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The ground in a scenery is already an irregular mesh, so the cook keeps it: it cuts the triangles along the tile grid, welds what coincides, and builds each coarser level by collapsing edges. Nothing is resampled, nothing is interpolated, and a hole the scenery left stays a hole. What was here before threw the triangles away, kept their vertices and built a fresh Delaunay triangulation over them, which filled every hole, merged the two heights of every retaining wall into one, and - because it never erased the super-triangle - emitted indices three too large together with triangles reaching out to the artificial corners. Tiles form a quadtree, as Cesium Quantized Mesh intends. A distant tile is a large one, so the horizon costs tens of tiles rather than the thousands a fixed grid needed, and the level to draw follows from the tile's own geometric error against what the screen can resolve - which is what the format carries that field for. Every vertex on a tile's border survives into all of its coarser levels, and so does every edge between two of them, so two neighbours drawn at different levels share their border exactly: there is nothing to stitch and nothing to morph. The file layout is the format's, with two deliberate departures, both written down in quantizedmeshformat.h: the geodetic header fields carry scenery metres, there being no geographic reference to convert from, and the material a vertex belongs to rides in an extension of ours. Texture coordinates are not stored at all - ground tiles in world space, so the coordinate follows from the position and from how many metres one repeat of the material covers, measured off the scenery once and kept in the terrain's table. Tiles live in one archive beside the scenery, an entry each, compressed on its own. Baltyk cooks to 546 kB against 2.2 MB of heightfields, quark to 361 kB against 9.6 MB, tomaszewo to 375 kB against 9.9 MB. Drawing is one call a frame: every resident tile lives in the same vertex and index buffer, with its vertices measured from the middle of the terrain so that the whole map fits in floats, and a frame is one glMultiDrawElementsBaseVertex over the tiles the walk chose and the frustum kept. On baltyk that settles at 291 tiles resident, 16 MB of mesh, 85 tiles and 6k triangles drawn. What counts as ground is what the scenery says, not what its triangles look like. A node under origin, rotate or scale is an object standing on the ground; a material with an alpha channel is a tree, a bush, a fence or a catenary mast. Everything else is laid whichever way it faces, so the side of an embankment or a cutting goes in with the rest instead of leaving a hole along every bank. Whatever is left out is recorded per node, and the scenery goes on drawing it. A cook is a cache: it is used again only when the archive, the note of which nodes went into it and the manifest of what the scenery was made from all agree. A manifest listing a file the scenery names but does not have used to fail that test for ever, since an absent file never matches - quark has such an include, and nothing beside it could ever be reused. tools/terraincook cooks the same way outside the engine, and meshtest beside it checks what the cook promises: a tile reads back as written, neighbouring tiles agree on their border to the millimetre, a hole is not filled in, a wall is laid exactly once, and a material's tiling comes out of the source. seamcheck.py goes: it tested the morphing constants of a heightfield nothing reads any more.
73 lines
3.1 KiB
C++
73 lines
3.1 KiB
C++
/*
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This Source Code Form is subject to the
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terms of the Mozilla Public License, v.
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2.0. If a copy of the MPL was not
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distributed with this file, You can
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obtain one at
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http://mozilla.org/MPL/2.0/.
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*/
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module;
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#include <algorithm>
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#include <array>
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#include <cmath>
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#include <cstddef>
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#include <cstdint>
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#include <string>
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#include <vector>
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export module eu07.rendering.terrainstatus;
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export {
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// Which level of the quadtree a tile is drawn at follows from what the coarser mesh would cost in
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// pixels. Every tile says how far its ground departs from the finest mesh, in metres; that error,
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// at the tile's distance, covers a number of pixels, and while it covers fewer than the detail
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// setting asks for there is nothing to gain by going finer. Pixelsperunit is the viewport height
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// over twice the tangent of half the vertical field of view - what a metre at a metre's distance
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// spans - so zooming in or a taller window pushes detail further out on its own.
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//
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// This is the format's own rule, and the reason a tile carries its error at all.
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inline constexpr std::size_t terrain_maxlevels { 16 };
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inline bool
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terrain_level_enough(
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double const Error, double const Distance, double const Pixelsperunit, double const Detail ) {
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return Error * Pixelsperunit <= std::max( 0.1, Detail ) * std::max( 1.0, Distance );
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}
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// how far the camera may move before which tiles are wanted is worked out again, as a share of the
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// finest tile's side
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inline constexpr double terrain_rescan_tiles { 0.25 };
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// what one terrain's streamer is doing, kept by it and read by the debug panel
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struct terrain_statistics {
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std::size_t resident { 0 }; // tiles held in the vertex and index buffers
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std::size_t chosen { 0 }; // tiles the last walk of the quadtree settled on drawing
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std::size_t drawn { 0 }; // of those, the ones inside the frustum in the last draw
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std::size_t triangles { 0 }; // triangles in the last draw
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std::size_t wanted { 0 }; // tiles the walk asked for and did not have
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std::size_t uploaded { 0 }; // tiles put in the buffers since opening
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std::size_t dropped { 0 }; // arrivals discarded as no longer wanted
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std::size_t gpubytes { 0 }; // what the two buffers hold
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std::array<std::size_t, terrain_maxlevels> perlevel {}; // tiles drawn at each level
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};
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// one terrain as the debug panel shows it. the renderer writes it once a frame from the main view,
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// the panel reads it; neither needs to know the other's types
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struct terrain_field_status {
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std::string path;
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float tilesize { 0.f }; // side of a tile at the finest level, in metres
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float range { 0.f };
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float detail { 0.f }; // pixels an error may cover before a finer level is used
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std::uint32_t levels { 0 };
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std::size_t backlog { 0 }; // tiles the loader has queued or finished and not handed over
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std::array<float, terrain_maxlevels> leveltile {}; // tile side at each level
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std::array<float, terrain_maxlevels> levelerror {}; // metres a level departs from the finest
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terrain_statistics stats;
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};
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inline std::vector<terrain_field_status> TerrainStatus;
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}
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