RosettaCodeData/Task/Bitmap/Prolog/bitmap.pro

:- module(bitmap, [
   new_bitmap/3,
   fill_bitmap/3,
   get_pixel0/3,
   set_pixel0/4 ]).

:- use_module(library(lists)).

%-----------------------------------------------------------------------------%
% Convenience Predicates
replicate(Term,Times,L):-
   length(L,Times),
   maplist(=(Term),L).

replace0(N,OL,E,NL):-
   nth0(N,OL,_,TL),
   nth0(N,NL,E,TL).
%-----------------------------------------------------------------------------%
% Bitmap Utilities
%
% The Bitmap structure is a list with pixels kept in row major order:
% [dimensions-[X,Y],pixels-[[n11,n12...],[n21,n22...]]]

% In this code what exactly an RGB value is doesn't matter however
% in other bitmap tasks it is assumed to be a list [R,G,B] where
% each is an int between 0 and 255, in code:
rgb_pixel(RGB):-
   length(RGB,3),
   maplist(integer,RGB),
   maplist(between(0,255),RGB).

%new_bitmap(Bitmap,Dimensions,RGB)
new_bitmap([[X,Y],Pixels],[X,Y],RGB) :-
   replicate(RGB,X,Row),
   replicate(Row,Y,Pixels).

%fill_bitmap(New_Bitmap,Bitmap,RGB)
fill_bitmap(New_Bitmap,[[X,Y],_],RGB) :-
   new_bitmap(New_Bitmap,[X,Y],RGB).

%here get and set use 0 based indexing
%get_pixel0(Bitmap,Coordinates,RGB)
get_pixel0([[_DimX,_DimY],Pixels],[X,Y],RGB) :-
   nth0(Y,Pixels,Row),
   nth0(X,Row,RGB).

%set_pixel0(New Bitmap, Bitmap, Coordinates, RGB)
set_pixel0([[DimX,DimY],New_Pixels],[[DimX,DimY],Pixels],[X,Y],RGB) :-
   nth0(Y,Pixels,Row),
   replace0(X,Row,RGB,New_Row),
   replace0(Y,Pixels,New_Row,New_Pixels).