Documentation tweaks.
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Par Winzell
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README.md
56
README.md
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@ -17,7 +17,7 @@ The tool can be invoked like so:
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Or perhaps, as part of a more complex pipeline:
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```
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> FBX2glTF --binary --draco --khr-materials-common \
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> FBX2glTF --binary --draco --verbose \
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--input ~/models/source/butterfly.fbx \
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--output ~/models/target/butterfly.glb
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```
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@ -41,18 +41,18 @@ Usage:
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behaviour!)
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--no-flip-v Suppress the default flipping of V texture
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coordinates
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--khr-materials-common (WIP) Use KHR_materials_common extensions to
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specify Unlit/Lambert/Blinn/Phong shaders.
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--pbr-metallic-roughness (WIP) Try to glean glTF 2.0 native PBR
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attributes from the FBX, or make a best effort
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to convert from traditional shader models.
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--pbr-specular-glossiness
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(WIP) Very experimentally employ the
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KHR_materials_pbrSpecularGlossiness extension.
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--pbr-metallic-roughness Try to glean glTF 2.0 native PBR attributes
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from the FBX.
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--khr-materials-unlit Use KHR_materials_unlit extension to specify
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Unlit shader.
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--blend-shape-normals Include blend shape normals, if reported
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present by the FBX SDK.
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--blend-shape-tangents Include blend shape tangents, if reported
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present by the FBX SDK.
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--long-indices arg Whether to use 32-bit indices
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(never|auto|always).
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--compute-normals arg When to compute normals for vertices
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(never|broken|missing|always).
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-k, --keep-attribute arg Used repeatedly to build a limiting set of
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vertex attributes to keep.
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-v, --verbose Enable verbose output.
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@ -73,6 +73,12 @@ Some of these switches are not obvious:
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Your FBX is likely constructed with the assumption that `(0, 0)` is bottom
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left, whereas glTF has `(0, 0)` as top left. To produce spec-compliant glTF,
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we must flip the texcoords. To request unflipped coordinates:
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- `--long-indices` lets you force the use of either 16-bit or 32-bit indices.
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The default option is auto, which make the choice on a per-mesh-size basis.
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- `--compute-mormals` controls when automatic vertex normals should be computed
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from the mesh. By default, empty normals (which are forbidden by glTF) are
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replaced. A choice of 'missing' implies 'broken', but additionally creates
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normals for models that lack them completely.
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- `--no-flip-v` will actively disable v coordinat flipping. This can be useful
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if your textures are pre-flipped, or if for some other reason you were already
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in a glTF-centric texture coordinate system.
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@ -216,19 +222,15 @@ and additionally, with Blinn/Phong:
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(All these can be either constants or textures.)
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#### Exporting as Unlit/Lambert/Phong
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If you have a model was constructed using the traditional workflow, you may
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choose to export it using the --khr-materials-common switch. This incurs a
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dependency on the glTF extension 'KHR_materials_common'; a client that accepts
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that extension is making a promise it'll do its best to render i.e. Lambert or
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Phong.
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You can use this flag even for PBR models, but the conversion is imperfect to
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say the least, and there is no reason why you would ever want to do such a
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thing.
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#### Exporting as Unlit
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If you have a model was constructed using an unlit workflow, e.g. a photogrammetry
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capture or a landscape with careful baked-in lighting, you may choose to export
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it using the --khr-materials-common switch. This incurs a dependency on the glTF
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extension 'KHR_materials_unlit; a client that accepts that extension is making
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a promise it'll do its best to render pixel values without lighting calculations.
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**Note that at the time of writing, this glTF extension is still undergoing the
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ratification process, and is furthermore likely to change names.**
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ratification process**
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#### Exporting as Metallic-Roughness PBR
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Given the command line flag --pbr-metallic-roughness, we throw ourselves into
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@ -242,20 +244,6 @@ that route should be digested propertly by FBX2glTF.
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(A happy note: Allegorithmic's Susbstance Painter also exports Stingray PBS,
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when hooked up to Maya.)
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If your model is not a Stingray PBS one, but you still wish to export PBR
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(perhaps you want to generate only core glTF wirhout reliance on extensions),
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this converter will try its best to convert your old textures. It calculates, on
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a pixel by pixel basis, reasonable values for base colour, metallicness and
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roughness, using your model's diffuse, specular, and shinines textures.
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It should noted here that this process cannot ever be perfect; this is very much
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an apples and oranges situation.
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A note of gratitude here to Gary Hsu who developed the formulae we use for this
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process. They can be eyeballed
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[here](https://github.com/KhronosGroup/glTF/blob/master/extensions/Khronos/KHR_materials_pbrSpecularGlossiness/examples/convert-between-workflows/js/three.pbrUtilities.js)
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for the curious.
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## Draco Compression
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The tool will optionally apply [Draco](https://github.com/google/draco)
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compression to the geometric data of each mesh (vertex indices, positions,
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12
src/main.cpp
12
src/main.cpp
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@ -57,9 +57,15 @@ int main(int argc, char *argv[])
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(
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"b,binary", "Output a single binary format .glb file.",
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cxxopts::value<bool>(gltfOptions.outputBinary))
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(
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"long-indices", "Whether to use 32-bit indices (never|auto|always).",
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cxxopts::value<std::vector<std::string>>())
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(
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"d,draco", "Apply Draco mesh compression to geometries.",
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cxxopts::value<bool>(gltfOptions.useDraco))
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(
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"compute-normals", "When to compute normals for vertices (never|broken|missing|always).",
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cxxopts::value<std::vector<std::string>>())
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("flip-u", "Flip all U texture coordinates.")
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("flip-v", "Flip all V texture coordinates (default behaviour!)")
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("no-flip-v", "Suppress the default flipping of V texture coordinates")
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@ -75,12 +81,6 @@ int main(int argc, char *argv[])
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(
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"blend-shape-tangents", "Include blend shape tangents, if reported present by the FBX SDK.",
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cxxopts::value<bool>(gltfOptions.useBlendShapeTangents))
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(
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"long-indices", "Whether to use 32-bit indices (never|auto|always).",
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cxxopts::value<std::vector<std::string>>())
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(
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"compute-normals", "When to compute normals for vertices (never|broken|missing|always).",
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cxxopts::value<std::vector<std::string>>())
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(
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"k,keep-attribute", "Used repeatedly to build a limiting set of vertex attributes to keep.",
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cxxopts::value<std::vector<std::string>>())
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