strategy - RTS game unit damage & defense calculation

How can I model armies attacking each other in an RTS?

I know how I would do it if it is an RPG game. Character has few stats that affect damage/defense and then compare it with enemy character and make calculations.

But what to do when you have an RTS game with lets say 3 kind of units (archers,knights,cavalry).

How would you do a calculation:

eg. 3 archers, 2 horsemen, 4 knights attack 3 knights and 5 horsemen?

One idea I had was to model units as having a certain amount of attack/defense against other units.

eg. Archer - 70% damage against knight, 10% defense against knight (90% damage against horseman (higher chance to hit bigger object)) (10% defense against horseman (if he comes closer))

Knight - 30% damage against archer, 20% defense against archer (50% damage against horseman, 40% defense against horseman)

Horsemen - 90% damage against archer, 20% defense against archer (70% damage against knight, 70% defense against knight)

In my game, players control armies (groups of units), which they send to attack enemy towns. At that point, I need to calculate how much damage the attacking army inflicted on the town (and vice-versa). I'm looking for some sort of formula or algorithm to help determine this.

Answer

One way I would solve this problem (albeit simplistically) is simple math. Assign each unit damage and health, eg:

• Archer: 3 attack, 2 health



• Horseman: 7 attack, 5 defense


• Knight: 4 attack, 4 defense

Then simply total it up and see who wins, eg.

3 archers, 2 horsemen, 4 knights = total of 37 attack, 32 health 3 knights, 5 horsemen = total of 47 attack, 37 health

If (again, simplistic model) both sides inflict damage simultaneously, both armies would die.

If another case occurred where, say, 30/36 health remains in one army, you choose how to distribute that amongst the units to decide which survives and which dies.

This is, as I said, a simple addition/subtraction model; you can add a lot more complexity, such as:

• Which army attacks first



• How damage is inflicted (one point to each unit round-robin, or fully on the first unit until it dies, or the strongest, or something else?)


• Who survives


• Attack precedence (eg. calculate archer damage first, then knights, then horsemen)


• etc.