MCGR: Model data changes for ColorSteps (II)

The biggest change here is to allow multiple ColorStops
with the same Offset. That allows to define gradients
with 'hard' color changes at any place using two
ColorStops with the same Offset and different Colors.
This required quite some adaptions, but works well.

Also removed in this context checking for all Colors
being the same to not mix up things. Also works well.

Also changed the need for having Start/EndColors AKA
ColorStops for 0.0 and 1.0 in place, instead 'imply'
the 1st ColorStop to also define the StartColor and
the last one the EndColor. This allows e.g. Gradient
definitions with two GradientStops at the same
Offset e.g. 0.5 with different colors to already
define a full Gradient.

Also added a tooling method to reverse ColorSteps,
which changes the order and mirrors the Offsets
(what even keeps an existing sort valid).
This is useful e.g. for GradientAxial which is the
only one where for decomposition the Gradient had
to be interpreted 'reverse' since it's defined
from center to edge, but for creating correct filled
polygons to represent this the inverse order had to
be used, creating polygons from edge to center.
This led to 'wild' code for this one of six cases
and prevented unifications with the other cases
(also made your brain flip).
Thus I adapted this now to use the reversed
ColorSteps consequently, and the same principle
loops than the other implementations to make things
easier for the future and to use common tooling.

Change-Id: If2943348d17d5b9cd165f4d78f22638a1dff5237
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/149208
Tested-by: Jenkins
Reviewed-by: Armin Le Grand <Armin.Le.Grand@me.com>

1 files changed, 37 insertions, 39 deletions

diff --git a/basegfx/source/tools/gradienttools.cxx b/basegfx/source/tools/gradienttools.cxx
index d43f7899121a..6055143d5abd 100644
--- a/basegfx/source/tools/gradienttools.cxx
+++ b/basegfx/source/tools/gradienttools.cxx
@@ -264,6 +264,17 @@ namespace basegfx
 
     namespace utils
     {
+        /* Tooling method to reverse ColorStops, including offsets.
+           When also mirroring offsets a valid sort keeps valid.
+        */
+        void reverseColorStops(ColorStops& rColorStops)
+        {
+            // can use std::reverse, but also need to adapt offset(s)
+            std::reverse(rColorStops.begin(), rColorStops.end());
+            for (auto& candidate : rColorStops)
+                candidate = ColorStop(1.0 - candidate.getStopOffset(), candidate.getStopColor());
+        }
+
         /* Tooling method to convert UNO API data to ColorStops
            This will try to extract ColorStop data from the given
            Any, so if it's of type awt::Gradient2 that data will be
@@ -374,13 +385,8 @@ namespace basegfx
              be removed)
            - contains no ColorStops with offset > 1.0 (will
              be removed)
-           - contains no two ColorStops with identical offsets
-             (will be removed, 1st one/smallest offset wins
-             which is also given by sort tooling)
+           - ColorStops with identical offsets are now allowed
            - will be sorted from lowest offset to highest
-           - if all colors are the same, the content will
-             be reduced to a single entry with offset 0.0
-             (force to StartColor)
 
            Some more notes:
            - It can happen that the result is empty
@@ -404,8 +410,15 @@ namespace basegfx
             if (1 == rColorStops.size())
             {
                 // no gradient at all, but preserve given color
-                // and force it to be the StartColor
-                rColorStops[0] = ColorStop(0.0, rColorStops[0].getStopColor());
+                // evtl. correct offset to be in valid range [0.0 .. 1.0]
+                // NOTE: This does not move it to 0.0 or 1.0, it *can* still
+                //       be somewhere in-between what is allowed
+                rColorStops[0] = ColorStop(
+                    std::max(0.0, std::min(1.0, rColorStops[0].getStopOffset())),
+                    rColorStops[0].getStopColor());
+
+                // done
+                return;
             }
 
             // start with sorting the input data. Remember that
@@ -414,9 +427,6 @@ namespace basegfx
             std::sort(rColorStops.begin(), rColorStops.end());
 
             // prepare status values
-            bool bSameColorInit(false);
-            bool bAllTheSameColor(true);
-            basegfx::BColor aFirstColor;
             size_t write(0);
 
             // use the paradigm of a band machine with two heads, read
@@ -428,7 +438,7 @@ namespace basegfx
                 // get offset of entry at read position
                 const double rOff(rColorStops[read].getStopOffset());
 
-                // step over < 0 values
+                // step over < 0 values, these are outside and will be removed
                 if (basegfx::fTools::less(rOff, 0.0))
                     continue;
 
@@ -438,23 +448,9 @@ namespace basegfx
                     break;
 
                 // entry is valid value at read position
-
-                // check/init for all-the-same color
-                if(bSameColorInit)
-                {
-                    // already initialized, compare
-                    bAllTheSameColor = bAllTheSameColor && aFirstColor == rColorStops[read].getStopColor();
-                }
-                else
-                {
-                    // do initialize, remember 1st valid color
-                    bSameColorInit = true;
-                    aFirstColor = rColorStops[read].getStopColor();
-                }
-
                 // copy if write target is empty (write at start) or when
-                // write target is different to read
-                if (0 == write || rOff != rColorStops[write-1].getStopOffset())
+                // write target is different to read in color or offset
+                if (0 == write || !(rColorStops[read] == rColorStops[write-1]))
                 {
                     if (write != read)
                     {
@@ -473,14 +469,6 @@ namespace basegfx
             {
                 rColorStops.resize(write);
             }
-
-            if (bSameColorInit && bAllTheSameColor && rColorStops.size() > 1)
-            {
-                // id all-the-same color is detected, reset to single
-                // entry, but also force to StartColor and preserve the color
-                rColorStops.resize(1);
-                rColorStops[0] = ColorStop(0.0, aFirstColor);
-            }
         }
 
         BColor modifyBColor(
@@ -493,11 +481,13 @@ namespace basegfx
                 return BColor();
 
             // outside range -> at start
-            if (fScaler <= 0.0)
+            const double fMin(rColorStops.front().getStopOffset());
+            if (fScaler < fMin)
                 return rColorStops.front().getStopColor();
 
             // outside range -> at end
-            if (fScaler >= 1.0)
+            const double fMax(rColorStops.back().getStopOffset());
+            if (fScaler > fMax)
                 return rColorStops.back().getStopColor();
 
             // special case for the 'classic' case with just two colors:
@@ -505,6 +495,9 @@ namespace basegfx
             // by avoiding some calculations and an O(log(N)) array access
             if (2 == rColorStops.size())
             {
+                if (fTools::equal(fMin, fMax))
+                    return rColorStops.front().getStopColor();
+
                 const basegfx::BColor aCStart(rColorStops.front().getStopColor());
                 const basegfx::BColor aCEnd(rColorStops.back().getStopColor());
                 const sal_uInt32 nSteps(
@@ -513,6 +506,11 @@ namespace basegfx
                         aCStart,
                         aCEnd));
 
+                // we need to extend the interpolation to the local
+                // range of ColorStops. Despite having two ColorStops
+                // these are not necessarily at 0.0 and 1.0, so mabe
+                // not the classical Start/EndColor (what is allowed)
+                fScaler = (fScaler - fMin) / (fMax - fMin);
                 return basegfx::interpolate(
                     aCStart,
                     aCEnd,
@@ -525,7 +523,7 @@ namespace basegfx
             //       debug test code created by the stl. In a pro version,
             //       all is good/fast as expected
             const auto upperBound(
-                std::lower_bound(
+                std::upper_bound(
                     rColorStops.begin(),
                     rColorStops.end(),
                     ColorStop(fScaler),