ActiveEdges.h

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// Jolt Physics Library (https://github.com/jrouwe/JoltPhysics)
// SPDX-FileCopyrightText: 2021 Jorrit Rouwe
// SPDX-License-Identifier: MIT
 
#pragma once
 
#include <Jolt/Geometry/ClosestPoint.h>
 
JPH_NAMESPACE_BEGIN
 
namespace ActiveEdges
{
    inline static bool                  IsEdgeActive(Vec3Arg inNormal1, Vec3Arg inNormal2, Vec3Arg inEdgeDirection)
    {
        // If normals are opposite the edges are active (the triangles are back to back)
        float cos_angle_normals = inNormal1.Dot(inNormal2);
        if (cos_angle_normals < -0.99984769515639123915701155881391f) // cos(179 degrees)
            return true;
            
        // Check if concave edge, if so we are not active
        if (inNormal1.Cross(inNormal2).Dot(inEdgeDirection) < 0.0f)
            return false;
 
        // Convex edge, active when angle bigger than threshold
        return cos_angle_normals < 0.99619469809174553229501040247389f; // cos(5 degrees)
    }
 
    inline static Vec3                  FixNormal(Vec3Arg inV0, Vec3Arg inV1, Vec3Arg inV2, Vec3Arg inTriangleNormal, uint8 inActiveEdges, Vec3Arg inPoint, Vec3Arg inNormal, Vec3Arg inMovementDirection)
    {
        // Check: All of the edges are active, we have the correct normal already. No need to call this function!
        JPH_ASSERT(inActiveEdges != 0b111);
 
        // If inNormal would affect movement less than inTriangleNormal use inNormal
        // This is done since it is really hard to make a distinction between sliding over a horizontal triangulated grid and hitting an edge (in this case you want to use the triangle normal)
        // and sliding over a triangulated grid and grazing a vertical triangle with an inactive edge (in this case using the triangle normal will cause the object to bounce back so we want to use the calculated normal).
        // To solve this we take a movement hint to give an indication of what direction our object is moving. If the edge normal results in less motion difference than the triangle normal we use the edge normal.
        float normal_length = inNormal.Length();
        float triangle_normal_length = inTriangleNormal.Length();
        if (inMovementDirection.Dot(inNormal) * triangle_normal_length < inMovementDirection.Dot(inTriangleNormal) * normal_length)
            return inNormal;
 
        // Check: None of the edges are active, we need to use the triangle normal
        if (inActiveEdges == 0)
            return inTriangleNormal;
 
        // Some edges are active.
        // If normal is parallel to the triangle normal we don't need to check the active edges.
        if (inTriangleNormal.Dot(inNormal) > 0.99619469809174553229501040247389f * normal_length * triangle_normal_length) // cos(5 degrees)
            return inNormal;
 
        const float cEpsilon = 1.0e-4f;
        const float cOneMinusEpsilon = 1.0f - cEpsilon;
 
        uint colliding_edge;
 
        // Test where the contact point is in the triangle
        float u, v, w;
        ClosestPoint::GetBaryCentricCoordinates(inV0 - inPoint, inV1 - inPoint, inV2 - inPoint, u, v, w);
        if (u > cOneMinusEpsilon)
        {
            // Colliding with v0, edge 0 or 2 needs to be active
            colliding_edge = 0b101;
        }
        else if (v > cOneMinusEpsilon)
        {
            // Colliding with v1, edge 0 or 1 needs to be active
            colliding_edge = 0b011;
        }
        else if (w > cOneMinusEpsilon)
        {
            // Colliding with v2, edge 1 or 2 needs to be active
            colliding_edge = 0b110;
        }
        else if (u < cEpsilon)
        {
            // Colliding with edge v1, v2, edge 1 needs to be active
            colliding_edge = 0b010;
        }
        else if (v < cEpsilon)
        {
            // Colliding with edge v0, v2, edge 2 needs to be active
            colliding_edge = 0b100;
        }
        else if (w < cEpsilon)
        {
            // Colliding with edge v0, v1, edge 0 needs to be active
            colliding_edge = 0b001;
        }
        else
        {
            // Interior hit
            return inTriangleNormal;
        }
 
        // If this edge is active, use the provided normal instead of the triangle normal
        return (inActiveEdges & colliding_edge) != 0? inNormal : inTriangleNormal;
    }
}
 
JPH_NAMESPACE_END