vector3, bool QA_CheckIfJumpable(double maxPitch = double.max)
{
    // gimpy-ass PM_SlideMove wannabe let's go
    if (floorsector)
    {
        double fas_floorz;
        Sector fas_sector;

        [fas_floorz, fas_sector] = floorsector.NextLowestFloorAt(pos.x, pos.y, pos.z, FFCF_3DRESTRICT, MaxStepHeight);

        vector3 normal = fas_sector.floorplane.Normal;
        double floorPitch = 90 - atan2(normal.z, (normal.x, normal.y).length());

        if (pos.z <= fas_floorz)
        {
            return normal, floorPitch < maxPitch;
        }
    }

    return (0, 0, 1), false;
}


bool QA_CheckJump()
{
    UserCmd cmd = player.cmd;

    if (player.onGround && (cmd.buttons & BT_JUMP) && level.IsJumpingAllowed() && !Q_BlockJump)
    {
        double jumpvelz = (JumpZ * 35) / TICRATE;
        double jumpfac  = 0;

        // [BC] If the player has the high jump power, double his jump velocity.
        // (actually, pick the best factors from all active items.)
        //
        // I would modify this to add the effective jump bonuses together,
        //  but that'd lead to serious jump height sequence breaks
        for (let p = Inv; p != null; p = p.Inv)
        {
            let pp = PowerHighJump(p);

            if (pp)
            {
                double f = pp.Strength;
                jumpfac = max(jumpfac, f);
            }
        }

        if (jumpfac > 0) { jumpvelz *= jumpfac; }


        vector3 floornormal;
        bool canjump;

        [floornormal, canjump] = QA_CheckIfJumpable(MAXSLOPEPITCH);
        if (!canjump) { return false; }

        vector3 newvel = vel;

        // Disgusting hack to get what our Z velocity should be
        // Breaks with teleporters, although I guess you could say it's
        //  kinda like portal jumping
        if (Q_GroundTime <= 1)
        {
            newvel.z = Q_LastVel.z - GetGravity();
        }

        double speedIntoFloor = -newvel dot floornormal;
        vector3 alignedvel = newvel + (floornormal * speedIntoFloor);

        vector3 jumpvector = (0, 0, jumpvelz);

        // Going into floor, align velocity to floor
        if ((Q_GroundTime <= 1 && newvel.z <= 0) || speedIntoFloor > 0)
        {
            newvel = alignedvel;

            // Angle jump off floor too since we're bunnyhopping
            if (Q_GroundTime <= 1)
            {
                jumpvector = floornormal * jumpvelz;
            }
        }

        newvel = alignedvel + (newvel - alignedvel) * Q_DoubleJumpFactor;
        vel = newvel + jumpvector;

        // XY changes always apply to ramp jumps, but Z changes can be disabled
        if (!Q_RampJump)
        {
            vel.z = newvel.z + jumpvelz;
        }

        if (!Q_Autohop) { Q_BlockJump  = true; }
        if (!(player.cheats & CF_PREDICTING)) { A_PlaySound("*jump", CHAN_BODY); }

        return true;
    }

    return false;
}