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Procedural texturing: Difference between revisions
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* <b>Landclass boundaries</b>: Procedural texturing can de-emphasize landclass boundaries. This happens for instance if a landclass uses both overlay and detail texture, and only the base texture is changed in the adjacent landclass. Since the noise is continuous across landclass boundaries, the change in base texture is masked by the continuous overlay components. However, procedural texturing can not remove the landclass seams, as a different texture mix is evaluated for every declared landclass. | * <b>Landclass boundaries</b>: Procedural texturing can de-emphasize landclass boundaries. This happens for instance if a landclass uses both overlay and detail texture, and only the base texture is changed in the adjacent landclass. Since the noise is continuous across landclass boundaries, the change in base texture is masked by the continuous overlay components. However, procedural texturing can not remove the landclass seams, as a different texture mix is evaluated for every declared landclass. | ||
* <b>Tiling for non-natural landclasses</b>: The de-tiling strategies described above are based on mixing texture components using noise functions. This works fine for natural landclasses, but human-influenced landclasses like agriculture or urban terrain are not well described by Perlin noise, and de-tiling crop fields using noise functions does not yield plausible results. A suitable function producing for instance plausible agriculture pattern has yet to be found. | * <b>Tiling for non-natural landclasses</b>: The de-tiling strategies described above are based on mixing texture components using noise functions. This works fine for natural landclasses, but human-influenced landclasses like agriculture or urban terrain are not well described by Perlin noise, and de-tiling crop fields using noise functions does not yield plausible results. A suitable function producing for instance plausible agriculture pattern has yet to be found. | ||
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* <b>Computational cost:</b> Especially on older graphics cards, multiple texture lookups combined with evaluating noise and other functions is significantly slower than just texturing the terrain with a single texture. Most optimization strategies used in other 3D games (such as filling the z-buffer early and discarding occluded pixels) do not work well for a flight simulator where most of the terrain is visible at any given time. | * <b>Computational cost:</b> Especially on older graphics cards, multiple texture lookups combined with evaluating noise and other functions is significantly slower than just texturing the terrain with a single texture. Most optimization strategies used in other 3D games (such as filling the z-buffer early and discarding occluded pixels) do not work well for a flight simulator where most of the terrain is visible at any given time. | ||
Some points have found a solution: | |||
* <b>Terrain tile boundaries</b>: Terrain is loaded in discrete chunks, so-called tiles. For technical reasons, the coordinate system used to address positions changes for each tile. In practice, this unfortunately implies that noise functions are discontinuous across tile boundaries, and this shows in more or less pronounced seams in the computed textures -> however this can be addressed by going from tile-based to FG world coordinates and using 3-d noise. Due to the large distances involved, small-scale noise becomes then numerically unstable, but noise wavelength above 250 m can safely be done in world coordinates, leading to appealing visuals both at large and small distance. | |||
== Further reading == | == Further reading == | ||