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Gltf transformation matrix #16

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Merged
Jannik-Hm merged 3 commits into from
Dec 2, 2025
Merged

Gltf transformation matrix #16

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23c261d
extended Mesh Add() to take multiple meshes
Jannik-Hm Dec 2, 2025
4519674
respect transformation matrix inside gltf + combine all gltf meshes i…
Jannik-Hm Dec 2, 2025
bcfabf2
fixed elements in gltf transformation matrix being mixed up
Jannik-Hm Dec 2, 2025
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4 changes: 2 additions & 2 deletions main.go
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Original file line number Diff line number Diff line change
Expand Up @@ -26,16 +26,16 @@ func LoadPrimitives() error {
// Note: requires LoadPrimitives() to be run beforehand if you want to get a primitive
func GetModel(conf ModelReaderConf, desiredSize *MeshTypes.Vector) (*MeshTypes.Mesh, error) {
var mesh *MeshTypes.Mesh
var err error

if conf.File != nil && conf.Filename != nil && *conf.Filename != "" {
filetype := filepath.Ext(*conf.Filename)
switch filetype {
case ".gltf", ".glb":
meshes, err := FileHandlers.LoadGLTF(conf.File, desiredSize)
mesh, err = FileHandlers.LoadGLTF(conf.File, desiredSize)
if err != nil {
return nil, err
}
mesh = meshes[0]
case ".3ds":
data, err := io.ReadAll(conf.File)
if err != nil {
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6 changes: 4 additions & 2 deletions pkg/MeshTypes/mesh.go
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Original file line number Diff line number Diff line change
Expand Up @@ -21,8 +21,10 @@ func (obj *Mesh) Copy() Mesh {
return Mesh{Triangles: triangles}
}

func (obj *Mesh) Add(mesh *Mesh) *Mesh {
obj.Triangles = append(obj.Triangles, mesh.Triangles...)
func (obj *Mesh) Add(mesh ...*Mesh) *Mesh {
for _, element := range mesh {
obj.Triangles = append(obj.Triangles, element.Triangles...)
}
return obj
}

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81 changes: 61 additions & 20 deletions pkg/file_handlers/gltf.go
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Original file line number Diff line number Diff line change
Expand Up @@ -10,34 +10,67 @@ import (
"github.com/qmuntal/gltf"
)

func LoadGLTF(file io.Reader, desiredSize *Types.Vector) ([]*Types.Mesh, error) {
func LoadGLTF(file io.Reader, desiredSize *Types.Vector) (*Types.Mesh, error) {
var doc gltf.Document
gltf.NewDecoder(file).Decode(&doc)

var meshes []*Types.Mesh
var meshes *Types.Mesh = &Types.Mesh{}

for _, m := range doc.Meshes {
transformationMatrices := map[int]Types.Matrix{}

for _, node := range doc.Nodes {
if node.Mesh == nil {
continue
}
matrix := node.MatrixOrDefault()
transformationMatrices[*node.Mesh] = Types.Matrix{
X00: matrix[0], X01: matrix[4], X02: matrix[8], X03: matrix[12],
X10: matrix[1], X11: matrix[5], X12: matrix[9], X13: matrix[13],
X20: matrix[2], X21: matrix[6], X22: matrix[10], X23: matrix[14],
X30: matrix[3], X31: matrix[7], X32: matrix[11], X33: matrix[15],
}
}

// calculate outer dimensions
min := Types.Vector{}
max := Types.Vector{}
for meshindex, m := range doc.Meshes {
for _, p := range m.Primitives {
// contains Min and Max attr (for dimension calc)
posAccessor := doc.Accessors[p.Attributes[gltf.POSITION]]
scaling := Types.Vector{X: 1, Y: 1, Z: 1}
if desiredSize != nil {
scaling = Types.Vector{
// axes inverted to convert to correct coordinate system
X: desiredSize.X / (posAccessor.Max[0] - posAccessor.Min[0]),
Y: desiredSize.Y / (posAccessor.Max[2] - posAccessor.Min[2]),
Z: desiredSize.Z / (posAccessor.Max[1] - posAccessor.Min[1]),
}
}
positions, err := gltfVec3(&doc, posAccessor, scaling)
// do transformation before getting the outer dimensions
tempMin := transformationMatrices[meshindex].MulPosition(Types.Vector{
X: posAccessor.Min[0],
Y: posAccessor.Min[2],
Z: posAccessor.Min[1],
})
tempMax := transformationMatrices[meshindex].MulPosition(Types.Vector{
X: posAccessor.Max[0],
Y: posAccessor.Max[2],
Z: posAccessor.Max[1],
})
min = min.Min(&tempMin)
max = max.Max(&tempMax)
}
}

scaling := Types.Vector{X: 1, Y: 1, Z: 1}
if desiredSize != nil {
scaling = desiredSize.Div(max.Sub(min))
}

for meshindex, m := range doc.Meshes {
for _, p := range m.Primitives {
posAccessor := doc.Accessors[p.Attributes[gltf.POSITION]]
positions, err := gltfVec3(&doc, posAccessor, transformationMatrices[meshindex], scaling)
if err != nil {
return nil, err
}

var normals []Types.Vector
if nIdx, ok := p.Attributes[gltf.NORMAL]; ok {
normalAccessor := doc.Accessors[nIdx]
normals, err = gltfVec3(&doc, normalAccessor, Types.Vector{X: 1, Y: 1, Z: 1})
normals, err = gltfVec3(&doc, normalAccessor, transformationMatrices[meshindex], Types.Vector{X: 1, Y: 1, Z: 1})
if err != nil {
return nil, err
}
Expand Down Expand Up @@ -68,14 +101,14 @@ func LoadGLTF(file io.Reader, desiredSize *Types.Vector) ([]*Types.Mesh, error)
mesh.AddTriangle(&Types.Triangle{V0: v0, V1: v1, V2: v2})
}

meshes = append(meshes, &mesh)
meshes.Add(&mesh)
}
}
}
return meshes, nil
}

func gltfVec3(doc *gltf.Document, acc *gltf.Accessor, scaling Types.Vector) ([]Types.Vector, error) {
func gltfVec3(doc *gltf.Document, acc *gltf.Accessor, transformationMatrix Types.Matrix, scaling Types.Vector) ([]Types.Vector, error) {
bufView := doc.BufferViews[*acc.BufferView]
buffer := doc.Buffers[bufView.Buffer]

Expand All @@ -87,10 +120,18 @@ func gltfVec3(doc *gltf.Document, acc *gltf.Accessor, scaling Types.Vector) ([]T
for i := 0; i < acc.Count; i++ {
base := i * 12
// axes inverted to convert to correct coordinate system
x := math.Float32frombits(binary.LittleEndian.Uint32(raw[base+0:]))
y := -(math.Float32frombits(binary.LittleEndian.Uint32(raw[base+8:])))
z := math.Float32frombits(binary.LittleEndian.Uint32(raw[base+4:]))
vectors[i] = Types.Vector{X: float64(x) * scaling.X, Y: float64(y) * scaling.Y, Z: float64(z) * scaling.Z}
vec := Types.Vector{
X: float64(math.Float32frombits(binary.LittleEndian.Uint32(raw[base+0:]))),
Y: float64(math.Float32frombits(binary.LittleEndian.Uint32(raw[base+4:]))),
Z: float64(math.Float32frombits(binary.LittleEndian.Uint32(raw[base+8:]))),
}
transformed := transformationMatrix.MulPosition(vec)
scaled := Types.Vector{
X: transformed.X,
Y: -transformed.Z,
Z: transformed.Y,
}.Mult(scaling)
vectors[i] = scaled // vec.Mult(scaling)
}

return vectors, nil
Expand Down