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-- Author : Julian Andres Guarin Reyes.

-- Project : JART, Just Another Ray Tracer.

-- email : jguarin2002 at gmail.com, j.guarin at javeriana.edu.co

-- This code was entirely written by Julian Andres Guarin Reyes.

-- The following code is licensed under GNU Public License

-- http://www.gnu.org/licenses/gpl-3.0.txt.

 -- This file is part of JART (Just Another Ray Tracer).

    -- JART (Just Another Ray Tracer) is free software: you can redistribute it and/or modify

    -- it under the terms of the GNU General Public License as published by

    -- the Free Software Foundation, either version 3 of the License, or

    -- (at your option) any later version.

    -- JART (Just Another Ray Tracer) is distributed in the hope that it will be useful,

    -- but WITHOUT ANY WARRANTY; without even the implied warranty of

    -- MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

    -- GNU General Public License for more details.

    -- You should have received a copy of the GNU General Public License

    -- along with JART (Just Another Ray Tracer).  If not, see <http://www.gnu.org/licenses/>.

-- A single fixed minimun distance comparison cell.

library ieee;

use ieee.std_logic_1164.all;

use ieee.std_logic_arith.all;

use ieee.std_logic_unsigned.all;

use work.powerGrid.all;

entity dComparisonCell is

        generic (       W               : integer := 32;        -- operands Width ( reference V.D and column V.D) 

                                idColW  : integer := 2;         -- Column Sphere ID width. 1 = 2 columns max, 2= 4 colums max... and so on.

                                idCol   : integer := 0           -- Column Id

        );

        port    (

                                clk, rst, ena   : in std_logic;

                                intd : in std_logic; -- Reference intersection signal.

                                intq : out std_logic;

                                cIdd    : in    std_logic_vector (idColW - 1 downto 0);  -- This is the reference column identification input.

                                cIdq    : out   std_logic_vector (idColW - 1 downto 0);  -- This is the sphere identification output.

                                refvd   : in    std_logic_vector (W - 1 downto 0);               -- This is the projection incoming from the previous cell.

                                colvd   : in    std_logic_vector (W - 1 downto 0);               -- This is the projection of the sphere position over the ray traced vector, a.k.a. V.D! .

                                selvd   : out   std_logic_vector (W - 1 downto 0)                -- This is the smallest value between refvd and colvd.

        );

end entity;

architecture rtl of dComparisonCell is

        signal          ssl32 : std_logic;      -- This signal indicates if refvd is less than colvd

        signal          qdist : std_logic_vector (idColW downto 0);

begin

        -- A less than B comparison, check if colvd is less than refvd, meaning the act V.D less than actual min V.D

        cl32                    : sl32  port map (      dataa   => colvd,

                                                                                datab   => refvd,

                                                                                AlB             => ssl32

                                                                                );

        -- A flip flop with 2 to 1 mux.Selects between the smallest vd.

        selectorVD              : scanFF        generic map (   W = W   )

                                                                port map        (       clk     => clk,

                                                                                                rst => rst,

                                                                                                ena     => ena,

                                                                                                sel => ssl32,

                                                                                                d0      => refvd,

                                                                                                d1      => colvd,

                                                                                                q       => selvd

                                                                                        );

        -- Another flip flip with 2 to 1 mux. Selects the id and intersection signal of the smallest vd.

        selectorID              : scanFF        generic map     (       W = idColW+1 )

                                                                port map        (       clk => clk,

                                                                                                rst     => rst,

                                                                                                ena     => ena

                                                                                                sel     => ssl32,

                                                                                                d0      => cIdd&intd,

                                                                                                d1      => conv_std_logic_vector(idCol,idColW)&ssl32,

                                                                                                q       => qdist;

                                                                                                );

        cIdq <= qdist(idColw downto 1);

        intq <= qdist(0);

end rtl;