Consider setting texture sampler sources to Shared:Wrap

[argallegos]

In the CesiumGlTFFunction and CesiumRasterOverlay material functions, we use a lot of Texture Sample nodes, which means that we are by default at 10/16 texture samplers for the M_CesiumOverlay material and 12/16 for M_CesiumOverlayWater. This definitely limits future materials that we or users may need to create.

If we set the Sampler Source on each Texture Sample to Shared:Wrap, we can significantly reduce the texture samplers to 3/16 for the overlay material and 4/16 for the water material.

From my preliminary testing, it hasn't changed the appearance of tilesets at all. In addition, it doesn't look like there are really known issues that arise from doing this. One user in this thread posted that Shared: Wrap doesn't work with Metal, which may cause trouble for mac builds. We should definitely test this out, and figure out if there are any other drawbacks of changing the Sampler Source to this. If not, this would be a helpful change.

If you want to test this out, I've set the materials to use Shared: Wrap in the reduce-tex-samples branch.

[argallegos]

Per conversation in stand up, the Gltf function will likely need to keep the sampler source as is, for tilesets with unconventional UV requirements. However, we can change the RasterOverlay function to use Shared: Wrap, which will still free up some texture samplers.

[j9liu]

While testing things, I noticed that our materials don't compile with "Forward Rendering" enabled in the project. It was due to exceeding the 16 sampler limit. But the recommended workaround to get more texture slots is to use the Shared:Wrap sampler, according to this thread: https://forums.unrealengine.com/t/sm5-errror-x4510-maximum-ps-5-0-sampler-register-index-16-exceeded/281091