Add Epson test page: text sizes, EAN-13, QR, and a raster image

ReceiptBuilder#image implements GS v 0 raster printing (no image library
needed for the demo -- a procedural 8px checkerboard proves it end to
end). Skipped attempting the printer's real-time clock: unsure the
TM-T20II actually has a battery-backed RTC (that's usually an option on
higher-end models), not worth guessing at an undocumented command.

app.rb

@@ -107,6 +107,60 @@ helpers do
     receipt.print!(PRINTER_DEVICE_EPSON)
   end
 
+  # Procedural 64x64 checkerboard (8px squares) -- no image library needed,
+  # just to prove GS v 0 raster printing works end to end.
+  def checkerboard_bitmap(size_px = 64, block_px = 8)
+    width_bytes = size_px / 8
+    bytes = "".b
+    size_px.times do |y|
+      row_block = y / block_px
+      width_bytes.times do |xb|
+        byte = 0
+        8.times do |bit|
+          x = xb * 8 + bit
+          col_block = x / block_px
+          byte |= (1 << (7 - bit)) if (row_block + col_block).even?
+        end
+        bytes << byte.chr
+      end
+    end
+    bytes
+  end
+
+  # Demonstrates most of what the printer can do: text sizes/styles, EAN-13,
+  # QR code, and a raster image -- mirrors /test-print's role for the Datamax.
+  def print_epson_test_page
+    receipt = ReceiptBuilder.new
+    receipt.align(:center).bold.size(:big).text("TM-T20II TEST\n").size(:normal).bold(false)
+    receipt.align(:left).text(('-' * 48) + "\n")
+
+    receipt.text("Normal text\n")
+    receipt.bold.text("Bold text\n").bold(false)
+    receipt.underline.text("Underlined text\n").underline(false)
+    receipt.size(:wide).text("Double width\n").size(:normal)
+    receipt.size(:high).text("Double height\n").size(:normal)
+    receipt.size(:big).text("Double both\n").size(:normal)
+    receipt.text(('-' * 48) + "\n")
+
+    receipt.align(:center)
+    receipt.text("EAN-13 barcode:\n")
+    receipt.ean13('2012345678902')
+    receipt.feed(1)
+
+    receipt.text("QR code:\n")
+    receipt.qr('https://git.priesol.net/randy/home-gitops')
+    receipt.feed(1)
+
+    receipt.text("Raster image:\n")
+    receipt.image(64, 64, checkerboard_bitmap)
+    receipt.feed(1)
+
+    receipt.align(:left).text(('-' * 48) + "\n")
+    receipt.text("Printed: #{Time.now.strftime('%Y-%m-%d %H:%M:%S')}\n")
+    receipt.feed(3).cut
+    receipt.print!(PRINTER_DEVICE_EPSON)
+  end
+
   ESCPOS_MNEMONICS = {
     'ESC' => "\x1B", 'GS' => "\x1D", 'FS' => "\x1C", 'DLE' => "\x10",
     'LF' => "\x0A", 'CR' => "\x0D", 'HT' => "\x09", 'NUL' => "\x00"
@@ -313,6 +367,16 @@ get '/epson' do
   erb :epson
 end
 
+post '/epson/test-print' do
+  begin
+    print_epson_test_page
+    flash 'Test page sent to Epson printer', 'success'
+  rescue => e
+    flash "Epson test print failed (#{e.message})", 'danger'
+  end
+  redirect '/epson'
+end
+
 post '/epson/print' do
   begin
     print_receipt(title: params[:title].to_s, body: params[:body].to_s, qr: params[:qr].to_s)

lib/receipt_builder.rb

@@ -93,6 +93,16 @@ class ReceiptBuilder
     self
   end
 
+  # Raster bit image (GS v 0) -- bytes must already be packed 1bpp,
+  # row-major, (width_px/8 rounded up) bytes per row, MSB-first, 1=black.
+  def image(width_px, height_px, bytes)
+    width_bytes = (width_px + 7) / 8
+    @buffer << "\x1D\x76\x30\x00"
+    @buffer << [width_bytes % 256, width_bytes / 256, height_px % 256, height_px / 256].pack('C4')
+    @buffer << bytes
+    self
+  end
+
   def feed(lines = 3)
     @buffer << ("\n" * lines)
     self

views/epson.erb

@@ -15,6 +15,10 @@
           <button class="btn btn-secondary" type="submit">Print</button>
         </form>
 
+        <form action="/epson/test-print" method="POST" class="mt-3">
+          <button class="btn btn-outline-secondary" type="submit">Print test page (sizes, barcode, QR, image)</button>
+        </form>
+
         <hr class="mt-4">
 
         <h5>Free text (ESC/POS mnemonic notation)</h5>