size the sparkle to the Pokemon it belongs to

Flat numbers cannot work here and both previous attempts proved it in
opposite directions. The first ring was 7 world units across, which is inside
anything bigger than a Rattata -- and additive drawing keeps the depth test,
so all sixty quads a frame were rejected and nobody saw them. Correcting by
eye gave a ring 24 across starting 20 units up, which is taller than the
tallest Pokemon in the game: it hung in the sky above a Ponyta with nothing
underneath it.

A mon on the map is 5 to 18 world pixels tall (StadiumMon REF_HEIGHT 14). One
ring cannot fit a Diglett and a Gyarados, so every distance is now a fraction
of the mon: Stadium pushes each side's worldHeight and worldRadius into
ShinyFx every frame -- worldRadius exists precisely so "a caller can size
something to its footprint" -- and the burst is measured off those.

Two more things the pictures showed. The ring is an ELLIPSE with its axes
measured separately: flattened enough to read as a ring from the battle's low
seat, a single radius reaches only a third of the body's height, so the top
and bottom stars sit on the Pokemon. And it OPENS from clear of the body
rather than from a point -- springing out of nothing means every star spends
the first frames stacked at the centre, which is the middle of the mon and
looks exactly like the sparkles being stuck inside it.

Shot against Ponyta and Gyarados, an order of magnitude apart in size: the
ring hugs each silhouette from outside and no star lands on either body.

lib/ShinyFx.lua

@@ -40,20 +40,58 @@ local BattleBillboard = V.require("BattleBillboard")
 
 local ShinyFx = {}
 
+local max, min = math.max, math.min
+
 -- ------- shape and timing
 
--- Sized against the mon CARD, which is what a Pokemon occupies here: a card
--- is BattleBillboard.FULL_W / FULL_PIC * GB_W units across, i.e. about 46
--- wide and 41 tall. The first version of this was built to numbers a tenth
--- of that and drew sixty quads a frame that nobody could see -- a ring seven
--- units across, inside a Gyarados.
+-- ------- sized to the Pokemon, not to a constant
+--
+-- A Pokemon on the map is between 5 and 18 world pixels tall
+-- (StadiumMon.MIN_HEIGHT/MAX_HEIGHT, REF_HEIGHT 14) and roughly its own
+-- radius wide. Every earlier attempt here used flat numbers and every one of
+-- them was wrong for most of the dex: first a ring 7 units across, which sat
+-- INSIDE anything bigger than a Rattata and was depth-rejected; then, over-
+-- correcting, a ring 24 across starting 20 units up -- taller than the
+-- tallest Pokemon there is, so it hung in the sky above a Ponyta with
+-- nothing under it.
+--
+-- One ring cannot fit a Diglett and a Gyarados. The burst is therefore a
+-- FRACTION of the mon it belongs to: Stadium hands us each side's
+-- worldHeight and worldRadius (StadiumMon has them, and worldRadius exists
+-- precisely so "a caller can size something to its footprint"), and every
+-- distance below is measured off those.
 ShinyFx.LIFE = 0.75          -- seconds from spring to gone
 ShinyFx.STARS = 10           -- around the ring
-ShinyFx.RISE = 14            -- world units the ring climbs over its life
-ShinyFx.SPREAD = 24          -- how far out the ring opens -- wider than the
-                             -- body, or the stars are inside the Pokemon
-ShinyFx.CHEST = 20           -- height above the tile the burst starts at
-ShinyFx.SIZE = 7             -- a star's world size at full brightness
+
+ShinyFx.CHEST_FRAC = 0.50    -- up the body: the ring is centred on the
+                             -- Pokemon, not perched above or below it
+ShinyFx.RISE_FRAC = 0.16     -- of its height, drifted up over the burst
+ShinyFx.SIZE_FRAC = 0.20     -- a star, as a fraction of the mon's height
+
+-- THE RING IS AN ELLIPSE AROUND THE SILHOUETTE, with its two axes measured
+-- separately. A single radius cannot do this: flattened enough to look like
+-- a ring seen from the battle's low seat, its vertical reach ends up a third
+-- of the body's height, so the top and bottom stars sit ON the Pokemon. The
+-- horizontal axis clears its width, the vertical axis clears its height.
+ShinyFx.RING_X_FRAC = 1.50   -- of the mon's RADIUS -- just outside its width
+ShinyFx.RING_X_MIN = 0.34    -- ...but never narrower than this of its height,
+                             -- for the thin ones (Onix, Ekans) whose radius
+                             -- alone would put the ring inside them
+ShinyFx.RING_Y_FRAC = 0.62   -- of its HEIGHT -- so the ring reaches its
+                             -- shoulders and its feet, not just its middle
+
+-- The burst OPENS from here rather than from nothing. Springing out of a
+-- point means every star spends the first frames stacked at the centre --
+-- which is the middle of the Pokemon, and reads exactly like the sparkles
+-- being stuck inside it. Starting already clear of the body and expanding
+-- the rest of the way keeps them outside for the whole life of the effect.
+ShinyFx.RING_START = 0.72
+
+-- What a side with no model gets: the flat-pic rung, where a pic stands
+-- FULL_W (16) units wide in a card. Close enough to a median Pokemon that
+-- the same fractions land sensibly.
+ShinyFx.DEFAULT_HEIGHT = 14
+ShinyFx.DEFAULT_RADIUS = 6
 
 -- Additive drawing keeps the depth TEST (Voxel3D.blend sets lequal with
 -- writes off), so a star level with the model is rejected by it however
@@ -63,6 +101,21 @@ ShinyFx.PULL_BONUS = 6
 
 -- one per side, nil when nothing is playing
 local live = { player = nil, enemy = nil }
+
+-- How big the Pokemon on each side actually is, pushed in by Stadium.update
+-- every frame it has a model. Kept here rather than reached for, because
+-- ShinyFx is drawn from BattleScene and asking Stadium from inside it would
+-- close a require loop between the three.
+local size = { player = nil, enemy = nil }
+
+-- world pixels, from StadiumMon:worldHeight/worldRadius. Pass nil height to
+-- say "no model on this side" -- the flat-pic rung, which falls back to the
+-- defaults above.
+function ShinyFx.setMetrics(side, height, radius)
+  if side ~= "player" and side ~= "enemy" then return end
+  if not (height and height > 0) then size[side] = nil return end
+  size[side] = { h = height, r = radius or 0 }
+end
 local star = nil             -- the generated star image, built once
 
 -- ------- the star
@@ -174,7 +227,18 @@ function ShinyFx.draw(arena, groundY, pull)
       local alpha = 1 - u * u
       local x, z = cell[1], cell[2]
       local yaw = BattleBillboard.yawToward(x, z, Voxel3D.eye)
-      local baseY = groundY + ShinyFx.CHEST + ShinyFx.RISE * e
+
+      -- every distance measured off THIS Pokemon (see the header)
+      local m = size[side]
+      local mh = (m and m.h) or ShinyFx.DEFAULT_HEIGHT
+      local mr = (m and m.r and m.r > 0 and m.r) or ShinyFx.DEFAULT_RADIUS
+      local ringX = max(mr * ShinyFx.RING_X_FRAC, mh * ShinyFx.RING_X_MIN)
+      local ringY = mh * ShinyFx.RING_Y_FRAC
+      local starK = mh * ShinyFx.SIZE_FRAC
+      -- open from clear of the body, not from a point (see RING_START)
+      local grow = ShinyFx.RING_START + (1 - ShinyFx.RING_START) * e
+      local baseY = groundY + mh * ShinyFx.CHEST_FRAC
+                    + mh * ShinyFx.RISE_FRAC * e
 
       if not drew then
         Voxel3D.blend("add")
@@ -188,12 +252,11 @@ function ShinyFx.draw(arena, groundY, pull)
         -- twinkle in lockstep when both are shiny
         local a = (i / ShinyFx.STARS) * math.pi * 2
                   + (side == "player" and 0.31 or 0)
-        local r = ShinyFx.SPREAD * e
         -- stars shrink as they fade, and alternate size so the ring reads
         -- as scattered rather than as a cog
-        local k = ShinyFx.SIZE * (1 - u * 0.6) * ((i % 2 == 0) and 0.7 or 1)
-        local ox = math.cos(a) * r
-        local oy = math.sin(a) * r * 0.55   -- flattened: we look from low
+        local k = starK * (1 - u * 0.6) * ((i % 2 == 0) and 0.7 or 1)
+        local ox = math.cos(a) * ringX * grow
+        local oy = math.sin(a) * ringY * grow
         local m = Mat4.mul(
           Mat4.mul(Mat4.translate(x, baseY, z), Mat4.rotateY(yaw)),
           Mat4.mul(Mat4.translate(ox, oy, 0), Mat4.scale(k, k, 1)))