Video inversion for Invaders


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I was hoping to clean this up a bit, but not had a chance yet, so here in case anyone wants to play ...

you need to lose dblscan.vhd from the project (the original scan doubler) and add the following source, VGA_Invert.vhd - this uses the same interface (was one of the limitations I set myself), but you will also need to generate a memory core to go with it - this needs to be called u_invert and have the following characteristics

simple dual port ram

write width 2

write depth 65536

ram A

write first

use ENA pin

ram B

write first

always enabled

with that added, then it should synthesise OK and work for you.

there are 2 'magic numbers' in the source that I used to centre the screen on my monitor - the original doubler has the picture way off to the left - your monitor may be different and need these changing.


  -- Output Screen Positioning


  constant Horizontal : natural := 140;

  constant Vertical : natural := 268;

the vertical one counts backwards, so needs to be > 244 (the number of vertical pixels)

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