glTF 2.0 introduced two PBR materials: The Metallic-Roughness and Specular-Glossiness workflow. As the Metallic-Roughness is integrated into core glTF 2.0, details are explained for this workflow. For Specular-Glossiness, it is similar or almost the same.
At point of writing, Blender supports two material settings: One for Blender Render and one for Cycles Render. Fortunately, the glTF 2.0 Materials can be simulated using the Cycles Render by implementing a custom node tree. Advantage is, that the preview of the Cycles output is almost 1:1 to the expected rendering output when using the glTF 2.0 materials.
However, this custom node tree needs to be imported and linked to a Blender file. For the future, it is planned to use the Eevee shader node, which will replace the current node group.
For shadeless materials, glTF 2.0 also has an Unlit material extension. Unlit materials use Diffuse or vertex colors as input, and cannot currently be created with Cycles nodes. Materials with the Shadeless setting enabled will automatically use the glTF 2.0 Unlit extension.
Following picture shows a basic Blender scene using the Cycles renderer.
If this scene would be exported, the perspective camera and Suzanne are written to the glTF 2.0 file. However, this scene would not contain any materials. As this glTF 2.0 file is valid, any glTF 2.0 render would use a default material.
The reason for this is, that with Cycles much more complex PBR shaders can be created, which cannot be exported to glTF 2.0 in this case. In this concrete Blender scene, the exporter skips the material.
In the following steps it is explained, how to integrate a glTF 2.0 material:
At first, it is required to link or append the Blender file, which contains the glTF 2.0 materials.
It is recommended for development to link the file, as any possible updates are automatically updated. As relative paths are used, this is not optimal for deployment, as the material information would get lost and finally the Blender file is broken.
For deployment, append is recommended, as even the final Blender file increases, any required information is kept in ths deployed file.
Navigate to the glTF2.blend file included in this repository, select NodeTree and finally the glTF Metallic Roughness entry. For a Specular-Glossiness material, choose glTF Specular Glossiness. After linking or appending the entry, the glTF 2.0 material is ready to be used in this Blender file.
For using the glTF 2.0 material, the current Material of Suzanne has to be altered:
Add the node group glTF Metallic Roughness to the material, delete the Diffuse BSDF shader and connect the node group to the Material Output node.
After changing the baseColorFactor property, Suzanne has again the red color.
That's it!
If this scene is exported, the glTF 2.0 file does contain a material.
The default exporter settings are configured in such a way, that the generated glTF 2.0 scene is almost identical to the Blender scene. However, in some cases, applying different settings do result in a better export result. Furthermore, the export settings allow an individual and adapted export depending on the users expectation.
The following sections explains the different export settings.
If this field is not empty, the given string is exported into the copyright property. This entry is not stored in the Blender scene file.
By default, any binary data like vertices and animations are exported into a .bin file. Enabling this option, the given data is embedded inside the .gltf file. This option is only availabe in the .gltf export, as for .glb, the integration is done automatically.
By default, any image is saved as a .png file. Enabling this option, the given images are embedded inside the .gltf file. This option is only availabe in the .gltf export, as for .glb, the integration is done automatically.
By default, the generated .gltf file contains line breaks and indentations for better human readability. If enabled, the exporter glTF 2.0 JSON file is tightly packed. This option is only availabe in the .gltf export, as for .glb, the stripping is applied automatically.
By default, all objects and it assets are exported. If enabled, only the selected items are exported.
In Blender, objects can be assigned to different layers. By default, all objects on all layers are exported. It is a common use case, that helper objects are placed on other layers and only the first layer contains the correct visual output. In such a case, objects could appear duplicated or in a wrong context. Enable this setting, if only the objects on the first layers should be exported.
In Blender, for some objects, it is possible to set custom properties. If enabled, these custom properties are exported into the extras property of the glTF 2.0 file.
Blender has the feature of modifiers, which most of them cannot be exported to glTF 2.0 by default. When exporting, apply these specific modifiers for a correct visual output of the scene. If this setting is enabled, all modifiers are applied automatically. Drawback is, that skinning and morphing is backed as well.
By default, vertex indices are exported as Unsigned short data type and is feasible in most cases. However, for large primitives, the mesh has to be split into several primitives, which causes a longer export time. Changing this value to Unsigned integer, no splitting has to be performed. Tradeoff is larger size of of the binary file. If Unsigned byte is used, the size of the vertex indices is minimal, but the amount of splitted primitives increases.
By default, if vertex indices can be represented with a smaller type size without splitting the primitive, the minimal type size is used. If this setting is enabled, all primitives are forced to have the same type size, as defined in the maximum indices field.
By default, if present, texture coordinates are exported.
By default normals are exported.
By default, if they can be calculated, tangents are exported.
By default, if present, vertex colors are exported.
By default, if glTF 2.0 materials are used, materials are exported.
By default cameras are exported.
By default, all perspective cameras are exported as finite perspective cameras. By enabling this option, all perspective cameras are exported as infinite ones.
By default, all animations are exported.
By default, all animations are exported within the playback range. If disabled, all animation data is exported. This property is only visible, if export animations is enabled.
By default, all keyframes are modified that the first keyframe starts with 0. If disabled, the keyframes keep their original value. This property is only visible, if export animations is enabled.
By default and if possible, only the keyframes of an animation are exported. However, mainly because of the non-quaternion to quaternion conversion, animations need to be sampled for proper animating the scene. This property is only visible, if export animations is enabled.
If the animations are not exported, this option gets visible. By default, the current frame is exported. If not, frame 0 is exported.
By default, all skinning data and animations are exported. If disabled, the armature position is exported.
If export skinning is enabled, this option is visible. If inverse kinematics are used, this option has to be enabled for a correct glTF 2.0 export. Tradoff is, because the animations are baked, that the animation data export is getting larger.
By default, morphing animation data is exported.
By default, morphing normal targets are exported. If disabled, tangents are not exported as well. Property is only visible, if export morphing is enabled.
By default, morphing tangent targets are exported. If disabled, tangents are not exported. Property is only visible, if export morphing and morphing normals is enabled.
As soon as the PBR materials and the glTF 2.0 node groups are used, Cycles can be used for previewing the scene. The following images are taken from 01_alpha_mask.blend, as the differences can be shown best by this example. The mesh of this example is a quad, where a texture - multiplied with a color factor - is used and aplha masking is applied. For each of the following images, just the Viewport Shading mode has been changed:
Solid - The whole quad is seen. No texture, color or alpha masking is visible.
Texture - Still, the whole quad is seen but influence of the texture is visible.
Material - Now, the whole quad is seen with influence of the texture and the color factor.
Rendered - This preview is a close WYSIWYG output. All parameters are applied and visible.
At point of writing, the PBR materials are simulated with Cycles using a specific node tree encapsulated in a node group. Two node groups are provided, one for the metallic roughness and one for the specular glossiness workflow.
Even possible in the Cycles node editor, specific requirements have to be fulfilled, that all parameters are exported to the glTF 2.0 file format successfully:
- If a parameter is marked as 'Node group only', the parameter has to be changed in the node group. Any input by a node is ignored.
- If a parameter is marked as 'Texture only', the parameter in the node group contains the default value. Changing this value is ignored. Only an 'Image Texture' input link is accepted.
- If a parameter is marked as 'Attribute only', the parameter in the node group contains the default value. Changing this value is ignored. Only an 'Attribute' input link is accepted.
All PBR materials share the same input parameters, which are listed in the following table:
| Material parameter export | Node group only | Texture only | Attribute only | Comments |
|---|---|---|---|---|
| Normal texture | X | |||
| Normal strength | X | |||
| Normal texture coordinate | 'UV' from 'UV MAP' to 'Vector' | |||
| Occlusion texture | X | |||
| Occlusion strength | X | |||
| Occlusion texture coordinate | 'UV' from 'UV MAP' to 'Vector' | |||
| Emissive texture | X | |||
| Emissive factor | X | |||
| Emissive texture coordinate | 'UV' from 'UV MAP' to 'Vector' | |||
| Alpha texture channel | X | |||
| Alpha cutoff | X | |||
| Alpha mode | X | |||
| Double sided | X | |||
| COLOR_0 | X | 'Name' from 'Attribute' to first 'Vertex Colors' |
Most of the input links are named by their depending glTF 2.0 property. In the following sections, the properties are explained, which are not straightforward to setup.
By default, the alpha mode is 'OPAQUE' and set to 'BLEND', if
- the BaseColorFactor or DiffuseFactor alpha value is less than 1.0
- the Alpha channel from the BaseColor or Diffuse image texture is connected.
Please note, that separate alpha maps are currently not specified in glTF 2.0 and so not working. The alpha channel has to be linked from the above defined image textures. Following picture shows the correct and simple usage for the glTF Metallic Roughness node:
To use 'MASK' for blending, the AlphaMode has to be set from 0.0 to 1.0. In this case, as specified by glTF 2.0, the AlphaCutoff value is used and exported.
In glTF 2.0, the information if a mesh has to be rendered double sided or not, is stored in the material and not the mesh. By default, double sided is disabled and if a glTF 2.0 scene is exported, the back faces are culled. If a mesh should be renderered without back face culling, enable the double sided material by setting the slider to 1.0.
By default, Use COLOR_0 is disabled and the slider has to be set to 1.0 for enabling it.
Furthermore, an Attribute input has to be linked to COLOR_0 for a correct export.
In the Name property field of the Attribute node, the string of the Vertex Colors has to be entered. In the following picture, the name is COLOR_0 but any name can be used.
This is the complete Metallic Roughness material node.
The specular glossiness material is not part of core glTF 2.0. The material is defined by the extension KHR_materials_pbrSpecularGlossiness.
The following section describes several tools, how they can optimal be used with the Blender glTF 2.0 exporter.
Substance Painter is a 3D painting software allowing you to texture, render and share your work.
Substance Painter 2017.3 and newer versions provide glTF 2.0 PBR presets.