tdf#160717: fix ex handling

Same as in commit e275726861
(tdf#160593: make sure to use current element's font size for em unit,
2024-04-18) for em.

Change-Id: Id9003c0426a6b373456da1aa1550f7ff07f766a3
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/166235
Tested-by: Mike Kaganski <mike.kaganski@collabora.com>
Reviewed-by: Mike Kaganski <mike.kaganski@collabora.com>

svgio/inc/SvgNumber.hxx

@@ -39,8 +39,8 @@ public:
     virtual basegfx::B2DRange getCurrentViewPort() const = 0;
     /// return font size of node, either set here or inherited from parents
     virtual double getCurrentFontSize() const = 0;
-    /// return xheight of node inherited from parents
-    virtual double getCurrentXHeightInherited() const = 0;
+    /// return xheight of node, either set here or inherited from parents
+    virtual double getCurrentXHeight() const = 0;
 };
 
 enum class SvgUnit

svgio/inc/svgnode.hxx

@@ -165,9 +165,7 @@ namespace svgio::svgreader
             /// InfoProvider support for %, em and ex values
             virtual basegfx::B2DRange getCurrentViewPort() const override;
             virtual double getCurrentFontSize() const override;
-            virtual double getCurrentXHeightInherited() const override;
-
-            double getCurrentXHeight() const;
+            virtual double getCurrentXHeight() const override;
 
             /// Id access
             std::optional<OUString> const & getId() const { return mpId; }

svgio/qa/cppunit/SvgImportTest.cxx

@@ -1679,11 +1679,12 @@ CPPUNIT_TEST_FIXTURE(Test, testDyInEms)
 
 CPPUNIT_TEST_FIXTURE(Test, testExs)
 {
-    // tdf#160594 given an SVG file with <tspan dy="3ex" style="font-size:1ex">:
+    // tdf#160594, tdf#160717 given an SVG file with <tspan dy="3ex" style="font-size:1ex">:
     xmlDocUniquePtr pDocument = dumpAndParseSvg(u"/svgio/qa/cppunit/data/dy_in_exs.svg");
 
     assertXPath(pDocument, "//textsimpleportion"_ostr, 2);
     assertXPath(pDocument, "//textsimpleportion[1]"_ostr, "height"_ostr, u"16"_ustr);
+    assertXPath(pDocument, "//textsimpleportion[1]"_ostr, "y"_ostr, u"20"_ustr);
 
     sal_Int32 nSize = getXPath(pDocument, "//textsimpleportion[2]"_ostr, "height"_ostr).toInt32();
     // Without the accompanying fix in place, this test would have failed with:
@@ -1691,6 +1692,17 @@ CPPUNIT_TEST_FIXTURE(Test, testExs)
     // - Actual  : 16
     // i.e. the parent font-size was used, instead of its x-size.
     CPPUNIT_ASSERT_LESS(sal_Int32(16), nSize);
+
+    sal_Int32 nYPos = getXPath(pDocument, "//textsimpleportion[2]"_ostr, "y"_ostr).toInt32();
+    // Then make sure that the vertical offset is based on x-size of tspan, not of its parent.
+    // Given the tspan's font-size is nSize, its x-size is less than nSize, and the expected
+    // vertical offset is less than 3 * nSize, which means that the resulting y is expected
+    // to be strictly less than 20 + 3 * nSize.
+    // Without the accompanying fix in place, this test would have failed with:
+    // - Expected less than: 44
+    // - Actual  : 44
+    // i.e. the parent x-size (or current font-size) was used, instead of current x-size.
+    CPPUNIT_ASSERT_LESS(sal_Int32(20 + 3 * nSize), nYPos);
 }
 
 CPPUNIT_PLUGIN_IMPLEMENT();

svgio/qa/cppunit/SvgNumberTest.cxx

@@ -40,7 +40,7 @@ public:
 
     double getCurrentFontSize() const override { return 12.0; }
 
-    double getCurrentXHeightInherited() const override { return 5.0; }
+    double getCurrentXHeight() const override { return 5.0; }
 };
 
 void TestNumber::testSetting()

svgio/source/svgreader/SvgNumber.cxx

@@ -39,7 +39,7 @@ double SvgNumber::solveNonPercentage(const InfoProvider& rInfoProvider) const
         case SvgUnit::em:
             return mfNumber * rInfoProvider.getCurrentFontSize();
         case SvgUnit::ex:
-            return mfNumber * rInfoProvider.getCurrentXHeightInherited() * 0.5;
+            return mfNumber * rInfoProvider.getCurrentXHeight();
         case SvgUnit::px:
             return mfNumber;
         case SvgUnit::pt:

svgio/source/svgreader/svgnode.cxx

@@ -703,25 +703,12 @@ namespace {
             return 0.0;
         }
 
-        double SvgNode::getCurrentXHeightInherited() const
-        {
-            if(getParent())
-            {
-                return getParent()->getCurrentXHeight();
-            }
-            else
-            {
-                return 0.0;
-            }
-        }
-
         double SvgNode::getCurrentXHeight() const
         {
-            if(getSvgStyleAttributes())
-                // for XHeight, use FontSize currently
-                return getSvgStyleAttributes()->getFontSizeNumber().solve(*this, NumberType::ycoordinate);
-
-            return getCurrentXHeightInherited();
+            // https://drafts.csswg.org/css-values-4/#ex
+            // for XHeight, use 0.5em fallback currently
+            // FIXME: use "x-height of the first available font"
+            return getCurrentFontSize() * 0.5;
         }
 
         void SvgNode::setId(OUString const & rId)