Badges: reduce memory usage when placing multiple per page (Z#23125583) (#3472)

Co-authored-by: Raphael Michel <michel@rami.io>

src/pretix/base/pdf.py

@@ -61,7 +61,8 @@ from django.utils.html import conditional_escape
 from django.utils.timezone import now
 from django.utils.translation import gettext_lazy as _, pgettext
 from i18nfield.strings import LazyI18nString
-from pypdf import PdfReader
+from pypdf import PdfReader, PdfWriter, Transformation
+from pypdf.generic import RectangleObject
 from reportlab.graphics import renderPDF
 from reportlab.graphics.barcode.qr import QrCodeWidget
 from reportlab.graphics.shapes import Drawing
@@ -1027,14 +1028,12 @@ class Renderer:
                 with open(os.path.join(d, 'out.pdf'), 'rb') as f:
                     return BytesIO(f.read())
         else:
-            from pypdf import PdfReader, PdfWriter, Transformation
-            from pypdf.generic import RectangleObject
             buffer.seek(0)
             new_pdf = PdfReader(buffer)
             output = PdfWriter()
 
             for i, page in enumerate(new_pdf.pages):
-                bg_page = copy.copy(self.bg_pdf.pages[i])
+                bg_page = copy.deepcopy(self.bg_pdf.pages[i])
                 bg_rotation = bg_page.get('/Rotate')
                 if bg_rotation:
                     # /Rotate is clockwise, transformation.rotate is counter-clockwise
@@ -1071,6 +1070,56 @@ class Renderer:
             return outbuffer
 
 
+def merge_background(fg_pdf, bg_pdf, out_file, compress):
+    if settings.PDFTK:
+        with tempfile.TemporaryDirectory() as d:
+            fg_filename = os.path.join(d, 'fg.pdf')
+            bg_filename = os.path.join(d, 'bg.pdf')
+            fg_pdf.write(fg_filename)
+            bg_pdf.write(bg_filename)
+            pdftk_cmd = [
+                settings.PDFTK,
+                fg_filename,
+                'multibackground',
+                bg_filename,
+                'output',
+                '-',
+            ]
+            if compress:
+                pdftk_cmd.append('compress')
+            subprocess.run(pdftk_cmd, check=True, stdout=out_file)
+    else:
+        output = PdfWriter()
+        for i, page in enumerate(fg_pdf.pages):
+            bg_page = copy.deepcopy(bg_pdf.pages[i])
+            bg_rotation = bg_page.get('/Rotate')
+            if bg_rotation:
+                # /Rotate is clockwise, transformation.rotate is counter-clockwise
+                t = Transformation().rotate(bg_rotation)
+                w = float(page.mediabox.getWidth())
+                h = float(page.mediabox.getHeight())
+                if bg_rotation in (90, 270):
+                    # offset due to rotation base
+                    if bg_rotation == 90:
+                        t = t.translate(h, 0)
+                    else:
+                        t = t.translate(0, w)
+                    # rotate mediabox as well
+                    page.mediabox = RectangleObject((
+                        page.mediabox.left.as_numeric(),
+                        page.mediabox.bottom.as_numeric(),
+                        page.mediabox.top.as_numeric(),
+                        page.mediabox.right.as_numeric(),
+                    ))
+                    page.trimbox = page.mediabox
+                elif bg_rotation == 180:
+                    t = t.translate(w, h)
+                page.add_transformation(t)
+            bg_page.merge_page(page)
+            output.add_page(bg_page)
+        output.write(out_file)
+
+
 @deconstructible
 class PdfLayoutValidator:
     def __call__(self, value):