LoD Body Refactoring

[Schneegans]

This pull request tries to optimize the rendering performance of the csp-lod-bodies plugin. For this, it does the following:

• Do not stitch terrain tiles together anymore.
• Instead, draw skirt polygons around the tiles to hide any seams.
• Use a TRIANGLE_STRIP instead of TRIANGLES for the tile geometry.
• Make the resolution of the tile's image data configurable (it used to be 257*257 pixels).
• Make the resolution of the tile's elevation data configurable (it also used to be 257*257 pixels).
• The gray image channel format has been removed to simplify things.
• There's a new option for setting the LoD-Factor range which is used if auto-lod is enabled.

However, it does not:

• Properly format the shader code.
• Optimize the CPU side of things.

The main advantages are:

• We can now draw less triangles with higher resolution imagery which results in better visuals and better performance 😄
• We can use tesseleation shaders in the future.
• We have removed nearly a thousand lines of code.

The main drawbacks of this approach are:

• There is now a one-to-one mapping between image and elevation tiles. Hence, both quadtrees have the same depth. If the image channel has a much higher resolution than the elevation channel, we will request many elevation tiles with very little information content. Hence, the cache and bandwidth usage may be a bit higher.
• We can only refine a tile when image and elevation data of all child nodes have been loaded. Before, it was possible to draw a node if either image or elevation data was available. This can lead to somewhat slower loading times.

Other notes:

• The MinMaxPyramid is not really required anymore. However, we may need this in future for the tesselation shaders so I left it in the code. Yet I am not sure whether it's still working 100% as I had to replace many hard-coded numbers...
• The depth of the skirts depends on the maximum elevation difference inside a tile. It is currently set to half the height scale of the tile.
• The default resolution for the image tiles is now set to 512, for elevation tiles to 128. The maximum LoD factor has been reduced to 40. But this may need to be adjusted.
• For now, it is not possible to change the tile resolution at run-time (a warning is printed if the user attempts to do this).
• There are many more things (especially on the CPU side) which could be refactored. But I tried to keep this PR managable :wink:
• Similarily, I added comments to new stuff, but didn't update comments for stuff which was already there. However, this should definitely be done as there's a lot of out-dated comments around...

[coveralls]

Pull Request Test Coverage Report for Build 4204419213

• 0 of 243 (0.0%) changed or added relevant lines in 18 files are covered.
• 30 unchanged lines in 14 files lost coverage.
• Overall coverage increased (+0.06%) to 3.109%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
plugins/csp-lod-bodies/src/MinMaxPyramid.hpp	0	1	0.0%
plugins/csp-lod-bodies/src/RenderDataDEM.cpp	0	1	0.0%
plugins/csp-lod-bodies/src/TileBounds.cpp	0	1	0.0%
plugins/csp-lod-bodies/src/PlanetShader.cpp	0	2	0.0%
plugins/csp-lod-bodies/src/Tile.hpp	0	2	0.0%
plugins/csp-lod-bodies/src/TerrainShader.cpp	0	4	0.0%
plugins/csp-lod-bodies/src/TileBase.cpp	0	4	0.0%
plugins/csp-lod-bodies/src/TileNode.cpp	0	4	0.0%
plugins/csp-lod-bodies/src/TileTextureArray.hpp	0	5	0.0%
plugins/csp-lod-bodies/src/VistaPlanet.cpp	0	6	0.0%
<!--	Total:	0	243	0.0%	-->

Files with Coverage Reduction	New Missed Lines	%
plugins/csp-lod-bodies/src/Plugin.cpp	1	0%
plugins/csp-lod-bodies/src/RenderDataDEM.cpp	1	0%
plugins/csp-lod-bodies/src/TileBase.hpp	1	0%
plugins/csp-lod-bodies/src/Tile.hpp	1	0%
plugins/csp-lod-bodies/src/TileNode.cpp	1	0%
plugins/csp-lod-bodies/src/TileRenderer.hpp	1	0%
plugins/csp-lod-bodies/src/TileSourceWebMapService.cpp	1	0%
plugins/csp-lod-bodies/src/TileTextureArray.hpp	1	0%
plugins/csp-lod-bodies/src/LodBody.cpp	2	0%
plugins/csp-lod-bodies/src/MinMaxPyramid.cpp	2	0%
<!--	Total:	30		-->

Totals
Change from base Build 4103295433:	0.06%
Covered Lines:	515
Relevant Lines:	16567

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💛 - Coveralls

[Schneegans]

Thanks a lot for this review! I hope that I addressed all of your concerns :smile:. Do you have any feedback regarding the chosen default values?

[JonasGilg]

Thanks a lot for this review! I hope that I addressed all of your concerns 😄. Do you have any feedback regarding the chosen default values?

One last comment remains. Otherwise it works great. I tried to break it with everything I could throw at it, but with the default configuration I wasn't able to find any bugs or holes in the ground. Only when I manually turned the LOD factor below 10 I was able to create situations where the planet surface had gaps between tiles, but at that point the application became useless anyways.

This is a great improvement. The render times are amazing!