Support terrain sample size greater than cell size

CHANGELOG.md

@@ -67,6 +67,7 @@
     Bug #7450: Evading obstacles does not work for actors missing certain animations
     Bug #7459: Icons get stacked on the cursor when picking up multiple items simultaneously
     Bug #7472: Crash when enchanting last projectiles
+    Bug #7505: Distant terrain does not support sample size greater than cell size
     Feature #3537: Shader-based water ripples
     Feature #5492: Let rain and snow collide with statics
     Feature #6447: Add LOD support to Object Paging

apps/openmw_test_suite/CMakeLists.txt

@@ -92,6 +92,8 @@ file(GLOB UNITTEST_SRC_FILES
     esm3/testinfoorder.cpp
 
     nifosg/testnifloader.cpp
+
+    esmterrain/testgridsampling.cpp
 )
 
 source_group(apps\\openmw_test_suite FILES openmw_test_suite.cpp ${UNITTEST_SRC_FILES})

apps/openmw_test_suite/esmterrain/testgridsampling.cpp

@@ -0,0 +1,366 @@
+#include <components/esmterrain/gridsampling.hpp>
+
+#include <gmock/gmock.h>
+#include <gtest/gtest.h>
+
+namespace ESMTerrain
+{
+    namespace
+    {
+        using namespace testing;
+
+        struct Sample
+        {
+            std::size_t mCellX = 0;
+            std::size_t mCellY = 0;
+            std::size_t mLocalX = 0;
+            std::size_t mLocalY = 0;
+            std::size_t mVertexX = 0;
+            std::size_t mVertexY = 0;
+        };
+
+        auto tie(const Sample& v)
+        {
+            return std::tie(v.mCellX, v.mCellY, v.mLocalX, v.mLocalY, v.mVertexX, v.mVertexY);
+        }
+
+        bool operator==(const Sample& l, const Sample& r)
+        {
+            return tie(l) == tie(r);
+        }
+
+        std::ostream& operator<<(std::ostream& stream, const Sample& v)
+        {
+            return stream << "Sample{.mCellX = " << v.mCellX << ", .mCellY = " << v.mCellY
+                          << ", .mLocalX = " << v.mLocalX << ", .mLocalY = " << v.mLocalY
+                          << ", .mVertexX = " << v.mVertexX << ", .mVertexY = " << v.mVertexY << "}";
+        }
+
+        struct Collect
+        {
+            std::vector<Sample>& mSamples;
+
+            void operator()(std::size_t cellX, std::size_t cellY, std::size_t localX, std::size_t localY,
+                std::size_t vertexX, std::size_t vertexY)
+            {
+                mSamples.push_back(Sample{
+                    .mCellX = cellX,
+                    .mCellY = cellY,
+                    .mLocalX = localX,
+                    .mLocalY = localY,
+                    .mVertexX = vertexX,
+                    .mVertexY = vertexY,
+                });
+            }
+        };
+
+        TEST(ESMTerrainSampleCellGrid, doesNotSupportCellSizeLessThanTwo)
+        {
+            const std::size_t cellSize = 2;
+            EXPECT_THROW(sampleCellGrid(cellSize, 0, 0, 0, 0, [](auto...) {}), std::invalid_argument);
+        }
+
+        TEST(ESMTerrainSampleCellGrid, doesNotSupportCellSizeMinusOneNotPowerOfTwo)
+        {
+            const std::size_t cellSize = 4;
+            EXPECT_THROW(sampleCellGrid(cellSize, 0, 0, 0, 0, [](auto...) {}), std::invalid_argument);
+        }
+
+        TEST(ESMTerrainSampleCellGrid, doesNotSupportZeroSampleSize)
+        {
+            const std::size_t cellSize = 1;
+            const std::size_t sampleSize = 0;
+            EXPECT_THROW(sampleCellGrid(cellSize, sampleSize, 0, 0, 0, [](auto...) {}), std::invalid_argument);
+        }
+
+        TEST(ESMTerrainSampleCellGrid, doesNotSupportSampleSizeNotPowerOfTwo)
+        {
+            const std::size_t cellSize = 1;
+            const std::size_t sampleSize = 3;
+            EXPECT_THROW(sampleCellGrid(cellSize, sampleSize, 0, 0, 0, [](auto...) {}), std::invalid_argument);
+        }
+
+        TEST(ESMTerrainSampleCellGrid, doesNotSupportCountLessThanTwo)
+        {
+            const std::size_t cellSize = 1;
+            const std::size_t sampleSize = 1;
+            const std::size_t distance = 2;
+            EXPECT_THROW(sampleCellGrid(cellSize, sampleSize, 0, 0, distance, [](auto...) {}), std::invalid_argument);
+        }
+
+        TEST(ESMTerrainSampleCellGrid, doesNotSupportCountMinusOneNotPowerOfTwo)
+        {
+            const std::size_t cellSize = 1;
+            const std::size_t sampleSize = 1;
+            const std::size_t distance = 4;
+            EXPECT_THROW(sampleCellGrid(cellSize, sampleSize, 0, 0, distance, [](auto...) {}), std::invalid_argument);
+        }
+
+        TEST(ESMTerrainSampleCellGrid, sampleSizeOneShouldProduceNumberOfSamplesEqualToCellSize)
+        {
+            const std::size_t cellSize = 3;
+            const std::size_t sampleSize = 1;
+            const std::size_t beginX = 0;
+            const std::size_t beginY = 0;
+            const std::size_t distance = 3;
+            std::vector<Sample> samples;
+            sampleCellGrid(cellSize, sampleSize, beginX, beginY, distance, Collect{ samples });
+            EXPECT_THAT(samples,
+                ElementsAre( //
+                    Sample{ .mCellX = 0, .mCellY = 0, .mLocalX = 0, .mLocalY = 0, .mVertexX = 0, .mVertexY = 0 },
+                    Sample{ .mCellX = 0, .mCellY = 0, .mLocalX = 1, .mLocalY = 0, .mVertexX = 1, .mVertexY = 0 },
+                    Sample{ .mCellX = 0, .mCellY = 0, .mLocalX = 2, .mLocalY = 0, .mVertexX = 2, .mVertexY = 0 },
+                    Sample{ .mCellX = 0, .mCellY = 0, .mLocalX = 0, .mLocalY = 1, .mVertexX = 0, .mVertexY = 1 },
+                    Sample{ .mCellX = 0, .mCellY = 0, .mLocalX = 1, .mLocalY = 1, .mVertexX = 1, .mVertexY = 1 },
+                    Sample{ .mCellX = 0, .mCellY = 0, .mLocalX = 2, .mLocalY = 1, .mVertexX = 2, .mVertexY = 1 },
+                    Sample{ .mCellX = 0, .mCellY = 0, .mLocalX = 0, .mLocalY = 2, .mVertexX = 0, .mVertexY = 2 },
+                    Sample{ .mCellX = 0, .mCellY = 0, .mLocalX = 1, .mLocalY = 2, .mVertexX = 1, .mVertexY = 2 },
+                    Sample{ .mCellX = 0, .mCellY = 0, .mLocalX = 2, .mLocalY = 2, .mVertexX = 2, .mVertexY = 2 }));
+        }
+
+        TEST(ESMTerrainSampleCellGrid, countShouldLimitScope)
+        {
+            const std::size_t cellSize = 3;
+            const std::size_t sampleSize = 1;
+            const std::size_t beginX = 0;
+            const std::size_t beginY = 0;
+            const std::size_t distance = 2;
+            std::vector<Sample> samples;
+            sampleCellGrid(cellSize, sampleSize, beginX, beginY, distance, Collect{ samples });
+            EXPECT_THAT(samples,
+                ElementsAre( //
+                    Sample{ .mCellX = 0, .mCellY = 0, .mLocalX = 0, .mLocalY = 0, .mVertexX = 0, .mVertexY = 0 },
+                    Sample{ .mCellX = 0, .mCellY = 0, .mLocalX = 1, .mLocalY = 0, .mVertexX = 1, .mVertexY = 0 },
+                    Sample{ .mCellX = 0, .mCellY = 0, .mLocalX = 0, .mLocalY = 1, .mVertexX = 0, .mVertexY = 1 },
+                    Sample{ .mCellX = 0, .mCellY = 0, .mLocalX = 1, .mLocalY = 1, .mVertexX = 1, .mVertexY = 1 }));
+        }
+
+        TEST(ESMTerrainSampleCellGrid, beginXAndCountShouldLimitScope)
+        {
+            const std::size_t cellSize = 3;
+            const std::size_t sampleSize = 1;
+            const std::size_t beginX = 1;
+            const std::size_t beginY = 0;
+            const std::size_t distance = 2;
+            std::vector<Sample> samples;
+            sampleCellGrid(cellSize, sampleSize, beginX, beginY, distance, Collect{ samples });
+            EXPECT_THAT(samples,
+                ElementsAre( //
+                    Sample{ .mCellX = 0, .mCellY = 0, .mLocalX = 1, .mLocalY = 0, .mVertexX = 0, .mVertexY = 0 },
+                    Sample{ .mCellX = 0, .mCellY = 0, .mLocalX = 2, .mLocalY = 0, .mVertexX = 1, .mVertexY = 0 },
+                    Sample{ .mCellX = 0, .mCellY = 0, .mLocalX = 1, .mLocalY = 1, .mVertexX = 0, .mVertexY = 1 },
+                    Sample{ .mCellX = 0, .mCellY = 0, .mLocalX = 2, .mLocalY = 1, .mVertexX = 1, .mVertexY = 1 }));
+        }
+
+        TEST(ESMTerrainSampleCellGrid, beginYAndCountShouldLimitScope)
+        {
+            const std::size_t cellSize = 3;
+            const std::size_t sampleSize = 1;
+            const std::size_t beginX = 0;
+            const std::size_t beginY = 1;
+            const std::size_t distance = 2;
+            std::vector<Sample> samples;
+            sampleCellGrid(cellSize, sampleSize, beginX, beginY, distance, Collect{ samples });
+            EXPECT_THAT(samples,
+                ElementsAre( //
+                    Sample{ .mCellX = 0, .mCellY = 0, .mLocalX = 0, .mLocalY = 1, .mVertexX = 0, .mVertexY = 0 },
+                    Sample{ .mCellX = 0, .mCellY = 0, .mLocalX = 1, .mLocalY = 1, .mVertexX = 1, .mVertexY = 0 },
+                    Sample{ .mCellX = 0, .mCellY = 0, .mLocalX = 0, .mLocalY = 2, .mVertexX = 0, .mVertexY = 1 },
+                    Sample{ .mCellX = 0, .mCellY = 0, .mLocalX = 1, .mLocalY = 2, .mVertexX = 1, .mVertexY = 1 }));
+        }
+
+        TEST(ESMTerrainSampleCellGrid, beginAndCountShouldLimitScope)
+        {
+            const std::size_t cellSize = 3;
+            const std::size_t sampleSize = 1;
+            const std::size_t beginX = 1;
+            const std::size_t beginY = 1;
+            const std::size_t distance = 2;
+            std::vector<Sample> samples;
+            sampleCellGrid(cellSize, sampleSize, beginX, beginY, distance, Collect{ samples });
+            EXPECT_THAT(samples,
+                ElementsAre( //
+                    Sample{ .mCellX = 0, .mCellY = 0, .mLocalX = 1, .mLocalY = 1, .mVertexX = 0, .mVertexY = 0 },
+                    Sample{ .mCellX = 0, .mCellY = 0, .mLocalX = 2, .mLocalY = 1, .mVertexX = 1, .mVertexY = 0 },
+                    Sample{ .mCellX = 0, .mCellY = 0, .mLocalX = 1, .mLocalY = 2, .mVertexX = 0, .mVertexY = 1 },
+                    Sample{ .mCellX = 0, .mCellY = 0, .mLocalX = 2, .mLocalY = 2, .mVertexX = 1, .mVertexY = 1 }));
+        }
+
+        TEST(ESMTerrainSampleCellGrid, beginAndCountShouldLimitScopeInTheMiddleOfCell)
+        {
+            const std::size_t cellSize = 5;
+            const std::size_t sampleSize = 1;
+            const std::size_t beginX = 1;
+            const std::size_t beginY = 1;
+            const std::size_t distance = 2;
+            std::vector<Sample> samples;
+            sampleCellGrid(cellSize, sampleSize, beginX, beginY, distance, Collect{ samples });
+            EXPECT_THAT(samples,
+                ElementsAre( //
+                    Sample{ .mCellX = 0, .mCellY = 0, .mLocalX = 1, .mLocalY = 1, .mVertexX = 0, .mVertexY = 0 },
+                    Sample{ .mCellX = 0, .mCellY = 0, .mLocalX = 2, .mLocalY = 1, .mVertexX = 1, .mVertexY = 0 },
+                    Sample{ .mCellX = 0, .mCellY = 0, .mLocalX = 1, .mLocalY = 2, .mVertexX = 0, .mVertexY = 1 },
+                    Sample{ .mCellX = 0, .mCellY = 0, .mLocalX = 2, .mLocalY = 2, .mVertexX = 1, .mVertexY = 1 }));
+        }
+
+        TEST(ESMTerrainSampleCellGrid, beginXWithCountLessThanCellSizeShouldLimitScopeAcrossCellBorder)
+        {
+            const std::size_t cellSize = 5;
+            const std::size_t sampleSize = 1;
+            const std::size_t beginX = 3;
+            const std::size_t beginY = 0;
+            const std::size_t distance = 3;
+            std::vector<Sample> samples;
+            sampleCellGrid(cellSize, sampleSize, beginX, beginY, distance, Collect{ samples });
+            EXPECT_THAT(samples,
+                ElementsAre( //
+                    Sample{ .mCellX = 0, .mCellY = 0, .mLocalX = 3, .mLocalY = 0, .mVertexX = 0, .mVertexY = 0 },
+                    Sample{ .mCellX = 0, .mCellY = 0, .mLocalX = 4, .mLocalY = 0, .mVertexX = 1, .mVertexY = 0 },
+                    Sample{ .mCellX = 1, .mCellY = 0, .mLocalX = 1, .mLocalY = 0, .mVertexX = 2, .mVertexY = 0 },
+                    Sample{ .mCellX = 0, .mCellY = 0, .mLocalX = 3, .mLocalY = 1, .mVertexX = 0, .mVertexY = 1 },
+                    Sample{ .mCellX = 0, .mCellY = 0, .mLocalX = 4, .mLocalY = 1, .mVertexX = 1, .mVertexY = 1 },
+                    Sample{ .mCellX = 1, .mCellY = 0, .mLocalX = 1, .mLocalY = 1, .mVertexX = 2, .mVertexY = 1 },
+                    Sample{ .mCellX = 0, .mCellY = 0, .mLocalX = 3, .mLocalY = 2, .mVertexX = 0, .mVertexY = 2 },
+                    Sample{ .mCellX = 0, .mCellY = 0, .mLocalX = 4, .mLocalY = 2, .mVertexX = 1, .mVertexY = 2 },
+                    Sample{ .mCellX = 1, .mCellY = 0, .mLocalX = 1, .mLocalY = 2, .mVertexX = 2, .mVertexY = 2 }));
+        }
+
+        TEST(ESMTerrainSampleCellGrid, beginXWithCountEqualToCellSizeShouldLimitScopeAcrossCellBorder)
+        {
+            const std::size_t cellSize = 3;
+            const std::size_t sampleSize = 1;
+            const std::size_t beginX = 1;
+            const std::size_t beginY = 0;
+            const std::size_t distance = 3;
+            std::vector<Sample> samples;
+            sampleCellGrid(cellSize, sampleSize, beginX, beginY, distance, Collect{ samples });
+            EXPECT_THAT(samples,
+                ElementsAre( //
+                    Sample{ .mCellX = 0, .mCellY = 0, .mLocalX = 1, .mLocalY = 0, .mVertexX = 0, .mVertexY = 0 },
+                    Sample{ .mCellX = 0, .mCellY = 0, .mLocalX = 2, .mLocalY = 0, .mVertexX = 1, .mVertexY = 0 },
+                    Sample{ .mCellX = 0, .mCellY = 0, .mLocalX = 1, .mLocalY = 1, .mVertexX = 0, .mVertexY = 1 },
+                    Sample{ .mCellX = 0, .mCellY = 0, .mLocalX = 2, .mLocalY = 1, .mVertexX = 1, .mVertexY = 1 },
+                    Sample{ .mCellX = 0, .mCellY = 0, .mLocalX = 1, .mLocalY = 2, .mVertexX = 0, .mVertexY = 2 },
+                    Sample{ .mCellX = 0, .mCellY = 0, .mLocalX = 2, .mLocalY = 2, .mVertexX = 1, .mVertexY = 2 },
+                    Sample{ .mCellX = 1, .mCellY = 0, .mLocalX = 1, .mLocalY = 0, .mVertexX = 2, .mVertexY = 0 },
+                    Sample{ .mCellX = 1, .mCellY = 0, .mLocalX = 1, .mLocalY = 1, .mVertexX = 2, .mVertexY = 1 },
+                    Sample{ .mCellX = 1, .mCellY = 0, .mLocalX = 1, .mLocalY = 2, .mVertexX = 2, .mVertexY = 2 }));
+        }
+
+        TEST(ESMTerrainSampleCellGrid, beginXWithCountGreaterThanCellSizeShouldLimitScopeAcrossCellBorder)
+        {
+            const std::size_t cellSize = 3;
+            const std::size_t sampleSize = 1;
+            const std::size_t beginX = 1;
+            const std::size_t beginY = 0;
+            const std::size_t distance = 5;
+            std::vector<Sample> samples;
+            sampleCellGrid(cellSize, sampleSize, beginX, beginY, distance, Collect{ samples });
+            EXPECT_THAT(samples,
+                ElementsAre( //
+                    Sample{ .mCellX = 0, .mCellY = 0, .mLocalX = 1, .mLocalY = 0, .mVertexX = 0, .mVertexY = 0 },
+                    Sample{ .mCellX = 0, .mCellY = 0, .mLocalX = 2, .mLocalY = 0, .mVertexX = 1, .mVertexY = 0 },
+                    Sample{ .mCellX = 0, .mCellY = 0, .mLocalX = 1, .mLocalY = 1, .mVertexX = 0, .mVertexY = 1 },
+                    Sample{ .mCellX = 0, .mCellY = 0, .mLocalX = 2, .mLocalY = 1, .mVertexX = 1, .mVertexY = 1 },
+                    Sample{ .mCellX = 0, .mCellY = 0, .mLocalX = 1, .mLocalY = 2, .mVertexX = 0, .mVertexY = 2 },
+                    Sample{ .mCellX = 0, .mCellY = 0, .mLocalX = 2, .mLocalY = 2, .mVertexX = 1, .mVertexY = 2 },
+                    Sample{ .mCellX = 1, .mCellY = 0, .mLocalX = 1, .mLocalY = 0, .mVertexX = 2, .mVertexY = 0 },
+                    Sample{ .mCellX = 1, .mCellY = 0, .mLocalX = 2, .mLocalY = 0, .mVertexX = 3, .mVertexY = 0 },
+                    Sample{ .mCellX = 1, .mCellY = 0, .mLocalX = 1, .mLocalY = 1, .mVertexX = 2, .mVertexY = 1 },
+                    Sample{ .mCellX = 1, .mCellY = 0, .mLocalX = 2, .mLocalY = 1, .mVertexX = 3, .mVertexY = 1 },
+                    Sample{ .mCellX = 1, .mCellY = 0, .mLocalX = 1, .mLocalY = 2, .mVertexX = 2, .mVertexY = 2 },
+                    Sample{ .mCellX = 1, .mCellY = 0, .mLocalX = 2, .mLocalY = 2, .mVertexX = 3, .mVertexY = 2 },
+                    Sample{ .mCellX = 2, .mCellY = 0, .mLocalX = 1, .mLocalY = 0, .mVertexX = 4, .mVertexY = 0 },
+                    Sample{ .mCellX = 2, .mCellY = 0, .mLocalX = 1, .mLocalY = 1, .mVertexX = 4, .mVertexY = 1 },
+                    Sample{ .mCellX = 2, .mCellY = 0, .mLocalX = 1, .mLocalY = 2, .mVertexX = 4, .mVertexY = 2 },
+                    Sample{ .mCellX = 0, .mCellY = 1, .mLocalX = 1, .mLocalY = 1, .mVertexX = 0, .mVertexY = 3 },
+                    Sample{ .mCellX = 0, .mCellY = 1, .mLocalX = 2, .mLocalY = 1, .mVertexX = 1, .mVertexY = 3 },
+                    Sample{ .mCellX = 0, .mCellY = 1, .mLocalX = 1, .mLocalY = 2, .mVertexX = 0, .mVertexY = 4 },
+                    Sample{ .mCellX = 0, .mCellY = 1, .mLocalX = 2, .mLocalY = 2, .mVertexX = 1, .mVertexY = 4 },
+                    Sample{ .mCellX = 1, .mCellY = 1, .mLocalX = 1, .mLocalY = 1, .mVertexX = 2, .mVertexY = 3 },
+                    Sample{ .mCellX = 1, .mCellY = 1, .mLocalX = 2, .mLocalY = 1, .mVertexX = 3, .mVertexY = 3 },
+                    Sample{ .mCellX = 1, .mCellY = 1, .mLocalX = 1, .mLocalY = 2, .mVertexX = 2, .mVertexY = 4 },
+                    Sample{ .mCellX = 1, .mCellY = 1, .mLocalX = 2, .mLocalY = 2, .mVertexX = 3, .mVertexY = 4 },
+                    Sample{ .mCellX = 2, .mCellY = 1, .mLocalX = 1, .mLocalY = 1, .mVertexX = 4, .mVertexY = 3 },
+                    Sample{ .mCellX = 2, .mCellY = 1, .mLocalX = 1, .mLocalY = 2, .mVertexX = 4, .mVertexY = 4 }));
+        }
+
+        TEST(ESMTerrainSampleCellGrid, sampleSizeGreaterThanOneShouldSkipPoints)
+        {
+            const std::size_t cellSize = 3;
+            const std::size_t sampleSize = 2;
+            const std::size_t beginX = 0;
+            const std::size_t beginY = 0;
+            const std::size_t distance = 3;
+            std::vector<Sample> samples;
+            sampleCellGrid(cellSize, sampleSize, beginX, beginY, distance, Collect{ samples });
+            EXPECT_THAT(samples,
+                ElementsAre( //
+                    Sample{ .mCellX = 0, .mCellY = 0, .mLocalX = 0, .mLocalY = 0, .mVertexX = 0, .mVertexY = 0 },
+                    Sample{ .mCellX = 0, .mCellY = 0, .mLocalX = 2, .mLocalY = 0, .mVertexX = 1, .mVertexY = 0 },
+                    Sample{ .mCellX = 0, .mCellY = 0, .mLocalX = 0, .mLocalY = 2, .mVertexX = 0, .mVertexY = 1 },
+                    Sample{ .mCellX = 0, .mCellY = 0, .mLocalX = 2, .mLocalY = 2, .mVertexX = 1, .mVertexY = 1 }));
+        }
+
+        TEST(ESMTerrainSampleCellGrid, shouldGroupByCell)
+        {
+            const std::size_t cellSize = 3;
+            const std::size_t sampleSize = 2;
+            const std::size_t beginX = 0;
+            const std::size_t beginY = 0;
+            const std::size_t distance = 5;
+            std::vector<Sample> samples;
+            sampleCellGrid(cellSize, sampleSize, beginX, beginY, distance, Collect{ samples });
+            EXPECT_THAT(samples,
+                ElementsAre( //
+                    Sample{ .mCellX = 0, .mCellY = 0, .mLocalX = 0, .mLocalY = 0, .mVertexX = 0, .mVertexY = 0 },
+                    Sample{ .mCellX = 0, .mCellY = 0, .mLocalX = 2, .mLocalY = 0, .mVertexX = 1, .mVertexY = 0 },
+                    Sample{ .mCellX = 0, .mCellY = 0, .mLocalX = 0, .mLocalY = 2, .mVertexX = 0, .mVertexY = 1 },
+                    Sample{ .mCellX = 0, .mCellY = 0, .mLocalX = 2, .mLocalY = 2, .mVertexX = 1, .mVertexY = 1 },
+                    Sample{ .mCellX = 1, .mCellY = 0, .mLocalX = 2, .mLocalY = 0, .mVertexX = 2, .mVertexY = 0 },
+                    Sample{ .mCellX = 1, .mCellY = 0, .mLocalX = 2, .mLocalY = 2, .mVertexX = 2, .mVertexY = 1 },
+                    Sample{ .mCellX = 0, .mCellY = 1, .mLocalX = 0, .mLocalY = 2, .mVertexX = 0, .mVertexY = 2 },
+                    Sample{ .mCellX = 0, .mCellY = 1, .mLocalX = 2, .mLocalY = 2, .mVertexX = 1, .mVertexY = 2 },
+                    Sample{ .mCellX = 1, .mCellY = 1, .mLocalX = 2, .mLocalY = 2, .mVertexX = 2, .mVertexY = 2 }));
+        }
+
+        TEST(ESMTerrainSampleCellGrid, sampleSizeGreaterThanCellSizeShouldPickSinglePointPerCell)
+        {
+            const std::size_t cellSize = 3;
+            const std::size_t sampleSize = 4;
+            const std::size_t beginX = 0;
+            const std::size_t beginY = 0;
+            const std::size_t distance = 9;
+            std::vector<Sample> samples;
+            sampleCellGrid(cellSize, sampleSize, beginX, beginY, distance, Collect{ samples });
+            EXPECT_THAT(samples,
+                ElementsAre( //
+                    Sample{ .mCellX = 0, .mCellY = 0, .mLocalX = 0, .mLocalY = 0, .mVertexX = 0, .mVertexY = 0 },
+                    Sample{ .mCellX = 1, .mCellY = 0, .mLocalX = 2, .mLocalY = 0, .mVertexX = 1, .mVertexY = 0 },
+                    Sample{ .mCellX = 3, .mCellY = 0, .mLocalX = 2, .mLocalY = 0, .mVertexX = 2, .mVertexY = 0 },
+                    Sample{ .mCellX = 0, .mCellY = 1, .mLocalX = 0, .mLocalY = 2, .mVertexX = 0, .mVertexY = 1 },
+                    Sample{ .mCellX = 1, .mCellY = 1, .mLocalX = 2, .mLocalY = 2, .mVertexX = 1, .mVertexY = 1 },
+                    Sample{ .mCellX = 3, .mCellY = 1, .mLocalX = 2, .mLocalY = 2, .mVertexX = 2, .mVertexY = 1 },
+                    Sample{ .mCellX = 0, .mCellY = 3, .mLocalX = 0, .mLocalY = 2, .mVertexX = 0, .mVertexY = 2 },
+                    Sample{ .mCellX = 1, .mCellY = 3, .mLocalX = 2, .mLocalY = 2, .mVertexX = 1, .mVertexY = 2 },
+                    Sample{ .mCellX = 3, .mCellY = 3, .mLocalX = 2, .mLocalY = 2, .mVertexX = 2, .mVertexY = 2 }));
+        }
+
+        TEST(ESMTerrainSampleCellGrid, sampleSizeGreaterThan2CellSizeShouldSkipCells)
+        {
+            const std::size_t cellSize = 3;
+            const std::size_t sampleSize = 8;
+            const std::size_t beginX = 0;
+            const std::size_t beginY = 0;
+            const std::size_t distance = 9;
+            std::vector<Sample> samples;
+            sampleCellGrid(cellSize, sampleSize, beginX, beginY, distance, Collect{ samples });
+            EXPECT_THAT(samples,
+                ElementsAre( //
+                    Sample{ .mCellX = 0, .mCellY = 0, .mLocalX = 0, .mLocalY = 0, .mVertexX = 0, .mVertexY = 0 },
+                    Sample{ .mCellX = 3, .mCellY = 0, .mLocalX = 2, .mLocalY = 0, .mVertexX = 1, .mVertexY = 0 },
+                    Sample{ .mCellX = 0, .mCellY = 3, .mLocalX = 0, .mLocalY = 2, .mVertexX = 0, .mVertexY = 1 },
+                    Sample{ .mCellX = 3, .mCellY = 3, .mLocalX = 2, .mLocalY = 2, .mVertexX = 1, .mVertexY = 1 }));
+        }
+    }
+}

components/esmterrain/gridsampling.hpp

@@ -0,0 +1,120 @@
+#ifndef OPENMW_COMPONENTS_ESMTERRAIN_GRIDSAMPLING_H
+#define OPENMW_COMPONENTS_ESMTERRAIN_GRIDSAMPLING_H
+
+#include <components/misc/mathutil.hpp>
+
+#include <cassert>
+#include <cstddef>
+#include <stdexcept>
+#include <string>
+#include <utility>
+
+namespace ESMTerrain
+{
+    inline std::pair<std::size_t, std::size_t> toCellAndLocal(
+        std::size_t begin, std::size_t global, std::size_t cellSize)
+    {
+        std::size_t cell = global / (cellSize - 1);
+        std::size_t local = global & (cellSize - 2);
+        if (global != begin && local == 0)
+        {
+            --cell;
+            local = cellSize - 1;
+        }
+        return { cell, local };
+    }
+
+    template <class F>
+    void sampleGrid(
+        std::size_t sampleSize, std::size_t beginX, std::size_t beginY, std::size_t endX, std::size_t endY, F&& f)
+    {
+        std::size_t vertY = 0;
+        for (std::size_t y = beginY; y < endY; y += sampleSize)
+        {
+            std::size_t vertX = 0;
+            for (std::size_t x = beginX; x < endX; x += sampleSize)
+                f(x, y, vertX++, vertY);
+            ++vertY;
+        }
+    }
+
+    template <class F>
+    void sampleCellGridSimple(std::size_t cellSize, std::size_t sampleSize, std::size_t beginX, std::size_t beginY,
+        std::size_t endX, std::size_t endY, F&& f)
+    {
+        assert(cellSize > 1);
+        assert(Misc::isPowerOfTwo(cellSize - 1));
+        assert(sampleSize != 0);
+
+        sampleGrid(sampleSize, beginX, beginY, endX, endY,
+            [&](std::size_t globalX, std::size_t globalY, std::size_t vertX, std::size_t vertY) {
+                const auto [cellX, x] = toCellAndLocal(beginX, globalX, cellSize);
+                const auto [cellY, y] = toCellAndLocal(beginY, globalY, cellSize);
+                f(cellX, cellY, x, y, vertX, vertY);
+            });
+    }
+
+    template <class F>
+    void sampleCellGrid(std::size_t cellSize, std::size_t sampleSize, std::size_t beginX, std::size_t beginY,
+        std::size_t distance, F&& f)
+    {
+        if (cellSize < 2 || !Misc::isPowerOfTwo(cellSize - 1))
+            throw std::invalid_argument("Invalid cell size for cell grid sampling: " + std::to_string(cellSize));
+
+        if (sampleSize == 0 || !Misc::isPowerOfTwo(sampleSize))
+            throw std::invalid_argument("Invalid sample size for cell grid sampling: " + std::to_string(sampleSize));
+
+        if (distance < 2 || !Misc::isPowerOfTwo(distance - 1))
+            throw std::invalid_argument("Invalid count for cell grid sampling: " + std::to_string(distance));
+
+        const std::size_t endX = beginX + distance;
+        const std::size_t endY = beginY + distance;
+
+        if (distance < cellSize || sampleSize > cellSize - 1)
+            return sampleCellGridSimple(cellSize, sampleSize, beginX, beginY, endX, endY, f);
+
+        const std::size_t beginCellX = beginX / (cellSize - 1);
+        const std::size_t beginCellY = beginY / (cellSize - 1);
+        const std::size_t endCellX = endX / (cellSize - 1);
+        const std::size_t endCellY = endY / (cellSize - 1);
+
+        std::size_t baseVertY = 0;
+
+        for (std::size_t cellY = beginCellY; cellY < endCellY; ++cellY)
+        {
+            const std::size_t offsetY = cellY * (cellSize - 1);
+            const std::size_t globalBeginY = offsetY <= beginY ? beginY : offsetY + sampleSize;
+            const std::size_t globalEndY = endY <= offsetY + cellSize ? endY : offsetY + cellSize;
+
+            assert(globalBeginY < globalEndY);
+
+            std::size_t baseVertX = 0;
+            std::size_t vertY = baseVertY;
+
+            for (std::size_t cellX = beginCellX; cellX < endCellX; ++cellX)
+            {
+                const std::size_t offsetX = cellX * (cellSize - 1);
+                const std::size_t globalBeginX = offsetX <= beginX ? beginX : offsetX + sampleSize;
+                const std::size_t globalEndX = endX <= offsetX + cellSize ? endX : offsetX + cellSize;
+
+                assert(globalBeginX < globalEndX);
+
+                vertY = baseVertY;
+                std::size_t vertX = baseVertX;
+
+                sampleGrid(sampleSize, globalBeginX, globalBeginY, globalEndX, globalEndY,
+                    [&](std::size_t globalX, std::size_t globalY, std::size_t localVertX, std::size_t localVertY) {
+                        vertX = baseVertX + localVertX;
+                        vertY = baseVertY + localVertY;
+                        f(cellX, cellY, globalX - offsetX, globalY - offsetY, vertX, vertY);
+                    });
+
+                baseVertX = vertX + 1;
+            }
+
+            baseVertY = vertY + 1;
+        }
+    }
+}
+
+#endif

components/esmterrain/storage.cpp

@@ -13,6 +13,8 @@
 #include <components/misc/strings/algorithm.hpp>
 #include <components/vfs/manager.hpp>
 
+#include "gridsampling.hpp"
+
 namespace ESMTerrain
 {
 
@@ -195,59 +197,42 @@ namespace ESMTerrain
 
         // LOD level n means every 2^n-th vertex is kept
         const std::size_t sampleSize = std::size_t{ 1 } << lodLevel;
-
-        const osg::Vec2f origin = center - osg::Vec2f(size, size) / 2;
-
-        const int startCellX = static_cast<int>(std::floor(origin.x()));
-        const int startCellY = static_cast<int>(std::floor(origin.y()));
-        const int landSize = ESM::getLandSize(worldspace);
-        const int landSizeInUnits = ESM::getCellSize(worldspace);
-
-        const std::size_t numVerts = static_cast<std::size_t>(size * (landSize - 1) / sampleSize + 1);
+        const std::size_t cellSize = static_cast<std::size_t>(ESM::getLandSize(worldspace));
+        const std::size_t numVerts = static_cast<std::size_t>(size * (cellSize - 1) / sampleSize) + 1;
 
         positions.resize(numVerts * numVerts);
         normals.resize(numVerts * numVerts);
         colours.resize(numVerts * numVerts);
 
-        // Only relevant for chunks smaller than (contained in) one cell
-        const int offsetX = (origin.x() - startCellX) * landSize;
-        const int offsetY = (origin.y() - startCellY) * landSize;
-
         LandCache cache;
 
         const bool alteration = useAlteration();
+        const int landSizeInUnits = ESM::getCellSize(worldspace);
+        const osg::Vec2f origin = center - osg::Vec2f(size, size) * 0.5f;
+        const int startCellX = static_cast<int>(std::floor(origin.x()));
+        const int startCellY = static_cast<int>(std::floor(origin.y()));
+        ESM::ExteriorCellLocation lastCellLocation(startCellX - 1, startCellY - 1, worldspace);
+        const LandObject* land = nullptr;
+        const ESM::LandData* heightData = nullptr;
+        const ESM::LandData* normalData = nullptr;
+        const ESM::LandData* colourData = nullptr;
         bool validHeightDataExists = false;
-        std::size_t baseVertY = 0; // of current cell corner
-        for (int cellY = startCellY; cellY < startCellY + std::ceil(size); ++cellY)
-        {
-            std::size_t baseVertX = 0; // of current cell corner
-            std::size_t vertY = baseVertY;
-            for (int cellX = startCellX; cellX < startCellX + std::ceil(size); ++cellX)
+
+        const auto handleSample = [&](std::size_t cellShiftX, std::size_t cellShiftY, std::size_t row, std::size_t col,
+                                      std::size_t vertX, std::size_t vertY) {
+            const int cellX = startCellX + cellShiftX;
+            const int cellY = startCellY + cellShiftY;
+            const ESM::ExteriorCellLocation cellLocation(cellX, cellY, worldspace);
+
+            if (lastCellLocation != cellLocation)
             {
-                int rowStart = offsetX;
-                int colStart = offsetY;
-                // Skip the first row / column unless we're at a chunk edge,
-                // since this row / column is already contained in a previous cell
-                // This is only relevant if we're creating a chunk spanning multiple cells
-                if (baseVertY != 0)
-                    colStart += sampleSize;
-                if (baseVertX != 0)
-                    rowStart += sampleSize;
-
-                const int rowEnd = std::min(
-                    static_cast<int>(rowStart + std::min(1.f, size) * (landSize - 1) + 1), static_cast<int>(landSize));
-                const int colEnd = std::min(
-                    static_cast<int>(colStart + std::min(1.f, size) * (landSize - 1) + 1), static_cast<int>(landSize));
-
-                if (colEnd <= colStart || rowEnd <= rowStart)
-                    continue;
-
-                const ESM::ExteriorCellLocation cellLocation(cellX, cellY, worldspace);
-                const LandObject* const land = getLand(cellLocation, cache);
-                const ESM::LandData* heightData = nullptr;
-                const ESM::LandData* normalData = nullptr;
-                const ESM::LandData* colourData = nullptr;
-                if (land)
+                land = getLand(cellLocation, cache);
+
+                heightData = nullptr;
+                normalData = nullptr;
+                colourData = nullptr;
+
+                if (land != nullptr)
                 {
                     heightData = land->getData(ESM::Land::DATA_VHGT);
                     normalData = land->getData(ESM::Land::DATA_VNML);
@@ -255,80 +240,67 @@ namespace ESMTerrain
                     validHeightDataExists = true;
                 }
 
-                vertY = baseVertY;
-                std::size_t vertX = baseVertX;
-                for (int col = colStart; col < colEnd; col += sampleSize)
-                {
-                    vertX = baseVertX;
-                    for (int row = rowStart; row < rowEnd; row += sampleSize)
-                    {
-                        assert(row >= 0 && row < landSize);
-                        assert(col >= 0 && col < landSize);
+                lastCellLocation = cellLocation;
+            }
 
-                        const int srcArrayIndex = col * landSize * 3 + row * 3;
+            float height = defaultHeight;
+            if (heightData != nullptr)
+                height = heightData->getHeights()[col * cellSize + row];
+            if (alteration)
+                height += getAlteredHeight(col, row);
 
-                        assert(vertX < numVerts);
-                        assert(vertY < numVerts);
+            const std::size_t vertIndex = vertX * numVerts + vertY;
 
-                        const std::size_t vertIndex = vertX * numVerts + vertY;
+            positions[vertIndex]
+                = osg::Vec3f((vertX / static_cast<float>(numVerts - 1) - 0.5f) * size * landSizeInUnits,
+                    (vertY / static_cast<float>(numVerts - 1) - 0.5f) * size * landSizeInUnits, height);
 
-                        float height = defaultHeight;
-                        if (heightData)
-                            height = heightData->getHeights()[col * landSize + row];
-                        if (alteration)
-                            height += getAlteredHeight(col, row);
-                        positions[vertIndex]
-                            = osg::Vec3f((vertX / static_cast<float>(numVerts - 1) - 0.5f) * size * landSizeInUnits,
-                                (vertY / static_cast<float>(numVerts - 1) - 0.5f) * size * landSizeInUnits, height);
+            const std::size_t srcArrayIndex = col * cellSize * 3 + row * 3;
 
-                        osg::Vec3f normal(0, 0, 1);
+            osg::Vec3f normal(0, 0, 1);
 
-                        if (normalData != nullptr)
-                        {
-                            for (int i = 0; i < 3; ++i)
-                                normal[i] = normalData->getNormals()[srcArrayIndex + i];
+            if (normalData != nullptr)
+            {
+                for (std::size_t i = 0; i < 3; ++i)
+                    normal[i] = normalData->getNormals()[srcArrayIndex + i];
 
-                            normal.normalize();
-                        }
+                normal.normalize();
+            }
 
-                        // Normals apparently don't connect seamlessly between cells
-                        if (col == landSize - 1 || row == landSize - 1)
-                            fixNormal(normal, cellLocation, col, row, cache);
+            // Normals apparently don't connect seamlessly between cells
+            if (col == cellSize - 1 || row == cellSize - 1)
+                fixNormal(normal, cellLocation, col, row, cache);
 
-                        // some corner normals appear to be complete garbage (z < 0)
-                        if ((row == 0 || row == landSize - 1) && (col == 0 || col == landSize - 1))
-                            averageNormal(normal, cellLocation, col, row, cache);
+            // some corner normals appear to be complete garbage (z < 0)
+            if ((row == 0 || row == cellSize - 1) && (col == 0 || col == cellSize - 1))
+                averageNormal(normal, cellLocation, col, row, cache);
 
-                        assert(normal.z() > 0);
+            assert(normal.z() > 0);
 
-                        normals[vertIndex] = normal;
+            normals[vertIndex] = normal;
 
-                        osg::Vec4ub color(255, 255, 255, 255);
+            osg::Vec4ub color(255, 255, 255, 255);
 
-                        if (colourData != nullptr)
-                            for (int i = 0; i < 3; ++i)
-                                color[i] = colourData->getColors()[srcArrayIndex + i];
+            if (colourData != nullptr)
+                for (std::size_t i = 0; i < 3; ++i)
+                    color[i] = colourData->getColors()[srcArrayIndex + i];
 
-                        if (alteration)
-                            adjustColor(col, row, heightData, color); // Does nothing by default, override in OpenMW-CS
+            // Does nothing by default, override in OpenMW-CS
+            if (alteration)
+                adjustColor(col, row, heightData, color);
 
-                        // Unlike normals, colors mostly connect seamlessly between cells, but not always...
-                        if (col == landSize - 1 || row == landSize - 1)
-                            fixColour(color, cellLocation, col, row, cache);
+            // Unlike normals, colors mostly connect seamlessly between cells, but not always...
+            if (col == cellSize - 1 || row == cellSize - 1)
+                fixColour(color, cellLocation, col, row, cache);
 
-                        colours[vertIndex] = color;
+            colours[vertIndex] = color;
+        };
 
-                        ++vertX;
-                    }
-                    ++vertY;
-                }
-                baseVertX = vertX;
-            }
-            baseVertY = vertY;
+        const std::size_t beginX = static_cast<std::size_t>((origin.x() - startCellX) * cellSize);
+        const std::size_t beginY = static_cast<std::size_t>((origin.y() - startCellY) * cellSize);
+        const std::size_t distance = static_cast<std::size_t>(size * (cellSize - 1)) + 1;
 
-            assert(baseVertX == numVerts); // Ensure we covered whole area
-        }
-        assert(baseVertY == numVerts); // Ensure we covered whole area
+        sampleCellGrid(cellSize, sampleSize, beginX, beginY, distance, handleSample);
 
         if (!validHeightDataExists && ESM::isEsm4Ext(worldspace))
             std::fill(positions.begin(), positions.end(), osg::Vec3f());

components/misc/mathutil.hpp

@@ -7,6 +7,8 @@
 #include <osg/Vec2f>
 #include <osg/Vec3f>
 
+#include <type_traits>
+
 namespace Misc
 {
 
@@ -63,8 +65,10 @@ namespace Misc
         return toEulerAnglesZYX(forward, up);
     }
 
-    inline bool isPowerOfTwo(int x)
+    template <class T>
+    bool isPowerOfTwo(T x)
     {
+        static_assert(std::is_integral_v<T>);
         return ((x > 0) && ((x & (x - 1)) == 0));
     }