return base_exp * level // 7
-def capture_chance(current_hp, max_hp, capture_rate,
- ball_bonus=1, status_bonus=1, heavy_modifier=0):
- """Calculates the chance that a Pokémon will be caught.
+def capture_chance(percent_hp, capture_rate,
+ ball_bonus=10, status_bonus=1,
+ capture_bonus=10, capture_modifier=0):
+ """Calculates the chance that a Pokémon will be caught, given its capture
+ rate and the percentage of HP it has remaining.
+
+ Bonuses are such that 10 means "unchanged".
Returns five values: the chance of a capture, then the chance of the ball
shaking three, two, one, or zero times. Each of these is a float such that
0.0 <= n <= 1.0. Feel free to ignore all but the first.
"""
- if heavy_modifier:
- # Only used by Heavy Ball. Changes the target's capture rate outright
- capture_rate += heavy_modifier
- if capture_rate <= 1:
- capture_rate = 1
-
- # This should really be integer math, right? But the formula uses FOURTH
- # ROOTS in a moment, so it can't possibly be. It probably doesn't matter
- # either way, so whatever; use regular ol' division. ball_bonus and
- # status_bonus can be 1.5, anyway.
- base_chance = ((3 * max_hp - 2 * current_hp) * capture_rate * ball_bonus) \
- / (3 * max_hp) \
- * status_bonus
-
- shake_index = (base_chance / 255) ** 0.25 * (2**16 - 1)
+ # HG/SS Pokéballs modify capture rate rather than the ball bonus
+ capture_rate = capture_rate * capture_bonus // 10 + capture_modifier
+ if capture_rate < 1:
+ capture_rate = 1
+ elif capture_rate > 255:
+ capture_rate = 255
+
+ # A slight math note:
+ # The actual formula uses (3 * max_hp - 2 * curr_hp) / (3 * max_hp)
+ # This uses (1 - 2/3 * curr_hp/max_hp)
+ # Integer division is taken into account by flooring immediately
+ # afterwards, so there should be no appreciable rounding error.
+ base_chance = int(
+ capture_rate * ball_bonus // 10 * (1 - 2/3 * percent_hp)
+ )
+ base_chance = base_chance * status_bonus // 10
+
+ # Shake index involves integer sqrt. Lovely.
+ isqrt = lambda x: int(x ** 0.5)
+ if not base_chance:
+ # This is very silly. Due to what must be an oversight, it's possible
+ # for the above formula to end with a zero chance to catch, which is
+ # then thrown blindly into the below denominator. Luckily, the games'
+ # division function is a no-op with a denominator of zero.. which
+ # means a base_chance of 0 is effectively a base chance of 1.
+ base_chance = 1
+ shake_index = 1048560 // isqrt(isqrt(16711680 // base_chance))
# Iff base_chance < 255, then shake_index < 65535.
- # The game now picks four random uwords. However many of them are <=
- # shake_index is the number of times the ball will shake. If all four are
- # <= shake_index, the Pokémon is caught.
+ # The Pokémon now has four chances to escape. The game starts picking
+ # random uint16s. If such a random number is < shake_index, the Pokémon
+ # stays in the ball, and it wobbles. If the number is >= shake_index, the
+ # ball breaks open then and there, and the capture fails.
+ # If all four are < shake_index, the Pokémon is caught.
- # If shake_index >= 65535, all four randoms must be <= it, and the Pokémon
+ # If shake_index >= 65535, all four randoms must be < it, and the Pokémon
# will be caught. Skip hard math
if shake_index >= 65535:
return (1.0, 0.0, 0.0, 0.0, 0.0)
# Something is guaranteed to happen.
# Alrighty. Here's some probability.
- # The chance that a single random number will be <= shake_index is:
- p = (shake_index + 1) / 65536
- # Now, the chance that two random numbers will be <= shake_index is p**2.
- # And the chance that neither will be is (1 - p)**2.
- # With me so far?
- # The chance that one will be and one will NOT be is p * (1 - p) * 2.
- # The 2 is because they can go in any order: the first could be less, or
- # the second could be less. That 2 is actually nCr(2, 1); the number of
- # ways of picking one item in any order from a group of two.
- # Try it yourself add up those three values and you'll get 1.
-
- # Right. Hopefully, the following now makes sense.
- # There are five cases: four randoms are <= shake_index (which means
- # capture), or three are, etc.
+ # The chance that a single random uint16 will be < shake_index, thus
+ # keeping the Pokémon in the ball, is:
+ p = shake_index / 65536
+
+ # Now, the chance for n wobbles is the chance that the Pokémon will stay in
+ # the ball for (n-1) attempts, then break out on the nth.
+ # The chance of capture is just the chance that the Pokémon stays in the
+ # ball for all four tries.
+
+ # There are five cases: captured, wobbled three times, etc.
return [
- p**i * (1 - p)**(4 - i) * nCr(4, i)
- for i in reversed(range(5))
+ p**4, # capture
+ p**3 * (1 - p),
+ p**2 * (1 - p),
+ p**1 * (1 - p),
+ (1 - p),
]
projects / zzz-pokedex.git / blobdiff