Home on the Ranged Target Cover

I had gotten to the point over the weekend where I was fairly comfortable with the final state of melee cover checks (with its weird alternate source points when attacking downward while standing on a ledge), and really began testing the ranged cover checks. What helped me in testing was adding the interaction alterations (for the attack interaction) to the status feedback so that the client could see cover and concealment affecting the attack. I’m going to need to examine the StepStatus a lot more closely to “pretty-up” the structure, and ensure that the right amount of information is sent to each client. I’m also going to need to put a facility to always send observed-activity info to various clients when an actor acts (right now, I only use ObservedActivityInfo when making an OpportunisticInquiry).

But anyway, back to ranged attacks. I noticed that a creature whose feet were blocked by only a small step was getting a lot of cover lines flagged (so that they could get a +4 cover bonus to armor-rating). I tried to compensate for this at first by proportionally moving the bottom points of the lowest cells upwards towards the top points, but this still kept them behind the step in certain cases.

Then, I planned to do some magic with checking the back-most low point(s) if the front-most low points were blocked. But I finally decided on boosting the low points upward again by an “absolute” amount relative to a fraction of the creature size (similar to how land movement has a maximum up-step size beyond which a climb check is needed, and representing the “bulk/core” of the creature’s body), rather than a fraction of the vector between low and high. If the low point boost is longer than the vector between low and high points, than the low point is simply omitted from the target corner set.

In the light amount of testing I performed, this seems like the best balance so far. But I’ll need more testing, and ultimately I need to vary the amount of low-point boost by creature body type, and whether the creature is prone or not.

(Slightly) Uphill Battle

Returning to the Ikosa Framework’s rules for cover; in addition to the special point identification mechanism for downward melee strikes, there are some special adjustments made to melee source corner points when melee attacks are made on the same level.

The main reason for adjustments to handle the cases when the source and target cell are on the same level, but the target is on a “slightly” higher step. In this case, the “front”-lower corner(s) of the source cell must go through the low step, creating cover. When attacking a target cell on the same level (based on cell-specific gravity), Ikosa adjusts the lower corners upward by 30% towards the upper corners on the same up-down edge. (It also adjusts the upper corners down 5%).

Currently these percent factors are hard-coded, but may likely be calculated by other factors in the future.

The “modeled” result is that a melee attack against a target on a platform less than 1.5 feet higher than the attacker does not automatically get penalized by cover.

(Note: when any component of a melee attack is upward or downward, these adjustments are not applied. Also, reach/ranged attacks originate from a single point, so there is no need to adjust source corners).

Covering Melee Corners

Traditional PnP tactical cover rules have some gray areas when it comes to complex 3-dimensional topography and large creatures. Mostly these are swept under the generalizations from the “flatness” of tradition PnP play. However, the Ikosa Framework must calculate cover within predictable constraints and more highly variable conditions.

For instance, melee cover (which can only occur when attacking into an adjacent cell) generally requires all “corners” of the source cell to have unhindered line of effect to the target cell. Assuming an attacking creature stands on a block of solid ground 5 foot higher than an adjacent target creature (such that the target creature is “diagonally-down” from the attacker), then lines from the back of the attacker must be blocked by the solid ground to attack the target; in exactly the same way as when attacking around a corner. It is unlikely that a game-master would rule the lower target had cover from the attacker standing on a higher platform, especially since attacking from higher ground typically gives a +1 to attack.

The Ikosa Framework has strategies to deal with this situation (and some processing optimizations).

Optimization first: When calculating cover (melee or reach/ranged) Ikosa must check lines between “corners” of the source (cell or point) and target (cell or cells) for terrain blockage or cover inducing effects in the cells being traversed by the lines.

To reduce processing, Ikosa only examines points that will reach from source to target without going through the source or target (thus culling certain points from consideration). This can be determined by looking at the relative integer cell coordinates between source and target cells to determine which faces are exposed to each other. When two cells are face to face, 4 points from the source and 4 points from the target are considered. When edge to edge, 6 and 6, and when corner to corner, 7 points each. Also, for reach/ranged attacks, there are additional target points possible (since for larger creatures the entire creature is being targeted, which spans many cells), but also additional culling (so that only points exposed to the source point) are considered.

For the downward attack mentioned above, Ikosa detects the gravity direction of the attacker and whether the terrain supports the attacker (thus creatures in flight above the surface are excluded from this test) and then excludes those faces from consideration if they would otherwise be needed. As a result, only attacker points that face-outward toward the target on the non gravitationally bound attacker face are used. In this case, only 4 points are considered (if the target is adjacent and down) or 6 (if target is diagonal and down).

If the attacker were in a cell 5 feet lower, however, the gravitationally bound face isn’t facing the target anyway, and since the all the target’s points are still usable, the higher target would have cover.