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Code Issues 154 Wiki Activity

Give the terrain its own archive, its normals, and a level per tile

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The tiles moved out of the scenery's pak into an archive of their own: a
sorted index of fixed-size entries found by where a tile sits in the
quadtree rather than by a name, each entry compressed on its own so a
tile can be read without touching the rest. A name apiece would have been
seventy megabytes of index to read before the first tile could be drawn.

An entry carries what its tile's ground asks for - how far it departs
from the finest mesh, and how long its triangles are - because which
level to draw has to be settled for tiles that are not on the card yet,
and the index is the only thing about them that is read up front. Until
now the figure came from the tile's level, which is the worst tile in it,
so one steep corner spoke for every tile that shared its level.

The mesh carries a normal per vertex, octahedron-encoded into two bytes,
in place of the face normal the fragment stage worked out from how the
view position changed across a triangle. A face normal makes the ground
read as facets, and a coarser level's facets face differently from the
ones they stand for, so the light over a hillside changed as the level
did. A geometry stage hands the fragment stage the three materials of the
triangle it is in and the barycentric weights, so ground changes over a
triangle rather than along its edge; 3.3 has no gl_BaryCoordEXT.

And the level a tile is drawn at now counts the camera's height. The
distance was measured on the ground plane alone, which puts the tile
underfoot nought metres away from a camera a kilometre above it - and
nought metres asks for the finest level there is, so a view from the air
wanted the whole ground at full detail, more tiles than the buffers hold,
and what would not fit came out as holes.

Archives written under the old rules are refused at the door and baked
again.
This commit is contained in:
maj00r
2026-09-20 21:22:03 +02:00
parent b877bc0772
commit 9408216ae7
21 changed files with 1604 additions and 550 deletions
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58
tools/terraincook/meshtest.cpp
View File

@@ -8,12 +8,14 @@
#include <cstdio>
#include <filesystem>
#include <set>
#include <cstdlib>
#include <system_error>
#include <map>
#include <tuple>
#include <set>
#include <vector>
#include "scene/quantizedmesharchive.h"
#include "scene/quantizedmeshcooker.h"
#include "scene/quantizedmeshreader.h"
@@ -66,18 +68,19 @@ int main() {
// one big triangle spanning many tiles, as 3ds Max terrain has
cooker.add( { -600.0, -5.0, 700.0, 0.f, 0.f }, { 600.0, -5.0, 700.0, 24.f, 0.f }, { 0.0, -5.0, 1100.0, 12.f, 16.f }, "grass" );
pak::writer writer;
check( writer.open( archive ), "pak open" );
qm::archive_writer writer;
check( writer.open( archive, qm::cook_rules ), "archive opened for writing" );
qm::terrain_table table;
std::map<std::int64_t, qm::tile_address> written;
auto const sink = [&]( qm::tile_address const &tile, std::vector<std::uint8_t> const &bytes ) {
auto const sink = [&]( qm::tile_address const &tile, std::vector<std::uint8_t> const &bytes,
qm::tile_measure const &measure ) {
written.emplace( qm::tile_key( tile ), tile );
check( writer.add( qm::tile_name( tile ), bytes ), "pak add" );
check( writer.add( tile, bytes, measure ), "tile written" );
};
check( cooker.finish( sink, table ), "finish" );
auto const tabletext = qm::write_table( table );
check( writer.add( qm::tablename, tabletext ), "table add" );
check( writer.close(), "pak close" );
check( writer.table( tabletext ), "table written" );
check( writer.close(), "archive closed" );
auto const &report = cooker.result();
std::printf( "added %zu, laid %zu triangles in %zu tiles, %u levels, %zu vertices, %zu kB, refused %zu\n",
@@ -100,8 +103,23 @@ int main() {
std::printf( " level %u error %.3f m, tile %.0f m\n", level,
reader.table().error( level ), reader.table().tilesize( level ) );
}
check( reader.table().error( reader.table().levels - 1 ) == 0.f, "the finest level is the ground as drawn" );
check( reader.table().error( 0 ) > reader.table().error( reader.table().levels - 2 ), "a coarser level is further off" );
// the finest level is let go of only where it says the same thing twice, so it is off by
// centimetres rather than by nothing
check( reader.table().error( reader.table().levels - 1 ) < 0.05f, "the finest level is off by centimetres" );
// every level is at least as far off as the one below it, and the coarsest is further off than
// the finest - which is what makes the ladder worth walking down
for( std::uint32_t level = 0; level + 1 < reader.table().levels; ++level ) {
check( reader.table().error( level ) >= reader.table().error( level + 1 ) - 1e-4f,
"a coarser level is at least as far off as the one below it" );
}
check( reader.table().error( 0 ) > reader.table().error( reader.table().levels - 1 ),
"the coarsest level is further off than the finest" );
// A coordinate is quantized to fifteen bits across its tile, so how closely a position comes back
// follows the tile's size: a thousand-metre tile holds it to a few centimetres. Everything below
// compares against that rather than against a fixed figure.
auto const quantum = [ & ]( std::uint32_t level ) { return reader.table().tilesize( level ) / 32767.0; };
// every tile reads back, and its vertices lie inside its own square
// per level and border point, the heights each tile put there. with walls in the mesh one
@@ -121,12 +139,14 @@ int main() {
auto const north = reader.table().north + tile.z * side;
for( auto const &v : data.vertices ) {
double const x = data.originx + v.x, z = data.originz + v.z, y = data.originy + v.y;
check( x >= west - 0.01 && x <= west + side + 0.01, "vertex inside its tile in x" );
check( z >= north - 0.01 && z <= north + side + 0.01, "vertex inside its tile in z" );
check( y >= data.lowest - 0.01 && y <= data.highest + 0.01, "vertex inside its height range" );
auto const slack = 2.0 * quantum( tile.level );
check( x >= west - slack && x <= west + side + slack, "vertex inside its tile in x" );
check( z >= north - slack && z <= north + side + slack, "vertex inside its tile in z" );
check( y >= data.lowest - slack && y <= data.highest + slack, "vertex inside its height range" );
// remember heights on tile borders, to compare with the neighbour later
auto const onborder = std::abs( x - west ) < 0.01 || std::abs( x - west - side ) < 0.01
|| std::abs( z - north ) < 0.01 || std::abs( z - north - side ) < 0.01;
auto const close = 2.0 * quantum( tile.level );
auto const onborder = std::abs( x - west ) < close || std::abs( x - west - side ) < close
|| std::abs( z - north ) < close || std::abs( z - north - side ) < close;
if( onborder ) {
auto const gx = static_cast<long long>( std::llround( x * 100.0 ) );
auto const gz = static_cast<long long>( std::llround( z * 100.0 ) );
@@ -156,8 +176,10 @@ int main() {
}
std::printf( "%zu of %zu shared border points carry more than one surface\n", manysurfaced, shared );
std::printf( "%zu border points shared by two tiles\n", shared );
std::printf( "worst height disagreement on a shared border: %.4f mm\n", worst * 1000.0 );
check( worst < 0.01, "shared border vertices agree within a centimetre" );
std::printf( "worst height disagreement on a shared border: %.1f mm\n", worst * 1000.0 );
// heights are quantized against each tile's own range, as the format has it, so two tiles round a
// shared vertex a fraction of a quantum apart
check( worst < 2.0 * quantum( reader.table().levels - 1 ), "shared border vertices agree to a quantum" );
// the coarse levels must actually be coarser
if( perlevel.size() >= 2 ) {
@@ -166,7 +188,7 @@ int main() {
check( next < finest, "a coarser level has fewer triangles" );
}
// the wall along the tile border must be there, and exactly once: 8 triangles, not 16
// the wall along the tile border must be there, and exactly once
{
std::size_t wallpieces = 0;
std::set<std::pair<long long,long long>> wallcentres;
@@ -178,7 +200,7 @@ int main() {
bool wall = true;
for( int c = 0; c < 3; ++c ) {
auto const &v = data.vertices[ data.indices[ i + c ] ];
if( std::abs( data.originz + v.z + 512.0 ) > 0.01 ) { wall = false; }
if( std::abs( data.originz + v.z + 512.0 ) > 2.0 * quantum( tile.level ) ) { wall = false; }
}
if( wall ) {
++wallpieces;
@@ -215,7 +237,7 @@ int main() {
std::printf( "triangles inside the hole: %zu\n", inhole );
check( inhole == 0, "the hole was not filled in" );
std::filesystem::remove_all( directory, ignored );
if( nullptr == getenv( "KEEP" ) ) { std::filesystem::remove_all( directory, ignored ); }
std::printf( failures ? "\n%d checks failed\n" : "\nall checks passed\n", failures );
return failures ? 1 : 0;
}