Improve outer border behaviour with nonzero gutter (#1087)

* table: Changed drawing of outer border when gutter is nonzero [#1071]

* test: Regenerated tests for new handling of outer border

* table: Apply the gutter spacing between outer border and table contents [#1071]

* Updated changelog for table outer border modification

* table: Changed outer border calculation to use border edge instead of centre

* table: Draw top and bottom outer border as one line

* test: Regenerated tests for new interpretation of gutter spacing

* table: Fixed header with gutter after pagebreak

Header rows need gutter between them, as well as before the start of
content; see test_table_with_colspan()

* test: Reproduced comparison PDFs for outer border change

Outer border top and bottom lines are now single continuous lines
instead of many line segments

Author: mjasperse

CHANGELOG.md

@@ -24,6 +24,9 @@ This can also be enabled programmatically with `warnings.simplefilter('default',
 * non-bold `TitleStyle` is now rendered as non-bold even when the current font is bold
 * calling `.table()` inside the `render_toc_function`
 * using `.set_text_shaping(True)` & `.offset_rendering()`
+* Fixed gutter handing when a pagebreak occurs within a table with header rows - thanks to @mjasperse
+### Changed
+* Outer table borders are now drawn continuously for nonzero `gutter_width`/`gutter_height`, with spacing applied inside the border similar to HTML tables - thanks to @mjasperse - cf. [#1071](https://github.com/py-pdf/fpdf2/issues/1071)
 
 ## [2.7.7] - 2023-12-10
 ### Added

fpdf/table.py

@@ -109,6 +109,13 @@ def __init__(
                     "outer_border_width is only allowed when borders_layout is ALL or NO_HORIZONTAL_LINES"
                 )
             self._outer_border_width = 0
+        if self._outer_border_width:
+            self._outer_border_margin = (
+                (gutter_width + outer_border_width / 2),
+                (gutter_height + outer_border_width / 2),
+            )
+        else:
+            self._outer_border_margin = (0, 0)
 
         # check first_row_as_headings for non-default case num_heading_rows != 1
         if self._num_heading_rows != 1:
@@ -186,27 +193,30 @@ def render(self):
             self._fpdf.l_margin = self._fpdf.x
 
         # Pre-Compute the relative x-positions of the individual columns:
-        cell_x_positions = [0]
+        xx = self._outer_border_margin[0]
+        cell_x_positions = [xx]
         if self.rows:
-            xx = 0
             for i in range(self.rows[0].cols_count):
                 xx += self._get_col_width(0, i)
                 xx += self._gutter_width
                 cell_x_positions.append(xx)
 
         # Starting the actual rows & cells rendering:
+        self._fpdf.y += self._outer_border_margin[1]
         for i in range(len(self.rows)):
             row_layout_info = self._get_row_layout_info(i)
             if row_layout_info.triggers_page_jump:
                 # pylint: disable=protected-access
                 self._fpdf._perform_page_break()
+                self._fpdf.y += self._outer_border_margin[1]
                 # repeat headings on top:
                 for row_idx in range(self._num_heading_rows):
                     self._render_table_row(
                         row_idx,
                         self._get_row_layout_info(row_idx),
                         cell_x_positions=cell_x_positions,
                     )
+                    self._fpdf.y += self._gutter_height
             elif i and self._gutter_height:
                 self._fpdf.y += self._gutter_height
             self._render_table_row(
@@ -384,14 +394,26 @@ def _render_table_cell(
                 _remember_linewidth = self._fpdf.line_width
                 self._fpdf.set_line_width(self._outer_border_width)
 
-                if i == 0:
-                    self._fpdf.line(x1, y1, x2, y1)
-                if i == len(self.rows) - 1:
-                    self._fpdf.line(x1, y2, x2, y2)
+                # draw the outer box separated by the gutter dimensions
+                # the top and bottom borders are one continuous line
+                # whereas the left and right borders are segments beause of possible pagebreaks
+                x1 = self._fpdf.l_margin
+                x2 = x1 + self._width
+                y1 = y1 - self._outer_border_margin[1]
+                y2 = y2 + self._outer_border_margin[1]
+
                 if j == 0:
+                    # lhs border
                     self._fpdf.line(x1, y1, x1, y2)
                 if j == len(row.cells) - 1:
+                    # rhs border
                     self._fpdf.line(x2, y1, x2, y2)
+                    # continuous top line border
+                    if i == 0:
+                        self._fpdf.line(x1, y1, x2, y1)
+                    # continuous bottom line border
+                    if i == len(self.rows) - 1:
+                        self._fpdf.line(x1, y2, x2, y2)
 
                 self._fpdf.set_line_width(_remember_linewidth)
 
@@ -483,8 +505,11 @@ def _get_col_width(self, i, j, colspan=1):
         between columns if the cell spans multiple columns."""
 
         cols_count = self.rows[i].cols_count
-        width = self._width - (cols_count - 1) * self._gutter_width
-
+        width = (
+            self._width
+            - (cols_count - 1) * self._gutter_width
+            - 2 * self._outer_border_margin[0]
+        )
         gutter_within_cell = max((colspan - 1) * self._gutter_width, 0)
 
         if not self._col_widths:

test/table/table_with_colspan.pdf

@@ -12,9 +12,9 @@
 HERE = Path(__file__).resolve().parent
 
 
-def run_comparison(pdf, name, tmp_path):
+def run_comparison(pdf, name, tmp_path, generate=False):
     filename = HERE / f"{name}.pdf"
-    assert_pdf_equal(pdf, filename, tmp_path, generate=False)
+    assert_pdf_equal(pdf, filename, tmp_path, generate=generate)
 
 
 IMG_DIR = HERE.parent / "image"