Fixes the bug of glShareTopology. This example mutates patchDescriptor in drawcontext, so it needs a write access.

Adding another GetPatchArray() returning non-const reference. We should think about better API for this.

examples/glShareTopology/glShareTopology.cpp

@@ -260,12 +260,12 @@ public:
 protected:
 
     TopologyBase(Far::PatchTables const * patchTables) {
-
         _drawContext = Osd::GLDrawContext::Create(patchTables, 7);
     }
 
     void updateVertexBufferStride(int stride) {
-        Osd::DrawContext::PatchArrayVector patchArrays =
+        // modifying patchArrays in drawcontext.
+        Osd::DrawContext::PatchArrayVector &patchArrays =
             _drawContext->GetPatchArrays();
         for (int i = 0; i < (int)patchArrays.size(); ++i) {
             Osd::DrawContext::PatchDescriptor desc = patchArrays[i].GetDescriptor();

opensubdiv/osd/drawContext.h

@@ -212,6 +212,12 @@ public:
         return _patchArrays;
     }
 
+    /// The writable accessor to the internal patch array (tentative).
+    /// We should have a different api something like ConvertPatchArrays().
+    PatchArrayVector &GetPatchArrays() {
+        return _patchArrays;
+    }
+
     // processes FarPatchArrays and inserts requisite sub-patches for the arrays
     // containing transition patches
     static void ConvertPatchArrays(Far::PatchTables::PatchArrayVector const &farPatchArrays,