TerraGear roadmap: Difference between revisions

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| simgear || btg file vertex attribute support || {{Progressbar|20}}
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| genapts || elevation source || {{pending}}
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| genapts || runway relative texture coordinates || {{pending}}
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| genapts || separate .btg for line data || {{Progressbar|90}}
| genapts || separate .btg for line data || {{Progressbar|90}}
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| genapts || pass runway touchdown point as vertex attribute || {{pending}}
| genapts || pass runway touchdown point as vertex attribute || {{pending}}
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| genapts || pass linear feature color and black border info in color btg section || {{pending}}
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|-genapts || support no bezier - low level detail for pavements || {{pending}}
|-genapts || support no bezier - low level detail for pavements || {{pending}}

Revision as of 20:52, 27 April 2014

Note: This project is currently under active development. And we're looking for volunteers interested in contributing.
So if you'd like to help in one way or another, please get in touch or just help improve the article in the meantime!
Useful Skills:
TerraGear, C++, Developing using CMake


Contributors: psadro_gm, papillon81

Mentors: psadro_gm (get in touch to learn more)
It's possible that this article hasn't been updated in a while, so to catch up with the latest developments, you are advised not to start working on anything directly related to this without first coordinating your ideas with fellow FlightGear contributors using the FlightGear developers mailing list or the FlightGear forums. See also the talk page.


This article describes content/features that may not yet be available in the latest stable version of FlightGear (2020.3).
You may need to install some extra components, use the latest development (Git) version or even rebuild FlightGear from source, possibly from a custom topic branch using special build settings: .

This feature is scheduled for FlightGear 3.x. 10}% completed

If you'd like to learn more about getting your own ideas into FlightGear, check out Implementing new features for FlightGear.

World Scenery 2.0 has been released. After 2 1/2 years of development, the tool-chain is considered stable. Although WS2.0 will continue to receive updates, and bug fixes, I'd like to start planning for the next major overhaul.

For World Scenery 3.0, flightgear will have a LOD system for the underlying mesh. The good news is, this new system is already in simgear (thanks to Mathias), and has been tested with 'hand stitched' .btg files. So our job, is to update the tools to be able to generate the scenery automatically.

Ideally, we would like to have at least 4 levels of detail.

The highest detail level being identical to WS2.0.
The second level of detail maintains the same elevation mesh, but removes line data from both airports and terrain. Airports are still smoothed, and cut in to the terrain.
The third level of detail is a simplified mesh, with simplified airports (no bezier interpolation) created as landclass polys (runway, taxiway, and grass). To be determined, is how to simplify the landclass polygons. possibly combining a small area landclass with it's neighbor.
Optional fourth level and more LODs would be refinements to the third - lower res mesh, and more landclass combining)
The lowest detail level being a sphere with a global texture.

In the terragear toolchain, there are 3 main directories: Data, Work, and Output. The Work directory structure will be overhauled to handle arbitrary tile sizes. The output directory needs to match what simgear .SPT files expect.

After conversing with i4dnf, some extra ideas have come up to fix some of the long standing scenery issues. As we move to a new scenery structure, that may not be 100% backward compatible, we should be able to add some additional capabilities to the .btg file format. NOTE: the .btg file format is extensible, so this may not require major changes and 'could' be backward compatible. Experimentation needed:

The first idea is separating the runway markings from the pavement. We have this somewhat working now, but the pavement shader is completely clueless about the marking shader. and bump mapping / dirtying effects cannot be normalized between the line and pavement - leading to visual artifacts. The marking shader needs to know the underlying pavement origin. To do this, the .BTG file needs to support multiple texture coordinates. 1 primary set to look up the line texture in the texture atlas, and another set relative to the origin of the pavement. i4dnf would also like to add dirty / tire marks to the runways. To do this, he needs to know where in the runway polygon, the thresholds are. In openGL, a vertex attribute would be passed to the shader to relay the information. The btg format should be expanded to allow vertex indices (of a triagle) to have attributes.

The second idea is to use multiple tcs to allow landclass shaders to know where in a tile they are located. If we have a per tile raster image with the landclasses encoded, then the borders between landclasses can be smoothed / modified by the shaders. We could also encode regional definitions into the same raster image to support irregular shaped region encoding. probably 8 bits for landclass, and 8 bits for region is enough.

It would be nice to have all landclass images and this single per tile image to all have the same resolution, so we could use a texture array. This allows us to draw an entire tile (other than linear road / rail / stream ) in one openGL draw call.

Progress

The below table is my first attempt at a work item breakdown. I imagine we'll need to add / remove entries as work progresses.

Tool Work item Progress
simgear btg file multiple tc support 60}% completed
simgear btg file vertex attribute support 20}% completed
genapts elevation source Pending Pending
genapts runway relative texture coordinates Pending Pending
genapts separate .btg for line data 90}% completed
genapts runway texture atlas 40}% completed
genapts linear and runway marking triangle vertices have texture coordinates of underlying pavements 50}% completed
genapts pass runway touchdown point as vertex attribute Pending Pending
genapts pass linear feature color and black border info in color btg section Pending Pending
genapts airport as landclass Pending Pending
hgtchop support arbitrary tile sizes / directory structure Pending Pending
imgchop new tool to support per tile raster images based on a global image. Could be used to chop i4dnf's ocean depth image Pending Pending
hgtfit support arbitrary tile sizes / directory structure Pending Pending
hgtfit port from terra to CGAL mesh simplification (optional / cleanup) Pending Pending
ogrdecode support arbitrary tile sizes / directory structure Pending Pending
tgconstruct add tile skirts to hide LOD gaps Pending Pending
tgconstruct generate per tile raster image of landclass data Pending Pending
tgconstruct generate per tile raster image of region data ( can be combined with landclass image to use just 1 texture unit) Pending Pending
tgconstruct generate landclass triangles with geodetic texture coordinates and per tile origin coordinates Pending Pending
tgconstruct arbitrary tile sizes / directory structure Pending Pending
tgconstruct .spt file generation Pending Pending

Development Notes

A fairly large snag while developing secondary texture coordinates : tc scaling is done per material, and the scaling needs to be looked up by material name. Currently, the btg file stores lists of triangles/strips/fans under a common material name. A draped material may lie on multiple underlying materials.

In the short term, my plan is to ignore texture coordinate scaling. The main use case for this is the linear features over airport pavements and runways. A quick check shows that these materials do not use tc scaling, so we should be ok.

If we get to the point where we drape roadways over general terrain, however, we will need a real solution.

preview

I'm getting close to a merge request for simgear changes so we can add bump maps and 'dirty maps' (i.e. skid marks) to the runways and taxiways that allow the same map to be used on both the draped details, and the pavement.

besides the taxiway, runway, grass (and borders) - all markings on the runways and taxiways use a single texture. This saves the number of state changes needed - improving performance.

Runtime Airport Generation

WIP.png Work in progress
This article or section will be worked on in the upcoming hours or days.
See history for the latest developments.