Blending output with paper

Pdf4QtLib/sources/pdftransparencyrenderer.cpp

@@ -650,15 +650,11 @@ const PDFFloatBitmap& PDFTransparencyRenderer::endPaint()
     return *getImmediateBackdrop();
 }
 
-QImage PDFTransparencyRenderer::toImage(bool use16Bit) const
+QImage PDFTransparencyRenderer::toImageImpl(const PDFFloatBitmapWithColorSpace& floatImage, bool use16Bit) const
 {
     QImage image;
 
-    if (m_transparencyGroupDataStack.size() == 1 && // We have finished the painting
+    Q_ASSERT(floatImage.getPixelFormat().getProcessColorChannelCount() == 3);
-        m_transparencyGroupDataStack.back().immediateBackdrop.getPixelFormat().getProcessColorChannelCount() == 3) // We have exactly three process colors (RGB)
-    {
-        const PDFFloatBitmapWithColorSpace& floatImage = m_transparencyGroupDataStack.back().immediateBackdrop;
-        Q_ASSERT(floatImage.getPixelFormat().hasOpacityChannel());
 
     if (use16Bit)
     {
@@ -718,6 +714,38 @@ QImage PDFTransparencyRenderer::toImage(bool use16Bit) const
             }
         }
     }
+
+    return image;
+}
+
+QImage PDFTransparencyRenderer::toImage(bool use16Bit, bool usePaper, PDFRGB paperColor) const
+{
+    QImage image;
+
+    if (m_transparencyGroupDataStack.size() == 1 && // We have finished the painting
+        m_transparencyGroupDataStack.back().immediateBackdrop.getPixelFormat().getProcessColorChannelCount() == 3) // We have exactly three process colors (RGB)
+    {
+        const PDFFloatBitmapWithColorSpace& floatImage = m_transparencyGroupDataStack.back().immediateBackdrop;
+        Q_ASSERT(floatImage.getPixelFormat().hasOpacityChannel());
+
+        if (!usePaper)
+        {
+            return toImageImpl(floatImage, use16Bit);
+        }
+
+        PDFFloatBitmapWithColorSpace paperImage(floatImage.getWidth(), floatImage.getHeight(), floatImage.getPixelFormat(), floatImage.getColorSpace());
+        paperImage.makeOpaque();
+        paperImage.fillChannel(0, paperColor[0]);
+        paperImage.fillChannel(1, paperColor[1]);
+        paperImage.fillChannel(2, paperColor[2]);
+
+        PDFFloatBitmap softMask(paperImage.getWidth(), paperImage.getHeight(), PDFPixelFormat::createOpacityMask());
+        softMask.makeOpaque();
+
+        QRect blendRegion(0, 0, floatImage.getWidth(), floatImage.getHeight());
+        PDFFloatBitmapWithColorSpace::blend(floatImage, paperImage, paperImage, paperImage, softMask, false, 1.0f, BlendMode::Normal, false, 0xFFFF, PDFFloatBitmap::OverprintMode::NoOveprint, blendRegion);
+
+        return toImageImpl(paperImage, use16Bit);
     }
 
     return image;

Pdf4QtLib/sources/pdftransparencyrenderer.h

@@ -214,10 +214,10 @@ public:
                       OverprintMode overprintMode,
                       QRect blendRegion);
 
-private:
     void fillProcessColorChannels(PDFColorComponent value);
     void fillChannel(size_t channel, PDFColorComponent value);
 
+private:
     PDFPixelFormat m_format;
     std::size_t m_width;
     std::size_t m_height;
@@ -443,9 +443,11 @@ public:
     /// This function should be called only after call to \p endPaint. After painting,
     /// when it is finished, the result float image can be converted to QImage with
     /// this function, but only, if the float image is RGB. If error occurs, empty
-    /// image is returned.
+    /// image is returned. Also, result image can be painted onto opaque paper
-    /// \param use16bit
+    /// with paper color \p paperColor.
-    QImage toImage(bool use16Bit) const;
+    /// \param use16bit Produce 16-bit image instead of standard 8-bit
+    /// \param usePaper Blend image with opaque paper, with color \p paperColor
+    QImage toImage(bool use16Bit, bool usePaper = false, PDFRGB paperColor = PDFRGB()) const;
 
     virtual void performPathPainting(const QPainterPath& path, bool stroke, bool fill, bool text, Qt::FillRule fillRule) override;
     virtual void performClipping(const QPainterPath& path, Qt::FillRule fillRule) override;
@@ -501,6 +503,9 @@ private:
     PDFMappedColor createMappedColor(const PDFColor& sourceColor,
                                      const PDFAbstractColorSpace* sourceColorSpace);
 
+    /// Converts RGB bitmap to the image.
+    QImage toImageImpl(const PDFFloatBitmapWithColorSpace& floatImage, bool use16Bit) const;
+
     PDFFloatBitmapWithColorSpace* getInitialBackdrop();
     PDFFloatBitmapWithColorSpace* getImmediateBackdrop();
     PDFFloatBitmapWithColorSpace* getBackdrop();

Pdf4QtViewerPlugins/OutputPreviewPlugin/outputpreviewdialog.cpp

@@ -26,7 +26,7 @@ namespace pdfplugin
 {
 
 OutputPreviewDialog::OutputPreviewDialog(const pdf::PDFDocument* document, pdf::PDFWidget* widget, QWidget* parent) :
-    QDialog(parent),
+    QDialog(parent, Qt::Dialog | Qt::WindowMaximizeButtonHint | Qt::WindowCloseButtonHint),
     ui(new Ui::OutputPreviewDialog),
     m_inkMapper(document),
     m_document(document),
@@ -80,7 +80,7 @@ void OutputPreviewDialog::updateImage()
     renderer.processContents();
     renderer.endPaint();
 
-    QImage image = renderer.toImage(false);
+    QImage image = renderer.toImage(false, true, pdf::PDFRGB{ 1.0f, 1.0f, 1.0f });
     ui->imageLabel->setPixmap(QPixmap::fromImage(image));
 }