fix: improve printing by producing a better-quality pdf instead (#764)

src/ui/EditorNS/editor.cpp

@@ -779,6 +779,48 @@ namespace EditorNS
 #endif
     }
 
+    QPromise<QByteArray> Editor::printToPdf(const QPageLayout& pageLayout)
+    {
+        // 1. Set theme to default because dark themes would force the printer to color the entire
+        //    document in the background color. Default theme has white background.
+        // 2. Set WebView's bg-color to white to prevent visual artifacts when printing less than one page.
+        // 3. Set C_CMD_DISPLAY_PRINT_STYLE to hide UI elements like the gutter.
+
+        return QPromise<QByteArray>(
+            [&](const QPromiseResolve<QByteArray>& resolve, const QPromiseReject<QByteArray>& reject) {
+
+#if QT_VERSION >= QT_VERSION_CHECK(5, 8, 0)
+                QColor prevBackgroundColor = m_webView->page()->backgroundColor();
+                QString prevStylesheet = m_webView->styleSheet();
+
+                setTheme(themeFromName("default"));
+                m_webView->page()->setBackgroundColor(Qt::transparent);
+                m_webView->setStyleSheet("background-color: white");
+                asyncSendMessageWithResultP("C_CMD_DISPLAY_PRINT_STYLE").wait();
+
+                m_webView->page()->printToPdf(
+                    [=](const QByteArray& data) {
+                        QTimer::singleShot(0, [=]() {
+                            asyncSendMessageWithResultP("C_CMD_DISPLAY_NORMAL_STYLE").wait();
+                            m_webView->setStyleSheet(prevStylesheet);
+                            m_webView->page()->setBackgroundColor(prevBackgroundColor);
+                            setTheme(themeFromName(NqqSettings::getInstance().Appearance.getColorScheme()));
+                        });
+
+                        if (data.isEmpty() || data.isNull()) {
+                            reject(QByteArray());
+                        } else {
+                            resolve(data);
+                        }
+                    },
+                    pageLayout);
+
+#else
+                reject(QByteArray());
+#endif
+            });
+    }
+
     QPromise<QString> Editor::getCurrentWord()
     {
         return asyncSendMessageWithResultP("C_FUN_GET_CURRENT_WORD")

src/ui/include/EditorNS/editor.h

@@ -389,7 +389,19 @@ namespace EditorNS
         std::shared_future<QVariant> asyncSendMessageWithResult(const QString &msg, const QVariant &data, std::function<void(QVariant)> callback = 0);
         std::shared_future<QVariant> asyncSendMessageWithResult(const QString &msg, std::function<void(QVariant)> callback = 0);
 
+        /**
+         * @brief Print the editor. As of Qt 5.11, it produces low-quality, non-vector graphics with big dimension.
+         * @param printer
+         */
         void print(std::shared_ptr<QPrinter> printer);
+
+        /**
+         * @brief Returns the content of the editor layed out in a pdf file that can be directly saved to disk.
+         *        This method produces light, vector graphics.
+         * @param pageLayout
+         * @return
+         */
+        QPromise<QByteArray> printToPdf(const QPageLayout &pageLayout = QPageLayout(QPageSize(QPageSize::A4), QPageLayout::Portrait, QMarginsF()));
     };
 
 }

src/ui/mainwindow.cpp

@@ -29,8 +29,10 @@
 #include <QLineEdit>
 #include <QMessageBox>
 #include <QMimeData>
+#include <QPageSetupDialog>
 #include <QScrollArea>
 #include <QScrollBar>
+#include <QTemporaryFile>
 #include <QTimer>
 #include <QToolBar>
 #include <QToolButton>
@@ -2235,16 +2237,39 @@ void MainWindow::runCommand()
 
 void MainWindow::on_actionPrint_triggered()
 {
-    std::shared_ptr<QPrinter> printer = std::make_shared<QPrinter>(QPrinter::HighResolution);
-    QPrintDialog dialog(printer.get());
-    if (dialog.exec() == QDialog::Accepted)
-        currentEditor()->print(printer);
+    // TODO If ghostscript is available on the system, we could
+    //        - show a QPrintDialog to the user
+    //        - generate the pdf file
+    //        - print the pdf via ghostscript
+    //      https://stackoverflow.com/questions/2599925/how-to-print-pdf-on-default-network-printer-using-ghostscript-gswin32c-exe-she
+
+    QPageSetupDialog dlg;
+    if (dlg.exec() == QDialog::Accepted) {
+        currentEditor()->printToPdf(dlg.printer()->pageLayout()).then([this](QByteArray data) {
+            QFile file(QDir::tempPath() + "/notepadqq.print." +
+                       QString::number(QDateTime::currentMSecsSinceEpoch(), 16) + ".pdf");
+
+            if (file.open(QIODevice::WriteOnly)) { // FIXME: Delete the file when we're done
+                file.write(data);
+                file.close();
+
+                bool ok = QDesktopServices::openUrl(QUrl::fromLocalFile(file.fileName()));
+                if (!ok) {
+                    QMessageBox::warning(this,
+                        QCoreApplication::applicationName(),
+                        tr("%1 wasn't able to open the produced pdf file:\n%2")
+                            .arg(QCoreApplication::applicationName(), file.fileName()),
+                        QMessageBox::Ok,
+                        QMessageBox::Ok);
+                }
+            }
+        });
+    }
 }
 
 void MainWindow::on_actionPrint_Now_triggered()
 {
-    std::shared_ptr<QPrinter> printer = std::make_shared<QPrinter>(QPrinter::HighResolution);
-    currentEditor()->print(printer);
+    qWarning() << "Not implemented.";
 }
 /*
 void MainWindow::on_actionLaunch_in_Chrome_triggered()