Hi qmuntal , I'm pretty new to this low level of glTF editing , I spent two days trying to make find the right parameters for the modeler's writeIndices All i'm trying to do now is write a simple triangle :

package main

import (
    "github.com/qmuntal/gltf"
    "github.com/qmuntal/gltf/modeler"
)

func drawTriangle() {
    doc := gltf.NewDocument()
    
    positionAccessor := modeler.WritePosition(doc, [][3]float32{{0, 0, 0}, {0, 10, 0}, {0, 0, 10}})
    indicesAccessor := modeler.WriteIndices(doc, []uint8{   0, 1, 0, 
                                                            0, 0, 1, 
                                                            0, 0, 1 })
    colorIndices := modeler.WriteColor(doc, [][3]uint8{{50, 155, 255}, {0, 100, 200}, {255, 155, 50}})
    
    doc.Meshes = []*gltf.Mesh{{
        Name: "Pyramid",
        Primitives: []*gltf.Primitive{{
            Indices: gltf.Index(indicesAccessor),
            Attributes: map[string]uint32{
              "POSITION": positionAccessor,
              "COLOR_0":  colorIndices,
            },
        }},
    }}
    doc.Nodes = []*gltf.Node{{Name: "Root", Mesh: gltf.Index(0)}}
    doc.Scenes[0].Nodes = append(doc.Scenes[0].Nodes, 0)
    if err := gltf.SaveBinary(doc, "./example.glb"); err != nil {
        panic(err)
    }
}
func main (){
    drawTriangle()
}

I tried two of the examples in the repo (the second one on the md file and example_test.go ) but they didn't work . the pyramid one on the md file is working fine and this code is trying to replicate your example but i don't know the data that i'm supposed to pass as indices . i tried

• Normals : passing 1,0,0,1,0,0,1,0,0

Thanks for these contributions . Lots of respect for your code .

When decoding very small files (smaller than one read chunk?), the inner decoder might return io.EOF as error, alongside the document (i.e. the document read might be valid, but it's overwritten with nil in case of io.EOF)

When Sampler's MagFilter, MinFilter, WrapS and WrapT fields are zero values, they won't be included in encoded JSON document. These fields' types have MarshalJSON implemented, but IIUC omitempty is evaluated before MarshalJSON and the values are omitted (because they're zero), so the encoded JSON won't have them. I think that there are 2 options for resolving this issue.

• A. Remove omitempty tag from MagFilter, MinFilter, WrapS and WrapT fields
• B. Ignore first value by assigning to blank identifier before MagLinear, MinLinear, WrapRepeat

What do you think? I'll try to make a PR after you decide.

I would like to see an API that lets someone supply a list of vertices, zero or more material definitions, and one or more lists of vertex indices to define triangles, each with an associated material reference, and have all the nuts and bolts of assembling the buffer, bufferviews, and accessors done automatically. Simply calling .Save on that type should allow the user to then persist this model to disk.

I don't know if that is within the scope of this library, and I felt it needed suggesting, in case it is.

KhronosGroup/glTF-Validator reports errors on glb file(see attachment test.glb.gz) generated by this package:

Error | Message | Pointer -- | -- | -- GLB_CHUNK_LENGTH_UNALIGNED | Length of 0x00000002 chunk is not aligned to 4-byte boundaries. |   GLB_CHUNK_TOO_BIG | Chunk (0x00000002) length (1179937895) does not fit total GLB length. |   GLB_UNEXPECTED_END_OF_CHUNK_DATA | Unexpected end of chunk data. |  

Warning | Message | Pointer -- | -- | -- GLB_UNKNOWN_CHUNK_TYPE | Unknown GLB chunk type: 0x00000002.

This is similar to #15 except that that was regarding a way to create a GLTF document whereas I would like a way to read GTLF document without any knowledge of GLTF.

The ideal API for me would take a document, a mesh index, and return vertices, normals, uvs, material indices, etc.

You could call the package scanner, reader, inspector, etc.

This PR has the decoder use binary.Size in favour of int(unsafe.Sizeof(header)), since the binary package is either way used for the parsing of the header.

This makes the implementation a bit more robust, since it should handle architectures that might align structures differently. Though in this particular case, due to the simplicity of the struct, it might actually be a bit more of a nit picking.

In addition, it also fixes a small typo (I assumed too small for a separate PR).

The only other place using the unsafe package that remains is the binary/unsafe.go file. I might be up to writing a separate PR in the future that reworks that to use the more manual approach, as used in binary/binary.go, if the owner of this repo is open to the idea of getting rid of unsafe.

I tried to embed the texture image into .glb using gltf.Modeler but generated a broken file.

in modeler.go

	buffer.ByteLength += uint32(len(buffer.Data))

I think, = should be correct, not +=.

I am using your project to create gltf file. I have draco precompressed geometry data like a.drc, and I referenced it in a buffer in document. When I save the document, the a.drc file will be overwrite. It size becomes zero.

This is how I define my buffer

buffer := gltf.Buffer{
		URI:       "a.drc",
		ByteLength:  123,
	}

This is how I save the doc

if err := gltf.Save(doc, path, false); err != nil {
	panic(err)
}

Getting EOF error when opening a .glb file converted from .gltf using gltf.SaveBinary().

Sample input .gltf file: https://github.com/qmuntal/gltf/files/9627951/simple.gltf.txt

Sample script:

import (
	"log"

	"github.com/qmuntal/gltf"
)

func main() {
	const simpleGltf = "simple.gltf"
	const outputGlb = "simple.glb"

	srcDoc, err := gltf.Open(simpleGltf)
	if nil != err {
		log.Fatal(err)
	}
	err = gltf.SaveBinary(srcDoc, outputGlb)
	if nil != err {
		log.Fatal(err)
	}

	tgtDoc, err2 := gltf.Open(outputGlb)
	if nil != err2 {
		log.Fatal(err2)
	}
	log.Println("SUCCESS!")
	log.Printf("DEBUG: %#v", tgtDoc)
}

NB: error seen using latest version of gltf package (v.0.22.1), but not using an older version (v.0.18.3). The output files slightly differ, it looks like the old version of the package was adding some nil "padding" at the end.

Take a look at the glTF sample files called Box With Spaces

This file has a uri reference to Box With Spaces.bin. But this library performs urlencode of the URI so spaces become %20 and then fails because it cannot find a file named Box%20With%20Spaces.bin

The url-encoding happens because of a round-trip through net/url.Parse

A solution would be to only use the parsed URL if the scheme is not empty. i.e. the URL is http/file/etc

Hi,

I'm very new to Go and gltf. Is there any chance of you (or someone else) adding a "Hello World" example to display a rotating cube? The program would read a gltf file (e.g. Box.gltf) using gltf.Open and extract the necessary vertices to display a rotating cube using the simplest vertex and frag shaders.

My main difficulty is going from opening a gltf.Document to displaying something. An example would be nice.

Thanks Andre