Create two moving objects with VGA controller - vhdl

Question

I am trying to implement a few "ball" bouncing around on a 800x600 screen. I dont completely understand how to make the 2nd ball move on the screen. Right now, it just stays on the screen statically at a certain position.
Here is a shot at what I've done so far.
library IEEE;
use IEEE.STD_LOGIC_1164.ALL;
use IEEE.STD_LOGIC_ARITH.ALL;
use IEEE.STD_LOGIC_UNSIGNED.ALL;
entity pong is
Port ( myclk : in STD_LOGIC;
rgb : out STD_LOGIC_VECTOR (2 downto 0);
hs : out STD_LOGIC;
vs : out STD_LOGIC);
end pong;
architecture Behavioral of pong is
signal clk: STD_LOGIC;
signal horz_scan: STD_LOGIC_VECTOR (9 downto 0);
signal vert_scan: STD_LOGIC_VECTOR (9 downto 0);
signal vinc_flag: STD_LOGIC;
signal dx: STD_LOGIC;
signal dy: STD_LOGIC;
signal refresh_counter: STD_LOGIC;
signal posx: integer := 300;
signal posy: integer := 300;
signal color: STD_LOGIC_VECTOR (2 downto 0) := "111";
signal vinc_flag2: STD_LOGIC;
signal dx2: STD_LOGIC;
signal dy2: STD_LOGIC;
signal posx2: integer := 300;
signal posy2: integer := 300;
signal color2: STD_LOGIC_VECTOR (2 downto 0) := "001";
signal refresh_counter2: STD_LOGIC;
signal horz_scan2: STD_LOGIC_VECTOR (9 downto 0);
signal vert_scan2: STD_LOGIC_VECTOR (9 downto 0);
signal clk2: STD_LOGIC;
begin
-- Clock divide by 1/2
process(myclk)
begin
if myclk = '1' and myclk'Event then
clk <= not clk;
end if;
end process;
-- horizonal clock
process(clk)
begin
if clk = '1' and clk'Event then
if horz_scan = "1100100000" then
horz_scan <= "0000000000";
else
horz_scan <= horz_scan + 1;
end if;
end if;
end process;
-- vertial clock (increments when the horizontal clock is on the front porch
process(vinc_flag)
begin
if vinc_flag = '1' and vinc_flag'Event then
if vert_scan = "1000001001" then
vert_scan <= "0000000000";
refresh_counter <= refresh_counter xor '1';
else
vert_scan <= vert_scan + 1;
end if;
end if;
end process;
process(vinc_flag2)
begin
if vinc_flag2 = '1' and vinc_flag2'Event then
if vert_scan2 = "1000001001" then
vert_scan2 <= "0000000000";
refresh_counter2 <= refresh_counter2 xor '1';
else
vert_scan2 <= vert_scan2 + 1;
end if;
end if;
end process;
process(refresh_counter)
begin
if refresh_counter = '1' and refresh_counter'Event then
if dx = '0' then
posx <= posx + 1;
else
posx <= posx -1;
end if;
if dy = '0' then
posy <= posy + 1;
else
posy <= posy -1;
end if;
color <= "100";
end if;
end process;
process(refresh_counter2)
begin
if refresh_counter2 = '1' and refresh_counter2'Event then
if dx2 = '0' then
posx2 <= posx2 + 1;
else
posx2 <= posx2 -1;
end if;
if dy2 = '0' then
posy2 <= posy2 + 1;
else
posy2 <= posy2 -1;
end if;
color2 <= "001";
end if;
end process;
process(posx)
begin
if posx = 144 then
dx <= '0';
elsif posx = 734 then
dx <= '1';
end if;
end process;
process(posy)
begin
if posy = 35 then
dy <= '0';
elsif posy = 465 then
dy <= '1';
end if;
end process;
process(posx2)
begin
if posx = 144 then
dx <= '0';
elsif posx = 734 then
dx <= '1';
end if;
end process;
process(posy2)
begin
if posy = 35 then
dy <= '0';
elsif posy = 465 then
dy <= '1';
end if;
end process;
-- horizontal sync for 96 horizontal clocks (96 pixels)
hs <= '1' when horz_scan < 96 else '0';
-- vertial sync for 2 scan lines
vs <= '1' when vert_scan(9 downto 1) = "000000000" else '0';
rgb <= color when (vert_scan >= posy and vert_scan < (posy+50) and horz_scan >= posx and horz_scan < posx+50) or (vert_scan >= posy2 and vert_scan < (posy2+50) and horz_scan >= posx2 and horz_scan < (posx2+50)) else "000";
vinc_flag <= '1' when horz_scan = "1100011000" else '0';
end Behavioral;

Answer 1

There seems to be a copy and paste error in your code. The last two processes are sensitive to posx2 and posy2 respectively, but you seem to be changing the state of the first ball (dx and dy). Shouldn't you be changing dx2 and dy2 instead?
Also, here are two suggestions to make your code more readable:
Instead of declaring your counters as std_logic_vectors and comparing them against bit-string literals (e.g., if vert_scan2 = "1000001001" then ...), why not declare the counters as integers? That would contribute to making you code more readable.
Don't use "magic numbers" or hardcoded literals spread throughout your code (e.g., in the expression if posx = 144 then ..., 144 is a magic number). Instead, create a constant with a meaningful name (constant BALL_X_POS_MIN: integer := 144;) and use it in your expressions (if posx = BALL_X_POS_MIN then ...).