diff --git a/modules/meshlet/include/vkcv/meshlet/Forsyth.hpp b/modules/meshlet/include/vkcv/meshlet/Forsyth.hpp
index f781b81ee551d5528b1b75b71b8f2e9518c013d1..7d917a6424060c2adc912f2efae99b82fec55a73 100644
--- a/modules/meshlet/include/vkcv/meshlet/Forsyth.hpp
+++ b/modules/meshlet/include/vkcv/meshlet/Forsyth.hpp
@@ -4,5 +4,15 @@
namespace vkcv::meshlet
{
+ /**
+ * Reorders the index buffer, simulating a LRU cache, so that vertices are grouped together in close triangle patches
+ * @param idxBuf current IndexBuffer
+ * @param vertexCount of the mesh
+ * @return new reordered index buffer to replace the input index buffer
+ * References:
+ * https://tomforsyth1000.github.io/papers/fast_vert_cache_opt.html
+ * https://www.martin.st/thesis/efficient_triangle_reordering.pdf
+ * https://github.com/vivkin/forsyth/blob/master/forsyth.h
+ */
std::vector<uint32_t> forsythReorder(const std::vector<uint32_t> &idxBuf, const size_t vertexCount);
}
diff --git a/modules/meshlet/src/vkcv/meshlet/Forsyth.cpp b/modules/meshlet/src/vkcv/meshlet/Forsyth.cpp
index f0c8e3502a76d71b920efbc45a3a4ce676f68ea1..1f5ccc061605c06bea9495e638a82765854a7889 100644
--- a/modules/meshlet/src/vkcv/meshlet/Forsyth.cpp
+++ b/modules/meshlet/src/vkcv/meshlet/Forsyth.cpp
@@ -2,10 +2,15 @@
#include <vkcv/Logger.hpp>
#include <array>
#include <cmath>
-#include <iostream>
namespace vkcv::meshlet
{
+ /*
+ * CACHE AND VALENCE
+ * SIZE AND SCORE CONSTANTS
+ * CHANGE AS NEEDED
+ */
+
// set these to adjust performance and result quality
const size_t VERTEX_CACHE_SIZE = 8;
const size_t CACHE_FUNCTION_LENGTH = 32;
@@ -26,6 +31,7 @@ namespace vkcv::meshlet
std::array<float, CACHE_SCORE_TABLE_SIZE> cachePositionScore = {};
std::array<float, VALENCE_SCORE_TABLE_SIZE> valenceScore = {};
+ // function to populate the cache position and valence score tables
void initScoreTables()
{
for(size_t i = 0; i < CACHE_SCORE_TABLE_SIZE; i++)
@@ -53,6 +59,13 @@ namespace vkcv::meshlet
}
}
+ /**
+ * Return the vertex' score, depending on its current active triangle count and cache position
+ * Add a valence boost to score, if active triangles are below VALENCE_SCORE_TABLE_SIZE
+ * @param numActiveTris the active triangles on this vertex
+ * @param cachePos the vertex' position in the cache
+ * @return vertex' score
+ */
float findVertexScore(uint32_t numActiveTris, int32_t cachePos)
{
if(numActiveTris == 0)
@@ -72,15 +85,8 @@ namespace vkcv::meshlet
std::vector<uint32_t> forsythReorder(const std::vector<uint32_t> &idxBuf, const size_t vertexCount)
{
initScoreTables();
- /**
- std::cout << "CACHE POSITION SCORES:" << std::endl;
- for(const auto element : cachePositionScore)
- std::cout << element << std::endl;
-
- std::cout << "VALENCE SCORES:" << std::endl;
- for(const auto element : valenceScore)
- std::cout << element << std::endl;
- **/
+
+ // get the total triangle count from the index buffer
const size_t triangleCount = idxBuf.size() / 3;
// per-vertex active triangle count
@@ -100,6 +106,20 @@ namespace vkcv::meshlet
// allocate remaining vectors
+ /**
+ * offsets: contains the vertices' offset into the triangleIndices vector
+ * Offset itself is the sum of triangles required by the previous vertices
+ *
+ * lastScore: the vertices' most recent calculated score
+ *
+ * cacheTag: the vertices' most recent cache score
+ *
+ * triangleAdded: boolean flags to denote whether a triangle has been processed or not
+ *
+ * triangleScore: total score of the three vertices making up the triangle
+ *
+ * triangleIndices: indices for the triangles
+ */
std::vector<uint32_t> offsets(vertexCount, 0);
std::vector<float> lastScore(vertexCount, 0.0f);
std::vector<int8_t> cacheTag(vertexCount, -1);
@@ -110,8 +130,8 @@ namespace vkcv::meshlet
std::vector<int32_t> triangleIndices(idxBuf.size(), 0);
- // count the triangle array offset for each vertex, initialize the rest of the data.
- // ??????????????????????????
+ // sum the number of active triangles for all previous vertices
+ // null the number of active triangles afterwards for recalculation in second loop
uint32_t sum = 0;
for(size_t i = 0; i < vertexCount; i++)
{
@@ -119,9 +139,8 @@ namespace vkcv::meshlet
sum += numActiveTris[i];
numActiveTris[i] = 0;
}
-
- // fill the vertex data structures with indices to the triangles using each vertex
- // ??????????????????????????
+ // create the triangle indices, using the newly calculated offsets, and increment numActiveTris
+ // every vertex should be referenced by a triangle index now
for(size_t i = 0; i < triangleCount; i++)
{
for(size_t j = 0; j < 3; j++)
@@ -132,8 +151,7 @@ namespace vkcv::meshlet
}
}
- // init score for all vertices
- // ??????????????????????????
+ // calculate and initialize the triangle score, by summing the vertices' score
for (size_t i = 0; i < vertexCount; i++)
{
lastScore[i] = findVertexScore(numActiveTris[i], static_cast<int32_t>(cacheTag[i]));
@@ -144,7 +162,7 @@ namespace vkcv::meshlet
}
}
- // find best triangle
+ // find best triangle to start reordering with
int32_t bestTriangle = -1;
float bestScore = -1.0f;
for(size_t i = 0; i < triangleCount; i++)
@@ -160,7 +178,7 @@ namespace vkcv::meshlet
std::vector<int32_t> outTriangles(triangleCount, 0);
uint32_t outPos = 0;
- // init cache (with -1)
+ // initialize cache (with -1)
std::array<int32_t, VERTEX_CACHE_SIZE + 3> cache = {};
for(auto &element : cache)
{
@@ -169,33 +187,42 @@ namespace vkcv::meshlet
uint32_t scanPos = 0;
+ // begin reordering routine
+ // output the currently best triangle, as long as there are triangles left to output
while(bestTriangle >= 0)
{
- // mark triangle as added
+ // mark best triangle as added
triangleAdded[bestTriangle] = true;
- // output triangle
+ // output this triangle
outTriangles[outPos++] = bestTriangle;
+ // push best triangle's vertices into the cache
for(size_t i = 0; i < 3; i++)
{
uint32_t v = idxBuf[3 * bestTriangle + i];
+ // get vertex' cache position, if its -1, set its position to the end
int8_t endPos = cacheTag[v];
if(endPos < 0)
endPos = static_cast<int8_t>(VERTEX_CACHE_SIZE + i);
+ // shift vertices' cache entries forward by one
for(int8_t j = endPos; j > i; j--)
{
cache[j] = cache[j - 1];
+ // if cache slot is valid vertex,
+ // update the vertex cache tag accordingly
if (cache[j] >= 0)
cacheTag[cache[j]]++;
}
+ // insert current vertex into its new target slot
cache[i] = static_cast<int32_t>(v);
cacheTag[v] = static_cast<int8_t>(i);
-
+ // find current triangle in the list of active triangles
+ // remove it by moving the last triangle into the slot the current triangle is holding.
for (size_t j = 0; j < numActiveTris[v]; j++)
{
if(triangleIndices[offsets[v] + j] == bestTriangle)
@@ -204,6 +231,7 @@ namespace vkcv::meshlet
break;
}
}
+ // shorten the list
numActiveTris[v]--;
}
@@ -214,6 +242,7 @@ namespace vkcv::meshlet
if (v < 0)
break;
+ // this vertex has been pushed outside of the actual cache
if(i >= VERTEX_CACHE_SIZE)
{
cacheTag[v] = -1;