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b3d -> glTF: Fix handling of static vertices in animated meshes

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Introduces a "neutral bone" to attach static vertices to.
This commit is contained in:
Lars Mueller 2023-04-02 14:52:57 +02:00
parent 88fec749f5
commit fc0585e86c
1 changed files with 53 additions and 14 deletions
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67
b3d.lua
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@ -705,7 +705,7 @@ do
end
local meshes = {}
local function add_mesh(mesh, weights)
local function add_mesh(mesh, weights, add_neutral_bone)
local attributes = {}
local vertices = mesh.vertices
@ -761,6 +761,7 @@ do
local max_count = 0
local joint_ids = {}
local normalized_weights = {}
-- Handle (supposedly) animated/dynamic vertices (can still be static by having zero weights)
for vertex_id, joint_weights in pairs(weights) do
local total_weight = 0
local count = 0
@ -768,13 +769,26 @@ do
total_weight = total_weight + weight
count = count + 1
end
joint_ids[vertex_id] = {}
normalized_weights[vertex_id] = {}
for joint, weight in pairs(joint_weights) do
table.insert(joint_ids[vertex_id], joint)
table.insert(normalized_weights[vertex_id], weight / total_weight)
if total_weight > 0 then -- animated?
joint_ids[vertex_id] = {}
normalized_weights[vertex_id] = {}
for joint, weight in pairs(joint_weights) do
table.insert(joint_ids[vertex_id], joint)
table.insert(normalized_weights[vertex_id], weight / total_weight)
end
max_count = math.max(max_count, count)
end
end
-- Now search for static vertices
for vertex_id in ipairs(mesh.vertices) do
if not joint_ids[vertex_id] then
-- Vertex isn't influenced by any bones => Add a dummy neutral bone to influence this vertex
-- See https://github.com/KhronosGroup/glTF/issues/2269
-- and https://github.com/KhronosGroup/glTF-Blender-IO/pull/1552/
joint_ids[vertex_id] = {add_neutral_bone()}
normalized_weights[vertex_id] = {1}
max_count = math.max(max_count, 1) -- it is (theoretically) possible that all vertices are static
end
max_count = math.max(max_count, count)
end
assert(max_count > 0) -- TODO (?) warning for max_count > 4
for set_start = 1, max_count, 4 do -- Iterate sets of 4 bones
@ -783,9 +797,10 @@ do
attributes[("JOINTS_%d"):format(set_id)] = add_accessor("VEC4", "unsigned_short", false, function(write_byte)
for vertex_id in ipairs(mesh.vertices) do
for i = set_start, set_start + 3 do
assert(#normalized_weights[vertex_id] == #joint_ids[vertex_id])
local id = (joint_ids[vertex_id] or {})[i] or 0
local weight = (normalized_weights[vertex_id] or {})[i] or 0
local vrt_joint_ids, vrt_norm_weights = assert(joint_ids[vertex_id]), assert(normalized_weights[vertex_id])
assert(#vrt_joint_ids == #vrt_norm_weights)
local id = vrt_joint_ids[i] or 0
local weight = vrt_norm_weights[i] or 0
if weight == 0 then
id = 0 -- required by the glTF spec
end
@ -955,10 +970,33 @@ do
for _, child in ipairs(node.children) do
table.insert(children, add_node(child, bind_mat, fps, anim))
end
local mesh, skin_id
local mesh, skin_id, neutral_node_id
if node.mesh then
mesh = add_mesh(node.mesh, anim.weights)
local neutral_joint_id
-- Lazily adds a placeholder for the neutral joint, returns joint ID
local function add_neutral_joint()
if neutral_joint_id then
return neutral_joint_id
end
neutral_node_id = #nodes -- 0-based
table.insert(nodes, {
name = "neutral_bone",
-- We need to flip the hierarchy: The neutral bone must be a parent of the mesh root;
-- if it were a sibling, there would be no common skeleton root (accepted by Blender but not by glTF validator);
-- if it were a child, transformations of the mesh root would affect it and it wouldn't be a neutral bone anymore.
children = {node_id},
-- translation, scale, rotation all default to identity
})
neutral_joint_id = #anim.joints -- 0-based
table.insert(anim.joints, neutral_node_id)
return neutral_joint_id -- 0-based
end
mesh = add_mesh(node.mesh, anim.weights, add_neutral_joint)
if anim.joints and anim.joints[1] then
if neutral_joint_id then
-- Duplicate the inverse bind matrix of the parent (which the neutral bone will be a child of)
table.insert(anim.inv_bind_mats, bind_mat or mat4.identity())
end
table.insert(skins, {
inverseBindMatrices = add_accessor("MAT4", "float", nil, function(write_byte)
for _, inv_bind_mat in ipairs(anim.inv_bind_mats) do
@ -973,7 +1011,7 @@ do
return #anim.inv_bind_mats
end),
joints = anim.joints,
skeleton = node_id,
skeleton = neutral_node_id, -- make the neutral bone the skeleton root
})
skin_id = #skins - 1 -- 0-based
end
@ -988,7 +1026,8 @@ do
scale = node.scale,
rotation = quaternion_to_gltf(node.rotation),
}
return node_id -- 0-based
-- If a neutral bone exists, return the neutral bone (which has the node as a child) instead of the node
return neutral_node_id or node_id -- 0-based
end
local scene, scenes