ObjectLayerPairFilterTable.h

Go to the documentation of this file.

// Jolt Physics Library (https://github.com/jrouwe/JoltPhysics)
// SPDX-FileCopyrightText: 2023 Jorrit Rouwe
// SPDX-License-Identifier: MIT
 
#pragma once
 
#include <Jolt/Physics/Collision/ObjectLayer.h>
 
JPH_NAMESPACE_BEGIN
 
class ObjectLayerPairFilterTable : public ObjectLayerPairFilter
{
private:
    uint                    GetBit(ObjectLayer inLayer1, ObjectLayer inLayer2) const
    {
        // We store the lower left half only, so swap the inputs when trying to access the top right half
        if (inLayer1 > inLayer2)
            swap(inLayer1, inLayer2);
 
        JPH_ASSERT(inLayer2 < mNumObjectLayers);
 
        // Calculate at which bit the entry for this pair resides
        // We use the fact that a row always starts at inLayer2 * (inLayer2 + 1) / 2
        // (this is the amount of bits needed to store a table of inLayer2 entries)
        return (inLayer2 * (inLayer2 + 1)) / 2 + inLayer1;
    }
 
public:
    JPH_OVERRIDE_NEW_DELETE
 
    explicit                ObjectLayerPairFilterTable(uint inNumObjectLayers) :
        mNumObjectLayers(inNumObjectLayers)
    {
        // By default nothing collides
        // For the first layer we only need to store 1 bit, for the second 2 bits, for the third 3 bits, etc.
        // We use the formula Sum_i=1^N i = N * (N + 1) / 2 to calculate the size of the table
        int table_size = (inNumObjectLayers * (inNumObjectLayers + 1) / 2 + 7) / 8;
        mTable.resize(table_size, 0);
    }
 
    uint                    GetNumObjectLayers() const
    {
        return mNumObjectLayers;
    }
 
    void                    DisableCollision(ObjectLayer inLayer1, ObjectLayer inLayer2)
    {
        uint bit = GetBit(inLayer1, inLayer2);
        mTable[bit >> 3] &= (0xff ^ (1 << (bit & 0b111)));
    }
 
    void                    EnableCollision(ObjectLayer inLayer1, ObjectLayer inLayer2)
    {
        uint bit = GetBit(inLayer1, inLayer2);
        mTable[bit >> 3] |= 1 << (bit & 0b111);
    }
 
    virtual bool            ShouldCollide(ObjectLayer inObject1, ObjectLayer inObject2) const override
    {
        // Test if the bit is set for this group pair
        uint bit = GetBit(inObject1, inObject2);
        return (mTable[bit >> 3] & (1 << (bit & 0b111))) != 0;
    }
 
private:
    uint                    mNumObjectLayers;                           
    Array<uint8>            mTable;                                     
};
 
JPH_NAMESPACE_END