Chart: Improve polynomial trendline equation rendering

Convert power figures in supersript figures
Replace minus sign

Change-Id: Ia0e77b5de3b6f2368efd1315576f9709d7b1b2d9
Reviewed-on: https://gerrit.libreoffice.org/23714
Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Markus Mohrhard <markus.mohrhard@googlemail.com>

3 files changed, 46 insertions, 12 deletions

diff --git a/chart2/inc/SpecialUnicodes.hxx b/chart2/inc/SpecialUnicodes.hxx
new file mode 100644
index 000000000000..6b3398daf840
--- /dev/null
+++ b/chart2/inc/SpecialUnicodes.hxx
@@ -0,0 +1,18 @@
+/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
+/*
+ * This file is part of the LibreOffice project.
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/.
+ */
+
+#ifndef INCLUDED_CHART2_INC_SPECIALUNICODES_HXX
+#define INCLUDED_CHART2_INC_SPECIALUNICODES_HXX
+
+const OUString aMinusSign ( sal_Unicode (0x2212) );
+const sal_Unicode aSuperscriptFigures[10]={ 0x2070, 0x00B9, 0x00B2, 0x00B3, 0x2074, 0x2075, 0x2076, 0x2077, 0x2078, 0x2079 };
+
+#endif
+
+/* vim:set shiftwidth=4 softtabstop=4 expandtab: */
diff --git a/chart2/qa/extras/chart2_trendcalculators.cxx b/chart2/qa/extras/chart2_trendcalculators.cxx
index 0fd3c1d27fb7..0c3b972c3031 100644
--- a/chart2/qa/extras/chart2_trendcalculators.cxx
+++ b/chart2/qa/extras/chart2_trendcalculators.cxx
@@ -10,6 +10,8 @@
 #include "charttest.hxx"
 #include <com/sun/star/chart2/XRegressionCurveContainer.hpp>
 #include <com/sun/star/chart2/XRegressionCurveCalculator.hpp>
+#include <SpecialUnicodes.hxx>
+
 
 // Define the index of sheets in the test document
 #define SHEET_POTENTIAL1          0
@@ -150,7 +152,7 @@ void Chart2TrendCalculators::testLinearRegression1()
         xValues[i] = d;
         yValues[i] = - 2.0 * d - 5.0 ;
     }
-    checkCalculator( xValues, yValues, "f(x) =  - 2x - 5");
+    checkCalculator( xValues, yValues, "f(x) = "+ aMinusSign +" 2x "+ aMinusSign +" 5");
 }
 
 // test y = A x ^ B
@@ -166,7 +168,8 @@ void Chart2TrendCalculators::testPolynomialRegression1()
         xValues[i] = d;
         yValues[i] =  - 2.0 * d * d + 4 * d - 5;
     }
-    checkCalculator( xValues, yValues, "f(x) =  - 2x^2 + 4x - 5");
+    OUString sExpectedFormula( "f(x) = "+ aMinusSign +" 2x" + OUString( aSuperscriptFigures[2] ) + " + 4x "+ aMinusSign +" 5" );
+    checkCalculator( xValues, yValues, sExpectedFormula );
 }
 
 void Chart2TrendCalculators::testExponentialRegression1()
diff --git a/chart2/source/tools/PolynomialRegressionCurveCalculator.cxx b/chart2/source/tools/PolynomialRegressionCurveCalculator.cxx
index 1d26611c865a..6dba3a26fa27 100644
--- a/chart2/source/tools/PolynomialRegressionCurveCalculator.cxx
+++ b/chart2/source/tools/PolynomialRegressionCurveCalculator.cxx
@@ -25,6 +25,9 @@
 #include <rtl/math.hxx>
 #include <rtl/ustrbuf.hxx>
 
+#include <SpecialUnicodes.hxx>
+
+
 using namespace com::sun::star;
 
 namespace chart
@@ -235,7 +238,7 @@ OUString PolynomialRegressionCurveCalculator::ImplGetRepresentation(
     const uno::Reference< util::XNumberFormatter >& xNumFormatter,
     sal_Int32 nNumberFormatKey ) const
 {
-    OUStringBuffer aBuf( "f(x) = ");
+    OUStringBuffer aBuf( "f(x) = " );
 
     sal_Int32 aLastIndex = mCoefficients.size() - 1;
     bool bFindValue = false;
@@ -248,12 +251,14 @@ OUString PolynomialRegressionCurveCalculator::ImplGetRepresentation(
         }
         else if (aValue < 0.0)
         {
-            aBuf.append( " - " );
+            if ( bFindValue ) // if it is not the first aValue
+                aBuf.append( " " );
+            aBuf.append( aMinusSign + " ");
             aValue = - aValue;
         }
         else
         {
-            if ( bFindValue )
+            if ( bFindValue ) // if it is not the first aValue
                 aBuf.append( " + " );
         }
         bFindValue = true;
@@ -263,17 +268,25 @@ OUString PolynomialRegressionCurveCalculator::ImplGetRepresentation(
 
         if(i > 0)
         {
-            if (i == 1)
-            {
-                aBuf.append( "x" );
-            }
-            else
+            aBuf.append( "x" );
+            if (i > 1)
             {
-                aBuf.append( "x^" );
-                aBuf.append(i);
+                if (i < 10) // simple case if only one digit
+                    aBuf.append( aSuperscriptFigures[ i ] );
+                else
+                {
+                    OUString aValueOfi = OUString::number( i );
+                    for ( sal_Int32 n = 0; n < aValueOfi.getLength() ; n++ )
+                    {
+                        sal_Int32 nIndex = aValueOfi[n] - sal_Unicode ( '0' );
+                        aBuf.append( aSuperscriptFigures[ nIndex ] );
+                    }
+                }
             }
         }
     }
+    if ( aBuf.toString() == "f(x) = " )
+        aBuf.append( "0" );
 
     return aBuf.makeStringAndClear();
 }