.org>
This commit is contained in:
Markus Armbruster 2020-09-14 07:27:45 +02:00
parent 4fca4dfddd
commit fe86ea430a
7 changed files with 2804 additions and 2766 deletions
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58
src/util/fairland.c
View file

@ -72,9 +72,11 @@
* islands are grown before smaller ones, to give the large ones the
* best chance to grow to their planned size.
*
* Then place one island's first sector into each sphere, randomly.
* Add one sector to each island in turn, until they have the intended
* size. Repeat until the specified number of islands has been grown.
* Then place one island's first sector into each sphere, using
* weighted random sampling with weights favoring sectors away from
* land and other spheres. Add one sector to each island in turn,
* until they have the intended size. Repeat until the specified
* number of islands has been grown.
*
* If placement fails due to lack of room, start over, just like for
* continents.
@ -907,14 +909,45 @@ bfs_enqueue_island(int c)
}
}
/*
* Enqueue spheres of influence borders for breadth-first search.
*/
static void
bfs_enqueue_border(void)
{
int x, y, off, dir, nx, ny, noff;
for (y = 0; y < WORLD_Y; y++) {
for (x = y % 2; x < WORLD_X; x += 2) {
off = XYOFFSET(x, y);
if (distance[off] <= id + 1)
continue;
if (closest[off] == (natid)-1)
continue;
for (dir = DIR_FIRST; dir <= DIR_LAST; dir++) {
nx = new_x(x + diroff[dir][0]);
ny = new_y(y + diroff[dir][1]);
noff = XYOFFSET(nx, ny);
if (closest[noff] != closest[off]) {
bfs_enqueue(closest[off], x, y, id + 1);
break;
}
}
}
}
}
/*
* Compute spheres of influence
* A continent's sphere of influence is the set of sectors closer to
* it than to any other continent.
* Set closest[XYOFFSET(x, y)] to the closest continent's number,
* -1 if no single continent is closest.
* Set distance[XYOFFSET(x, y)] to the distance to the closest coastal
* land sector.
* Set distance[XYOFFSET(x, y)] to the minimum of the distance to the
* closest coastal land sector and the distance to just outside the
* sphere of influence plus @id. For sea sectors within a continent's
* sphere of influence, distance[off] - id is the distance to the
* border of the area where additional islands can be placed.
*/
static void
init_spheres_of_influence(void)
@ -925,6 +958,8 @@ init_spheres_of_influence(void)
for (c = 0; c < nc; c++)
bfs_enqueue_island(c);
bfs_run_queue();
bfs_enqueue_border();
bfs_run_queue();
}
/*
@ -1092,17 +1127,20 @@ grow_continents(void)
* Return 1 on success, 0 on error.
*/
static int
place_island(int c)
place_island(int c, int isiz)
{
int n, x, y, newx, newy;
int n, x, y, d, w, newx, newy;
n = 0;
for (y = 0; y < WORLD_Y; y++) {
for (x = y % 2; x < WORLD_X; x += 2) {
if (can_grow_at(c, x, y)) {
n++;
if (!roll0(n)) {
d = distance[XYOFFSET(x, y)];
assert(d > id);
w = (d - id) * (d - id);
n += MIN(w, (isiz + 2) / 3);
if (roll0(n) < w) {
newx = x;
newy = y;
}
@ -1166,7 +1204,7 @@ grow_islands(void)
for (j = 0; j < nc; j++) {
isecs[c + j] = 0;
if (!place_island(c + j)) {
if (!place_island(c + j, isiz)) {
qprint("\nNo room for island #%d\n", c - nc + j + 1);
free(island_size);
return 0;