I don't know if this is a bug, or if it is intentional, but I ran into it and thought I'd post it here. This only shows up when you mod terrain impassability. (Since the only time vanilla BTS uses this is to make a unit unable to enter oceans, it doesn't appear normally). It happens in BTS 3.19. Anyway, I thought I'd post it here.

When I make a unit unable to pass into a certain terrain, everything works fine. However, I can walk into a feature such as a forest even if that forest is on blocked terrain.

I ran into this bug while modding Fall from Heaven 2 (a unit that was blocked from moving on non-Snow terrain could move into non-Snow tiles with Forests or other features on them.

A quick test in Beyond the Sword unmodded revealed the same was true when I blocked the Lion from moving into Plains, allowing it to walk over forests on plains tiles.

The code in CvUnit::canMoveInto that is responsible is below:

if (pPlot->getFeatureType() != NO_FEATURE)
{
if (m_pUnitInfo->getFeatureImpassable(pPlot->getFeatureType()))
{
TechTypes eTech = (TechTypes)m_pUnitInfo->getFeaturePassableTech(pPlot->getFeatureType());
if (NO_TECH == eTech || !GET_TEAM(getTeam()).isHasTech(eTech))
{
if (DOMAIN_SEA != getDomainType() || pPlot->getTeam() != getTeam()) // sea units can enter impassable in own cultural borders
{
return false;
}
}
}
}
else
{
if (m_pUnitInfo->getTerrainImpassable(pPlot->getTerrainType()))
{
TechTypes eTech = (TechTypes)m_pUnitInfo->getTerrainPassableTech(pPlot->getTerrainType());
if (NO_TECH == eTech || !GET_TEAM(getTeam()).isHasTech(eTech))
{
if (DOMAIN_SEA != getDomainType() || pPlot->getTeam() != getTeam()) // sea units can enter impassable in own cultural borders
{
if (bIgnoreLoad || !canLoad(pPlot))
{
return false;
}
}
}
}
}
}

If there is a feature on the plot, the game doesn't even check if you can pass the terrain. Either someone at Firaxis forgot a line of code or this was done by design.

That is quite bizarre ... certainly fixing this isn't going to affect any BtS units as all of the features are either land based or impassable:

Ice (impassable)
Jungle
Oasis
Floodplains
Forest
Fallout

Why would they have set things up with the feature check first? I can't think of any reason why it would be that way.

This is a total stab in the dark, but could it be related to the fact that the feature is the more important aspect of a tile in circumstances where you get a movement bonus due to features? (By my lights, "double movement in woods" would still cause you to only be able to take one step onto a forest/hill, but in the game the double movement in the forests is more important than the extra cost for moving onto a hill.)

I consider that an unintended feature, myself. Is a hill easier to climb just because it has trees on it? (Of course, having a 1 MP unit suddenly have 2 MP when it moves into a forest/hill first is just as wonky, so I guess it balances out.)

I noticed this bug too, and it caused me to have to do a lot of extra work for my Mountains mod, getting around this. It would be nice to be fixed.

Although to some this may be an unintended feature, I must say, to any modder, this is more of a nightmare...