ENH: TextAppearanceStream: Scale and wrap text

This patch scales and/or wrap text that does not
fit into a text field unaltered, under the condition
that font size was set to 0 in the default
appearance stream.

We only wrap text if the multiline bit was set in
the corresponding annotation's field flags, otherwise
we just scale the font until it fits.

We move the escaping of parentheses below, so that it
does not interfere with calculating the width of a
text string.

Author: PJBrs

pypdf/generic/_appearance_stream.py

@@ -2,6 +2,7 @@
 from typing import Any, Optional, Union, cast
 
 from .._cmap import _default_fonts_space_width, build_char_map_from_dict
+from .._codecs.core_fontmetrics import CORE_FONT_METRICS
 from .._font import FontDescriptor
 from .._utils import logger_warning
 from ..constants import AnnotationDictionaryAttributes, FieldDictionaryAttributes
@@ -132,6 +133,7 @@ def _generate_appearance_stream_data(
         text: str = "",
         selection: Optional[list[str]] = None,
         rectangle: Union[RectangleObject, tuple[float, float, float, float]] = (0.0, 0.0, 0.0, 0.0),
+        font_descriptor: FontDescriptor = CORE_FONT_METRICS["Helvetica"],
         font_glyph_byte_map: Optional[dict[str, bytes]] = None,
         font_name: str = "/Helv",
         font_size: float = 0.0,
@@ -169,10 +171,27 @@ def _generate_appearance_stream_data(
 
         # If font_size is 0, apply the logic for multiline or large-as-possible font
         if font_size == 0:
+            if selection:              # Don't wrap text when dealing with a /Ch field, in order to prevent problems
+                multiline = False      # with matching "selection" with "line" later on.
             if multiline:
                 font_size = DEFAULT_FONT_SIZE_IN_MULTILINE
             else:
                 font_size = rectangle.height - 2
+            lines, font_size = self._scale_text(
+                font_descriptor,
+                font_size,
+                rectangle.width - 3,   # One point margin left and right, and an additional point because the first
+                                       # offset takes one extra point (see below, under "line_number == 0:")
+                rectangle.height - 3,  # One point margin for top and bottom, one point extra for the first line
+                                       # (see y_offset)
+                text,
+                multiline,
+            )
+        else:
+            lines = [(
+                font_descriptor.text_width(line) * font_size / 1000,
+                line
+            ) for line in text.replace("\n", "\r").split("\r")]
 
         # Set the vertical offset
         y_offset = rectangle.height - 1 - font_size
@@ -183,7 +202,7 @@ def _generate_appearance_stream_data(
             f"re\nW\nBT\n{default_appearance}\n".encode()
         )
 
-        for line_number, line in enumerate(text.replace("\n", "\r").split("\r")):
+        for line_number, (line_width, line) in enumerate(lines):
             if selection and line in selection:
                 # Might be improved, but cannot find how to get fill working => replaced with lined box
                 ap_stream += (
@@ -240,6 +259,7 @@ def __init__(
         # If a font resource was added, get the font character map
         if font_resource:
             font_resource = cast(DictionaryObject, font_resource.get_object())
+            font_descriptor = FontDescriptor.from_font_resource(font_resource)
             _font_subtype, _, font_encoding, font_map = build_char_map_from_dict(
                 200, font_resource
             )
@@ -260,11 +280,13 @@ def __init__(
         else:
             logger_warning(f"Font dictionary for {font_name} not found.", __name__)
             font_glyph_byte_map = {}
+            font_descriptor = FontDescriptor()
 
         ap_stream_data = self._generate_appearance_stream_data(
             text,
             selection,
             rectangle,
+            font_descriptor,
             font_glyph_byte_map,
             font_name,
             font_size,