Redo scale handling of pdf when printing

Since 7f89bad our printer handling produces low quality
images, the reason for that is the we first render
with pdfium to bitmap which is fixed to twice size of pdf
document in points, then it is downscaled/upscaled by
qpainter. This issue is even more visible when print preview
is requested on hdpi screen.

Simplify the code and do the "scaling" already when rendering
bitmap with pdfium.

Task-number: QTBUG-75092
Fixes: QTBUG-78161
Change-Id: I616ad1f371e7d3457a04b0a254603ed235c387bc
Reviewed-by: Michael Brüning <michael.bruning@qt.io>

1 files changed, 16 insertions, 26 deletions

diff --git a/src/webenginewidgets/printer_worker.cpp b/src/webenginewidgets/printer_worker.cpp
index 94a862cda..8e1c2a985 100644
--- a/src/webenginewidgets/printer_worker.cpp
+++ b/src/webenginewidgets/printer_worker.cpp
@@ -94,17 +94,9 @@ void PrinterWorker::print()
         documentCopies = 1;
     }
 
-    bool isLandscape = pdfiumWrapper.pageIsLandscape(0);
-    QPageLayout::Orientation prevOrientation = m_printer->pageLayout().orientation();
-    m_printer->setPageOrientation(isLandscape ? QPageLayout::Landscape : QPageLayout::Portrait);
+    qreal resolution = m_printer->resolution() / 72.0; // pdfium uses points so 1/72 inch
 
     QPainter painter;
-    if (!painter.begin(m_printer)) {
-        qWarning("Failure to print on printer %ls: Could not open printer for painting.",
-                  qUtf16Printable(m_printer->printerName()));
-        Q_EMIT resultReady(false);
-        return;
-    }
 
     for (int printedDocuments = 0; printedDocuments < documentCopies; printedDocuments++) {
         if (printedDocuments > 0)
@@ -113,11 +105,20 @@ void PrinterWorker::print()
         int currentPageIndex = fromPage;
 
         for (int i = 0; true; i++) {
-            prevOrientation = m_printer->pageLayout().orientation();
-            isLandscape = pdfiumWrapper.pageIsLandscape(currentPageIndex - 1);
+            QSizeF documentSize = (pdfiumWrapper.pageSize(currentPageIndex - 1) * resolution);
+            bool isLandscape = documentSize.width() > documentSize.height();
             m_printer->setPageOrientation(isLandscape ? QPageLayout::Landscape : QPageLayout::Portrait);
-
-            QSize pageSize = m_printer->pageRect().size();
+            QRectF pageRect = m_printer->pageRect(QPrinter::DevicePixel);
+            documentSize = documentSize.scaled(pageRect.size(), Qt::KeepAspectRatio);
+
+            // setPageOrientation has to be called before qpainter.begin() or before qprinter.newPage() so correct metrics is used,
+            // therefore call begin now for only first page
+            if (!painter.isActive() && !painter.begin(m_printer)) {
+                qWarning("Failure to print on printer %ls: Could not open printer for painting.",
+                          qUtf16Printable(m_printer->printerName()));
+                Q_EMIT resultReady(false);
+                return;
+            }
 
             if (i > 0)
                 m_printer->newPage();
@@ -132,21 +133,12 @@ void PrinterWorker::print()
                 if (printedPages > 0)
                     m_printer->newPage();
 
-                QImage currentImage = pdfiumWrapper.pageAsQImage(currentPageIndex - 1);
+                QImage currentImage = pdfiumWrapper.pageAsQImage(currentPageIndex - 1,documentSize.width(),documentSize.height());
                 if (currentImage.isNull()) {
                     Q_EMIT resultReady(false);
                     return;
                 }
-
-                QRect targetRect = currentImage.rect();
-                // Scale down currentImage by both width and height to fit into the drawable area of the page.
-                float scaleFactor = (float)pageSize.width() / (float)targetRect.width();
-                targetRect = QRect(0, 0, targetRect.width() * scaleFactor, targetRect.height() * scaleFactor);
-                scaleFactor = (float)pageSize.height() / (float)targetRect.height();
-                targetRect = QRect(0, 0, targetRect.width() * scaleFactor, targetRect.height() * scaleFactor);
-
-                // Painting operations are automatically clipped to the bounds of the drawable part of the page.
-                painter.drawImage(targetRect, currentImage, currentImage.rect());
+                painter.drawImage(0,0, currentImage);
             }
 
             if (currentPageIndex == toPage)
@@ -156,8 +148,6 @@ void PrinterWorker::print()
                 currentPageIndex++;
             else
                 currentPageIndex--;
-
-            m_printer->setPageOrientation(prevOrientation);
         }
     }
     painter.end();