[FEATURE] QgsTextRenderer class for rich text rendering

Moves all the drawing code out of labeling into a new class
which just handles rendering text. This allows other parts
of the code to utilise all the advanced formatting options
that labeling supports, eg rendering text with shadows,
buffers and backgrounds.

python/core/qgspallabeling.sip

@@ -649,61 +649,6 @@ class QgsLabelCandidate
     double cost;
 };
 
-/** \ingroup core
-  * Maintains current state of more grainular and temporal values when creating/painting
-  * component parts of an individual label (e.g. buffer, background, shadow, etc.).
-  */
-class QgsLabelComponent
-{
-%TypeHeaderCode
-#include <qgspallabeling.h>
-%End
-
-  public:
-    QgsLabelComponent();
-
-    // methods
-
-    QString text() const;
-    void setText( const QString& text );
-
-    const QgsPoint& origin() const;
-    void setOrigin( const QgsPoint& point );
-
-    bool useOrigin() const;
-    void setUseOrigin( const bool use );
-
-    double rotation() const;
-    void setRotation( const double rotation );
-
-    double rotationOffset() const;
-    void setRotationOffset( const double rotation );
-
-    bool useRotation() const;
-    void setUseRotation( const bool use );
-
-    const QgsPoint& center() const;
-    void setCenter( const QgsPoint& point );
-
-    bool useCenter() const;
-    void setUseCenter( const bool use );
-
-    const QgsPoint& size() const;
-    void setSize( const QgsPoint& point );
-
-    const QgsPoint& offset() const;
-    void setOffset( const QgsPoint& point );
-
-    const QPicture* picture() const;
-    void setPicture( QPicture* picture );
-
-    double pictureBuffer() const;
-    void setPictureBuffer( const double buffer );
-
-    double dpiRatio() const;
-    void setDpiRatio( const double ratio );
-};
-
 
 /**
  * Class that stores computed placement from labeling engine.
@@ -736,14 +681,6 @@ class QgsPalLabeling : QgsLabelingEngineInterface
 %End
 
   public:
-    enum DrawLabelType
-    {
-      LabelText,
-      LabelBuffer,
-      LabelShape,
-      LabelSVG,
-      LabelShadow
-    };
 
     QgsPalLabeling();
     ~QgsPalLabeling();
@@ -830,18 +767,6 @@ class QgsPalLabeling : QgsLabelingEngineInterface
     //! @note not available in python bindings
     // void drawLabelCandidateRect( pal::LabelPosition* lp, QPainter* painter, const QgsMapToPixel* xform );
 
-    static void drawLabelBuffer( QgsRenderContext& context,
-                                 const QgsLabelComponent &component,
-                                 const QgsTextFormat& format );
-
-    static void drawLabelBackground( QgsRenderContext& context,
-                                     QgsLabelComponent component,
-                                     const QgsTextFormat& format );
-
-    static void drawLabelShadow( QgsRenderContext &context,
-                                 const QgsLabelComponent &component,
-                                 const QgsTextFormat& format );
-
     //! load/save engine settings to project file
     void loadEngineSettings();
     void saveEngineSettings();

python/core/qgstextrenderer.sip

@@ -856,6 +856,15 @@ class QgsTextFormat
      */
     QFont font() const;
 
+    /** Returns a font with the size scaled to match the format's size settings (including
+     * units and map unit scale) for a specified render context.
+     * @param context destination render context
+     * @returns font with scaled size
+     * @see font()
+     * @see size()
+     */
+    QFont scaledFont( const QgsRenderContext& context ) const;
+
     /** Sets the font used for rendering text. Note that the size of the font
      * is not used, and setSize() should be called instead to explicitly set the size
      * of rendered text.
@@ -1021,6 +1030,21 @@ class QgsTextRenderer
 
   public:
 
+    enum TextPart
+    {
+      Text,
+      Buffer,
+      Background,
+      Shadow
+    };
+
+    enum HAlignment
+    {
+      AlignLeft,
+      AlignCenter,
+      AlignRight,
+    };
+
     /** Calculates pixel size (considering output size should be in pixel or map units, scale factors and optionally oversampling)
      * @param size size to convert
      * @param c rendercontext
@@ -1041,4 +1065,63 @@ class QgsTextRenderer
      */
     static double scaleToPixelContext( double size, const QgsRenderContext& c, QgsUnitTypes::RenderUnit unit, bool rasterfactor = false, const QgsMapUnitScale& mapUnitScale = QgsMapUnitScale() );
 
+    /** Draws text within a rectangle using the specified settings.
+     * @param rect destination rectangle for text
+     * @param rotation text rotation
+     * @param textLines list of lines of text to draw
+     * @param context render context
+     * @param format text format
+     * @param drawAsOutlines set to false to render text as text. This allows outputs to
+     * formats like SVG to maintain text as text objects, but at the cost of degraded
+     * rendering and may result in side effects like misaligned text buffers.
+     */
+    static void drawText( const QRectF& rect, double rotation, HAlignment alignment, const QStringList& textLines,
+                          QgsRenderContext& context, const QgsTextFormat& format,
+                          bool drawAsOutlines = true );
+
+    /** Draws text at a point origin using the specified settings.
+     * @param point origin of text
+     * @param rotation text rotation
+     * @param textLines list of lines of text to draw
+     * @param context render context
+     * @param format text format
+     * @param drawAsOutlines set to false to render text as text. This allows outputs to
+     * formats like SVG to maintain text as text objects, but at the cost of degraded
+     * rendering and may result in side effects like misaligned text buffers.
+     */
+    static void drawText( const QPointF& point, double rotation, HAlignment alignment, const QStringList& textLines,
+                          QgsRenderContext& context, const QgsTextFormat& format,
+                          bool drawAsOutlines = true );
+
+    /** Draws a single component of rendered text using the specified settings.
+     * @param rect destination rectangle for text
+     * @param rotation text rotation
+     * @param textLines list of lines of text to draw
+     * @param context render context
+     * @param format text format
+     * @param part component of text to draw
+     * @param drawAsOutlines set to false to render text as text. This allows outputs to
+     * formats like SVG to maintain text as text objects, but at the cost of degraded
+     * rendering and may result in side effects like misaligned text buffers.
+     */
+    static void drawPart( const QRectF& rect, double rotation, HAlignment alignment, const QStringList& textLines,
+                          QgsRenderContext& context, const QgsTextFormat& format,
+                          TextPart part, bool drawAsOutlines = true );
+
+    /** Draws a single component of rendered text using the specified settings.
+     * @param origin origin for start of text. Y coordinate will be used as baseline.
+     * @param rotation text rotation
+     * @param textLines list of lines of text to draw
+     * @param context render context
+     * @param format text format
+     * @param part component of text to draw. Note that Shadow parts cannot be drawn
+     * individually and instead are drawn with their associated part (eg drawn together
+     * with the text or background parts)
+     * @param drawAsOutlines set to false to render text as text. This allows outputs to
+     * formats like SVG to maintain text as text objects, but at the cost of degraded
+     * rendering and may result in side effects like misaligned text buffers.
+     */
+    static void drawPart( const QPointF& origin, double rotation, HAlignment alignment, const QStringList& textLines,
+                          QgsRenderContext& context, const QgsTextFormat& format,
+                          TextPart part, bool drawAsOutlines = true );
 };

src/app/qgslabelinggui.cpp

@@ -771,7 +771,7 @@ void QgsLabelingGui::init()
   mZIndexSpinBox->setValue( lyr.zIndex );
 
   mRefFont = format.font();
-  mFontSizeSpinBox->setValue( format.font().pointSizeF() );
+  mFontSizeSpinBox->setValue( format.size() );
   btnTextColor->setColor( format.color() );
   mFontTranspSpinBox->setValue( 100 - 100 * format.opacity() );
   comboBlendMode->setBlendMode( format.blendMode() );

src/app/qgslabelpreview.cpp

@@ -73,9 +73,9 @@ void QgsLabelPreview::paintEvent( QPaintEvent *e )
   if ( mFormat.buffer().size() != 0 )
   {
     mContext.setPainter( &p );
-    QgsLabelComponent component;
-    component.setText( text() );
-    QgsPalLabeling::drawLabelBuffer( mContext, component, mFormat );
+    QgsTextRenderer::Component component;
+    component.text = text();
+    QgsTextRenderer::drawBuffer( mContext, component, mFormat );
   }
 
   QPainterPath path;