[FEATURE] New decoration type for showing composer map extents

Adds a new (disabled by default) decoration item for showing
the extents of composer maps in the main canvas. When enabled,
the extents of all maps within all composers will be shown
using a lightly dotted border. The border symbol is configurable
for improved legibility against different map backgrounds.

This is useful when you're tweaking the positioning of map elements
such as labels, and need to know what the actual visible region
of composer maps are.

src/app/CMakeLists.txt

@@ -24,6 +24,8 @@ SET(QGIS_APP_SRCS
   qgsdecorationitem.cpp
   qgsdecorationcopyright.cpp
   qgsdecorationcopyrightdialog.cpp
+  qgsdecorationlayoutextent.cpp
+  qgsdecorationlayoutextentdialog.cpp
   qgsdecorationnortharrow.cpp
   qgsdecorationnortharrowdialog.cpp
   qgsdecorationscalebar.cpp
@@ -209,6 +211,8 @@ SET (QGIS_APP_MOC_HDRS
   qgsdecorationitem.h
   qgsdecorationcopyright.h
   qgsdecorationcopyrightdialog.h
+  qgsdecorationlayoutextent.h
+  qgsdecorationlayoutextentdialog.h
   qgsdecorationnortharrow.h
   qgsdecorationnortharrowdialog.h
   qgsdecorationscalebar.h

src/app/qgisapp.cpp

@@ -161,6 +161,7 @@ Q_GUI_EXPORT extern int qt_defaultDpiX();
 #include "qgsdecorationnortharrow.h"
 #include "qgsdecorationscalebar.h"
 #include "qgsdecorationgrid.h"
+#include "qgsdecorationlayoutextent.h"
 #include "qgsencodingfiledialog.h"
 #include "qgserror.h"
 #include "qgserrordialog.h"
@@ -3527,11 +3528,15 @@ void QgisApp::createDecorations()
   QgsDecorationGrid *mDecorationGrid = new QgsDecorationGrid( this );
   connect( mActionDecorationGrid, &QAction::triggered, mDecorationGrid, &QgsDecorationGrid::run );
 
+  QgsDecorationLayoutExtent *decorationLayoutExtent = new QgsDecorationLayoutExtent( this );
+  connect( mActionDecorationLayoutExtent, &QAction::triggered, decorationLayoutExtent, &QgsDecorationLayoutExtent::run );
+
   // add the decorations in a particular order so they are rendered in that order
   addDecorationItem( mDecorationGrid );
   addDecorationItem( mDecorationCopyright );
   addDecorationItem( mDecorationNorthArrow );
   addDecorationItem( mDecorationScaleBar );
+  addDecorationItem( decorationLayoutExtent );
   connect( mMapCanvas, &QgsMapCanvas::renderComplete, this, &QgisApp::renderDecorationItems );
   connect( this, &QgisApp::newProject, this, &QgisApp::projectReadDecorationItems );
   connect( this, &QgisApp::projectRead, this, &QgisApp::projectReadDecorationItems );

src/app/qgsdecorationitem.h

@@ -61,6 +61,8 @@ class APP_EXPORT QgsDecorationItem : public QObject, public QgsMapDecoration
      */
     void setPlacement( Placement placement ) { mPlacement = placement; }
 
+    QString name() const { return mName; }
+
   signals:
     void toggled( bool t );
 
@@ -73,14 +75,13 @@ class APP_EXPORT QgsDecorationItem : public QObject, public QgsMapDecoration
     //! Show the dialog box
     virtual void run() {}
 
-    virtual void setName( const char *name );
-    virtual QString name() { return mName; }
-
     //! Redraws the decoration
     void update();
 
   protected:
 
+    void setName( const char *name );
+
     //! True if decoration item has to be displayed
     bool mEnabled;
 

src/app/qgsdecorationlayoutextent.cpp

@@ -0,0 +1,153 @@
+/***************************************************************************
+                          qgsdecorationlayoutextent.cpp
+                              ----------------------
+    begin                : May 2017
+    copyright            : (C) 2017 by Nyall Dawson
+    email                : nyall dot dawson at gmail dot com
+
+ ***************************************************************************/
+
+/***************************************************************************
+ *                                                                         *
+ *   This program is free software; you can redistribute it and/or modify  *
+ *   it under the terms of the GNU General Public License as published by  *
+ *   the Free Software Foundation; either version 2 of the License, or     *
+ *   (at your option) any later version.                                   *
+ *                                                                         *
+ ***************************************************************************/
+
+#include "qgsdecorationlayoutextent.h"
+#include "qgsdecorationlayoutextentdialog.h"
+
+#include "qgslayoutmanager.h"
+#include "qgscomposition.h"
+#include "qgscomposermap.h"
+#include "qgsgeometry.h"
+#include "qgscsexception.h"
+#include "qgslinesymbollayer.h"
+
+#include "qgisapp.h"
+#include "qgsapplication.h"
+#include "qgslogger.h"
+#include "qgsmapcanvas.h"
+#include "qgsproject.h"
+#include "qgssymbollayerutils.h"
+#include "qgsreadwritecontext.h"
+
+#include <QPainter>
+
+QgsDecorationLayoutExtent::QgsDecorationLayoutExtent( QObject *parent )
+  : QgsDecorationItem( parent )
+{
+  mPlacement = BottomRight;
+  mMarginUnit = QgsUnitTypes::RenderMillimeters;
+
+  setName( "Layout Extent" );
+  projectRead();
+}
+
+void QgsDecorationLayoutExtent::projectRead()
+{
+  QgsDecorationItem::projectRead();
+
+  QDomDocument doc;
+  QDomElement elem;
+  QgsReadWriteContext rwContext;
+  rwContext.setPathResolver( QgsProject::instance()->pathResolver() );
+  QString xml = QgsProject::instance()->readEntry( mNameConfig, QStringLiteral( "/Symbol" ) );
+  mSymbol.reset( nullptr );
+  if ( !xml.isEmpty() )
+  {
+    doc.setContent( xml );
+    elem = doc.documentElement();
+    mSymbol.reset( QgsSymbolLayerUtils::loadSymbol<QgsFillSymbol>( elem, rwContext ) );
+  }
+  if ( ! mSymbol )
+  {
+    mSymbol.reset( new QgsFillSymbol() );
+    QgsSimpleLineSymbolLayer *layer = new QgsSimpleLineSymbolLayer( QColor( 0, 0, 0, 100 ), 0, Qt::DashLine );
+    mSymbol->changeSymbolLayer( 0, layer );
+  }
+}
+
+void QgsDecorationLayoutExtent::saveToProject()
+{
+  QgsDecorationItem::saveToProject();
+  // write symbol info to xml
+  QDomDocument doc;
+  QDomElement elem;
+  QgsReadWriteContext rwContext;
+  rwContext.setPathResolver( QgsProject::instance()->pathResolver() );
+  if ( mSymbol )
+  {
+    elem = QgsSymbolLayerUtils::saveSymbol( QStringLiteral( "Symbol" ), mSymbol.get(), doc, rwContext );
+    doc.appendChild( elem );
+    // FIXME this works, but XML will not be valid as < is replaced by &lt;
+    QgsProject::instance()->writeEntry( mNameConfig, QStringLiteral( "/Symbol" ), doc.toString() );
+  }
+}
+
+void QgsDecorationLayoutExtent::run()
+{
+  QgsDecorationLayoutExtentDialog dlg( *this, QgisApp::instance() );
+  dlg.exec();
+}
+
+
+void QgsDecorationLayoutExtent::render( const QgsMapSettings &mapSettings, QgsRenderContext &context )
+{
+  if ( !enabled() )
+    return;
+
+  if ( !mSymbol )
+    return;
+
+  context.painter()->save();
+  context.painter()->setRenderHint( QPainter::Antialiasing, true );
+  mSymbol->startRender( context );
+
+  const QgsMapToPixel &m2p = mapSettings.mapToPixel();
+  QTransform transform = m2p.transform();
+
+  Q_FOREACH ( QgsComposition *composition, QgsProject::instance()->layoutManager()->compositions() )
+  {
+    Q_FOREACH ( const QgsComposerMap *map, composition->composerMapItems() )
+    {
+      QPolygonF extent = map->visibleExtentPolygon();
+      QgsGeometry g = QgsGeometry::fromQPolygonF( extent );
+
+      if ( map->crs() !=
+           mapSettings.destinationCrs() )
+      {
+        // reproject extent
+        QgsCoordinateTransform ct( map->crs(),
+                                   mapSettings.destinationCrs() );
+        g = g.densifyByCount( 20 );
+        try
+        {
+          g.transform( ct );
+        }
+        catch ( QgsCsException & )
+        {
+        }
+      }
+
+      g.transform( transform );
+      extent = g.asQPolygonF();
+      mSymbol->renderPolygon( extent, nullptr, nullptr, context );
+    }
+  }
+  mSymbol->stopRender( context );
+  context.painter()->restore();
+}
+
+QgsFillSymbol *QgsDecorationLayoutExtent::symbol() const
+{
+  return mSymbol.get();
+}
+
+void QgsDecorationLayoutExtent::setSymbol( QgsFillSymbol *symbol )
+{
+  mSymbol.reset( symbol );
+}
+

src/app/qgsdecorationlayoutextent.h

@@ -0,0 +1,60 @@
+/***************************************************************************
+                          qgsdecorationlayoutextent.h
+                              -------------------
+    begin                : May 2017
+    copyright            : (C) 2017 by Nyall Dawson
+    email                : nyall dot dawson at gmail dot com
+
+ ***************************************************************************/
+
+/***************************************************************************
+ *                                                                         *
+ *   This program is free software; you can redistribute it and/or modify  *
+ *   it under the terms of the GNU General Public License as published by  *
+ *   the Free Software Foundation; either version 2 of the License, or     *
+ *   (at your option) any later version.                                   *
+ *                                                                         *
+ ***************************************************************************/
+#ifndef QGSDECORATIONLAYOUTEXTENT_H
+#define QGSDECORATIONLAYOUTEXTENT_H
+
+#include "qgsdecorationitem.h"
+
+#include <QColor>
+#include <QFont>
+#include <QObject>
+#include "qgis_app.h"
+#include "qgssymbol.h"
+#include <memory>
+
+class QgsDecorationLayoutExtentDialog;
+
+class APP_EXPORT QgsDecorationLayoutExtent : public QgsDecorationItem
+{
+    Q_OBJECT
+  public:
+
+    //! Constructor
+    QgsDecorationLayoutExtent( QObject *parent = nullptr );
+
+    QgsFillSymbol *symbol() const;
+    void setSymbol( QgsFillSymbol *symbol SIP_TRANSFER );
+
+  public slots:
+    //! set values on the gui when a project is read or the gui first loaded
+    void projectRead() override;
+    //! save values to the project
+    void saveToProject() override;
+
+    //! Show the dialog box
+    void run() override;
+    //! render the copyright label
+    void render( const QgsMapSettings &mapSettings, QgsRenderContext &context ) override;
+
+  private:
+    std::unique_ptr< QgsFillSymbol > mSymbol;
+
+    friend class QgsDecorationLayoutExtentDialog;
+};
+
+#endif //QGSDECORATIONLAYOUTEXTENT_H

src/app/qgsdecorationlayoutextentdialog.cpp

@@ -0,0 +1,110 @@
+/***************************************************************************
+                          qgsdecorationlayoutextentdialog.cpp
+                              ----------------------------
+    begin                : May 2017
+    copyright            : (C) 2017 by Nyall Dawson
+    email                : nyall dot dawson at gmail dot com
+
+ ***************************************************************************/
+/***************************************************************************
+ *                                                                         *
+ *   This program is free software; you can redistribute it and/or modify  *
+ *   it under the terms of the GNU General Public License as published by  *
+ *   the Free Software Foundation; either version 2 of the License, or     *
+ *   (at your option) any later version.                                   *
+ *                                                                         *
+ ***************************************************************************/
+
+#include "qgsdecorationlayoutextentdialog.h"
+
+#include "qgsdecorationlayoutextent.h"
+
+#include "qgslogger.h"
+#include "qgshelp.h"
+#include "qgsstyle.h"
+#include "qgssymbol.h"
+#include "qgssymbolselectordialog.h"
+#include "qgisapp.h"
+#include "qgsguiutils.h"
+#include "qgssettings.h"
+
+QgsDecorationLayoutExtentDialog::QgsDecorationLayoutExtentDialog( QgsDecorationLayoutExtent &deco, QWidget *parent )
+  : QDialog( parent )
+  , mDeco( deco )
+{
+  setupUi( this );
+
+  QgsSettings settings;
+  restoreGeometry( settings.value( "/Windows/DecorationLayoutExtent/geometry" ).toByteArray() );
+
+  updateGuiElements();
+  connect( buttonBox->button( QDialogButtonBox::Apply ), &QAbstractButton::clicked, this, &QgsDecorationLayoutExtentDialog::apply );
+  connect( mSymbolButton, &QPushButton::clicked, this, &QgsDecorationLayoutExtentDialog::changeSymbol );
+}
+
+void QgsDecorationLayoutExtentDialog::updateGuiElements()
+{
+  grpEnable->setChecked( mDeco.enabled() );
+
+  if ( mDeco.symbol() )
+  {
+    mSymbol.reset( static_cast<QgsFillSymbol *>( mDeco.symbol()->clone() ) );
+    QIcon icon = QgsSymbolLayerUtils::symbolPreviewIcon( mSymbol.get(), mSymbolButton->iconSize() );
+    mSymbolButton->setIcon( icon );
+  }
+}
+
+void QgsDecorationLayoutExtentDialog::updateDecoFromGui()
+{
+  mDeco.setEnabled( grpEnable->isChecked() );
+
+  if ( mSymbol )
+  {
+    mDeco.setSymbol( mSymbol->clone() );
+  }
+}
+
+QgsDecorationLayoutExtentDialog::~QgsDecorationLayoutExtentDialog()
+{
+  QgsSettings settings;
+  settings.setValue( QStringLiteral( "/Windows/DecorationLayoutExtent/geometry" ), saveGeometry() );
+}
+
+void QgsDecorationLayoutExtentDialog::on_buttonBox_accepted()
+{
+  apply();
+  accept();
+}
+
+void QgsDecorationLayoutExtentDialog::apply()
+{
+  updateDecoFromGui();
+  mDeco.update();
+}
+
+void QgsDecorationLayoutExtentDialog::on_buttonBox_rejected()
+{
+  reject();
+}
+
+void QgsDecorationLayoutExtentDialog::changeSymbol()
+{
+  if ( !mSymbol )
+    return;
+
+  QgsFillSymbol *symbol = mSymbol->clone();
+  QgsSymbolSelectorDialog dlg( symbol, QgsStyle::defaultStyle(), nullptr, this );
+  if ( dlg.exec() == QDialog::Rejected )
+  {
+    delete symbol;
+  }
+  else
+  {
+    mSymbol.reset( symbol );
+    if ( mSymbol )
+    {
+      QIcon icon = QgsSymbolLayerUtils::symbolPreviewIcon( mSymbol.get(), mSymbolButton->iconSize() );
+      mSymbolButton->setIcon( icon );
+    }
+  }
+}