characters/skin_joint_helper.gd

@@ -1,74 +1,80 @@
-extends Object
+extends Object
 class_name SkinJointHelper
 
-## Handles bending with JOINTS instead of letting the mesh collapse.
+## Articulates a joint through a CHAIN of helper bones so the limb cannot pinch.
 ##
-## Linear-blend skinning averages TRANSFORMS, not shapes. A vertex weighted half
-## to the thigh and half to the shin is placed at the average of two rotations,
-## and when the joint bends that average falls inside the limb — the leg pinches
-## and reads as "the thighs get really thin". Measured per vertex against the
-## rest transforms, Taila's thigh was losing up to 20% of its radius along its
-## whole length during a jump, not just at the knee.
+## Linear-blend skinning averages TRANSFORMS, not shapes. Blending two rotations
+## that are θ apart shortens anything perpendicular to the bend by cos(θ/2), so a
+## vertex sitting between the thigh and the shin is pulled inside the leg the
+## moment the knee folds. That is the thigh going thin during a jump.
 ##
-## The fix is to stop any vertex ever blending across a full bend. At each leg
-## joint we insert a helper bone that sits on the child's rest transform and is
-## driven to HALF the child's rotation. Vertices in that joint's blend zone are
-## re-weighted off the parent/child pair and onto the helper, so the sharpest
-## blend any vertex sees is half the joint angle — and halving the angle roughly
-## quarters the collapse. This is the standard half-angle (or "twist") joint
-## used to make skinned limbs hold their volume.
+## The collapse depends only on the WIDEST angle any single vertex has to blend
+## across, so the fix is to make that angle small. Insert SEGMENTS-1 helper bones
+## through the joint, each driven to its fraction of the child's rotation, and
+## give every blend-zone vertex to the two ADJACENT bones it falls between. No
+## vertex then blends across more than θ/SEGMENTS, and the worst collapse drops
+## from cos(θ/2) to cos(θ/2·SEGMENTS):
 ##
-## KNEES ONLY, deliberately. Adding hip (hips->thigh) and ankle (shin->foot)
-## helpers was tried and reverted: it made the knee region measurably WORSE
-## (0.80 -> 0.50) and dragged the skirt down with it (0.80 -> 0.72). The knee is
-## the joint that actually bends far enough to pinch; the hip mostly swings,
-## which linear-blend skinning handles far better. Re-measure before adding a
-## joint here — more helpers is not automatically better.
+##     θ = 120°     1 step (raw)  0.50     2 steps (half-angle)  0.87
+##                  4 steps       0.97     6 steps               0.985
 ##
-## install() returns the [child_bone, helper_bone] pairs; the caller MUST drive
-## them every frame from inside the skeleton's modification pass (see
+## Nothing is scaled and nothing is snapped rigid — the limb is simply
+## articulated finely enough that averaging no longer eats it. This is why the
+## fix is more joints rather than volume-correction: a bone scale fattens every
+## vertex on the bone whether it was collapsing or not (tried; it ballooned parts
+## of the thigh to 167% while the worst vertices stayed put).
+##
+## KNEES ONLY. Hip and ankle helpers were tried twice and measured worse both
+## times — the hip swings rather than folds, so it was adding a blend for
+## nothing, and it dragged the skirt down with it (0.80 -> 0.72). Re-measure
+## before adding a joint here.
+##
+## install() returns [child_bone, helper_bone, fraction] triples; the caller MUST
+## drive them every frame from inside the skeleton's modification pass (see
 ## SkinnedPlayerModel.ShooterPoseModifier). A helper that is not updated in step
 ## with its child deforms the limb instead of saving it.
 
-## [parent, child] per joint, both sides. The helper is parented to `parent` and
-## takes `child`'s rest transform.
+## [parent, child] per joint, both sides.
 const JOINTS := [
 	["DEF-thigh.L", "DEF-shin.L"], ["DEF-thigh.R", "DEF-shin.R"],
 ]
+## Angular steps through each joint. 4 leaves at most a quarter of the bend for
+## any one vertex to blend across, which is a ~3% collapse at a hard tuck.
+const SEGMENTS := 4
 ## A vertex needs at least this much of BOTH bones before it is worth moving.
 const MIN_BLEND := 0.02
-## Joints are for the LIMB only. A helper is driven to half its child's swing,
-## which is right for a thigh but wrong for a skirt — cloth wants to hang from
-## the hips, not follow half a leg swing. Moving skirt vertices onto the hip
-## helper measurably made them worse (0.80 -> 0.72), so anything hanging clear
-## of the leg's own bone chain by more than this is left alone.
-const LIMB_HINTS := ["DEF-thigh", "DEF-shin", "DEF-foot", "DEF-toe"]
+## And the joint must hold at least this share of the vertex overall, or it is a
+## stray cross-body influence rather than the joint this vertex belongs to.
+const DOMINANT_SHARE := 0.5
 
 
-## Returns an Array of [child_bone_idx, helper_bone_idx].
+## Returns an Array of [child_bone_idx, helper_bone_idx, fraction].
 static func install(root: Node, skeleton: Skeleton3D) -> Array:
 	if skeleton == null:
 		return []
 	var driven: Array = []
-	# child bone -> [helper bone, parent bone]
-	var helper_of_child := {}
+	# child bone -> [parent bone, [helper bones, inner first]]
+	var joint_helpers := {}
 	for joint in JOINTS:
 		var parent := skeleton.find_bone(joint[0])
 		var child := skeleton.find_bone(joint[1])
 		if parent < 0 or child < 0:
 			continue
-		var hname: String = "HELPER-" + joint[1]
-		if skeleton.find_bone(hname) >= 0:
+		if skeleton.find_bone("HELPER1-" + joint[1]) >= 0:
 			continue  # already installed
+		var helpers: Array = []
+		for step in range(1, SEGMENTS):
+			var hname: String = "HELPER%d-%s" % [step, joint[1]]
 			skeleton.add_bone(hname)
 			var h := skeleton.find_bone(hname)
 			skeleton.set_bone_parent(h, parent)
-		# Same rest as the child, so "half the child's local rotation" lands the
-		# helper exactly halfway through the bend.
+			# Same rest as the child, so "this fraction of the child's local
+			# rotation" lands the helper at that fraction of the bend.
 			skeleton.set_bone_rest(h, skeleton.get_bone_rest(child))
 			skeleton.reset_bone_pose(h)
-		helper_of_child[child] = [h, parent]
-		driven.append([child, h])
+			helpers.append(h)
+			driven.append([child, h, float(step) / float(SEGMENTS)])
+		joint_helpers[child] = [parent, helpers]
 	if driven.is_empty():
 		return []
 
@@ -82,14 +88,14 @@ static func install(root: Node, skeleton: Skeleton3D) -> Array:
 			continue
 		if mi.mesh.get_blend_shape_count() > 0:
 			continue  # rebuilding would drop the blend shapes
-		_reweight(mi, skeleton, helper_of_child, chain_l, chain_r, limb_radius)
+		_reweight(mi, skeleton, joint_helpers, chain_l, chain_r, limb_radius)
 	return driven
 
 
 ## Rest-pose joints down one leg, as a polyline for limb-membership tests.
 static func _leg_chain(skeleton: Skeleton3D, suffix: String) -> PackedVector3Array:
 	var out := PackedVector3Array()
-	for stem in LIMB_HINTS:
+	for stem in ["DEF-thigh", "DEF-shin", "DEF-foot", "DEF-toe"]:
 		var i := skeleton.find_bone(stem + suffix)
 		if i >= 0:
 			out.append(skeleton.get_bone_global_rest(i).origin)
@@ -108,27 +114,14 @@ static func _dist_to_chain(p: Vector3, chain: PackedVector3Array) -> float:
 
 
 ## Drive the helpers. MUST run inside the skeleton's modification pass.
-##
-## Two things happen per joint:
-##
-##   ROTATION — the helper takes half the child's bend, so no vertex ever blends
-##   across the full angle.
-##
-## Scaling the helper to widen the joint back out was tried and removed. The
-## geometry is right — a blend across θ thins by cos(θ/2), which is |q.w| — but a
-## BONE scale is far too blunt an instrument for it: it fattens every vertex on
-## the helper regardless of whether that vertex was collapsing, which ballooned
-## parts of the thigh to 167% while the worst-collapsing vertices (which are not
-## on the helper at all) did not move off 0.83. Per-vertex correction is what
-## that idea needs, and a bone cannot express it.
 static func update(skeleton: Skeleton3D, driven: Array) -> void:
 	for d in driven:
-		skeleton.set_bone_pose_rotation(d[1],
-			Quaternion.IDENTITY.slerp(skeleton.get_bone_pose_rotation(d[0]), 0.5))
+		skeleton.set_bone_pose_rotation(d[1], Quaternion.IDENTITY.slerp(
+			skeleton.get_bone_pose_rotation(d[0]), d[2]))
 
 
 static func _reweight(mi: MeshInstance3D, skeleton: Skeleton3D,
-		helper_of_child: Dictionary, chain_l: PackedVector3Array,
+		joint_helpers: Dictionary, chain_l: PackedVector3Array,
 		chain_r: PackedVector3Array, limb_radius: float) -> void:
 	var skin: Skin = mi.skin
 	var bone_of := {}
@@ -141,19 +134,22 @@ static func _reweight(mi: MeshInstance3D, skeleton: Skeleton3D,
 	for b in skin.get_bind_count():
 		bind_of_bone[bone_of[b]] = b
 
-	# One bind per helper, sharing the child's bind pose — their global rests
-	# are identical, so the inverse-bind matrix is the same.
-	# joint list of [parent_bind, child_bind, helper_bind]
+	# Per joint: the ordered bind chain parent -> helpers -> child. Helpers share
+	# the child's bind pose because their global rests are identical.
 	var jobs: Array = []
-	for child in helper_of_child:
-		var helper: int = helper_of_child[child][0]
-		var parent: int = helper_of_child[child][1]
+	for child in joint_helpers:
+		var parent: int = joint_helpers[child][0]
+		var helpers: Array = joint_helpers[child][1]
 		if not bind_of_bone.has(child) or not bind_of_bone.has(parent):
 			continue
 		var child_bind: int = bind_of_bone[child]
-		skin.add_named_bind(skeleton.get_bone_name(helper),
+		var chain: Array = [bind_of_bone[parent]]
+		for h in helpers:
+			skin.add_named_bind(skeleton.get_bone_name(h),
 				skin.get_bind_pose(child_bind))
-		jobs.append([bind_of_bone[parent], child_bind, skin.get_bind_count() - 1])
+			chain.append(skin.get_bind_count() - 1)
+		chain.append(child_bind)
+		jobs.append(chain)
 	if jobs.is_empty():
 		return
 
@@ -191,15 +187,28 @@ static func _reweight_surface(arrays: Array, jobs: Array,
 	var touched := 0
 
 	for v in verts.size():
-		# NO limb-radius gate here. It was added to keep a hip helper off the
-		# skirt, and with knees only there is nothing to protect against — but
-		# it does exclude the outside of the knee, which sits further from the
-		# bone axis than the limb radius and is exactly what needs helping
-		# (measured: gating it put the knee back to 0.50).
-		for job in jobs:
-			var parent_bind: int = job[0]
-			var child_bind: int = job[1]
-			var helper_bind: int = job[2]
+		# Cloth is not a limb. The gate is generous — the outside of a knee sits
+		# further from the bone axis than the limb radius and DOES need helping —
+		# but without it the skirt and the outer boot flare get bound to a knee
+		# helper and swing with the shin.
+		if minf(_dist_to_chain(verts[v], chain_l),
+				_dist_to_chain(verts[v], chain_r)) > limb_radius * 1.6:
+			continue
+		# Pick the joint this vertex most belongs to — the chain holding the most
+		# of its weight — NOT merely the first chain that matches.
+		#
+		# Taking the first match bound right-thigh vertices that still carried a
+		# little residual left-leg weight to the LEFT knee's helpers, which then
+		# dragged them across the body: measured worst 0.46, and no amount of
+		# extra subdivision touched it because the vertex was on the wrong
+		# joint entirely.
+		var best_chain: Array = []
+		var best_kp := -1
+		var best_kc := -1
+		var best_total := 0.0
+		for chain in jobs:
+			var parent_bind: int = chain[0]
+			var child_bind: int = chain[chain.size() - 1]
 			var k_parent := -1
 			var k_child := -1
 			for k in per:
@@ -212,26 +221,30 @@ static func _reweight_surface(arrays: Array, jobs: Array,
 				continue
 			var w_parent: float = weights[v * per + k_parent]
 			var w_child: float = weights[v * per + k_child]
-			var m: float = minf(w_parent, w_child)
-			if m < MIN_BLEND:
+			if minf(w_parent, w_child) < MIN_BLEND:
 				continue
-			# Move 2m onto the helper, taking m from each side. The slot whose
-			# weight falls to zero is reused, so no extra influence slot is
-			# needed and the weights still sum to exactly 1.
-			if w_parent <= w_child:
-				bones[v * per + k_parent] = helper_bind
-				weights[v * per + k_parent] = 2.0 * m
-				weights[v * per + k_child] = w_child - m
-			else:
-				bones[v * per + k_child] = helper_bind
-				weights[v * per + k_child] = 2.0 * m
-				weights[v * per + k_parent] = w_parent - m
+			var total: float = w_parent + w_child
+			if total > best_total:
+				best_total = total
+				best_chain = chain
+				best_kp = k_parent
+				best_kc = k_child
+		# The joint must genuinely own this vertex. Below this it is a stray
+		# cross-body influence, and re-binding it would pull the mesh across.
+		if best_chain.is_empty() or best_total < DOMINANT_SHARE:
+			continue
+		# How far through the joint the vertex sits, then hand it to the two
+		# ADJACENT bones either side of that point. Its widest blend is now one
+		# segment instead of the whole joint.
+		var w_c: float = weights[v * per + best_kc]
+		var pos: float = (w_c / best_total) * float(SEGMENTS)
+		var lo: int = clampi(int(floor(pos)), 0, SEGMENTS - 1)
+		var frac: float = clampf(pos - float(lo), 0.0, 1.0)
+		bones[v * per + best_kp] = best_chain[lo]
+		weights[v * per + best_kp] = best_total * (1.0 - frac)
+		bones[v * per + best_kc] = best_chain[lo + 1]
+		weights[v * per + best_kc] = best_total * frac
 		touched += 1
-			# ONE joint per vertex. Falling through to the next job would read
-			# the bones this one just rewrote and move the vertex twice, which
-			# corrupts the blend rather than halving it (measured: the knee got
-			# worse, 0.80 -> 0.50, purely from cascading).
-			break
 	if touched > 0:
 		arrays[Mesh.ARRAY_BONES] = bones
 		arrays[Mesh.ARRAY_WEIGHTS] = weights

characters/skin_leg_repair.gd

@@ -255,12 +255,14 @@ static func _repair_surface(arrays: Array, side: PackedInt32Array,
 			# is left blended so it can keep draping.
 			var dl: float = _dist_to_chain(verts[v], chain_l)
 			var dr: float = _dist_to_chain(verts[v], chain_r)
-			var near: float = minf(dl, dr)
-			var far: float = maxf(dl, dr)
-			if near > limb_radius or far < near * 1.25:
-				continue  # drapes over both, or hugs neither — leave it alone
-			keep = -1 if dl < dr else 1
-			vside[v] = keep
+			if minf(dl, dr) > limb_radius:
+				continue  # hugs neither chain — cloth, leave it alone
+			# Side comes from WEIGHT, not from which chain is nearer. An earlier
+			# version also demanded one chain be 1.25x closer than the other,
+			# which skipped everything near the centre line — and that is exactly
+			# where the damage was: inner-thigh vertices kept 21% of the OPPOSITE
+			# leg and were torn apart when the legs split (measured 0.46). A limb
+			# vertex belongs to whichever leg actually drives it.
 		# Drop the losing leg's influence and renormalise what remains.
 		var total := 0.0
 		for k in per:
@@ -310,7 +312,46 @@ static func _repair_surface(arrays: Array, side: PackedInt32Array,
 				weights[v * per + k] /= sum
 		snapped += 1
 
-	# Step 3 — drop triangles that still span the legs below the knee.
+	# Step 3 — belt and braces: NO vertex that sits on a limb may carry any
+	# weight from the opposite leg, at any height. The staged rules above each
+	# have their own guards and between them they were still letting inner-thigh
+	# vertices through with ~20% of the far leg, which tears them apart when the
+	# legs split (measured 0.46 — the worst collapse left on the model). This is
+	# unconditional and runs last so nothing can reintroduce it.
+	for v in verts.size():
+		var near_l: float = _dist_to_chain(verts[v], chain_l)
+		var near_r: float = _dist_to_chain(verts[v], chain_r)
+		# Generous radius: the limb radius is measured from the bone AXIS, so a
+		# vertex on the front or back of a thigh clears it easily, and those were
+		# exactly the ones slipping through with opposite-leg weight. The skirt
+		# hangs far enough out to stay outside even this.
+		if minf(near_l, near_r) > limb_radius * 1.6:
+			continue  # cloth
+		var own: int = -1 if near_l < near_r else 1
+		# Prefer the leg that actually drives it; fall back to the nearer chain.
+		var wl2 := 0.0
+		var wr2 := 0.0
+		for k in per:
+			match side[bones[v * per + k]]:
+				-1: wl2 += weights[v * per + k]
+				1: wr2 += weights[v * per + k]
+		if maxf(wl2, wr2) > 0.0:
+			own = -1 if wl2 >= wr2 else 1
+		if minf(wl2, wr2) <= 0.0:
+			continue  # already single-legged
+		var tot := 0.0
+		for k in per:
+			var b2: int = bones[v * per + k]
+			if side[b2] != 0 and side[b2] != own:
+				weights[v * per + k] = 0.0
+			tot += weights[v * per + k]
+		if tot > 0.0:
+			for k in per:
+				weights[v * per + k] /= tot
+		vside[v] = own
+		snapped += 1
+
+	# Step 4 — drop triangles that still span the legs below the knee.
 	var removed := 0
 	if not idx.is_empty():
 		var keep_idx := PackedInt32Array()