feat: Add debug rectangle drawing for PDF characters

- Implement _draw_chars_rectangle method in add_debug_information
- Draw red rectangles with thin line width around each character
- Collect characters from various page components (paragraphs, lines, formulas)
- Support debug visualization for character bounding boxes

babeldoc/document_il/backend/pdf_creater.py

@@ -141,7 +141,12 @@ def _debug_render_rectangle(
         draw_op.append(
             rectangle.graphic_state.passthrough_per_char_instruction.encode(),
         )  # Green stroke
-        draw_op.append(b" 1 w ")  # Line width
+        if rectangle.linewidth is not None:
+            draw_op.append(
+                f" {rectangle.linewidth} w ".encode(),
+            )
+        else:
+            draw_op.append(b" 1 w ")  # Line width
 
         # Draw four lines manually
         # Bottom line

babeldoc/document_il/midend/add_debug_information.py

@@ -4,6 +4,7 @@
 from babeldoc.document_il import GraphicState
 from babeldoc.document_il.utils.style_helper import BLUE
 from babeldoc.document_il.utils.style_helper import ORANGE
+from babeldoc.document_il.utils.style_helper import RED
 from babeldoc.document_il.utils.style_helper import YELLOW
 from babeldoc.translation_config import TranslationConfig
 
@@ -24,11 +25,17 @@ def process(self, docs: il_version_1.Document):
         for page in docs.page:
             self.process_page(page)
 
-    def _create_rectangle(self, box: il_version_1.Box, color: GraphicState):
+    def _create_rectangle(
+        self,
+        box: il_version_1.Box,
+        color: GraphicState,
+        line_width: float = 1,
+    ):
         rect = il_version_1.PdfRectangle(
             box=box,
             graphic_state=color,
             debug_info=True,
+            linewidth=line_width,
         )
         return rect
 
@@ -62,6 +69,7 @@ def _create_text(self, text: str, color: GraphicState, box: il_version_1.Box):
         )
 
     def process_page(self, page: il_version_1.Page):
+        self._draw_chars_rectangle(page)
         # Add page number text at top-left corner
         page_width = page.cropbox.box.x2 - page.cropbox.box.x
         page_height = page.cropbox.box.y2 - page.cropbox.box.y
@@ -136,3 +144,26 @@ def process_page(self, page: il_version_1.Page):
                 )
 
         page.pdf_paragraph.extend(new_paragraphs)
+
+    def _draw_chars_rectangle(self, page: il_version_1.Page):
+        chars = []
+        chars.extend(page.pdf_character)
+
+        for para in page.pdf_paragraph:
+            for comp in para.pdf_paragraph_composition:
+                if comp.pdf_line:
+                    chars.extend(comp.pdf_line.pdf_character)
+                elif comp.pdf_same_style_characters:
+                    chars.extend(comp.pdf_same_style_characters.pdf_character)
+                elif comp.pdf_formula:
+                    chars.extend(comp.pdf_formula.pdf_character)
+                elif comp.pdf_character:
+                    chars.append(comp.pdf_character)
+                elif comp.pdf_same_style_unicode_characters:
+                    continue
+                else:
+                    raise ValueError(f"Unknown composition type: {comp}")
+
+        for char in chars:
+            rect = self._create_rectangle(char.box, RED, line_width=0.1)
+            page.pdf_rectangle.append(rect)