June 2018 Update

Task/Bitmap-Write-a-PPM-file/Erlang/bitmap-write-a-ppm-file.erl

@@ -0,0 +1,45 @@
+-module(ppm).
+
+-export([ppm/1, write/2]).
+
+-define(WHITESPACE, <<10>>).
+-define(SPACE, <<32>>).
+
+% data structure introduced in task Bitmap (module ros_bitmap.erl)
+-record(bitmap, {
+    pixels = nil,
+    shape = {0, 0}
+  }).
+
+% create ppm image from bitmap record
+ppm(Bitmap) ->
+    {Width, Height} = Bitmap#bitmap.shape,
+    Pixels = ppm_pixels(Bitmap),
+    Maxval = 255,  % original ppm format maximum
+    list_to_binary([
+      header(), width_and_height(Width, Height), maxval(Maxval), Pixels]).
+
+% write bitmap as ppm file
+write(Bitmap, Filename) ->
+    Ppm = ppm(Bitmap),
+    {ok, File} = file:open(Filename, [binary, write]),
+    file:write(File, Ppm),
+    file:close(File).
+
+%%%%%%%%%%%% four parts of ppm file %%%%%%%%%%%%%%%%%%%%%%
+header() ->
+    [<<"P6">>, ?WHITESPACE].
+
+width_and_height(Width, Height) ->
+    [encode_decimal(Width), ?SPACE, encode_decimal(Height), ?WHITESPACE].
+
+maxval(Maxval) ->
+   [encode_decimal(Maxval), ?WHITESPACE].
+
+ppm_pixels(Bitmap) ->
+    % 24 bit color depth
+    array:to_list(Bitmap#bitmap.pixels).
+
+%%%%%%%%%%%% Internals %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+encode_decimal(Number) ->
+    integer_to_list(Number).