VGA Signal Definitions

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Hello, I am currently working on modifying a script for VGA but I am having trouble understanding the final process of the script. The video signal generation process is as follows:

Code:
--VIDEO SIGNAL GENERATION PROCESS
--COMBINATIONAL
--INPUTS : coun_hor, blank_hor, blank_ver
--OUTPUTS : red,green,blue
RGB:process(coun_hor, blank_hor, blank_vert)
begin
  if((blank_hor and blank_vert) = '1') then
        red <= std_logic_vector(coun_hor(HCBIT - 1 downto HCBIT - 8));
        green <= std_logic_vector(coun_hor(green'range));
        blue <= std_logic_vector(coun_hor(3 downto 0) & "0000");
  else
        red <= (others => '0');
        green <= (others => '0');
        blue <= (others => '0');
  end if;
end process RGB;
Parameter descriptions:
constant HCBIT is it width of the horizontal counter ie 11
blank_hor and blank_vert are the horizontal and vertical blanking signals respectively.
coun_hor is the horizontal pixel counter signal.
red, green and blue are defined are std_logic_vectors of length 7 downto 0.

I understand that the else statement will output black to the screen when the blanking signals are set to low but I'm having trouble understanding the definitions of the signals red,green and blue.

Any help is greatly appreciated.
 
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It looks like your pixel counter has dual usage, with bits 10-3 defining the red index, and bits 3-0 defining the blue; are you sure HCBIT isn't 12 and not 11? that would make it 11-4 and 3-0 to skip the shared bit.

I'm curious about green'range; I don't recognize that syntax.

John D
 

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