[composer] Prevent zooming out/in too far

Would cause issues when scale became 0 and it was impossible
to further interact with the composer.

(cherry-picked from aa53cfe)

python/gui/qgscomposerview.sip

@@ -112,6 +112,13 @@ class QgsComposerView : QGraphicsView
     /** Set zoom level, where a zoom level of 1.0 corresponds to 100%*/
     void setZoomLevel( double zoomLevel );
 
+    /** Scales the view in a safe way, by limiting the acceptable range
+     * of the scale applied.
+     * @param scale factor to scale view by
+     * @note added in QGIS 2.16
+     */
+    void scaleSafe( double scale );
+
     /** Sets whether a preview effect should be used to alter the view's appearance
      * @param enabled Set to true to enable the preview effect on the view
      * @note added in 2.3

src/app/composer/qgscomposer.cpp

@@ -1227,15 +1227,15 @@ void QgsComposer::on_mActionZoomAll_triggered()
 
 void QgsComposer::on_mActionZoomIn_triggered()
 {
-  mView->scale( 2, 2 );
+  mView->scaleSafe( 2 );
   mView->updateRulers();
   mView->update();
   emit zoomLevelChanged();
 }
 
 void QgsComposer::on_mActionZoomOut_triggered()
 {
-  mView->scale( .5, .5 );
+  mView->scaleSafe( 0.5 );
   mView->updateRulers();
   mView->update();
   emit zoomLevelChanged();

src/gui/qgscomposerview.cpp

@@ -47,6 +47,9 @@
 #include "qgscursors.h"
 #include "qgscomposerutils.h"
 
+#define MIN_VIEW_SCALE 0.05
+#define MAX_VIEW_SCALE 1000.0
+
 QgsComposerView::QgsComposerView( QWidget* parent, const char* name, const Qt::WindowFlags& f )
     : QGraphicsView( parent )
     , mCurrentTool( Select )
@@ -1651,11 +1654,11 @@ void QgsComposerView::wheelZoom( QWheelEvent * event )
   //zoom composition
   if ( zoomIn )
   {
-    scale( zoomFactor, zoomFactor );
+    scaleSafe( zoomFactor );
   }
   else
   {
-    scale( 1 / zoomFactor, 1 / zoomFactor );
+    scaleSafe( 1 / zoomFactor );
   }
 
   //update composition for new zoom
@@ -1683,14 +1686,22 @@ void QgsComposerView::setZoomLevel( double zoomLevel )
     dpi = 72;
 
   //desired pixel width for 1mm on screen
-  double scale = zoomLevel * dpi / 25.4;
+  double scale = qBound( MIN_VIEW_SCALE, zoomLevel * dpi / 25.4, MAX_VIEW_SCALE );
   setTransform( QTransform::fromScale( scale, scale ) );
 
   updateRulers();
   update();
   emit zoomLevelChanged();
 }
 
+void QgsComposerView::scaleSafe( double scale )
+{
+  double currentScale = transform().m11();
+  scale *= currentScale;
+  scale = qBound( MIN_VIEW_SCALE, scale, MAX_VIEW_SCALE );
+  setTransform( QTransform::fromScale( scale, scale ) );
+}
+
 void QgsComposerView::setPreviewModeEnabled( bool enabled )
 {
   if ( !mPreviewEffect )

src/gui/qgscomposerview.h

@@ -143,6 +143,13 @@ class GUI_EXPORT QgsComposerView: public QGraphicsView
     /** Set zoom level, where a zoom level of 1.0 corresponds to 100%*/
     void setZoomLevel( double zoomLevel );
 
+    /** Scales the view in a safe way, by limiting the acceptable range
+     * of the scale applied.
+     * @param scale factor to scale view by
+     * @note added in QGIS 2.16
+     */
+    void scaleSafe( double scale );
+
     /** Sets whether a preview effect should be used to alter the view's appearance
      * @param enabled Set to true to enable the preview effect on the view
      * @note added in 2.3

tests/src/python/CMakeLists.txt

@@ -24,6 +24,7 @@ ADD_PYTHON_TEST(PyQgsComposerMap test_qgscomposermap.py)
 ADD_PYTHON_TEST(PyQgsComposerMapGrid test_qgscomposermapgrid.py)
 ADD_PYTHON_TEST(PyQgsComposerPicture test_qgscomposerpicture.py)
 ADD_PYTHON_TEST(PyQgsComposerShapes test_qgscomposershapes.py)
+ADD_PYTHON_TEST(PyQgsComposerView test_qgscomposerview.py)
 ADD_PYTHON_TEST(PyQgsComposition test_qgscomposition.py)
 ADD_PYTHON_TEST(PyQgsConditionalStyle test_qgsconditionalstyle.py)
 ADD_PYTHON_TEST(PyQgsCoordinateTransform test_qgscoordinatetransform.py)

tests/src/python/test_qgscomposerview.py

@@ -0,0 +1,65 @@
+# -*- coding: utf-8 -*-
+"""QGIS Unit tests for QgsComposerView.
+
+.. note:: 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.
+"""
+__author__ = 'Nyall Dawson'
+__date__ = '29/05/2016'
+__copyright__ = 'Copyright 2016, The QGIS Project'
+# This will get replaced with a git SHA1 when you do a git archive
+__revision__ = '$Format:%H$'
+
+import qgis  # NOQA
+
+import os
+
+from qgis.gui import (QgsComposerView)
+from qgis.PyQt.QtCore import QRectF
+from qgis.PyQt.QtGui import QTransform
+
+from qgis.testing import start_app, unittest
+
+start_app()
+
+
+class TestQgsComposerView(unittest.TestCase):
+
+    def testScaleSafe(self):
+        """ test scaleSafe method """
+
+        view = QgsComposerView()
+        view.fitInView(QRectF(0, 0, 10, 10))
+        scale = view.transform().m11()
+        view.scaleSafe(2)
+        self.assertAlmostEqual(view.transform().m11(), 2)
+        view.scaleSafe(4)
+        self.assertAlmostEqual(view.transform().m11(), 8)
+
+        # try to zoom in heaps
+        view.scaleSafe(99999999)
+        # assume we have hit the limit
+        scale = view.transform().m11()
+        view.scaleSafe(2)
+        self.assertAlmostEqual(view.transform().m11(), scale)
+
+        view.setTransform(QTransform.fromScale(1, 1))
+        self.assertAlmostEqual(view.transform().m11(), 1)
+        # test zooming out
+        view.scaleSafe(0.5)
+        self.assertAlmostEqual(view.transform().m11(), 0.5)
+        view.scaleSafe(0.1)
+        self.assertAlmostEqual(view.transform().m11(), 0.05)
+
+        # try zooming out heaps
+        view.scaleSafe(0.000000001)
+        # assume we have hit the limit
+        scale = view.transform().m11()
+        view.scaleSafe(0.5)
+        self.assertAlmostEqual(view.transform().m11(), scale)
+
+
+if __name__ == '__main__':
+    unittest.main()