From d4f5d4a6f60445bdfc67c4fe559bdf7136fa4863 Mon Sep 17 00:00:00 2001
From: Philipp Oeser <philipp@blender.org>
Date: Wed, 26 Jun 2024 15:38:26 +0200
Subject: [PATCH] Fix #123770: Vertex paint Accumulate option breaks Blur
 action

Accumulating allocates previous colors (which are used in
`do_vpaint_brush_blur_XXX`).

The actual problem here was that the  state of `brush_use_accumulate`
was not consistent across the lifetime of strokes.
Vertexpaint was doing the allocation in `vertex_paint_init_stroke`
(**before** `update_cache_invariants` where the mode gets changed to
`BRUSH_STROKE_SMOOTH` etc.), so here it still seemed we would use
accumulation, whereas later (after internally switching the tool/brush)
this was not the case anymore, leading to wrong behavior of
`do_vpaint_brush_blur_XXX`.

So now move the allocation to `init_session_data` (same as for
weightpaint) to make sure all codepaths have a consistent state of
`brush_use_accumulate`.

NOTE: this was made more obvious since 6de6d7267f3d added SHIFT-blurring
to the keymap

Pull Request: https://projects.blender.org/blender/blender/pulls/123778
---
 .../editors/sculpt_paint/paint_vertex.cc      | 37 +++++++++----------
 1 file changed, 18 insertions(+), 19 deletions(-)

diff --git a/source/blender/editors/sculpt_paint/paint_vertex.cc b/source/blender/editors/sculpt_paint/paint_vertex.cc
index db6e6dd4679..de3022114e9 100644
--- a/source/blender/editors/sculpt_paint/paint_vertex.cc
+++ b/source/blender/editors/sculpt_paint/paint_vertex.cc
@@ -273,6 +273,22 @@ void init_session_data(const ToolSettings &ts, Object &ob)
       }
     }
   }
+  else if (ob.mode == OB_MODE_VERTEX_PAINT) {
+    /* Allocate scratch array for previous colors if needed. */
+    SculptSession &ss = *ob.sculpt;
+    if (!vwpaint::brush_use_accumulate(*ts.vpaint)) {
+      if (ss.cache->prev_colors_vpaint.is_empty()) {
+        const Mesh *mesh = BKE_object_get_original_mesh(&ob);
+        const GVArray attribute = *mesh->attributes().lookup(mesh->active_color_attribute);
+        ss.cache->prev_colors_vpaint = GArray(attribute.type(), attribute.size());
+        attribute.type().value_initialize_n(ss.cache->prev_colors_vpaint.data(),
+                                            ss.cache->prev_colors_vpaint.size());
+      }
+    }
+    else {
+      ss.cache->prev_colors_vpaint = {};
+    }
+  }
 }
 
 Vector<PBVHNode *> pbvh_gather_generic(Object &ob, const VPaint &wp, const Brush &brush)
@@ -743,26 +759,9 @@ static void paint_and_tex_color_alpha_intern(const VPaint &vp,
   }
 }
 
-static void vertex_paint_init_stroke(Scene &scene, Depsgraph &depsgraph, Object &ob)
+static void vertex_paint_init_stroke(Depsgraph &depsgraph, Object &ob)
 {
   vwpaint::init_stroke(depsgraph, ob);
-
-  SculptSession &ss = *ob.sculpt;
-  ToolSettings &ts = *scene.toolsettings;
-
-  /* Allocate scratch array for previous colors if needed. */
-  if (!vwpaint::brush_use_accumulate(*ts.vpaint)) {
-    if (ss.cache->prev_colors_vpaint.is_empty()) {
-      const Mesh *mesh = BKE_object_get_original_mesh(&ob);
-      const GVArray attribute = *mesh->attributes().lookup(mesh->active_color_attribute);
-      ss.cache->prev_colors_vpaint = GArray(attribute.type(), attribute.size());
-      attribute.type().value_initialize_n(ss.cache->prev_colors_vpaint.data(),
-                                          ss.cache->prev_colors_vpaint.size());
-    }
-  }
-  else {
-    ss.cache->prev_colors_vpaint = {};
-  }
 }
 
 /** \} */
@@ -999,7 +998,7 @@ static bool vpaint_stroke_test_start(bContext *C, wmOperator *op, const float mo
   paint_stroke_set_mode_data(stroke, vpd);
 
   /* If not previously created, create vertex/weight paint mode session data */
-  vertex_paint_init_stroke(scene, depsgraph, ob);
+  vertex_paint_init_stroke(depsgraph, ob);
   vwpaint::update_cache_invariants(C, vp, ss, op, mouse);
   vwpaint::init_session_data(ts, ob);