tdf#117949 Use small overlap for SVG gradient representation

Change-Id: Idd55df31aa87cc40dbb15001479cdc79e918ac19
Reviewed-on: https://gerrit.libreoffice.org/55376Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Armin Le Grand <Armin.Le.Grand@cib.de>

drawinglayer/source/primitive2d/svggradientprimitive2d.cxx

@@ -915,14 +915,21 @@ namespace drawinglayer
                 // use color distance and discrete lengths to calculate step count
                 const sal_uInt32 nSteps(calculateStepsForSvgGradient(getColorA(), getColorB(), fDelta, fDiscreteUnit));
 
+                // tdf#117949 Use a small amount of discrete overlap at the edges. Usually this
+                // should be exactly 0.0 and 1.0, but there were cases when this gets clipped
+                // against the mask polygon which got numerically problematic.
+                // This change is unnecessary in that respect, but avoids that numerical havoc
+                // by at the same time doing no real harm AFAIK
+                // TTTT: Remove again when clipping is fixed (!)
+
                 // prepare polygon in needed width at start position (with discrete overlap)
                 const basegfx::B2DPolygon aPolygon(
                     basegfx::utils::createPolygonFromRect(
                         basegfx::B2DRange(
                             getOffsetA() - fDiscreteUnit,
-                            0.0,
+                            -0.0001, // TTTT -> should be 0.0, see comment above
                             getOffsetA() + (fDelta / nSteps) + fDiscreteUnit,
-                            1.0)));
+                            1.0001))); // TTTT -> should be 1.0, see comment above
 
                 // prepare loop (inside to outside, [0.0 .. 1.0[)
                 double fUnitScale(0.0);