Drop picture files on a folio to add them

Picture files (png, jpg, bmp, svg) dragged from the file manager onto a
folio are added there: the first centred on the drop point, the others
cascaded from it, and one undo step removes them all. A picture larger
than the visible part of the folio is scaled down to fit it. Files that
cannot be used are listed once after the others have been placed, and a
drop holding only other files (a .qet project) still reaches the main
window, which opens it.

The checks a picture must pass before it is embedded in the project
move into ImageDrop::load and are now shared by the drop, the add image
dialog and the script API: a regular file of at most 10 MB, and at most
64 megapixels, read from the header before any pixel is allocated.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

sources/imagedrop.cpp

@@ -0,0 +1,103 @@
+/*
+	Copyright 2006-2026 The QElectroTech Team
+	This file is part of QElectroTech.
+
+	QElectroTech is free software: you can redistribute it and/or modify
+	it under the terms of the GNU General Public License as published by
+	the Free Software Foundation, either version 2 of the License, or
+	(at your option) any later version.
+
+	QElectroTech is distributed in the hope that it will be useful,
+	but WITHOUT ANY WARRANTY; without even the implied warranty of
+	MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+	GNU General Public License for more details.
+
+	You should have received a copy of the GNU General Public License
+	along with QElectroTech.  If not, see <http://www.gnu.org/licenses/>.
+*/
+#include "imagedrop.h"
+
+#include <QCoreApplication>
+#include <QFileInfo>
+#include <QImageReader>
+#include <QMimeData>
+#include <QUrl>
+
+#include <algorithm>
+
+namespace
+{
+	bool isImageFile(const QUrl &url)
+	{
+		if (!url.isLocalFile())
+			return false;
+		const QString suffix = QFileInfo(url.toLocalFile()).suffix().toLower();
+		return ImageDrop::supportedSuffixes().contains(suffix);
+	}
+
+	QString tr(const char *text)
+	{
+		return QCoreApplication::translate("ImageDrop", text);
+	}
+}
+
+QStringList ImageDrop::supportedSuffixes()
+{
+	return {QStringLiteral("png"), QStringLiteral("jpg"), QStringLiteral("jpeg"),
+			QStringLiteral("bmp"), QStringLiteral("svg")};
+}
+
+QStringList ImageDrop::imageFiles(const QMimeData *mime)
+{
+	QStringList files;
+	if (!mime || !mime->hasUrls())
+		return files;
+	for (const QUrl &url : mime->urls())
+		if (isImageFile(url))
+			files << url.toLocalFile();
+	return files;
+}
+
+bool ImageDrop::hasOnlyOtherUrls(const QMimeData *mime)
+{
+	return mime && mime->hasUrls() && imageFiles(mime).isEmpty();
+}
+
+QImage ImageDrop::load(const QString &path, QString *error)
+{
+	auto fail = [error](const QString &message) {
+		if (error)
+			*error = message;
+		return QImage();
+	};
+
+	const QFileInfo info(path);
+	if (!info.isFile())
+		return fail(tr("not a file"));
+	if (info.size() > maxFileBytes)
+		return fail(tr("the file is larger than 10 MB"));
+
+	QImageReader reader(path);
+	const QSize size = reader.size();
+	if (size.isValid() && qint64(size.width()) * size.height() > maxPixels)
+		return fail(tr("the image has too many pixels"));
+
+	const QImage image = reader.read();
+	if (image.isNull())
+		return fail(tr("unable to read the image"));
+	return image;
+}
+
+qreal ImageDrop::fitScale(const QSizeF &size, const QSizeF &available)
+{
+	if (size.isEmpty() || available.isEmpty())
+		return 1.0;
+	const qreal scale = std::min(available.width() * fitMargin / size.width(),
+								 available.height() * fitMargin / size.height());
+	return std::min(1.0, scale);
+}
+
+QPointF ImageDrop::cascadeOffset(int index)
+{
+	return QPointF(cascadeStep * index, cascadeStep * index);
+}