Add CMYK support for pens/fills in the PDF engine

Insofar, painting with a CMYK color (pen/brush) was completely ignored
by QPdfWriter, although the PDF format can faithfully represent CMYK
colors.

This commit adds support for CMYK colors in the PDF engine. The support
is opt-in, in the name of backwards compatibility; an enumeration on
QPdfWriter controls the output.

QPrinter was using a hidden hook in QPdfEngine in order to do grayscale
printing; this hook can now be made public API through the same
enumeration.

This work has been kindly sponsored by the QGIS project
(https://qgis.org/).

[ChangeLog][QtGui][QPdfWriter] QPdfWriter can now use CMYK colors
directly, without converting them into RGB colors.

Change-Id: Ia27c19ec81a58ab68ddc8b9c89c4e57d7d637301
Reviewed-by: Lars Knoll <lars@knoll.priv.no>

1 files changed, 33 insertions, 4 deletions

diff --git a/src/gui/painting/qpdf_p.h b/src/gui/painting/qpdf_p.h
index 2c70ddf664..b97d0df31f 100644
--- a/src/gui/painting/qpdf_p.h
+++ b/src/gui/painting/qpdf_p.h
@@ -142,7 +142,7 @@ public:
     };
 
     QPdfEngine();
-    QPdfEngine(QPdfEnginePrivate &d);
+    explicit QPdfEngine(QPdfEnginePrivate &d);
     ~QPdfEngine() {}
 
     void setOutputFilename(const QString &filename);
@@ -157,6 +157,18 @@ public:
 
     void addFileAttachment(const QString &fileName, const QByteArray &data, const QString &mimeType);
 
+    // keep in sync with QPdfWriter
+    enum class ColorModel
+    {
+        RGB,
+        Grayscale,
+        CMYK,
+        Auto,
+    };
+
+    ColorModel colorModel() const;
+    void setColorModel(ColorModel model);
+
     // reimplementations QPaintEngine
     bool begin(QPaintDevice *pdev) override;
     bool end() override;
@@ -240,6 +252,7 @@ public:
     bool needsTransform;
     qreal opacity;
     QPdfEngine::PdfVersion pdfVersion;
+    QPdfEngine::ColorModel colorModel;
 
     QHash<QFontEngine::FaceId, QFontSubset *> fonts;
 
@@ -255,7 +268,6 @@ public:
     QString creator;
     bool embedFonts;
     int resolution;
-    bool grayscale;
 
     // Page layout: size, orientation and margins
     QPageLayout m_pageLayout;
@@ -265,8 +277,22 @@ private:
     int generateGradientShader(const QGradient *gradient, const QTransform &matrix, bool alpha = false);
     int generateLinearGradientShader(const QLinearGradient *lg, const QTransform &matrix, bool alpha);
     int generateRadialGradientShader(const QRadialGradient *gradient, const QTransform &matrix, bool alpha);
-    int createShadingFunction(const QGradient *gradient, int from, int to, bool reflect, bool alpha);
+    struct ShadingFunctionResult
+    {
+        int function;
+        QPdfEngine::ColorModel colorModel;
+        void writeColorSpace(QPdf::ByteStream *stream) const;
+    };
+    ShadingFunctionResult createShadingFunction(const QGradient *gradient, int from, int to, bool reflect, bool alpha);
+
+    enum class ColorDomain {
+        Stroking,
+        NonStroking,
+        NonStrokingPattern,
+    };
 
+    QPdfEngine::ColorModel colorModelForColor(const QColor &color) const;
+    void writeColor(ColorDomain domain, const QColor &color);
     void writeInfo();
     int writeXmpDcumentMetaData();
     int writeOutputIntent();
@@ -316,7 +342,10 @@ private:
 
     // various PDF objects
     int pageRoot, namesRoot, destsRoot, attachmentsRoot, catalog, info;
-    int graphicsState, patternColorSpace;
+    int graphicsState;
+    int patternColorSpaceRGB;
+    int patternColorSpaceGrayscale;
+    int patternColorSpaceCMYK;
     QList<uint> pages;
     QHash<qint64, uint> imageCache;
     QHash<QPair<uint, uint>, uint > alphaCache;