tdf#155549 MCGR: Recreate 'axial' from symmetric 'linear'

When exporting a shape with an axial gradient fill to OOXML, it is
converted to a linear gradient with multiple color stops. Versions
before MCGR had recreated it as axial gradient on import from OOXML.
But now LO is able to handle multiple color stops and so the linear
gradient from OOXML is imported as linear gradient in LO.

When such file is then written as ODF, the multiple color stops are
in elements in extended namespace and versions before MCGR do not
understand them. They show only the first and last color (which are
equal) and the gradient is lost.

With this patch LO converts the linear gradient back to an axial gradient
on export to ODF. The exported axial gradient is rendered in a version
with MCGR same as the linear gradient when opening the OOXML file. The
difference is, that versions without MCGR now render an axial gradient
with two colors.

Change-Id: I2b416b4cdca75d8327107a4f259d63c2e6e97ac3
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/152574
Tested-by: Jenkins
Reviewed-by: Regina Henschel <rb.henschel@t-online.de>

1 files changed, 7 insertions, 0 deletions

diff --git a/include/basegfx/utils/bgradient.hxx b/include/basegfx/utils/bgradient.hxx
index b7c2cf8c9e3f..fd8dcae7e2d2 100644
--- a/include/basegfx/utils/bgradient.hxx
+++ b/include/basegfx/utils/bgradient.hxx
@@ -273,6 +273,9 @@ public:
     // try to detect if an empty/no-color-change area exists
     // at the start and return offset to it. Returns 0.0 if not.
     double detectPossibleOffsetAtStart() const;
+
+    // returns true if the color stops are symmetrical in color and offset, otherwise false.
+    bool isSymmetrical() const;
 };
 
 class BASEGFX_DLLPUBLIC BGradient final
@@ -338,6 +341,10 @@ public:
     void tryToRecreateBorder(basegfx::BColorStops* pAssociatedTransparencyStops = nullptr);
     void tryToApplyBorder();
     void tryToApplyStartEndIntensity();
+
+    // If a linear gradient is symmetrical it is converted to an axial gradient.
+    // Does nothing in other cases and for other gradient types.
+    void tryToConvertToAxial();
 };
 }