From cdf564277c4d31d98dad78c0d7ad03603896cf4b Mon Sep 17 00:00:00 2001
From: Stefan Werner <stefan.werner@tangent-animation.com>
Date: Wed, 20 Jan 2021 11:17:32 +0100
Subject: [PATCH 1/2] Particles: Fixed thread work size calculation.

Dividing the workload by number of tasks in float is imprecise and
lead in some cases to particles not being calculated at all
(example: 20000 particles, 144 tasks).

Switching this calculation to integer makes sure we don't lose count.

Differential Revision: https://developer.blender.org/D10157
---
 .../blenkernel/intern/particle_system.c       | 20 +++++++++++--------
 1 file changed, 12 insertions(+), 8 deletions(-)

diff --git a/source/blender/blenkernel/intern/particle_system.c b/source/blender/blenkernel/intern/particle_system.c
index ad98079bc27..55d4043f96c 100644
--- a/source/blender/blenkernel/intern/particle_system.c
+++ b/source/blender/blenkernel/intern/particle_system.c
@@ -475,20 +475,24 @@ void psys_tasks_create(ParticleThreadContext *ctx,
 {
   ParticleTask *tasks;
   int numtasks = min_ii(BLI_system_thread_count() * 4, endpart - startpart);
-  float particles_per_task = numtasks > 0 ? (float)(endpart - startpart) / (float)numtasks : 0;
+  int particles_per_task = numtasks > 0 ? (endpart - startpart) / numtasks : 0;
+  int remainder = numtasks > 0 ? (endpart - startpart) - particles_per_task * numtasks : 0;
 
   tasks = MEM_callocN(sizeof(ParticleTask) * numtasks, "ParticleThread");
   *r_numtasks = numtasks;
   *r_tasks = tasks;
 
-  float pnext;
-  float p = (float)startpart;
-  for (int i = 0; i < numtasks; i++, p = pnext) {
-    pnext = p + particles_per_task;
-
+  int p = startpart;
+  for (int i = 0; i < numtasks; i++) {
     tasks[i].ctx = ctx;
-    tasks[i].begin = (int)p;
-    tasks[i].end = min_ii((int)pnext, endpart);
+    tasks[i].begin = p;
+    p = p + particles_per_task + (i < remainder ? 1 : 0);
+    tasks[i].end = p;
+  }
+
+  /* Verify that all particles are accounted for. */
+  if (numtasks > 0) {
+    BLI_assert(tasks[numtasks - 1].end == endpart);
   }
 }
 

From 0373d1b09fc9db2c237a507dc6ef649c5d2b8703 Mon Sep 17 00:00:00 2001
From: Antonio Vazquez <blendergit@gmail.com>
Date: Fri, 22 Jan 2021 11:25:32 +0100
Subject: [PATCH 2/2] GPencil: Fix unreported Vertex Paint masking error

The masking was not working as expected and allowed to paint non selected strokes.
---
 source/blender/editors/gpencil/gpencil_vertex_paint.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/source/blender/editors/gpencil/gpencil_vertex_paint.c b/source/blender/editors/gpencil/gpencil_vertex_paint.c
index 62ddfaab012..e2c81d53fba 100644
--- a/source/blender/editors/gpencil/gpencil_vertex_paint.c
+++ b/source/blender/editors/gpencil/gpencil_vertex_paint.c
@@ -845,6 +845,13 @@ static bool gpencil_vertexpaint_select_stroke(tGP_BrushVertexpaintData *gso,
 
   bool saved = false;
 
+  /* Check stroke masking. */
+  if (GPENCIL_ANY_VERTEX_MASK(gso->mask)) {
+    if ((gps->flag & GP_STROKE_SELECT) == 0) {
+      return false;
+    }
+  }
+
   /* Check if the stroke collide with brush. */
   if (!ED_gpencil_stroke_check_collision(gsc, gps, gso->mval, radius, diff_mat)) {
     return false;