Fix a regression in calibre 6.0 that broke processing of very high resolution images. Fixes #1983484 [Cover creation fails](https://bugs.launchpad.net/calibre/+bug/1983484)

src/calibre/gui2/__init__.py

@@ -37,6 +37,7 @@ from calibre.utils.config import Config, ConfigProxy, JSONConfig, dynamic
 from calibre.utils.config_base import tweaks
 from calibre.utils.date import UNDEFINED_DATE
 from calibre.utils.file_type_icons import EXT_MAP
+from calibre.utils.img import set_image_allocation_limit
 from calibre.utils.localization import get_lang
 from calibre.utils.resources import user_dir
 from polyglot import queue
@@ -1102,6 +1103,7 @@ class Application(QApplication):
             QApplication.setDesktopFileName(override_program_name)
         QApplication.setAttribute(Qt.ApplicationAttribute.AA_ShareOpenGLContexts, True)  # needed for webengine
         QApplication.__init__(self, args)
+        set_image_allocation_limit()
         self.palette_manager.initialize()
         icon_resource_manager.initialize()
         sh = self.styleHints()
@@ -1446,6 +1448,7 @@ def ensure_app(headless=True):
                 QApplication.setAttribute(Qt.ApplicationAttribute.AA_UseSoftwareOpenGL, True)
             QApplication.setAttribute(Qt.ApplicationAttribute.AA_ShareOpenGLContexts)
             _store_app = QApplication(args)
+            set_image_allocation_limit()
             if headless and has_headless:
                 _store_app.headless = True
             import traceback

src/calibre/gui2/progress_indicator/QProgressIndicator.cpp

@@ -8,6 +8,7 @@
 #include <QFormLayout>
 #include <QDialogButtonBox>
 #include <QPainterPath>
+#include <QImageReader>
 #include <algorithm>
 #include <qdrawutil.h>
 
@@ -423,3 +424,13 @@ QMenu*
 menu_for_action(const QAction *ac) {
     return ac->menu<QMenu*>();
 }
+
+void
+set_image_allocation_limit(int megabytes) {
+    QImageReader::setAllocationLimit(megabytes);
+}
+
+int
+get_image_allocation_limit() {
+    return QImageReader::allocationLimit();
+}

src/calibre/gui2/progress_indicator/QProgressIndicator.h

@@ -160,3 +160,5 @@ void set_no_activate_on_click(QWidget *widget);
 void draw_snake_spinner(QPainter &painter, QRect rect, int angle, const QColor & light, const QColor & dark);
 void set_menu_on_action(QAction* ac, QMenu* menu);
 QMenu* menu_for_action(const QAction *ac);
+void set_image_allocation_limit(int megabytes);
+int get_image_allocation_limit();

src/calibre/gui2/progress_indicator/QProgressIndicator.sip

@@ -87,3 +87,5 @@ void set_no_activate_on_click(QWidget *widget);
 void draw_snake_spinner(QPainter &painter, QRect rect, int angle, const QColor & light, const QColor & dark) /ReleaseGIL/;
 void set_menu_on_action(QAction* ac, QMenu* menu);
 QMenu* menu_for_action(const QAction *ac);
+void set_image_allocation_limit(int megabytes);
+int get_image_allocation_limit();

src/calibre/utils/img.py

@@ -8,6 +8,7 @@ import shutil
 import subprocess
 import sys
 import tempfile
+from contextlib import suppress
 from io import BytesIO
 from qt.core import (
     QBuffer, QByteArray, QColor, QImage, QImageReader, QImageWriter, QIODevice,
@@ -106,6 +107,14 @@ def gif_data_to_png_data(data, discard_animation=False):
 # Loading images {{{
 
 
+def set_image_allocation_limit(size_in_mb=1024):
+    with suppress(ImportError):  # for people running form source
+        from calibre_extensions.progress_indicator import (
+            set_image_allocation_limit as impl
+        )
+        impl(size_in_mb)
+
+
 def null_image():
     ' Create an invalid image. For internal use. '
     return QImage()
@@ -115,6 +124,7 @@ def image_from_data(data):
     ' Create an image object from data, which should be a bytestring. '
     if isinstance(data, QImage):
         return data
+    set_image_allocation_limit()
     i = QImage()
     if not i.loadFromData(data):
         q = what(None, data)