Overhaul debug rendering to support possible use of Helvetica for testing

src/ocrmypdf/_pipeline.py

@@ -34,7 +34,7 @@ from ocrmypdf.exceptions import (
     UnsupportedImageFormatError,
 )
 from ocrmypdf.helpers import IMG2PDF_KWARGS, Resolution, safe_symlink
-from ocrmypdf.hocrtransform import HocrTransform
+from ocrmypdf.hocrtransform import DebugRenderOptions, HocrTransform
 from ocrmypdf.pdfa import generate_pdfa_ps
 from ocrmypdf.pdfinfo import Colorspace, Encoding, PageInfo, PdfInfo
 from ocrmypdf.pluginspec import OrientationConfidence
@@ -741,12 +741,21 @@ def render_hocr_page(hocr: Path, page_context: PageContext) -> Path:
         return output_file
 
     dpi = get_page_square_dpi(page_context, calculate_image_dpi(page_context))
-    debug_mode = options.pdf_renderer == 'hocrdebug'
-
+    debug = options.pdf_renderer == 'hocrdebug'
+    debug_render_options = None
+    if debug:
+        debug_render_options = DebugRenderOptions(
+            render_baseline=True,
+            render_triangle=True,
+            render_line_bbox=False,
+            render_word_bbox=True,
+            render_paragraph_bbox=False,
+            render_space_bbox=False,
+        )
     HocrTransform(
         hocr_filename=hocr,
         dpi=dpi.to_scalar(),  # square
-        debug=debug_mode,
+        debug_render_options=debug_render_options,
     ).to_pdf(
         out_filename=output_file,
         image_filename=None,

src/ocrmypdf/hocrtransform/_font.py

@@ -18,7 +18,12 @@ from pikepdf.canvas import Font
 log = logging.getLogger(__name__)
 
 
-class GlyphlessFont(Font):
+class EncodableFont(Font):
+    def text_encode(self, text: str) -> bytes:
+        raise NotImplementedError()
+
+
+class GlyphlessFont(EncodableFont):
     CID_TO_GID_DATA = zlib.compress(b"\x00\x01" * 65536)
     GLYPHLESS_FONT_NAME = 'pdf.ttf'
     GLYPHLESS_FONT = (package_files('ocrmypdf.data') / GLYPHLESS_FONT_NAME).read_bytes()
@@ -27,11 +32,14 @@ class GlyphlessFont(Font):
     def __init__(self):
         pass
 
-    def text_width(self, text: str, fontsize: float) -> int:
+    def text_width(self, text: str, fontsize: float) -> float:
         """Estimate the width of a text string when rendered with the given font."""
         # NFKC: split ligatures, combine diacritics
         return len(unicodedata.normalize("NFKC", text)) * (fontsize / self.CHAR_ASPECT)
 
+    def text_encode(self, text: str) -> bytes:
+        return text.encode('utf-16be')
+
     def register(self, pdf: Pdf):
         """Register the glyphless font.
 
@@ -110,3 +118,24 @@ class GlyphlessFont(Font):
         font_descriptor.FontFile2 = pdf.make_stream(self.GLYPHLESS_FONT)
         cid_font_type2.FontDescriptor = font_descriptor
         return basefont
+
+
+class Helvetica(EncodableFont):
+    """Helvetica font."""
+
+    def text_width(self, text: str, fontsize: float) -> float:
+        """Estimate the width of a text string when rendered with the given font."""
+        return len(text) * fontsize / 2.0
+
+    def text_encode(self, text: str) -> bytes:
+        return text.encode('pdfdoc', errors='ignore')
+
+    def register(self, pdf: Pdf) -> Dictionary:
+        """Register the font."""
+        return pdf.make_indirect(
+            Dictionary(
+                BaseFont=Name.Helvetica,
+                Type=Name.Font,
+                Subtype=Name.Type1,
+            )
+        )

src/ocrmypdf/hocrtransform/_hocr.py

@@ -27,11 +27,11 @@ from pikepdf.canvas import (
     MAGENTA,
     RED,
     Canvas,
-    Font,
     Text,
     TextDirection,
 )
 
+from ocrmypdf.hocrtransform._font import EncodableFont as Font
 from ocrmypdf.hocrtransform._font import GlyphlessFont
 
 log = logging.getLogger(__name__)
@@ -45,12 +45,12 @@ Element = ElementTree.Element
 class DebugRenderOptions:
     """A class for managing rendering options."""
 
-    render_paragraph_bbox: bool
-    render_baseline: bool
-    render_triangle: bool
-    render_line_bbox: bool
-    render_word_bbox: bool
-    render_space_bbox: bool
+    render_paragraph_bbox: bool = False
+    render_baseline: bool = False
+    render_triangle: bool = False
+    render_line_bbox: bool = False
+    render_word_bbox: bool = False
+    render_space_bbox: bool = False
 
 
 class HocrTransformError(Exception):
@@ -81,8 +81,22 @@ class HocrTransform:
         debug: bool = False,
         fontname: Name = Name("/f-0-0"),
         font: Font = GlyphlessFont(),
+        debug_render_options: DebugRenderOptions | None = None,
     ):
         """Initialize the HocrTransform object."""
+
+        if debug:
+            log.warning("Use debug_render_options instead", DeprecationWarning)
+            self.render_options = DebugRenderOptions(
+                render_baseline=debug,
+                render_triangle=debug,
+                render_line_bbox=False,
+                render_word_bbox=debug,
+                render_paragraph_bbox=False,
+                render_space_bbox=False,
+            )
+        else:
+            self.render_options = debug_render_options or DebugRenderOptions()
         self.dpi = dpi
         self.hocr = ElementTree.parse(os.fspath(hocr_filename))
         self._fontname = fontname
@@ -103,14 +117,6 @@ class HocrTransform:
             self.height = (coords.ury - coords.lly) / (self.dpi / INCH)
             # Stop after first div that has page coordinates
             break
-        self.render_options = DebugRenderOptions(
-            render_baseline=debug,
-            render_triangle=debug,
-            render_line_bbox=False,
-            render_word_bbox=debug,
-            render_paragraph_bbox=False,
-            render_space_bbox=False,
-        )
 
     def _get_element_text(self, element: Element):
         """Return the textual content of the element and its children."""
@@ -311,8 +317,7 @@ class HocrTransform:
             line_box_height = abs(line_box.height) / cos(angle)
             fontsize = line_box_height + intercept
             text.font(self._fontname, fontsize)
-            if invisible_text or True:
-                text.render_mode(3)  # Invisible (indicates OCR text)
+            text.render_mode(3 if invisible_text else 0)
 
             self._debug_draw_baseline(
                 canvas, line_matrix.inverse().transform(line_box), 0
@@ -365,7 +370,7 @@ class HocrTransform:
         if font_width > 0:
             text.text_transform(Matrix(1, 0, 0, -1, box.llx, 0))
             text.horiz_scale(100 * box.width / font_width)
-            text.show(elemtxt.encode('utf-16be'))
+            text.show(self._font.text_encode(elemtxt))
 
         # Get coordinates of the next word (if there is one)
         hocr_next_box = (
@@ -389,7 +394,7 @@ class HocrTransform:
         space_width = self._font.text_width(' ', fontsize)
         if space_width > 0:
             text.horiz_scale(100 * space_box.width / space_width)
-            text.show(' '.encode('utf-16be'))
+            text.show(self._font.text_encode(' '))
 
     def _debug_draw_paragraph_boxes(self, canvas: Canvas, color=CYAN):
         """Draw boxes around paragraphs in the document."""