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Avoid crash caused by, and improve, 'findSpawnPos()' (#8728)

Avoid an unsuitable spawn position (which if outside mapgen limits can
cause a crash) if the main 0-3999 loop reaches its end. Fallback to a
spawn at 0,0,0.
Check the mapgen-returned 'spawn_level' value for being outside limits.
When 'air_count' reaches 2, move back down 1 to spawn in the lower
empty node.
If the spawn position is disallowed by 'objectpos_over_limit()', 'break'
from loop instead of 'continue' because positions above are probably
also over limit.
Reset 'air_count' to 0 if an obstruction is found, to make 'air_count'
consecutive empty nodes.
Allow spawn in 'airlike' drawtype nodes such as mod-added vacuum,
alien atmospheres, fog etc.
Add clarifying comments and improve codestyle.
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paramat committed Aug 7, 2019
1 parent 0c533dc commit 37923920a07f06d201662d8f1f4e5821efcc7b09
Showing with 31 additions and 12 deletions.
  1. +31 −12 src/server.cpp
@@ -3512,52 +3512,71 @@ v3f Server::findSpawnPos()
{
ServerMap &map = m_env->getServerMap();
v3f nodeposf;
if (g_settings->getV3FNoEx("static_spawnpoint", nodeposf)) {
if (g_settings->getV3FNoEx("static_spawnpoint", nodeposf))
return nodeposf * BS;
}

bool is_good = false;
// Limit spawn range to mapgen edges (determined by 'mapgen_limit')
s32 range_max = map.getMapgenParams()->getSpawnRangeMax();

// Try to find a good place a few times
for(s32 i = 0; i < 4000 && !is_good; i++) {
for (s32 i = 0; i < 4000 && !is_good; i++) {
s32 range = MYMIN(1 + i, range_max);
// We're going to try to throw the player to this position
v2s16 nodepos2d = v2s16(
-range + (myrand() % (range * 2)),
-range + (myrand() % (range * 2)));

// Get spawn level at point
s16 spawn_level = m_emerge->getSpawnLevelAtPoint(nodepos2d);
// Continue if MAX_MAP_GENERATION_LIMIT was returned by
// the mapgen to signify an unsuitable spawn position
if (spawn_level == MAX_MAP_GENERATION_LIMIT)
// Continue if MAX_MAP_GENERATION_LIMIT was returned by the mapgen to
// signify an unsuitable spawn position, or if outside limits.
if (spawn_level >= MAX_MAP_GENERATION_LIMIT ||
spawn_level <= -MAX_MAP_GENERATION_LIMIT)
continue;

v3s16 nodepos(nodepos2d.X, spawn_level, nodepos2d.Y);

// Consecutive empty nodes
s32 air_count = 0;
for (s32 i = 0; i < 10; i++) {

// Search upwards from 'spawn level' for 2 consecutive empty nodes, to
// avoid obstructions in already-generated mapblocks.
// In ungenerated mapblocks consisting of 'ignore' nodes, there will be
// no obstructions, but mapgen decorations are generated after spawn so
// the player may end up inside one.
for (s32 i = 0; i < 8; i++) {
v3s16 blockpos = getNodeBlockPos(nodepos);
map.emergeBlock(blockpos, true);
content_t c = map.getNodeNoEx(nodepos).getContent();
if (c == CONTENT_AIR || c == CONTENT_IGNORE) {

// In generated mapblocks allow spawn in all 'airlike' drawtype nodes.
// In ungenerated mapblocks allow spawn in 'ignore' nodes.
if (m_nodedef->get(c).drawtype == NDT_AIRLIKE || c == CONTENT_IGNORE) {
air_count++;
if (air_count >= 2) {
// Spawn in lower empty node
nodepos.Y--;
nodeposf = intToFloat(nodepos, BS);
// Don't spawn the player outside map boundaries
if (objectpos_over_limit(nodeposf))
continue;
// Exit this loop, positions above are probably over limit
break;

// Good position found, cause an exit from main loop
is_good = true;
break;
}
} else {
air_count = 0;
}
nodepos.Y++;
}
}

return nodeposf;
if (is_good)
return nodeposf;

// No suitable spawn point found, return fallback 0,0,0
return v3f(0.0f, 0.0f, 0.0f);
}

void Server::requestShutdown(const std::string &msg, bool reconnect, float delay)

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