glTF-Renderer

Introduction: Sample glTF Renderer for Android
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glTF is a new standard 3D transmission format by the Khronos Group. Facebook has recently made sharing 3D content in newsfeed as easy as sharing an image or a video using glTF 2.0.

This demo shows the mechanics of parsing and rendering a sample "Hello World!" glTF file. This code is reference material for the Android Makers Paris 2018 talk titled: "The JPEG of 3D: Bringing 3D scenes and objects into your 2D Android app with glTF".

It provides a straightforward look at how to render a 3D scene using glTF and the OpenGL ES API. This is a good reference for developers who are learning about 3D rendering on Android. This is low level GPU driver API code; you may want to check out the new Sceneform API in the AR Core 1.2 SDK if you want a high-level API that can render glTF, OBJ, and FBX 3D scenes.

The renderer is trivial and will only work with the hello-world.gltf example. It is not intended to be a full glTF renderer but rather a minimal-abstraction view at the basics of how a glTF file is parsed and rendered. In some cases the renderer might be making assumptions for the hello-world.gltf use case that would not be valid for a generic glTF file.

The demo will render the hello-world.gltf scene, a single triangle using the default glTF material (using unlit red for the sample), into the TextureView's SurfaceTexture.

The code will:

  • Create a render thread with a message queue for the TextureView (SampleGLTFView)
  • Once the SurfaceTexture for the TextureView is available, it will initialize the loading of the helloworld.gltf asset
  • SampleGLTFRenderer.createOnGlThread(context, "helloworld.gltf") is called to initialize shader program and use SampleGLTFReader.read(input) to parse the JSON file and generate a "scene graph"
  • SampleGLTFRenderer.createGLTFRenderObjects(gltfScene) is called to create the GPU ready representation of the helloworld.gltf scene
  • Each frame the Choreographer VSYNC triggers SampleGLTFRenderer.draw(viewMatrix, projectionMatrix) which executes OpenGL ES draw commmands using the buffer data from the helloworld.gltf file.

SampleGLTFRenderer will also plug-in to the AR Core SDK hello_ar_java sample (https://github.com/google-ar/arcore-android-sdk/tree/v1.2.1/samples/hello_ar_java); just replace the usage of ObjectRenderer with SampleGLTFRenderer in HelloArActivity so you can render the helloworld.gltf triangle in AR.

In HelloArActivity.onSurfaceCreated(...):

  • sampleGLTFRenderer.createOnGlthread(context, "helloworld.gltf")

In HelloArActivity.onDrawFrame(...):

  • sampleGLTFRenderer.updateModelMatrix(anchorMatrix, scaleMatrix)
  • sampleGLTFRenderer.draw(viewmtx, projmtx)

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Disclaimer

  • This code is intended as a limited example for learning purposes and is by no means production quality.
  • It may not be entirely stable.
  • It has been tested on limited high end Android devices
  • It's not intended as a demonstration of "the right way" to do things.
  • It will not be supported.

Requirements

Requires Android OS version Marshmallow 6.0 (API 23) or higher

To build you'll need the Android SDK with build tools.

Note: This code was developed on Android Studio 3.1.2

Usage

Open the directory in Android Studio and the gradle project should be imported. Run & Debug options should allow you to build the project.

Command Line

Assure you have a local.properties file in the top level directory with: sdk.dir=/path/to/your/Android/sdk

$ gradlew installDebug
$ adb shell am start -n com.facebook.sample/.SampleGLTFActivity

License

glTF-Renderer is Creative Commons CC BY-NC 4.0 Attribution-NonCommercial licensed, as found in the LICENSE file.

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