Fix #122856: Sculpt trim and filter tools do not show brush cursor

This commit adds a new poll function specifically for determining if the
sculpt cursor should be drawn. This function whitelists a hardcoded set
of non-brush operators to display the cursor for.

In testing, this extra check has negligable performance impact. On
average it takes 0.012ms per execution.

Pull Request: https://projects.blender.org/blender/blender/pulls/123570

source/blender/editors/sculpt_paint/sculpt.cc

@@ -70,6 +70,7 @@
 #include "DEG_depsgraph.hh"
 
 #include "WM_api.hh"
+#include "WM_toolsystem.hh"
 #include "WM_types.hh"
 
 #include "ED_gpencil_legacy.hh"
@@ -4303,6 +4304,51 @@ bool SCULPT_poll(bContext *C)
   return SCULPT_mode_poll(C) && blender::ed::sculpt_paint::paint_brush_tool_poll(C);
 }
 
+/**
+ * While most non-brush tools in sculpt mode do not use the brush cursor, the trim tools
+ * and the filter tools are expected to have the cursor visible so that some functionality is
+ * easier to visually estimate.
+ *
+ * See: #122856
+ */
+static bool is_brush_related_tool(bContext *C)
+{
+  Paint *paint = BKE_paint_get_active_from_context(C);
+  Object *ob = CTX_data_active_object(C);
+  ScrArea *area = CTX_wm_area(C);
+  ARegion *region = CTX_wm_region(C);
+
+  if (paint && ob && BKE_paint_brush(paint) &&
+      (area && ELEM(area->spacetype, SPACE_VIEW3D, SPACE_IMAGE)) &&
+      (region && region->regiontype == RGN_TYPE_WINDOW))
+  {
+    bToolRef *tref = area->runtime.tool;
+    if (tref && tref->runtime && tref->runtime->keymap[0]) {
+      std::array<wmOperatorType *, 7> trim_operators = {
+          WM_operatortype_find("SCULPT_OT_trim_box_gesture", false),
+          WM_operatortype_find("SCULPT_OT_trim_lasso_gesture", false),
+          WM_operatortype_find("SCULPT_OT_trim_line_gesture", false),
+          WM_operatortype_find("SCULPT_OT_trim_polyline_gesture", false),
+          WM_operatortype_find("SCULPT_OT_mesh_filter", false),
+          WM_operatortype_find("SCULPT_OT_cloth_filter", false),
+          WM_operatortype_find("SCULPT_OT_color_filter", false),
+      };
+
+      return std::any_of(trim_operators.begin(), trim_operators.end(), [tref](wmOperatorType *ot) {
+        PointerRNA ptr;
+        return WM_toolsystem_ref_properties_get_from_operator(tref, ot, &ptr);
+      });
+    }
+  }
+  return false;
+}
+
+bool SCULPT_brush_cursor_poll(bContext *C)
+{
+  using namespace blender::ed::sculpt_paint;
+  return SCULPT_mode_poll(C) && (paint_brush_tool_poll(C) || is_brush_related_tool(C));
+}
+
 static const char *sculpt_tool_name(const Sculpt &sd)
 {
   const Brush &brush = *BKE_paint_brush_for_read(&sd.paint);

source/blender/editors/sculpt_paint/sculpt_intern.hh

@@ -673,6 +673,11 @@ bool SCULPT_mode_poll_view3d(bContext *C);
  */
 bool SCULPT_poll(bContext *C);
 
+/**
+ * Determines whether or not the brush cursor should be shown in the viewport
+ */
+bool SCULPT_brush_cursor_poll(bContext *C);
+
 /**
  * Returns true if sculpt session can handle color attributes
  * (BKE_pbvh_type(*ss->pbvh) == PBVH_FACES).  If false an error

source/blender/editors/sculpt_paint/sculpt_ops.cc

@@ -371,7 +371,7 @@ void ED_object_sculptmode_enter_ex(Main &bmain,
   Paint *paint = BKE_paint_get_active_from_paintmode(&scene, PaintMode::Sculpt);
   BKE_paint_init(&bmain, &scene, PaintMode::Sculpt, PAINT_CURSOR_SCULPT);
 
-  ED_paint_cursor_start(paint, SCULPT_poll);
+  ED_paint_cursor_start(paint, SCULPT_brush_cursor_poll);
 
   /* Check dynamic-topology flag; re-enter dynamic-topology mode when changing modes,
    * As long as no data was added that is not supported. */