Fix bug in drawing squares, implement find_differences

Makefile

@@ -1,6 +1,9 @@
 test:
 	crystal spec --profile --rand --error-trace
 
+test-no-rand:
+	crystal spec --profile --error-trace
+
 benchmark:
 	crystal run scripts/benchmark.cr --release
 

spec/cr-image/operation/draw_spec.cr

@@ -6,23 +6,23 @@ Spectator.describe CrImage::Operation::Draw do
   alias Color = CrImage::Color
 
   specs_for_operator(draw_square(image.to_gray.threshold(8).region, Color.of("#00f")),
-    gray_hash: "23be9687013d598d9416fa3cf428d699f5fe9572",
-    rgba_hash: "1235b84c0debd42b71b5d20786386f7451928321"
+    gray_hash: "4d8323c4cfce2cae736185b0b714252ac4547f79",
+    rgba_hash: "ba0d7b953555121c252843f3db01d0a1c2c9dd89"
   )
 
   specs_for_operator(draw_square!(image.to_gray.threshold(8).region, Color.of("#00f")),
-    gray_hash: "23be9687013d598d9416fa3cf428d699f5fe9572",
-    rgba_hash: "1235b84c0debd42b71b5d20786386f7451928321",
+    gray_hash: "4d8323c4cfce2cae736185b0b714252ac4547f79",
+    rgba_hash: "ba0d7b953555121c252843f3db01d0a1c2c9dd89",
   )
 
   specs_for_operator(draw_square(20, 20, 100, 100, Color.of("#00f")),
-    gray_hash: "1ed4dcb15c6bc97af31eb8dadd05717eea09c082",
-    rgba_hash: "6aa0ca38d5e245291632f1d6f2861bad5e05d4be"
+    gray_hash: "48acaf112aa49d6b7d8073b37883f03fb4c2b2e5",
+    rgba_hash: "ad5686a6597cdf660077d9457ddd6b3a1733a2b3"
   )
 
   specs_for_operator(draw_square!(20, 20, 100, 100, Color.of("#00f")),
-    gray_hash: "1ed4dcb15c6bc97af31eb8dadd05717eea09c082",
-    rgba_hash: "6aa0ca38d5e245291632f1d6f2861bad5e05d4be",
+    gray_hash: "48acaf112aa49d6b7d8073b37883f03fb4c2b2e5",
+    rgba_hash: "ad5686a6597cdf660077d9457ddd6b3a1733a2b3",
   )
 
   specs_for_operator(draw_square(20, 20, 100, 100, Color.of("#0f0"), fill: true),

src/cr-image/map.cr

@@ -34,6 +34,9 @@ module CrImage
     abstract def sum : T
     abstract def max : T
     abstract def min : T
+
+    abstract def -(other : NumericMap(T)) : NumericMap(T)
+    abstract def +(other : NumericMap(T)) : NumericMap(T)
   end
 
   # A collection of implementations of `NumericMap(T)`, intended to be included in base classes.
@@ -190,6 +193,11 @@ module CrImage
       @raw.sum
     end
 
+    def -(other : NumericMap(T)) : self
+      raise Exception.new "Unable to subtract a map of different dimensions: #{width}x#{height} vs #{other.width}x#{other.height}" unless width == other.width && height == other.height
+      self.class.new(width, raw.map_with_index { |v, i| v - other.raw[i] })
+    end
+
     # Construct a `Mask` from this `GrayscaleImage` using the passed in block to determine if a given pixel should be true or not
     #
     # ```

src/cr-image/mask.cr

@@ -483,4 +483,8 @@ class CrImage::Mask
   def closing!(*, diagonal : Bool = true) : Mask
     dilate!(diagonal: diagonal).erode!(diagonal: diagonal)
   end
+
+  def |(other : Mask) : Mask
+    Mask.new(width, BitArray.new(size) { |i| bits[i] | other.bits[i] })
+  end
 end

src/cr-image/operation/draw.cr

@@ -28,8 +28,8 @@ module CrImage::Operation::Draw
   end
 
   def draw_square!(x : Int, y : Int, box_width : Int, box_height : Int, color : Color, *, fill : Bool = false) : self
-    raise "Box dimensions extend #{x + box_width - width} pixels beyond width of the image (#{width})" if (x + box_width) > width
-    raise "Box dimensions extend #{y + box_height - height} pixels beyond height of the image (#{height})" if (y + box_height) > height
+    raise "Box dimensions extend #{x + box_width - width + 1} pixels beyond width of the image (#{width})" if (x + box_width) > width
+    raise "Box dimensions extend #{y + box_height - height + 1} pixels beyond height of the image (#{height})" if (y + box_height) > height
 
     x_i = x.to_i
     y_i = y.to_i
@@ -42,7 +42,7 @@ module CrImage::Operation::Draw
           channel[((y_i + i) * width + x_i), box_width] = Array(UInt8).new(box_width) { color[channel_type] }
         else
           channel.unsafe_put((y_i + i) * width + x_i, color[channel_type])
-          channel.unsafe_put((y_i + i) * width + x_i + box_width, color[channel_type])
+          channel.unsafe_put((y_i + i) * width + x_i + box_width - 1, color[channel_type])
         end
       end
     end

src/tutorials/tutorial.cr

@@ -3,5 +3,6 @@
 # See:
 # * `EdgeDetection`
 # * `ChromaKey`
+# * `FindDifferences`
 module Tutorial
 end