Fix faint slide starting partway down (#671)

The faint slide was shortened from 30 to Timing.FAINT_SLIDE (14) frames
in the timing-parity pass, but fxFaintOffset still computed the offset
with a stale (30 - frames) * 2.  With frames starting at 14 the sprite
teleported 32px down on the first frame and only slid the remaining
28px, cutting the animation short.

SlideDownFaintedMonPic drops the pic one 8px row per 2-frame step, so
the offset advances Timing.FAINT_SLIDE_STEP (4px) per frame at 1x and
covers the full 56px PIC_HEIGHT over the 14-frame budget.

src/battle/BattleState.lua

@@ -4542,11 +4542,15 @@ end
 -- pixels, so it scales with the pic's draw scale (the player's default 2x
 -- sinks 2x as fast to sink at the same visual rate); a mod scale composes
 -- the same way.  scale defaults to the vanilla side scale when unknown.
+-- SlideDownFaintedMonPic drops the pic one 8px row per 2-frame step, so
+-- the offset advances Timing.FAINT_SLIDE_STEP (4px) per frame at 1x --
+-- the full 56px PIC_HEIGHT slide over the 14-frame budget (#671: the
+-- old (30 - frames) math teleported the sprite 32px down on frame one).
 function BattleState:fxFaintOffset(battler, scale)
   local fx = self.fx
   if self:fxFaintActive(battler) then
     scale = scale or (battler.isPlayer and 2 or 1)
-    return (30 - fx.faint.frames) * 2 * scale
+    return (Timing.FAINT_SLIDE - fx.faint.frames) * Timing.FAINT_SLIDE_STEP * scale
   end
   return 0
 end

src/core/Timing.lua

@@ -129,6 +129,7 @@ Timing.NO_MOVES_LEFT      = 60 -- core.asm:2753-2754
 Timing.TRAINER_VICTORY    = 40 -- core.asm:940-941
 Timing.PLAYER_BLACKOUT    = 40 -- core.asm:1143-1144
 Timing.FAINT_SLIDE_ROW    = 2  -- core.asm:1216-1217, per row
+Timing.FAINT_SLIDE_STEP   = 8 / Timing.FAINT_SLIDE_ROW -- 4px per frame at 1x
 Timing.TRAINER_SLIDE_COL  = 2  -- core.asm:1267-1268, per column
 
 -- HP bar (engine/gfx/hp_bar.asm) ---------------------------------------------

tests/engine/timing_parity.lua

@@ -273,6 +273,26 @@ T.eq(Timing.BLINK_MON % 10, 0,
 -- SlideDownFaintedMonPic: b = PIC_HEIGHT slide steps of DelayFrames 2
 T.eq(Timing.FAINT_SLIDE, 14, "the faint slide is 7 steps x 2 frames")
 
+-- #671: the slide must start at the sprite's resting spot and sink the
+-- full PIC_HEIGHT (7 rows x 8px = 56px at 1x) across those 14 frames.
+-- The old (30 - frames) * 2 math teleported the pic 32px down on frame
+-- one once the budget was shortened from 30 to 14 frames.
+local faintBattle = newBattle()
+faintBattle.fx = { faint = { battler = faintBattle.enemy,
+                             frames = Timing.FAINT_SLIDE } }
+T.eq(faintBattle:fxFaintOffset(faintBattle.enemy, 1), 0,
+  "the faint slide starts at offset 0 (#671)")
+faintBattle.fx.faint.frames = Timing.FAINT_SLIDE - 7
+T.eq(faintBattle:fxFaintOffset(faintBattle.enemy, 1),
+     7 * Timing.FAINT_SLIDE_STEP,
+  "the slide sinks one 8px row per step")
+faintBattle.fx.faint.frames = 1
+T.eq(faintBattle:fxFaintOffset(faintBattle.enemy, 1),
+     (Timing.FAINT_SLIDE - 1) * Timing.FAINT_SLIDE_STEP,
+  "the slide reaches 52px by the last visible frame")
+T.eq(Timing.FAINT_SLIDE * Timing.FAINT_SLIDE_STEP, 56,
+  "and covers the full 7-row pic height over the whole budget")
+
 T.eq(Timing.MOVE_STATUS_OR_MISS, 30,
   "a status move or a miss holds DelayFrames 30 before its text")