A-M baby

Task/Bitmap-Bresenhams-line-algorithm/J/bitmap-bresenhams-line-algorithm-1.j

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+thru=: <./ + -~ i.@+ _1 ^ >        NB. integers from x through y
+
+NB.*getBresenhamLine v Returns points for a line given start and end points
+NB. y is: y0 x0 ,: y1 x1
+getBresenhamLine=: monad define
+  steep=. ([: </ |@-~/) y
+  points=. |."1^:steep y
+  slope=. %~/ -~/ points
+  ypts=. thru/ {."1 points
+  xpts=. ({: + 0.5 <.@:+ slope * ypts - {.) {.points
+  |."1^:steep ypts,.xpts
+)
+
+NB.*drawLines v Draws lines (x) on image (y)
+NB. x is: 2-item list (start and end points) ; (color)
+drawLines=: (1&{:: ;~ [: ; [: <@getBresenhamLine"2 (0&{::))@[ setPixels ]

Task/Bitmap-Bresenhams-line-algorithm/J/bitmap-bresenhams-line-algorithm-2.j

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+   myimg=: 0 255 0 makeRGB 20 32                       NB. 32 by 20 green image
+   myimg=: ((1 1 ,: 5 11) ; 255 0 0 ) drawLines myimg  NB. draw red line from xy point 1 1 to 11 5
+
+NB. Works for lists of 2 by 2 arrays each defining a line's start and end point.
+   Diamond=: _2]\ _2]\ 9 5 5 15 , 5 15 9 25 , 9 25 13 15 , 13 15 9 5
+   Square =: _2]\ _2]\ 5 5 5 25 , 5 25 13 25 , 13 25 13 5 , 13 5 5 5
+   viewRGB myimg=: (Diamond;255 0 0) drawLines myimg   NB. draw 4 red lines to form a diamond
+   viewRGB myimg=: (Square;0 0 255) drawLines myimg    NB. draw 4 blue lines to form a square
+   viewRGB (Diamond;255 0 0) drawLines (Square;0 0 255) drawLines myimg