Graphical progressive fill

[Joel via Digitalmars-d-learn]

I've been trying to fill in areas with a colour but can't work it 
out. I want something like the effect where it fills with 
diamonds. Not all at once but building up in the main program 
loop.

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#              #
#              #
#      #      #
#              #
#              #
########
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#              #
#      #      #
#   ###    #
#      #      #
#              #
########

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#        #     #
#     ###    #
#  ##### #
#     ###   #
#        #     #
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