Compress position escape sequences;

Compression is achieved by not repeatedly sending a position when only the x
coordinate has changed; i.e. we are on the same line, just advancing a
character.

In the test application, we have gone from sending 72260 characters to the
terminal to just 13971- approximately 80% reduction. Reported compression time
has changed from average 20.6ms to 13.2ms- a ~35% improvement.

Also, add more documentation.

Work related to #302.

lib/vedeu/output/compressor.rb

@@ -62,7 +62,7 @@ def compress
           out = ''
 
           content.each do |cell|
-            out << cell.position.to_s
+            out << position_for(cell)
             out << colour_for(cell)
             out << style_for(cell)
             out << cell.value
@@ -91,6 +91,23 @@ def uncompress
         out
       end
 
+      # Compress by not repeatedly sending a position when only the x
+      # coordinate has changed; i.e. we are on the same line, just
+      # advancing a character.
+      #
+      # @param char [Vedeu::Views::Char]
+      # @return [String]
+      def position_for(char)
+        return ''.freeze if char.position.y == @y
+
+        @y = char.position.y
+        char.position.to_s
+      end
+
+      # Compress by not repeatedly sending the same colours for each
+      # character which has the same colours as the last character
+      # output.
+      #
       # @param char [Vedeu::Views::Char]
       # @return [String]
       def colour_for(char)
@@ -100,6 +117,10 @@ def colour_for(char)
         @colour.to_s
       end
 
+      # Compress by not repeatedly sending the same style(s) for each
+      # character which has the same style(s) as the last character
+      # output.
+      #
       # @param char [Vedeu::Views::Char]
       # @return [String]
       def style_for(char)

test/lib/vedeu/output/compressor_test.rb

@@ -28,50 +28,57 @@ module Output
           context 'when the output is all Vedeu::Views::Char elements' do
             let(:output) {
               Vedeu::Models::Page.coerce([
-                Vedeu::Views::Char.new(value:  'Y',
-                                       colour: { foreground: '#ff0000' }),
-                Vedeu::Views::Char.new(value:  'e',
-                                       colour: { foreground: '#ff0000' }),
-                Vedeu::Views::Char.new(value:  's',
-                                       colour: { foreground: '#ff0000' }),
+                Vedeu::Views::Char.new(value:    'Y',
+                                       colour:   { foreground: '#ff0000' },
+                                       position: [1, 1]),
+                Vedeu::Views::Char.new(value:    'e',
+                                       colour:   { foreground: '#ff0000' },
+                                       position: [1, 2]),
+                Vedeu::Views::Char.new(value:    's',
+                                       colour:   { foreground: '#ff0000' },
+                                       position: [1, 3])
               ])
             }
             it 'converts the non-Vedeu::Views::Char elements into String ' \
                'elements' do
-              subject.must_equal("\e[38;2;255;0;0mYes")
+              subject.must_equal("\e[1;1H\e[38;2;255;0;0mYes")
             end
           end
 
           context 'when the output is all Vedeu::Views::Char elements' do
             let(:output) {
               Vedeu::Models::Page.coerce([
-                Vedeu::Views::Char.new(value:  'a',
-                                       colour: { foreground: '#ff0000' }),
-                Vedeu::Views::Char.new(value:  'b',
-                                       colour: { foreground: '#ff0000' }),
-                Vedeu::Views::Char.new(value:  'c',
-                                       colour: { foreground: '#0000ff' }),
-                Vedeu::Views::Char.new(value:  'd',
-                                       colour: { foreground: '#0000ff' }),
+                Vedeu::Views::Char.new(value:    'a',
+                                       colour:   { foreground: '#ff0000' },
+                                       position: [1, 1]),
+                Vedeu::Views::Char.new(value:    'b',
+                                       colour:   { foreground: '#ff0000' },
+                                       position: [1, 2]),
+                Vedeu::Views::Char.new(value:    'c',
+                                       colour:   { foreground: '#0000ff' },
+                                       position: [1, 3]),
+                Vedeu::Views::Char.new(value:    'd',
+                                       colour:   { foreground: '#0000ff' },
+                                       position: [1, 4]),
               ])
             }
             it 'compresses multiple colours and styles where possible' do
-              subject.must_equal("\e[38;2;255;0;0mab\e[38;2;0;0;255mcd")
+              subject.must_equal("\e[1;1H\e[38;2;255;0;0mab\e[38;2;0;0;255mcd")
             end
           end
 
           context 'when the output is not all Vedeu::Views::Char ' \
                   'elements' do
             let(:output) {
               Vedeu::Models::Page.coerce([
-                Vedeu::Views::Char.new(value: 'N'),
+                Vedeu::Views::Char.new(value: 'N', position: [1, 1]),
                 Vedeu::Models::Escape.new(value: "\e[?25l"),
-                Vedeu::Views::Char.new(value: 't'),
+                Vedeu::Views::Char.new(value: 't', position: [1, 3]),
               ])
             }
             it 'converts the non-Vedeu::Views::Char elements into String ' \
                'elements' do
-              subject.must_equal("N\e[1;1H\e[?25lt")
+              subject.must_equal("\e[1;1HN\e[?25lt")
             end
           end
         end