Add water mask material

[ggetz]

Description

Adds a new water mask globe material.

The motivation is so that custom globe materials can be written that shade only the land or only the sea, as demonstrated in the new Sandcastle example.

In order to do this, I separated the concerns of having a water mask from displaying the water effect in packages/engine/Source/Scene/GlobeSurfaceShaderSet.js, and added the new material shader.

Issue number and link

N/A

Testing plan

1. Ensure the new Sandcastle example works.
2. Alter the properties of the customElevationMaterial (such as by using the waterMaskMaterial.diffuse value) to see how the mask interacts with the diffuse channel.
3. Test the uniforms by setting

material.materials.waterMaskMaterial.uniforms.landColor = Cesium.Color.YELLOW.clone();
material.materials.waterMaskMaterial.uniforms.waterColor = Cesium.Color.BLUE.clone();

Author checklist

• I have submitted a Contributor License Agreement
• I have added my name to CONTRIBUTORS.md
• I have updated CHANGES.md with a short summary of my change
• I have added or updated unit tests to ensure consistent code coverage
• I have updated the inline documentation, and included code examples where relevant
• I have performed a self-review of my code

[github-actions]

Thank you for the pull request, @ggetz!

✅ We can confirm we have a CLA on file for you.

[ggetz]

@jjspace A reminder to review this PR.

[jjspace]

Sorry for the delay getting back to this. As far as I can tell (with my more limited knowledge of shaders/materials) all the code looks good. I was also able to test and the sandcastles work as expected.

I think the only thing I might add is that it could be nice to demonstrate the testing plan you outlined in the new sandcastle example. Just a simple material picker like this for people (like me) that are less experienced with our Material api to know how to do that.

[ggetz]

Thanks @jjspace!

I think the only thing I might add is that it could be nice to demonstrate the testing plan you outlined in the new sandcastle example. Just a simple material picker like this for people (like me) that are less experienced with our Material api to know how to do that.

I would generally agree with this feedback. However, for this particular example, I think that distracts from the intended use case and make things a bit more complicated in the code example, which I'd like to avoid if possible.