From bec59756d407dcb1e0054b334d240d6dca49426d Mon Sep 17 00:00:00 2001
From: Arseny Kapoulkine <arseny.kapoulkine@gmail.com>
Date: Sun, 9 Jul 2017 20:15:03 -0700
Subject: [PATCH] Refactor vertex fetch optimizer and add more assertions

We now range check indices in most algorithms and do some other sanity
checks. Also analyzers now correctly handle empty meshes.
---
 src/overdrawoptimizer.cpp |  1 +
 src/vcacheanalyzer.cpp    | 10 ++++++----
 src/vcacheoptimizer.cpp   |  6 +++++-
 src/vfetchanalyzer.cpp    |  3 ++-
 src/vfetchoptimizer.cpp   | 18 +++++++++++-------
 5 files changed, 25 insertions(+), 13 deletions(-)

diff --git a/src/overdrawoptimizer.cpp b/src/overdrawoptimizer.cpp
index a3981cd9..96f83c40 100644
--- a/src/overdrawoptimizer.cpp
+++ b/src/overdrawoptimizer.cpp
@@ -168,6 +168,7 @@ static void generateSoftBoundaries(std::vector<unsigned int>& destination, const
 	{
 		size_t start = clusters[it];
 		size_t end = (it + 1 < cluster_count) ? clusters[it + 1] : index_count / 3;
+		assert(start <= end);
 
 		while (start != end)
 		{
diff --git a/src/vcacheanalyzer.cpp b/src/vcacheanalyzer.cpp
index 26f0a487..9cd75461 100644
--- a/src/vcacheanalyzer.cpp
+++ b/src/vcacheanalyzer.cpp
@@ -1,6 +1,7 @@
 // This file is part of meshoptimizer library; see meshoptimizer.hpp for version/license details
 #include "meshoptimizer.hpp"
 
+#include <cassert>
 #include <vector>
 
 namespace meshopt
@@ -14,9 +15,10 @@ static VertexCacheStatistics analyzeVertexCacheImpl(const T* indices, size_t ind
 	std::vector<unsigned int> cache_time_stamps(vertex_count, 0);
 	unsigned int time_stamp = cache_size + 1;
 
-	for (const T* indices_end = indices + index_count; indices != indices_end; ++indices)
+	for (size_t i = 0; i < index_count; ++i)
 	{
-		T index = *indices;
+		T index = indices[i];
+		assert(index < vertex_count);
 
 		if (time_stamp - cache_time_stamps[index] > cache_size)
 		{
@@ -26,8 +28,8 @@ static VertexCacheStatistics analyzeVertexCacheImpl(const T* indices, size_t ind
 		}
 	}
 
-	result.acmr = float(result.vertices_transformed) / float(index_count / 3);
-	result.atvr = float(result.vertices_transformed) / float(vertex_count);
+	result.acmr = index_count == 0 ? 0 : float(result.vertices_transformed) / float(index_count / 3);
+	result.atvr = vertex_count == 0 ? 0 : float(result.vertices_transformed) / float(vertex_count);
 
 	return result;
 }
diff --git a/src/vcacheoptimizer.cpp b/src/vcacheoptimizer.cpp
index b49e14c5..d610f05e 100644
--- a/src/vcacheoptimizer.cpp
+++ b/src/vcacheoptimizer.cpp
@@ -22,6 +22,8 @@ static void buildAdjacency(Adjacency& adjacency, const T* indices, size_t index_
 
 	for (size_t i = 0; i < index_count; ++i)
 	{
+		assert(indices[i] < vertex_count);
+
 		adjacency.triangle_counts[indices[i]]++;
 	}
 
@@ -41,7 +43,9 @@ static void buildAdjacency(Adjacency& adjacency, const T* indices, size_t index_
 
 	std::vector<unsigned int> filled_triangle_counts(vertex_count, 0);
 
-	for (size_t i = 0; i < index_count / 3; ++i)
+	size_t face_count = index_count / 3;
+
+	for (size_t i = 0; i < face_count; ++i)
 	{
 		unsigned int a = indices[i * 3 + 0], b = indices[i * 3 + 1], c = indices[i * 3 + 2];
 
diff --git a/src/vfetchanalyzer.cpp b/src/vfetchanalyzer.cpp
index 781dff43..ca215b96 100644
--- a/src/vfetchanalyzer.cpp
+++ b/src/vfetchanalyzer.cpp
@@ -21,6 +21,7 @@ static VertexFetchStatistics analyzeVertexFetchImpl(const T* indices, size_t ind
 	for (size_t i = 0; i < index_count; ++i)
 	{
 		T index = indices[i];
+		assert(index < vertex_count);
 
 		size_t start_address = index * vertex_size;
 		size_t end_address = start_address + vertex_size;
@@ -40,7 +41,7 @@ static VertexFetchStatistics analyzeVertexFetchImpl(const T* indices, size_t ind
 		}
 	}
 
-	result.overfetch = float(result.bytes_fetched) / float(vertex_count * vertex_size);
+	result.overfetch = vertex_count == 0 ? 0 : float(result.bytes_fetched) / float(vertex_count * vertex_size);
 
 	return result;
 }
diff --git a/src/vfetchoptimizer.cpp b/src/vfetchoptimizer.cpp
index 840a8b6c..cb4ac7a1 100644
--- a/src/vfetchoptimizer.cpp
+++ b/src/vfetchoptimizer.cpp
@@ -16,21 +16,25 @@ static void optimizeVertexFetchImpl(void* destination, const void* vertices, T*
 	// build vertex remap table
 	std::vector<unsigned int> vertex_remap(vertex_count, static_cast<unsigned int>(-1));
 
-	size_t vertex = 0;
+	unsigned int vertex = 0;
 
-	for (T* indices_end = indices + index_count; indices != indices_end; ++indices)
+	for (size_t i = 0; i < index_count; ++i)
 	{
-		unsigned int& index = vertex_remap[*indices];
+		T index = indices[i];
+		assert(index < vertex_count);
 
-		if (index == static_cast<unsigned int>(-1)) // vertex was not added to destination VB
+		unsigned int& remap = vertex_remap[index];
+
+		if (remap == static_cast<unsigned int>(-1)) // vertex was not added to destination VB
 		{
 			// add vertex
-			memcpy(static_cast<char*>(destination) + vertex * vertex_size, static_cast<const char*>(vertices) + *indices * vertex_size, vertex_size);
+			memcpy(static_cast<char*>(destination) + vertex * vertex_size, static_cast<const char*>(vertices) + index * vertex_size, vertex_size);
 
-			index = static_cast<unsigned int>(vertex++);
+			remap = vertex++;
 		}
 
-		*indices = static_cast<T>(index);
+		// modify indices in place
+		indices[i] = static_cast<T>(remap);
 	}
 }