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Mikktspace: Reduce number of data queries to caller 

The current code for computing tangents is not exactly fast.
This has been a long-standing issue, and recently came up again with T97378.

The main bottleneck is fetching the mesh data, since it's handled through a callback system and each vertex might have its data queried dozens of times.

I've tried a lot of things to optimize `mikktspace.c`, but unfortunately most weren't that useful:
- Vectorizing SVec3 gives a ~5% speedup, but I'm not sure if the additional ~70 lines of code are worth it
- Keeping an internal copy of the data instead of re-querying all the time helps a lot (~50-60% time reduction), but requires a lot of extra memory (~100 byte per face)
- Going C++ and replacing the internal quicksort with std::sort shows no difference
- Restructuring the entire file to be a header-only library so that the callbacks can be inlined gives ~10% reduction, but is a major change and deviation from the original library

In the end, two simple fixes that actually help remain:
- Don't re-query the number of faces in each loop iteration
- Don't bother looking for identical vertices if there's only one vertex with that hash

With this, time for the test case in T97378 goes from 6.64sec to 4.92sec. It's something I guess.

I feel like completely refactoring this library would not be a bad idea at some point, but for now it does the job...

Differential Revision: https://developer.blender.org/D14675
This commit is contained in:
Lukas Stockner 2022-04-17 20:27:57 +02:00
parent cfce5a32a7
commit c486da0238
Notes: blender-bot 2023-02-14 05:43:04 +01:00 
Referenced by issue #97591, Cycles HIP error with image textures on Linux and RDNA1
Referenced by issue #97595, Regression: GeoNode attribute output passing does not work in the latest nightly
Referenced by issue #97553, Regression: Sculpt Brushes not supported in Multiresolution and Dyntopo Mode
1 changed files with 21 additions and 17 deletions
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38
intern/mikktspace/mikktspace.c
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@ -565,23 +565,26 @@ static void GenerateSharedVerticesIndexList(int piTriList_in_and_out[],
break;
}
for (int i = blockstart; i < blockend; i++) {
int index1 = piTriList_in_and_out[indices[i]];
const SVec3 vP = GetPosition(pContext, index1);
const SVec3 vN = GetNormal(pContext, index1);
const SVec3 vT = GetTexCoord(pContext, index1);
for (int i2 = i + 1; i2 < blockend; i2++) {
int index2 = piTriList_in_and_out[indices[i2]];
if (index1 == index2)
continue;
/* If there's only one vertex with this hash, we don't have anything to compare. */
if (blockend > blockstart + 1) {
for (int i = blockstart; i < blockend; i++) {
int index1 = piTriList_in_and_out[indices[i]];
const SVec3 vP = GetPosition(pContext, index1);
const SVec3 vN = GetNormal(pContext, index1);
const SVec3 vT = GetTexCoord(pContext, index1);
for (int i2 = i + 1; i2 < blockend; i2++) {
int index2 = piTriList_in_and_out[indices[i2]];
if (index1 == index2)
continue;
if (veq(vP, GetPosition(pContext, index2)) && veq(vN, GetNormal(pContext, index2)) &&
veq(vT, GetTexCoord(pContext, index2))) {
piTriList_in_and_out[indices[i2]] = index1;
/* Once i2>i has been identified as a duplicate, we can stop since any
* i3>i2>i that is a duplicate of i (and therefore also i2) will also be
* compared to i2 and therefore be identified there anyways. */
break;
if (veq(vP, GetPosition(pContext, index2)) && veq(vN, GetNormal(pContext, index2)) &&
veq(vT, GetTexCoord(pContext, index2))) {
piTriList_in_and_out[indices[i2]] = index1;
/* Once i2>i has been identified as a duplicate, we can stop since any
* i3>i2>i that is a duplicate of i (and therefore also i2) will also be
* compared to i2 and therefore be identified there anyways. */
break;
}
}
}
}
@ -645,7 +648,8 @@ static int GenerateInitialVerticesIndexList(STriInfo pTriInfos[],
{
int iTSpacesOffs = 0, f = 0, t = 0;
int iDstTriIndex = 0;
for (f = 0; f < pContext->m_pInterface->m_getNumFaces(pContext); f++) {
const int iNrFaces = pContext->m_pInterface->m_getNumFaces(pContext);
for (f = 0; f < iNrFaces; f++) {
const int verts = pContext->m_pInterface->m_getNumVerticesOfFace(pContext, f);
if (verts != 3 && verts != 4)
continue;