[layout expressions] add Y page offset expression

this is useful for dynamically position items relative to pages in multi-pages layouts
qgis · Aug 21, 2020 · 6ac8f61 · 6ac8f61
1 parent a462a17
commit 6ac8f61
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diff --git a/src/core/expression/qgsexpression.cpp b/src/core/expression/qgsexpression.cpp
@@ -736,6 +736,7 @@ void QgsExpression::initVariableHelp()
   sVariableHelpTexts()->insert( QStringLiteral( "layout_page" ), QCoreApplication::translate( "variable_help", "Current page number in composition." ) );
   sVariableHelpTexts()->insert( QStringLiteral( "layout_pageheight" ), QCoreApplication::translate( "variable_help", "Composition page height in mm." ) );
   sVariableHelpTexts()->insert( QStringLiteral( "layout_pagewidth" ), QCoreApplication::translate( "variable_help", "Composition page width in mm." ) );
+  sVariableHelpTexts()->insert( QStringLiteral( "layout_pageoffsets" ), QCoreApplication::translate( "variable_help", "Array of Y coordinate of the top of each page." ) );
   sVariableHelpTexts()->insert( QStringLiteral( "layout_dpi" ), QCoreApplication::translate( "variable_help", "Composition resolution (DPI)." ) );
 
   //atlas variables

diff --git a/src/core/expression/qgsexpressioncontextutils.cpp b/src/core/expression/qgsexpressioncontextutils.cpp
@@ -510,6 +510,15 @@ QgsExpressionContextScope *QgsExpressionContextUtils::layoutScope( const QgsLayo
     scope->addVariable( QgsExpressionContextScope::StaticVariable( QStringLiteral( "layout_pageheight" ), s.height(), true ) );
     scope->addVariable( QgsExpressionContextScope::StaticVariable( QStringLiteral( "layout_pagewidth" ), s.width(), true ) );
   }
+
+  QVariantList offsets;
+  for ( int i = 0; i < layout->pageCollection()->pageCount(); i++ )
+  {
+    QPointF p = layout->pageCollection()->pagePositionToLayoutPosition( i, QgsLayoutPoint( 0, 0 ) );
+    offsets << p.y();
+  }
+  scope->addVariable( QgsExpressionContextScope::StaticVariable( QStringLiteral( "layout_pageoffsets" ), offsets, true ) );
+
   scope->addVariable( QgsExpressionContextScope::StaticVariable( QStringLiteral( "layout_dpi" ), layout->renderContext().dpi(), true ) );
 
   scope->addFunction( QStringLiteral( "item_variables" ), new GetLayoutItemVariables( layout ) );