Data commit

Task/Bitmap-Read-a-PPM-file/Ruby/bitmap-read-a-ppm-file.rb

@@ -0,0 +1,33 @@
+class Pixmap
+  # 'open' is a class method
+  def self.open(filename)
+    bitmap = nil
+    File.open(filename, 'r') do |f|
+      header = [f.gets.chomp, f.gets.chomp, f.gets.chomp]
+      width, height = header[1].split.map {|n| n.to_i }
+      if header[0] != 'P6' or header[2] != '255' or width < 1 or height < 1
+        raise StandardError, "file '#{filename}' does not start with the expected header"
+      end
+      f.binmode
+      bitmap = self.new(width, height)
+      height.times do |y|
+        width.times do |x|
+          # read 3 bytes
+          red, green, blue = f.read(3).unpack('C3')
+          bitmap[x,y] = RGBColour.new(red, green, blue)
+        end
+      end
+    end
+    bitmap
+  end
+end
+
+# create an image: a green cross on a blue background
+colour_bitmap = Pixmap.new(20, 30)
+colour_bitmap.fill(RGBColour::BLUE)
+colour_bitmap.height.times {|y| [9,10,11].each {|x| colour_bitmap[x,y]=RGBColour::GREEN}}
+colour_bitmap.width.times  {|x| [14,15,16].each {|y| colour_bitmap[x,y]=RGBColour::GREEN}}
+colour_bitmap.save('testcross.ppm')
+
+# then, convert to grayscale
+Pixmap.open('testcross.ppm').to_grayscale!.save('testgray.ppm')