From 0acd86abcac0af783662819cfeca2c15f892d4c6 Mon Sep 17 00:00:00 2001
From: Sean Kim <SeanCTKim@protonmail.com>
Date: Wed, 19 Feb 2025 22:07:34 +0100
Subject: [PATCH] Fix: Vertex Paint average brush produces incorrect results

This commit moves the initialization of the node-sized accumulation
array out of the parallel loop to avoid odd optimization errors when
differing between debug and release builds as well as errors due to
integer overflow in both builds.

Additionally it only accumulates results from affected nodes.

Pull Request: https://projects.blender.org/blender/blender/pulls/134720
---
 source/blender/editors/sculpt_paint/paint_vertex.cc | 10 ++++------
 1 file changed, 4 insertions(+), 6 deletions(-)

diff --git a/source/blender/editors/sculpt_paint/paint_vertex.cc b/source/blender/editors/sculpt_paint/paint_vertex.cc
index eaeb4121fe9..de23d04df0a 100644
--- a/source/blender/editors/sculpt_paint/paint_vertex.cc
+++ b/source/blender/editors/sculpt_paint/paint_vertex.cc
@@ -1567,12 +1567,10 @@ static void calculate_average_color(VPaintData &vpd,
     using Blend = typename Traits::BlendType;
     const Span<Color> colors = attribute.typed<T>().template cast<Color>();
 
-    Array<VPaintAverageAccum<Blend>> accum(nodes.size());
+    Array<VPaintAverageAccum<Blend>> accum(nodes.size(), {0, {0, 0, 0}});
     node_mask.foreach_index(GrainSize(1), [&](const int i) {
-      LocalData &tls = all_tls.local();
       VPaintAverageAccum<Blend> &accum2 = accum[i];
-      accum2.len = 0;
-      memset(accum2.value, 0, sizeof(accum2.value));
+      LocalData &tls = all_tls.local();
 
       const Span<int> verts = nodes[i].verts();
       tls.factors.resize(verts.size());
@@ -1620,12 +1618,12 @@ static void calculate_average_color(VPaintData &vpd,
     Blend accum_value[3] = {0};
     Color blend(0, 0, 0, 0);
 
-    for (int i = 0; i < nodes.size(); i++) {
+    node_mask.foreach_index([&](const int i) {
       accum_len += accum[i].len;
       accum_value[0] += accum[i].value[0];
       accum_value[1] += accum[i].value[1];
       accum_value[2] += accum[i].value[2];
-    }
+    });
     if (accum_len != 0) {
       blend.r = Traits::round(sqrtf(Traits::divide_round(accum_value[0], accum_len)));
       blend.g = Traits::round(sqrtf(Traits::divide_round(accum_value[1], accum_len)));