[FEATURE] New reusable interactive widget for editing gradient ramps

Supports:

- drag to move color stops
- double clicking to add a new stop
- pressing delete will remove the selected stop
- pressing arrow keys will move the selected stop, shift+arrow= larger
  move
- drag and drop a color onto the widget to add a new stop

Sponsored by North Road

python/gui/gui.sip

@@ -82,6 +82,7 @@
 %Include qgsformannotationitem.sip
 %Include qgsgenericprojectionselector.sip
 %Include qgsgeometryrubberband.sip
+%Include qgsgradientstopeditor.sip
 %Include qgsgroupwmsdatadialog.sip
 %Include qgshighlight.sip
 %Include qgshistogramwidget.sip

python/gui/qgsgradientstopeditor.sip

@@ -0,0 +1,115 @@
+/** \ingroup gui
+ * \class QgsGradientStopEditor
+ * An interactive editor for previewing a gradient color ramp and modifying the position of color
+ * stops along the gradient.
+ * \note Added in version 2.16
+ */
+
+class QgsGradientStopEditor : QWidget
+{
+%TypeHeaderCode
+#include <qgsgradientstopeditor.h>
+%End
+
+  public:
+
+    /** Constructor for QgsGradientStopEditor.
+     * @param parent parent widget
+     * @param ramp optional initial gradient ramp
+     */
+    QgsGradientStopEditor( QWidget* parent /TransferThis/ = nullptr, QgsVectorGradientColorRampV2* ramp = nullptr );
+
+    /** Sets the current ramp shown in the editor.
+     * @param ramp color ramp
+     * @see gradientRamp()
+     */
+    void setGradientRamp( const QgsVectorGradientColorRampV2& ramp );
+
+    /** Returns the current ramp created by the editor.
+     * @see setGradientRamp()
+     */
+    QgsVectorGradientColorRampV2 gradientRamp() const;
+
+    /** Sets the currently selected stop.
+     * @param index index of stop, where 0 corresponds to the first stop
+     * @see selectedStop()
+     */
+    void selectStop( int index );
+
+    /** Returns details about the currently selected stop.
+     * @see selectStop()
+     */
+    QgsGradientStop selectedStop() const;
+
+    virtual QSize sizeHint() const;
+    void paintEvent( QPaintEvent* event );
+
+  public slots:
+
+    /** Sets the color for the current selected stop.
+     * @param color new stop color
+     * @see setSelectedStopOffset()
+     * @see setSelectedStopDetails()
+     * @see setColor1()
+     * @see setColor2()
+     */
+    void setSelectedStopColor( const QColor& color );
+
+    /** Sets the offset for the current selected stop. This slot has no effect if either the
+     * first or last stop is selected, as they cannot be repositioned.
+     * @param offset new stop offset
+     * @see setSelectedStopColor()
+     * @see setSelectedStopDetails()
+     */
+    void setSelectedStopOffset( double offset );
+
+    /** Sets the color and offset for the current selected stop.
+     * @param color new stop color
+     * @param offset new stop offset
+     * @see setSelectedStopColor()
+     * @see setSelectedStopOffset()
+     */
+    void setSelectedStopDetails( const QColor& color, double offset );
+
+    /** Deletes the current selected stop. This slot has no effect if either the
+     * first or last stop is selected, as they cannot be deleted.
+     */
+    void deleteSelectedStop();
+
+    /** Sets the color for the first stop.
+     * @param color new stop color
+     * @see setColor2()
+     * @see setSelectedStopColor()
+     */
+    void setColor1( const QColor& color );
+
+    /** Sets the color for the last stop.
+     * @param color new stop color
+     * @see setColor1()
+     * @see setSelectedStopColor()
+     */
+    void setColor2( const QColor& color );
+
+  signals:
+
+    //! Emmitted when the gradient ramp is changed by a user
+    void changed();
+
+    /** Emmitted when the current selected stop changes.
+     * @param stop details about newly selected stop
+     */
+    void selectedStopChanged( const QgsGradientStop& stop );
+
+  protected:
+
+    virtual void mouseMoveEvent( QMouseEvent *event );
+    virtual void mousePressEvent( QMouseEvent *event );
+    virtual void mouseDoubleClickEvent( QMouseEvent * event );
+    virtual void keyPressEvent( QKeyEvent * event );
+
+    //Reimplemented to accept dragged colors
+    void dragEnterEvent( QDragEnterEvent * e );
+
+    //Reimplemented to accept dropped colors
+    void dropEvent( QDropEvent *e );
+};

src/gui/CMakeLists.txt

@@ -212,6 +212,7 @@ SET(QGIS_GUI_SRCS
   qgsformannotationitem.cpp
   qgsgenericprojectionselector.cpp
   qgsgeometryrubberband.cpp
+  qgsgradientstopeditor.cpp
   qgsgroupwmsdatadialog.cpp
   qgshighlight.cpp
   qgshistogramwidget.cpp
@@ -357,6 +358,7 @@ SET(QGIS_GUI_MOC_HDRS
   qgsfocuswatcher.h
   qgsformannotationitem.h
   qgsgenericprojectionselector.h
+  qgsgradientstopeditor.h
   qgsgroupwmsdatadialog.h
   qgshistogramwidget.h
   qgshtmlannotationitem.h