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112 lines
5.0 KiB
C#
112 lines
5.0 KiB
C#
using System;
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using OpenTK;
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namespace ClassicalSharp {
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public static class Picking {
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// http://www.xnawiki.com/index.php/Voxel_traversal
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//https://web.archive.org/web/20120113051728/http://www.xnawiki.com/index.php?title=Voxel_traversal
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/// <summary> Determines the picked block based on the given origin and direction vector.<br/>
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/// Marks pickedPos as invalid if a block could not be found due to going outside map boundaries
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/// or not being able to find a suitable candiate within the given reach distance. </summary>
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public static void CalculatePickedBlock( Game window, Vector3 origin, Vector3 dir, float reach, PickedPos pickedPos ) {
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// Implementation based on: "A Fast Voxel Traversal Algorithm for Ray Tracing"
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// John Amanatides, Andrew Woo
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// http://www.cse.yorku.ca/~amana/research/grid.pdf
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// http://www.devmaster.net/articles/raytracing_series/A%20faster%20voxel%20traversal%20algorithm%20for%20ray%20tracing.pdf
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// The cell in which the ray starts.
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Vector3I start = Vector3I.Floor( origin ); // Rounds the position's X, Y and Z down to the nearest integer values.
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int x = start.X, y = start.Y, z = start.Z;
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// Determine which way we go.
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int stepX = Math.Sign( dir.X ), stepY = Math.Sign( dir.Y ), stepZ = Math.Sign( dir.Z );
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// Calculate cell boundaries. When the step (i.e. direction sign) is positive,
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// the next boundary is AFTER our current position, meaning that we have to add 1.
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// Otherwise, it is BEFORE our current position, in which case we add nothing.
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Vector3I cellBoundary = new Vector3I(
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x + (stepX > 0 ? 1 : 0),
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y + (stepY > 0 ? 1 : 0),
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z + (stepZ > 0 ? 1 : 0) );
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// NOTE: we want it so if dir.x = 0, tmax.x = positive infinity
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// Determine how far we can travel along the ray before we hit a voxel boundary.
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Vector3 tMax = new Vector3(
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(cellBoundary.X - origin.X) / dir.X, // Boundary is a plane on the YZ axis.
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(cellBoundary.Y - origin.Y) / dir.Y, // Boundary is a plane on the XZ axis.
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(cellBoundary.Z - origin.Z) / dir.Z ); // Boundary is a plane on the XY axis.
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if( Single.IsNaN( tMax.X ) || Single.IsInfinity( tMax.X ) ) tMax.X = Single.PositiveInfinity;
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if( Single.IsNaN( tMax.Y ) || Single.IsInfinity( tMax.Y ) ) tMax.Y = Single.PositiveInfinity;
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if( Single.IsNaN( tMax.Z ) || Single.IsInfinity( tMax.Z ) ) tMax.Z = Single.PositiveInfinity;
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// Determine how far we must travel along the ray before we have crossed a gridcell.
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Vector3 tDelta = new Vector3( stepX / dir.X, stepY / dir.Y, stepZ / dir.Z );
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if( Single.IsNaN( tDelta.X ) ) tDelta.X = Single.PositiveInfinity;
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if( Single.IsNaN( tDelta.Y ) ) tDelta.Y = Single.PositiveInfinity;
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if( Single.IsNaN( tDelta.Z ) ) tDelta.Z = Single.PositiveInfinity;
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Map map = window.Map;
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BlockInfo info = window.BlockInfo;
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float reachSquared = reach * reach;
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int iterations = 0;
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// For each step, determine which distance to the next voxel boundary is lowest (i.e.
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// which voxel boundary is nearest) and walk that way.
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while( iterations < 10000 ) {
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byte block = GetBlock( map, x, y, z, origin );
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Vector3 min = new Vector3( x, y, z ) + info.MinBB[block];
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Vector3 max = new Vector3( x, y, z ) + info.MaxBB[block];
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float dx = Math.Min( Math.Abs( origin.X - min.X ), Math.Abs( origin.X - max.X ) );
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float dy = Math.Min( Math.Abs( origin.Y - min.Y ), Math.Abs( origin.Y - max.Y ) );
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float dz = Math.Min( Math.Abs( origin.Z - min.Z ), Math.Abs( origin.Z - max.Z ) );
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if( dx * dx + dy * dy + dz * dz > reachSquared ) {
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pickedPos.SetAsInvalid();
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return;
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}
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if( window.CanPick( block ) ) {
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// This cell falls on the path of the ray. Now perform an additional bounding box test,
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// since some blocks do not occupy a whole cell.
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float t0, t1;
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if( Intersection.RayIntersectsBox( origin, dir, min, max, out t0, out t1 ) ) {
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Vector3 intersect = origin + dir * t0;
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pickedPos.SetAsValid( min, max, block, intersect );
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return;
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}
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}
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if( tMax.X < tMax.Y && tMax.X < tMax.Z ) {
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// tMax.X is the lowest, an YZ cell boundary plane is nearest.
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x += stepX;
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tMax.X += tDelta.X;
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} else if( tMax.Y < tMax.Z ) {
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// tMax.Y is the lowest, an XZ cell boundary plane is nearest.
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y += stepY;
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tMax.Y += tDelta.Y;
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} else {
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// tMax.Z is the lowest, an XY cell boundary plane is nearest.
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z += stepZ;
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tMax.Z += tDelta.Z;
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}
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iterations++;
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}
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throw new InvalidOperationException( "did over 10000 iterations in GetPickedBlockPos(). " +
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"Something has gone wrong. (dir: " + dir + ")" );
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}
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static byte GetBlock( Map map, int x, int y, int z, Vector3 origin ) {
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if( x >= 0 && z >= 0 && x < map.Width && z < map.Length ) {
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if( y >= map.Height ) return 0;
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if( y >= 0 ) return map.GetBlock( x, y, z );
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// special case: we want to be able to pick bedrock when we're standing on top of it
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if( origin.Y >= 0 && y == -1 )
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return (byte)Block.Bedrock;
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}
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return 0;
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}
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}
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} |