PDFBOX-5660: optimize, as suggested by Valery Bokov, closes #369

git-svn-id: https://svn.apache.org/repos/asf/pdfbox/trunk@1930416 13f79535-47bb-0310-9956-ffa450edef68

Author: THausherr

pdfbox/src/main/java/org/apache/pdfbox/rendering/PageDrawer.java

@@ -87,6 +87,7 @@
 import org.apache.pdfbox.pdmodel.graphics.color.PDSeparation;
 import org.apache.pdfbox.pdmodel.graphics.form.PDFormXObject;
 import org.apache.pdfbox.pdmodel.graphics.form.PDTransparencyGroup;
+import org.apache.pdfbox.pdmodel.graphics.form.PDTransparencyGroupAttributes;
 import org.apache.pdfbox.pdmodel.graphics.image.PDImage;
 import org.apache.pdfbox.pdmodel.graphics.image.PDImageXObject;
 import org.apache.pdfbox.pdmodel.graphics.optionalcontent.PDOptionalContentGroup;
@@ -1825,7 +1826,8 @@ private TransparencyGroup(PDTransparencyGroup form, boolean isSoftMask, Matrix c
             height = maxY - minY;
 
             // FIXME - color space
-            if (isGray(form.getGroup().getColorSpace(form.getResources())))
+            PDTransparencyGroupAttributes group = form.getGroup();
+            if (isGray(group.getColorSpace(form.getResources())))
             {
                 image = create2ByteGrayAlphaImage(width, height);
             }
@@ -1834,7 +1836,7 @@ private TransparencyGroup(PDTransparencyGroup form, boolean isSoftMask, Matrix c
                 image = new BufferedImage(width, height, BufferedImage.TYPE_INT_ARGB);
             }
 
-            boolean needsBackdrop = !isSoftMask && !form.getGroup().isIsolated() &&
+            boolean needsBackdrop = !isSoftMask && !group.isIsolated() &&
                 hasBlendMode(form, new HashSet<>());
             BufferedImage backdropImage = null;
             // Position of this group in parent group's coordinates