Take width of single line text field widget into account when auto-si…

…zing

The current implementation only takes care of making the text not too
tall for the widget. However, if the field value is longer it is
truncated by HexaPDF whereas other PDF libraries/apps shrink the font
size.

This change adjusts HexaPDF's behaviour to be more in line with other
common PDF libraries/apps.

CHANGELOG.md

@@ -41,6 +41,8 @@
 * Validation of standard encryption dictionary to auto-correct invalid /U and
   /O fields in case they are padded with zeros
 * [HexaPDF::Document#wrap] handling of sub-type mapping in case of missing type
+* [HexaPDF::Type::AcroForm::AppearanceGenerator] to also take a text field
+  widget's width into account when auto-sizing
 
 
 ## 0.32.2 - 2023-05-06

lib/hexapdf/type/acro_form/appearance_generator.rb

@@ -200,7 +200,7 @@ def create_push_button_appearances
         def create_text_appearances
           default_resources = @document.acro_form.default_resources
           font, font_size, font_color = retrieve_font_information(default_resources)
-          style = HexaPDF::Layout::Style.new(font: font, fill_color: font_color)
+          style = HexaPDF::Layout::Style.new(font: font, font_size: font_size, fill_color: font_color)
           border_style = @widget.border_style
           padding = [1, border_style.width].max
 
@@ -226,8 +226,6 @@ def create_text_appearances
 
           canvas = form.canvas
           apply_background_and_border(border_style, canvas)
-          style.font_size = calculate_font_size(font, font_size, height, border_style)
-          style.clear_cache
 
           canvas.marked_content_sequence(:Tx) do
             if @field.field_value || @field.concrete_field_type == :list_box
@@ -362,6 +360,7 @@ def draw_marker(canvas, width, height, border_width, marker_style)
         def draw_single_line_text(canvas, width, height, style, padding)
           value, text_color = apply_javascript_formatting(@field.field_value)
           style.fill_color = text_color if text_color
+          calculate_and_apply_font_size(value, style, width, height, padding)
           fragment = HexaPDF::Layout::TextFragment.create(value, style)
 
           if @field.concrete_field_type == :comb_text_field
@@ -431,6 +430,11 @@ def draw_multiline_text(canvas, width, height, style, padding)
 
         # Draws the visible option items of the list box in the widget's rectangle.
         def draw_list_box(canvas, width, height, style, padding)
+          if style.font_size == 0
+            style.font_size = 12 # Seems to be Adobe's default
+            style.clear_cache
+          end
+
           option_items = @field.option_items
           top_index = @field.list_box_top_index
           items = [Layout::TextFragment.create(option_items[top_index..-1].join("\n"), style)]
@@ -475,24 +479,20 @@ def retrieve_font_information(resources)
           [font, font_size, font_color]
         end
 
-        # Calculates the font size for text fields based on the font and font size of the default
-        # appearance string, the annotation rectangle's height and the border style.
-        def calculate_font_size(font, font_size, height, border_style)
-          if font_size == 0
-            case @field.concrete_field_type
-            when :multiline_text_field
-              0 # Handled by multiline drawing code
-            when :list_box
-              12 # Seems to be Adobe's default
-            else
-              unit_font_size = (font.wrapped_font.bounding_box[3] - font.wrapped_font.bounding_box[1]) *
-                font.scaling_factor / 1000.0
-              # The constant factor was found empirically by checking what Adobe Reader etc. do
-              (height - 2 * border_style.width) / unit_font_size * 0.83
-            end
-          else
-            font_size
-          end
+        # Calculates the font size for single line text fields using auto-sizing, based on the font
+        # and font size of the default appearance string, the annotation rectangle's height and
+        # width and the given padding. The font size is then applied to the provided style object.
+        def calculate_and_apply_font_size(value, style, width, height, padding)
+          return if style.font_size != 0
+
+          font = style.font
+          unit_font_size = (font.wrapped_font.bounding_box[3] - font.wrapped_font.bounding_box[1]) *
+            font.scaling_factor / 1000.0
+          # The constant factor was found empirically by checking what Adobe Reader etc. do
+          style.font_size = (height - 2 * padding) / unit_font_size * 0.85
+          fragment = HexaPDF::Layout::TextFragment.create(value, style)
+          style.font_size = [style.font_size, style.font_size * (width - 4 * padding) / fragment.width].min
+          style.clear_cache
         end
 
         # Handles Javascript formatting routines for single-line text fields.

test/hexapdf/type/acro_form/test_appearance_generator.rb

@@ -467,12 +467,20 @@ def check_rotation(angle, width, height, matrix)
       it "calculates the font size based on the rectangle height and border width" do
         @generator.create_appearances
         assert_operators(@widget[:AP][:N].stream,
-                         [:set_font_and_size, [:F1, 12.923875]],
+                         [:set_font_and_size, [:F1, 13.235294]],
                          range: 5)
         @widget.border_style(width: 2, color: :transparent)
         @generator.create_appearances
         assert_operators(@widget[:AP][:N].stream,
-                         [:set_font_and_size, [:F1, 11.487889]],
+                         [:set_font_and_size, [:F1, 11.764706]],
+                         range: 5)
+      end
+
+      it "shrinks the font size if necessary to fit the rectangle width" do
+        @field.field_value = "This is some arbitrary, long text"
+        @generator.create_appearances
+        assert_operators(@widget[:AP][:N].stream,
+                         [:set_font_and_size, [:F1, 6.909955]],
                          range: 5)
       end
 
@@ -573,7 +581,7 @@ def assert_format(arg_string, result, range)
             assert_format("2, 3, #{style}, 0, \"E\", true",
                           [[:set_device_rgb_non_stroking_color, [style % 2, 0.0, 0.0]],
                            [:begin_text],
-                           [:set_text_matrix, [1, 0, 0, 1, 2, 3.240724]],
+                           [:set_text_matrix, [1, 0, 0, 1, 2, 3.183272]],
                            [:show_text, [result]]], 6..9)
           end
         end
@@ -598,10 +606,10 @@ def assert_format(arg_string, result, range)
                           [:append_rectangle, [1, 1, 98, 9.25]],
                           [:clip_path_non_zero],
                           [:end_path],
-                          [:set_font_and_size, [:F1, 6.641436]],
+                          [:set_font_and_size, [:F1, 6.801471]],
                           [:set_device_rgb_non_stroking_color, [1.0, 0.0, 0.0]],
                           [:begin_text],
-                          [:set_text_matrix, [1, 0, 0, 1, 2, 3.240724]],
+                          [:set_text_matrix, [1, 0, 0, 1, 2, 3.183272]],
                           [:show_text, ["Text"]],
                           [:end_text],
                           [:restore_graphics_state],