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Add highly experimental b3d to glTF conversion

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Lars Mueller 2023-02-26 18:35:43 +01:00
parent f225499795
commit f7d2b005e1
1 changed files with 495 additions and 3 deletions
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498
b3d.lua
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@ -1,10 +1,12 @@
-- Localize globals
local assert, error, math, modlib, next, ipairs, pairs, setmetatable, string_char, table
= assert, error, math, modlib, next, ipairs, pairs, setmetatable, string.char, table
local assert, error, math, minetest, modlib, next, ipairs, pairs, setmetatable, string_char, table
= assert, error, math, minetest, modlib, next, ipairs, pairs, setmetatable, string.char, table
local mat4 = modlib.matrix4
local read_int, read_single = modlib.binary.read_int, modlib.binary.read_single
local write_int, write_single = modlib.binary.write_int, modlib.binary.write_single
local write_int, write_uint, write_single = modlib.binary.write_int, modlib.binary.write_uint, modlib.binary.write_single
local fround = modlib.math.fround
@ -534,6 +536,496 @@ function write(self, stream)
end
end
-- B3D to glTF converter
-- See https://registry.khronos.org/glTF/specs/2.0/glTF-2.0.html
--! Highly experimental; expect bugs!
do
-- glTF constants
local array_buffer = 34962 -- "Buffer containing vertex attributes, such as vertices, texcoords or colors."
local element_array_buffer = 34963 -- "Buffer used for element indices."
local component_type = {
signed_byte = 5120,
unsigned_byte = 5121,
signed_short = 5122,
unsigned_short = 5123,
unsigned_int = 5125,
float = 5126,
}
-- Coordinate system conversions:
-- "Blitz 3D uses a left-handed system: X+ is to the right. Y+ is up. Z+ is forward."
-- "glTF uses a right-handed coordinate system. glTF defines +Y as up, +Z as forward, and -X as right;
-- the front of a glTF asset faces +Z."
local function translation_to_gltf(vec)
return {-vec[1], vec[2], vec[3]} -- invert the X-axis
end
local function quaternion_to_gltf(quat)
-- TODO (!) is this correct?
return {-quat[1], quat[2], quat[3], quat[4]} -- invert the X-axis
end
-- Convert a color from table format to glTF RGBA list format
local function color_to_gltf(col)
return {col.r, col.g, col.b, col.a}
end
-- Basic helpers for writing to the buffer, all parameterized in terms of `write_byte`
local function write_index(write_byte, index)
write_uint(write_byte, index - 1 --[[1-based to 0-based]], 4)
end
local function write_float(write_byte, float)
assert(-math.huge < float and float < math.huge)
assert(-math.huge < fround(float) and fround(float) < math.huge, ("%.18g got %.18g"):format(float, fround(float)))
write_single(write_byte, fround(float))
end
local function write_floats(write_byte, floats, expected_len)
assert(#floats == expected_len)
for i = 1, expected_len do
write_float(write_byte, floats[i])
end
end
local function write_vector(write_byte, vec)
return write_floats(write_byte, vec, 3)
end
local function write_translation(write_byte, vec)
return write_vector(write_byte, translation_to_gltf(vec))
end
local function write_quaternion(write_byte, quat)
-- XYZW order is already correct, but we still need to convert left-handed to right-handed
return write_floats(write_byte, quaternion_to_gltf(quat), 4)
end
function to_gltf(self)
-- Accessor helper: Stores arrays of raw data in a buffer, produces views & accessors.
-- Everything is dumped in the same large buffer.
local buffer_rope = {} -- buffer content (table of strings)
local buffer_views = {} -- glTF buffer views
local accessors = {} -- glTF accessors
local offset = 0 -- current byte offset
local function add_accessor(
type, -- name of the composite type (e.g. SCALAR, VEC3, VEC4, MAT4, ...)
comp_type, -- name of the component type (e.g. float, unsigned_int, ...)
index, -- true / false / nil: whether this is an index (true) or vertex data (false) or neither (nil)
func -- `function(write_byte) ... return count, min, max end` to be called to write to the buffer view;
-- the count of elements written must be returned; min and max may be returned
)
local bytes_written = 0
local count, min, max = func(function(byte)
table.insert(buffer_rope, string_char(byte))
bytes_written = bytes_written + 1
end)
assert(count)
-- Add buffer view
table.insert(buffer_views, {
buffer = 0, -- 0-based - there only is one buffer
byteOffset = offset,
byteLength = bytes_written,
target = ((index == true) and element_array_buffer) -- index data
or ((index == false) and array_buffer) -- vertex data
or nil, -- no target hint
})
table.insert(accessors, {
bufferView = #buffer_views - 1, -- 0-based
byteOffset = 0, -- view has correct offset
componentType = assert(component_type[comp_type]),
type = type,
count = count,
min = min,
max = max,
})
offset = offset + bytes_written
return #accessors - 1 -- 0-based index of the accessor
end
local textures = {} -- glTF textures
local function add_texture(name)
-- TODO (?) add an appropriate sampler
table.insert(textures, {name = name})
return #textures - 1 -- 0-based texture index
end
for _, tex in ipairs(self.textures) do
-- Assert that all values we don't map properly yet are defaults
-- TODO dig into Blitz3D sources to figure out the meaning of flags & blend
-- TODO (...) deal with flag value of 65536:
-- "The flags field value can conditional an additional flag value of '65536'.
-- This is used to indicate that the texture uses secondary UV values, ala the TextureCoords command."
assert(tex.flags == 1) -- TODO (?) see https://github.com/blitz-research/blitz3d/blob/master/gxruntime/gxcanvas.h#L59
assert(tex.blend == 2)
-- Assert that the texture isn't transformed
assert(tex.rotation == 0)
assert(tex.pos[1] == 0 and tex.pos[2] == 0)
assert(tex.scale[1] == 1 and tex.scale[2] == 1)
add_texture(tex.file)
end
-- Map brushes to materials (& textures)
local materials = {}
for i, brush in ipairs(self.brushes) do
-- Assert defaults
-- See https://github.com/blitz-research/blitz3d/blob/6beb288cb5962393684a59a4a44ac11524894939/blitz3d/brush.cpp#L164-L167:
-- 0 = default/replace, 1 = alpha, 2 = multiply, 3 = add
assert(brush.blend == 1) -- (alpha)
-- TODO (...) figure out what these "effects" are and if/how to map them to glTF
assert(brush.fx == 0)
assert(#brush.texture_id <= 1) -- TODO (...) this supports only a single texture per brush for now
local index
if brush.texture_id[1] then
index = brush.texture_id[1] -- 0-based
else
-- Implementations seem to implicitly assume textures for brushes
index = add_texture(brush.name)
end
materials[i] = {
name = brush.name,
alphaMode = "BLEND",
pbrMetallicRoughness = {
baseColorFactor = color_to_gltf(brush.color),
metallicFactor = brush.shininess, -- TODO (?) are these really equivalent?
-- Add texture if there is none
baseColorTexture = {
index = index,
-- `texCoord = 0` is the default already, no need to set it
},
},
}
end
local meshes = {}
local function add_mesh(mesh, weights)
local attributes = {}
local vertices = mesh.vertices
attributes.POSITION = add_accessor("VEC3", "float", false, function(write_byte)
local inf = math.huge
local min_pos, max_pos = {inf, inf, inf}, {-inf, -inf, -inf}
for _, vertex in ipairs(mesh.vertices) do
local pos = translation_to_gltf(vertex.pos)
write_vector(write_byte, pos)
min_pos = modlib.vector.combine(min_pos, pos, math.min)
max_pos = modlib.vector.combine(max_pos, pos, math.max)
end
return #mesh.vertices, min_pos, max_pos -- vertex accessors MUST provide min & max
end)
local has_normals = vertices.flags % 2 == 1 -- lowest bit set?
if has_normals then
attributes.NORMAL = add_accessor("VEC3", "float", false, function(write_byte)
for _, vertex in ipairs(mesh.vertices) do
write_translation(write_byte, vertex.normal)
end
return #mesh.vertices
end)
end
local has_colors = vertices.flags % 4 >= 2 -- second lowest bit set?
if has_colors then
attributes.COLOR_0 = add_accessor("VEC4", "float", false, function(write_byte)
for _, vertex in ipairs(mesh.vertices) do
write_floats(write_byte, color_to_gltf(vertex.color), 4)
end
return #mesh.vertices
end)
end
if vertices.tex_coord_sets >= 1 then
assert(vertices.tex_coord_set_size == 2)
for tex_coord_set = 1, vertices.tex_coord_sets do
local tcs_id = tex_coord_set - 1 -- 0-based
attributes[("TEXCOORD_%d"):format(tcs_id)] = add_accessor("VEC2", "float", false, function(write_byte)
for _, vertex in ipairs(mesh.vertices) do
write_floats(write_byte, vertex.tex_coords[tex_coord_set], 2)
end
return #mesh.vertices
end)
end
end
if next(weights) ~= nil then
-- Count (& pack into list) joints influencing vertices, normalize weights
local max_count = 0
local joint_ids = {}
local normalized_weights = {}
for vertex_id, joint_weights in pairs(weights) do
local total_weight = 0
local count = 0
for _, weight in pairs(joint_weights) 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)
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
local set_id = math.floor(set_start / 4) -- 0-based => floor rather than ceil
-- Write the joint IDs
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
if weight == 0 then
id = 0 -- required by the glTF spec
end
write_uint(write_byte, id, 2)
end
end
return #mesh.vertices
end)
-- Write the corresponding weights
attributes[("WEIGHTS_%d"):format(set_id)] = add_accessor("VEC4", "float", false, function(write_byte)
for vertex_id in ipairs(mesh.vertices) do
for i = set_start, set_start + 3 do
local weight = (normalized_weights[vertex_id] or {})[i] or 0
write_float(write_byte, weight)
end
end
return #mesh.vertices
end)
end
end
-- Write the indices per triangle set
local primitives = {}
for i, triangle_set in ipairs(mesh.triangle_sets) do
local index_accessor = add_accessor("SCALAR", "unsigned_int", true, function(write_byte)
for _, tri in ipairs(triangle_set.vertex_ids) do
-- Flip winding order due to the coordinate system transformation
-- TODO (!) is this correct?
for j = 3, 1, -1 do
write_index(write_byte, tri[j])
end
end
return 3 * #triangle_set.vertex_ids
end)
-- Each triangle set is equivalent to one glTF "primitive"
primitives[i] = {
attributes = attributes,
indices = index_accessor,
material = (triangle_set.brush_id or mesh.brush_id) - 1, -- 0-based
-- `mode = 4` (triangles) is the default already, no need to set it
}
end
table.insert(meshes, {primitives = primitives})
return #meshes - 1 -- 0-based
end
-- glTF lists
local nodes = {}
local skins = {}
local samplers = {}
local channels = {}
local function add_node(
node, -- b3d node to add
bind_mat, -- bind matrix of the parent bone (may be `nil` if none)
fps, -- fps of the parent bone (may be `nil` if none)
anim -- shared animation of the parent mesh
)
table.insert(nodes, false) -- HACK first insert a placeholder to get a fixed ID
local node_id = #nodes - 1 -- 0-indexed <=> before `table.insert`!
-- Animation (speed)?
fps = node.animation and node.animation.fps or fps
-- Keyframes?
if node.keys then
-- Convert from a list of keyframes of three overrides to three lists of channels
local targets = {
translation = {output_type = "VEC3", b3d_field = "position", write_value = write_translation},
scale = {output_type = "VEC3", b3d_field = "scale", write_value = write_vector},
rotation = {output_type = "VEC4", b3d_field = "rotation", write_value = write_quaternion}
}
for _, keyframe in ipairs(node.keys) do
local frame = keyframe.frame
for _, target in pairs(targets) do
local value = keyframe[target.b3d_field]
if value then
table.insert(target, {frame = frame, value = value})
end
end
end
for target, keyframes in pairs(targets) do
if #keyframes > 0 then
-- Write input (timestamps)
local input = add_accessor("SCALAR", "float", nil, function(write_byte)
local min, max = math.huge, -math.huge
for _, keyframe in ipairs(keyframes) do
local sec = keyframe.frame / (fps or 60) -- convert frames to seconds; default FPS is 60
write_float(write_byte, sec)
min, max = math.min(min, sec), math.max(max, sec)
end
return #keyframes, {min}, {max} -- min and max are mandatory
end)
-- Write output (overrides)
local output = add_accessor(keyframes.output_type, "float", nil, function(write_byte)
for _, keyframe in ipairs(keyframes) do
keyframes.write_value(write_byte, keyframe.value)
end
return #keyframes
end)
table.insert(samplers, {
input = input,
output = output,
-- interpolation default is already linear, matching b3d
})
table.insert(channels, {
sampler = #samplers - 1, -- 0-based
target = {
node = node_id,
path = target,
}
})
end
end
end
if node.mesh then
-- Initialize skeletal animation
assert(not anim)
anim = {
weights = {},
joints = {},
inv_bind_mats = {},
}
end
if node.bone then
local joint_id = #anim.joints
table.insert(anim.joints, node_id)
-- "To compose the local transformation matrix, TRS properties MUST be converted to matrices and postmultiplied in
-- the T * R * S order; first the scale is applied to the vertices, then the rotation, and then the translation."
local translation = translation_to_gltf(node.position)
local rotation = modlib.quaternion.normalize(quaternion_to_gltf(node.rotation))
local scale = node.scale
local loc_trans_mat = mat4.scale(scale)
:compose(mat4.rotation(rotation))
:compose(mat4.translation(translation))
-- Compute a proper inverse bind matrix as the inverse of the product of the transformation matrices
-- along the path from the root (the mesh) to the current node (the bone).
-- See e.g. https://stackoverflow.com/questions/17127994/opengl-bone-animation-why-do-i-need-inverse-of-bind-pose-when-working-with-gp
-- https://computergraphics.stackexchange.com/questions/7603/confusion-about-how-inverse-bind-pose-is-actually-calculated-and-used
bind_mat = bind_mat and bind_mat:multiply(loc_trans_mat) or loc_trans_mat
table.insert(anim.inv_bind_mats, bind_mat:inverse())
-- Insert into reverse lookup `anim.weights[vertex_id][joint_id] = weight`
-- such that writing the mesh can then write the weights per vertex
for vertex_id, weight in pairs(node.bone) do
if weight > 0 then
anim.weights[vertex_id] = anim.weights[vertex_id] or {}
anim.weights[vertex_id][joint_id] = weight
end
end
end
local children = {}
for _, child in ipairs(node.children) do
table.insert(children, add_node(child, bind_mat, fps, anim))
end
local mesh, skin_id
if node.mesh then
mesh = add_mesh(node.mesh, anim.weights)
if anim.joints and anim.joints[1] then
table.insert(skins, {
inverseBindMatrices = add_accessor("MAT4", "float", nil, function(write_byte)
for _, inv_bind_mat in ipairs(anim.inv_bind_mats) do
assert(#inv_bind_mat == 4)
-- glTF uses column-major order (we use row-major order)
for i = 1, 4 do
for j = 1, 4 do
write_float(write_byte, inv_bind_mat[j][i])
end
end
end
return #anim.inv_bind_mats
end),
joints = anim.joints,
skeleton = anim.joints[1],
})
skin_id = #skins - 1 -- 0-based
end
end
-- Now replace the placeholder
nodes[node_id + 1 --[[0-based to 1-based]]] = {
name = node.name,
mesh = mesh,
skin = skin_id,
children = children[1] and children, -- glTF does not allow empty lists
translation = translation_to_gltf(node.position),
scale = node.scale,
rotation = quaternion_to_gltf(node.rotation),
}
return node_id -- 0-based
end
local scene, scenes
if self.node then
scene, scenes = 0, {{nodes = {add_node(self.node)}}}
end
local buffer_string = table.concat(buffer_rope)
return {
asset = {
generator = "modlib b3d:to_gltf",
version = "2.0"
},
-- Textures
textures = textures[1] and textures, -- glTF does not allow empty lists
materials = materials,
-- Accessors, buffer views & buffers
accessors = accessors,
bufferViews = buffer_views,
buffers = {
{
byteLength = #buffer_string,
uri = "data:application/octet-stream;base64,"
.. assert(minetest.encode_base64, "b3d:to_gltf needs `minetest.encode_base64`!")(buffer_string)
},
},
-- Meshes & nodes
meshes = meshes,
nodes = nodes,
-- A scene is not strictly needed but is useful for getting rid of validator warnings & having a proper root defined
scene = scene,
scenes = scenes,
-- Animation
skins = skins,
-- B3D only contains (up to) a single animation
animations = channels[1] and {
{
channels = channels,
samplers = samplers,
},
},
}
end
end
function write_gltf(self, file)
modlib.json:write_file(self:to_gltf(), file)
end
local binary_search_frame = modlib.table.binary_search_comparator(function(a, b)
return modlib.table.default_comparator(a, b.frame)
end)