ScaleHelpers.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/Physics/PhysicsSettings.h>
 
JPH_NAMESPACE_BEGIN
 
namespace ScaleHelpers
{
    static constexpr float  cScaleToleranceSq = 1.0e-8f;
 
    inline bool             IsNotScaled(Vec3Arg inScale)                                    { return inScale.IsClose(Vec3::sReplicate(1.0f), cScaleToleranceSq); }
 
    inline bool             IsUniformScale(Vec3Arg inScale)                                 { return inScale.Swizzle<SWIZZLE_Y, SWIZZLE_Z, SWIZZLE_X>().IsClose(inScale, cScaleToleranceSq); }
 
    inline float            ScaleConvexRadius(float inConvexRadius, Vec3Arg inScale)        { return min(inConvexRadius * inScale.Abs().ReduceMin(), cDefaultConvexRadius); }
 
    inline bool             IsInsideOut(Vec3Arg inScale)                                    { return (CountBits(Vec3::sLess(inScale, Vec3::sZero()).GetTrues() & 0x7) & 1) != 0; }
 
    inline Vec3             MakeUniformScale(Vec3Arg inScale)                               { return Vec3::sReplicate((inScale.GetX() + inScale.GetY() + inScale.GetZ()) / 3.0f); }
 
    inline bool             CanScaleBeRotated(QuatArg inRotation, Vec3Arg inScale)
    {
        // inScale is a scale in local space of the shape, so the transform for the shape (ignoring translation) is: T = Mat44::sScale(inScale) * mRotation.
        // when we pass the scale to the child it needs to be local to the child, so we want T = mRotation * Mat44::sScale(ChildScale).
        // Solving for ChildScale: ChildScale = mRotation^-1 * Mat44::sScale(inScale) * mRotation = mRotation^T * Mat44::sScale(inScale) * mRotation
        // If any of the off diagonal elements are non-zero, it means the scale / rotation is not compatible.
        Mat44 r = Mat44::sRotation(inRotation);
        Mat44 child_scale = r.Multiply3x3LeftTransposed(r.PostScaled(inScale));
 
        // Get the columns, but zero the diagonal
        Vec4 zero = Vec4::sZero();
        Vec4 c0 = Vec4::sSelect(child_scale.GetColumn4(0), zero, UVec4(0xffffffff, 0, 0, 0)).Abs();
        Vec4 c1 = Vec4::sSelect(child_scale.GetColumn4(1), zero, UVec4(0, 0xffffffff, 0, 0)).Abs();
        Vec4 c2 = Vec4::sSelect(child_scale.GetColumn4(2), zero, UVec4(0, 0, 0xffffffff, 0)).Abs();
 
        // Check if all elements are less than epsilon
        Vec4 epsilon = Vec4::sReplicate(1.0e-6f);
        return UVec4::sAnd(UVec4::sAnd(Vec4::sLess(c0, epsilon), Vec4::sLess(c1, epsilon)), Vec4::sLess(c2, epsilon)).TestAllTrue();
    }
 
    inline Vec3             RotateScale(QuatArg inRotation, Vec3Arg inScale)
    {
        // Get the diagonal of mRotation^T * Mat44::sScale(inScale) * mRotation (see comment at CanScaleBeRotated)
        Mat44 r = Mat44::sRotation(inRotation);
        return r.Multiply3x3LeftTransposed(r.PostScaled(inScale)).GetDiagonal3();
    }
}
 
JPH_NAMESPACE_END