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166 lines
5.2 KiB
C++
166 lines
5.2 KiB
C++
//
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//---------------------------------------------------------------------------
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// AABB-tree used for ray testing
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// Copyright(C) 2017 Magnus Norddahl
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// All rights reserved.
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//
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// This program is free software: you can redistribute it and/or modify
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// it under the terms of the GNU Lesser General Public License as published by
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// the Free Software Foundation, either version 3 of the License, or
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// (at your option) any later version.
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//
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// This program is distributed in the hope that it will be useful,
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// but WITHOUT ANY WARRANTY; without even the implied warranty of
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// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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// GNU Lesser General Public License for more details.
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//
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// You should have received a copy of the GNU Lesser General Public License
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// along with this program. If not, see http://www.gnu.org/licenses/
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//
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//--------------------------------------------------------------------------
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//
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#include <algorithm>
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#include "hw_aabbtree.h"
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namespace hwrenderer
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{
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TArray<int> LevelAABBTree::FindNodePath(unsigned int line, unsigned int node)
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{
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const AABBTreeNode &n = nodes[node];
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if (n.aabb_left > treelines[line].x || n.aabb_right < treelines[line].x ||
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n.aabb_top > treelines[line].y || n.aabb_bottom < treelines[line].y)
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{
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return {};
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}
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TArray<int> path;
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if (n.line_index == -1)
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{
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path = FindNodePath(line, n.left_node);
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if (path.Size() == 0)
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path = FindNodePath(line, n.right_node);
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if (path.Size())
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path.Push(node);
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}
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else if (n.line_index == (int)line)
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{
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path.Push(node);
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}
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return path;
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}
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double LevelAABBTree::RayTest(const DVector3 &ray_start, const DVector3 &ray_end)
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{
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// Precalculate some of the variables used by the ray/line intersection test
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DVector2 raydelta = ray_end - ray_start;
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double raydist2 = raydelta | raydelta;
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DVector2 raynormal = DVector2(raydelta.Y, -raydelta.X);
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double rayd = raynormal | ray_start;
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if (raydist2 < 1.0)
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return 1.0f;
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double hit_fraction = 1.0;
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// Walk the tree nodes
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int stack[32];
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int stack_pos = 1;
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stack[0] = nodes.Size() - 1; // root node is the last node in the list
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while (stack_pos > 0)
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{
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int node_index = stack[stack_pos - 1];
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if (!OverlapRayAABB(ray_start, ray_end, nodes[node_index]))
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{
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// If the ray doesn't overlap this node's AABB we're done for this subtree
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stack_pos--;
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}
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else if (nodes[node_index].line_index != -1) // isLeaf(node_index)
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{
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// We reached a leaf node. Do a ray/line intersection test to see if we hit the line.
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hit_fraction = std::min(IntersectRayLine(ray_start, ray_end, nodes[node_index].line_index, raydelta, rayd, raydist2), hit_fraction);
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stack_pos--;
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}
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else if (stack_pos == 32)
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{
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stack_pos--; // stack overflow - tree is too deep!
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}
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else
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{
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// The ray overlaps the node's AABB. Examine its child nodes.
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stack[stack_pos - 1] = nodes[node_index].left_node;
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stack[stack_pos] = nodes[node_index].right_node;
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stack_pos++;
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}
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}
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return hit_fraction;
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}
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bool LevelAABBTree::OverlapRayAABB(const DVector2 &ray_start2d, const DVector2 &ray_end2d, const AABBTreeNode &node)
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{
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// To do: simplify test to use a 2D test
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DVector3 ray_start = DVector3(ray_start2d, 0.0);
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DVector3 ray_end = DVector3(ray_end2d, 0.0);
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DVector3 aabb_min = DVector3(node.aabb_left, node.aabb_top, -1.0);
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DVector3 aabb_max = DVector3(node.aabb_right, node.aabb_bottom, 1.0);
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// Standard 3D ray/AABB overlapping test.
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// The details for the math here can be found in Real-Time Rendering, 3rd Edition.
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// We could use a 2D test here instead, which would probably simplify the math.
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DVector3 c = (ray_start + ray_end) * 0.5f;
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DVector3 w = ray_end - c;
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DVector3 h = (aabb_max - aabb_min) * 0.5f; // aabb.extents();
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c -= (aabb_max + aabb_min) * 0.5f; // aabb.center();
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DVector3 v = DVector3(fabs(w.X), fabs(w.Y), fabs(w.Z));
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if (fabs(c.X) > v.X + h.X || fabs(c.Y) > v.Y + h.Y || fabs(c.Z) > v.Z + h.Z)
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return false; // disjoint;
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if (fabs(c.Y * w.Z - c.Z * w.Y) > h.Y * v.Z + h.Z * v.Y ||
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fabs(c.X * w.Z - c.Z * w.X) > h.X * v.Z + h.Z * v.X ||
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fabs(c.X * w.Y - c.Y * w.X) > h.X * v.Y + h.Y * v.X)
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return false; // disjoint;
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return true; // overlap;
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}
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double LevelAABBTree::IntersectRayLine(const DVector2 &ray_start, const DVector2 &ray_end, int line_index, const DVector2 &raydelta, double rayd, double raydist2)
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{
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// Check if two line segments intersects (the ray and the line).
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// The math below does this by first finding the fractional hit for an infinitely long ray line.
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// If that hit is within the line segment (0 to 1 range) then it calculates the fractional hit for where the ray would hit.
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//
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// This algorithm is homemade - I would not be surprised if there's a much faster method out there.
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const double epsilon = 0.0000001;
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const AABBTreeLine &line = treelines[line_index];
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DVector2 raynormal = DVector2(raydelta.Y, -raydelta.X);
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DVector2 line_pos(line.x, line.y);
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DVector2 line_delta(line.dx, line.dy);
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double den = raynormal | line_delta;
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if (fabs(den) > epsilon)
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{
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double t_line = (rayd - (raynormal | line_pos)) / den;
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if (t_line >= 0.0 && t_line <= 1.0)
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{
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DVector2 linehitdelta = line_pos + line_delta * t_line - ray_start;
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double t = (raydelta | linehitdelta) / raydist2;
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return t > 0.0 ? t : 1.0;
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}
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}
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return 1.0;
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}
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}
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