Bugfix for GridHandle::read(). (#2237)

* Bugfix for GridHandle::read().

Signed-off-by: Andrew Reidmeyer <areidmeyer@nvidia.com>

* Simplify.

Signed-off-by: Andrew Reidmeyer <areidmeyer@nvidia.com>

* Adding pendingchanges file.

Signed-off-by: Andrew Reidmeyer <areidmeyer@nvidia.com>

* Tweak wording.

Signed-off-by: Andrew Reidmeyer <areidmeyer@nvidia.com>

* Add a test

Signed-off-by: Jonathan Swartz <jonathan@jswartz.info>

* Requested change.

Signed-off-by: Andrew Reidmeyer <areidmeyer@nvidia.com>

---------

Signed-off-by: Andrew Reidmeyer <areidmeyer@nvidia.com>
Signed-off-by: Jonathan Swartz <jonathan@jswartz.info>
Co-authored-by: Jonathan Swartz <jonathan@jswartz.info>

Author: areidmeyer

nanovdb/nanovdb/GridHandle.h

@@ -400,6 +400,7 @@ GridHandle<BufferT>::deviceGrid(uint32_t n) const
 template<typename BufferT>
 void GridHandle<BufferT>::read(std::istream& is, const BufferT& pool)
 {
+    const std::streampos start = is.tellg();// remember where the raw buffer begins
     GridData data;
     is.read((char*)&data, sizeof(GridData));
     if (data.isValid()) {
@@ -410,7 +411,7 @@ void GridHandle<BufferT>::read(std::istream& is, const BufferT& pool)
             sum += data.mGridSize;
         }
         auto buffer = BufferT::create(size + sum, &pool);
-        is.seekg(-int64_t(sum + sizeof(GridData)), std::ios::cur);// rewind to start
+        is.seekg(start);// rewind to the start of the raw buffer
         is.read((char*)(buffer.data()), buffer.size());
         *this = GridHandle(std::move(buffer));
     } else {

nanovdb/nanovdb/unittest/TestNanoVDB.cc

@@ -8386,6 +8386,38 @@ TEST_F(TestNanoVDB, CustomStreamGridHandleIO)
     }
 }// CustomStreamGridHandleIO
 
+// make -j testNanoVDB && ./unittest/testNanoVDB --gtest_filter="*GridHandleReadMultiGridRawBuffer"
+TEST_F(TestNanoVDB, GridHandleReadMultiGridRawBuffer)
+{
+    std::vector<nanovdb::GridHandle<>> handles;
+    handles.emplace_back(nanovdb::tools::createLevelSetSphere<float>(20.0));
+    handles.emplace_back(nanovdb::tools::createLevelSetSphere<float>(40.0));
+    ASSERT_EQ(2u, handles.size());
+    ASSERT_NE(handles[0].bufferSize(), handles[1].bufferSize());
+
+    auto mergedHandle = nanovdb::mergeGrids<nanovdb::HostBuffer, std::vector>(handles);
+    ASSERT_EQ(2u, mergedHandle.gridCount());
+
+    std::stringstream stream(std::ios_base::in | std::ios_base::out | std::ios_base::binary);
+    mergedHandle.write(stream);
+    stream.seekg(0);
+
+    nanovdb::GridHandle<> handle;
+    handle.read(stream);
+
+    EXPECT_EQ(mergedHandle.bufferSize(), handle.bufferSize());
+    EXPECT_EQ(2u, handle.gridCount());
+    for (uint32_t i = 0; i < handle.gridCount(); ++i) {
+        const auto* grid = handle.grid<float>(i);
+        ASSERT_TRUE(grid);
+        EXPECT_EQ(i, grid->gridIndex());
+        EXPECT_EQ(2u, grid->gridCount());
+        EXPECT_EQ(handles[i].bufferSize(), grid->gridSize());
+        EXPECT_TRUE(nanovdb::tools::validateChecksum(grid));
+        EXPECT_TRUE(nanovdb::tools::validateChecksum(grid, nanovdb::CheckMode::Full));
+    }
+}// GridHandleReadMultiGridRawBuffer
+
 // make -j testNanoVDB && ./unittest/testNanoVDB --gtest_filter="*strcpy"
 TEST_F(TestNanoVDB, strcpy)
 {

pendingchanges/gridhandlereadbugfix.txt

@@ -0,0 +1,3 @@
+NanoVDB:
+  Bug Fixes:
+  - Fixed seek offset over-counting in NanoVDB GridHandle read for cases with multiple grids per handle.