Fix problem with desc coordinates domain for gradient

DEVSIX-2086

Author: BezrukovM

kernel/src/main/java/com/itextpdf/kernel/colors/gradients/AbstractLinearGradientBuilder.java

@@ -281,15 +281,18 @@ private static PdfShading.Axial createAxialShading(Point[] baseCoordinatesVector
             // to ensure that stops list covers the full domain. For repeat and reflect cases
             // this is done by adjusting the initial stops to cover the evaluated domain
             coordinatesDomain[0] = Math.max(coordinatesDomain[0], stopsToConstruct.get(0).getOffset());
-            coordinatesDomain[1] = Math
-                    .min(coordinatesDomain[1], stopsToConstruct.get(stopsToConstruct.size() - 1).getOffset());
+            coordinatesDomain[1] = Math.min(coordinatesDomain[1],
+                    stopsToConstruct.get(stopsToConstruct.size() - 1).getOffset());
+            coordinatesDomain[1] = Math.max(coordinatesDomain[0], coordinatesDomain[1]);
         }
 
         // workaround for PAD case
         if (spreadMethod == GradientSpreadMethod.PAD) {
             coordinatesDomain = modifyNormalizedStopsForPad(stopsToConstruct, coordinatesDomain);
         }
 
+        assert coordinatesDomain[0] <= coordinatesDomain[1];
+
         Point[] actualCoordinates = createCoordinatesForNewDomain(coordinatesDomain, baseCoordinatesVector);
 
         PdfShading.Axial axial = new PdfShading.Axial(

kernel/src/test/java/com/itextpdf/kernel/colors/gradients/LinearGradientBuilderTest.java

@@ -124,6 +124,32 @@ public void buildWithTwoStopsInTheMiddleTest() throws IOException, InterruptedEx
         generateAndComparePdfs("buildWithTwoStopsInTheMiddleTest.pdf", targetBoundingBox, null, gradientBuilder);
     }
 
+    @Test
+    public void buildWithTwoStopsBeforeTheBeginningTest() throws IOException, InterruptedException {
+        Rectangle targetBoundingBox = new Rectangle(50f, 450f, 300f, 300f);
+        AbstractLinearGradientBuilder gradientBuilder = new LinearGradientBuilder()
+                .setGradientVector(targetBoundingBox.getLeft() + 100f, targetBoundingBox.getBottom() + 100f,
+                        targetBoundingBox.getRight() - 100f, targetBoundingBox.getTop() - 100f)
+                .setSpreadMethod(GradientSpreadMethod.PAD)
+                .addColorStop(new GradientColorStop(ColorConstants.RED.getColorValue(), -0.1d, OffsetType.RELATIVE))
+                .addColorStop(new GradientColorStop(ColorConstants.BLUE.getColorValue(),  -0.2d, OffsetType.RELATIVE));
+
+        generateAndComparePdfs("buildWithTwoStopsBeforeTheBeginningTest.pdf", targetBoundingBox, null, gradientBuilder);
+    }
+
+    @Test
+    public void buildWithTwoStopsAfterTheEndTest() throws IOException, InterruptedException {
+        Rectangle targetBoundingBox = new Rectangle(50f, 450f, 300f, 300f);
+        AbstractLinearGradientBuilder gradientBuilder = new LinearGradientBuilder()
+                .setGradientVector(targetBoundingBox.getLeft() + 100f, targetBoundingBox.getBottom() + 100f,
+                        targetBoundingBox.getRight() - 100f, targetBoundingBox.getTop() - 100f)
+                .setSpreadMethod(GradientSpreadMethod.PAD)
+                .addColorStop(new GradientColorStop(ColorConstants.RED.getColorValue(), 1.2d, OffsetType.RELATIVE))
+                .addColorStop(new GradientColorStop(ColorConstants.BLUE.getColorValue(), 0d, OffsetType.RELATIVE));
+
+        generateAndComparePdfs("buildWithTwoStopsAfterTheEndTest.pdf", targetBoundingBox, null, gradientBuilder);
+    }
+
     @Test
     public void padCaseWithVeryCloseCornerStopsTest() throws IOException, InterruptedException {
         Rectangle targetBoundingBox = new Rectangle(50f, 450f, 300f, 300f);