This is mainly useful for continuous integration where GPUs are generally not available on cloud machines. To perform software rasterization, these scripts are centered around Mesa's software rasterizers, but nothing bars us from using another rasterizer like SwiftShader. Additionally, we should be able to use GPUs where available (though this is more of a future work).

The script render.py contains the core logic for taking input parameters (such as the test description file) and then running gltf_viewer to produce the renderings.

In the test directory is a list of test descriptions that are specified in json. Please see sample.json to parse the structure.

Running the test locally

To run the same presbumit as test-renderdiff, you can do
```
bash test/renderdiff/test.sh
```
This script will generate the renderings based on the current state of your repo. Additionally, it will also compare the generated images with corresponding images in the golden repo.
To just render without running the test, you could use the following script
```
bash test/renderdiff/generate.sh
```

Update the golden images

The golden images are stored in a github repository: https://github.com/google/filament-assets. Filament team members should have access to write to the repository. A typical flow for updating the goldens is to upload your changed images into branch of filament-assets. This branch is paired with a PR or commit on the filament repo.

As an example, imagine I am working on a PR, and I've uploaded my change, which is in a branch called my-pr-branch, to filament. This PR requires updating the golden. We would do it in the following fashion

Using a script to update the golden repo

Run interactive mode in the update_golden.py script.
```
python3 test/renderdiff/src/update_golden.py
```
This will guide you through a series of steps to push the changes to a remote branch on filament-assets.

Manually updating the golden repo

Check out the golden repo

git clone git@github.com:google/filament-assets.git

Create a branch on the golden repo

cd filament-assets
git switch -c my-pr-branch-golden

Copy the new images to their appropriate place in filament-assets
Push the filament-assets working branch to remote
```
git push origin my-pr-branch-golden
```
In the commit message of your working branch on filament, add the following line
```
RDIFF_BBRANCH=my-pr-branch-golden
```

Manually updating the golden repo

Doing the above has multiple effects:

The presubmit test test-renderdiff will test against the provided branch of the golden repo (i.e. my-pr-branch-golden).
If the PR is merged, then there is another workflow that will merge my-pr-branch-golden to the main branch of the golden repo.