1 files changed, 56 insertions, 1 deletions

diff --git a/src/sp-paint-server.h b/src/sp-paint-server.h
index c1c8d651e..91d292424 100644
--- a/src/sp-paint-server.h
+++ b/src/sp-paint-server.h
@@ -17,8 +17,16 @@
 
 #include <cairo.h>
 #include <2geom/rect.h>
+#include <sigc++/slot.h>
 #include "sp-object.h"
 
+namespace Inkscape {
+
+class Drawing;
+class DrawingPattern;
+
+}
+
 #define SP_PAINT_SERVER(obj) (dynamic_cast<SPPaintServer*>((SPObject*)obj))
 #define SP_IS_PAINT_SERVER(obj) (dynamic_cast<const SPPaintServer*>((SPObject*)obj) != NULL)
 
@@ -31,12 +39,59 @@ public:
     bool isSolid() const;
     virtual bool isValid() const;
 
-    virtual cairo_pattern_t* pattern_new(cairo_t *ct, Geom::OptRect const &bbox, double opacity) = 0;
+    //There are two ways to render a paint. The simple one is to create cairo_pattern_t structure
+    //on demand by pattern_new method. It is used for gradients. The other one is to add elements
+    //representing PaintServer in NR tree. It is used by hatches and patterns.
+    //Either pattern new or all three methods show, hide, setBBox need to be implemented
+    virtual Inkscape::DrawingPattern *show(Inkscape::Drawing &drawing, unsigned int key) {return NULL;}
+    virtual void hide(unsigned int key) {};
+    virtual void setBBox(unsigned int key, Geom::OptRect const &bbox) {};
+
+    virtual cairo_pattern_t* pattern_new(cairo_t *ct, Geom::OptRect const &bbox, double opacity) {return NULL;}
 
 protected:
     bool swatch;
 };
 
+/**
+ * Returns the first of {src, src-\>ref-\>getObject(),
+ * src-\>ref-\>getObject()-\>ref-\>getObject(),...}
+ * for which \a match is true, or NULL if none found.
+ *
+ * The raison d'être of this routine is that it correctly handles cycles in the href chain (e.g., if
+ * a gradient gives itself as its href, or if each of two gradients gives the other as its href).
+ *
+ * \pre SP_IS_GRADIENT(src).
+ */
+template <class PaintServer>
+PaintServer *chase_hrefs(PaintServer *src, sigc::slot<bool, PaintServer const *> match) {
+    /* Use a pair of pointers for detecting loops: p1 advances half as fast as p2.  If there is a
+       loop, then once p1 has entered the loop, we'll detect it the next time the distance between
+       p1 and p2 is a multiple of the loop size. */
+    PaintServer *p1 = src, *p2 = src;
+    bool do1 = false;
+    for (;;) {
+        if (match(p2)) {
+            return p2;
+        }
+
+        p2 = p2->ref->getObject();
+        if (!p2) {
+            return p2;
+        }
+        if (do1) {
+            p1 = p1->ref->getObject();
+        }
+        do1 = !do1;
+
+        if ( p2 == p1 ) {
+            /* We've been here before, so return NULL to indicate that no matching gradient found
+             * in the chain. */
+            return NULL;
+        }
+    }
+}
+
 #endif // SEEN_SP_PAINT_SERVER_H
 /*
   Local Variables: