Add a GetNumSamplesFromRegion function which returns the number of samples given a region and step size. Update Terrain Feature Processor to use this function to get the number of samples instead of computing num samples independently.

Signed-off-by: amzn-sj <srikkant@amazon.com>

Code/Framework/AzFramework/AzFramework/Terrain/TerrainDataRequestBus.h

@@ -161,6 +161,10 @@ namespace AzFramework
                 SurfacePointListFillCallback perPositionCallback,
                 Sampler sampleFilter = Sampler::DEFAULT) const = 0;
 
+            //! Returns the number of samples for a given region and step size.
+            virtual AZStd::pair<size_t, size_t> GetNumSamplesFromRegion(const AZ::Aabb& inRegion,
+                const AZ::Vector2& stepSize) const = 0;
+
             //! Given a region(aabb) and a step size, call the provided callback function with surface data corresponding to the
             //! coordinates in the region.
             virtual void ProcessHeightsFromRegion(const AZ::Aabb& inRegion,

Code/Framework/AzFramework/Tests/Mocks/Terrain/MockTerrainDataRequestBus.h

@@ -92,6 +92,8 @@ namespace UnitTest
             ProcessSurfaceWeightsFromListOfVector2, void(const AZStd::span<AZ::Vector2>&, AzFramework::Terrain::SurfacePointListFillCallback, Sampler));
         MOCK_CONST_METHOD3(
             ProcessSurfacePointsFromListOfVector2, void(const AZStd::span<AZ::Vector2>&, AzFramework::Terrain::SurfacePointListFillCallback, Sampler));
+        MOCK_CONST_METHOD2(
+            GetNumSamplesFromRegion, AZStd::pair<size_t, size_t>(const AZ::Aabb&, const AZ::Vector2&));
         MOCK_CONST_METHOD4(
             ProcessHeightsFromRegion, void(const AZ::Aabb&, const AZ::Vector2&, AzFramework::Terrain::SurfacePointRegionFillCallback, Sampler));
         MOCK_CONST_METHOD4(

Gems/Terrain/Code/Source/TerrainRenderer/TerrainFeatureProcessor.cpp

@@ -208,12 +208,21 @@ namespace Terrain
         }
         
         int32_t xStart = aznumeric_cast<int32_t>(AZStd::ceilf(m_dirtyRegion.GetMin().GetX() / m_sampleSpacing));
-        int32_t xEnd = aznumeric_cast<int32_t>(AZStd::floorf(m_dirtyRegion.GetMax().GetX() / m_sampleSpacing)) + 1;
         int32_t yStart = aznumeric_cast<int32_t>(AZStd::ceilf(m_dirtyRegion.GetMin().GetY() / m_sampleSpacing));
-        int32_t yEnd = aznumeric_cast<int32_t>(AZStd::floorf(m_dirtyRegion.GetMax().GetY() / m_sampleSpacing)) + 1;
-        uint32_t updateWidth = xEnd - xStart;
-        uint32_t updateHeight = yEnd - yStart;
 
+        AZ::Vector2 stepSize(m_sampleSpacing);
+        AZ::Vector3 maxBound(
+            m_dirtyRegion.GetMax().GetX() + m_sampleSpacing, m_dirtyRegion.GetMax().GetY() + m_sampleSpacing, 0.0f);
+        AZ::Aabb region;
+        region.Set(m_dirtyRegion.GetMin(), maxBound);
+
+        AZStd::pair<size_t, size_t> numSamples;
+        AzFramework::Terrain::TerrainDataRequestBus::BroadcastResult(
+            numSamples, &AzFramework::Terrain::TerrainDataRequests::GetNumSamplesFromRegion,
+            region, stepSize);
+
+        uint32_t updateWidth = numSamples.first;
+        uint32_t updateHeight = numSamples.second;
         AZStd::vector<uint16_t> pixels;
         pixels.reserve(updateWidth * updateHeight);
         {
@@ -238,14 +247,9 @@ namespace Terrain
                 pixels.push_back(uint16Height);
             };
 
-            AZ::Vector2 stepSize(m_sampleSpacing);
-            AZ::Vector3 maxBound(
-                m_dirtyRegion.GetMax().GetX() + m_sampleSpacing, m_dirtyRegion.GetMax().GetY() + m_sampleSpacing, 0.0f);
-            AZ::Aabb region;
-            region.Set(m_dirtyRegion.GetMin(), maxBound);
             AzFramework::Terrain::TerrainDataRequestBus::Broadcast(
                 &AzFramework::Terrain::TerrainDataRequests::ProcessHeightsFromRegion,
-                region, stepSize, perPositionCallback,AzFramework::Terrain::TerrainDataRequests::Sampler::EXACT);
+                region, stepSize, perPositionCallback, AzFramework::Terrain::TerrainDataRequests::Sampler::EXACT);
         }
 
         if (m_heightmapImage)

Gems/Terrain/Code/Source/TerrainSystem/TerrainSystem.cpp

@@ -690,6 +690,16 @@ void TerrainSystem::ProcessSurfacePointsFromListOfVector2(
     }
 }
 
+AZStd::pair<size_t, size_t> TerrainSystem::GetNumSamplesFromRegion(
+    const AZ::Aabb& inRegion,
+    const AZ::Vector2& stepSize) const
+{
+    const size_t numSamplesX = aznumeric_cast<size_t>(ceil(inRegion.GetExtents().GetX() / stepSize.GetX()));
+    const size_t numSamplesY = aznumeric_cast<size_t>(ceil(inRegion.GetExtents().GetY() / stepSize.GetY()));
+
+    return AZStd::make_pair(numSamplesX, numSamplesY);
+}
+
 void TerrainSystem::ProcessHeightsFromRegion(
     const AZ::Aabb& inRegion,
     const AZ::Vector2& stepSize,

Gems/Terrain/Code/Source/TerrainSystem/TerrainSystem.h

@@ -163,6 +163,10 @@ namespace Terrain
             AzFramework::Terrain::SurfacePointListFillCallback perPositionCallback,
             Sampler sampleFilter = Sampler::DEFAULT) const override;
 
+        //! Returns the number of samples for a given region and step size.
+        virtual AZStd::pair<size_t, size_t> GetNumSamplesFromRegion(const AZ::Aabb& inRegion,
+            const AZ::Vector2& stepSize) const override;
+
         //! Given a region(aabb) and a step size, call the provided callback function with surface data corresponding to the
         //! coordinates in the region.
         virtual void ProcessHeightsFromRegion(const AZ::Aabb& inRegion,