Fix unit scale use when when units were disabled

UnitSettings::scale_length was used to scale reported
values for operators (translate, shrink-fatten, voxel-size).

This isn't expected as the value isn't editable when the unit-system
is set to None.

Add BKE_unit_value_as_string_scaled utility function for clarity &
to ensure scaling is only applied when it should be.

source/blender/blenkernel/BKE_unit.hh

@@ -37,6 +37,17 @@ size_t BKE_unit_value_as_string(char *str,
                                 const UnitSettings *settings,
                                 bool pad);
 
+/**
+ * A version of #BKE_unit_value_as_string with the `value` scaled by #BKE_unit_value_scale.
+ */
+size_t BKE_unit_value_as_string_scaled(char *str,
+                                       int str_maxncpy,
+                                       double value,
+                                       int prec,
+                                       int type,
+                                       const UnitSettings *settings,
+                                       bool pad);
+
 /**
  * Replace units with values, used before python button evaluation.
  *

source/blender/blenkernel/intern/unit.cc

@@ -1886,6 +1886,18 @@ size_t BKE_unit_value_as_string(char *str,
   return unit_as_string_main(str, str_maxncpy, value, prec, type, do_split, pad, units);
 }
 
+size_t BKE_unit_value_as_string_scaled(char *str,
+                                       int str_maxncpy,
+                                       double value,
+                                       int prec,
+                                       int type,
+                                       const UnitSettings *settings,
+                                       bool pad)
+{
+  return BKE_unit_value_as_string(
+      str, str_maxncpy, BKE_unit_value_scale(settings, type, value), prec, type, settings, pad);
+}
+
 double BKE_unit_value_scale(const UnitSettings *unit, const int unit_type, double value)
 {
   if (unit->system == USER_UNIT_NONE) {

source/blender/draw/intern/draw_manager_text.cc

@@ -362,15 +362,10 @@ void DRW_text_edit_mesh_measure_stats(const ARegion *region,
             v2 = ob->object_to_world().view<3, 3>() * v2;
           }
 
-          const size_t numstr_len = unit->system ?
+          const size_t numstr_len =
-                                        BKE_unit_value_as_string(numstr,
+              unit->system ?
-                                                                 sizeof(numstr),
+                  BKE_unit_value_as_string_scaled(
-                                                                 len_v3v3(v1, v2) *
+                      numstr, sizeof(numstr), len_v3v3(v1, v2), 3, B_UNIT_LENGTH, unit, false) :
-                                                                     unit->scale_length,
-                                                                 3,
-                                                                 B_UNIT_LENGTH,
-                                                                 unit,
-                                                                 false) :
                   SNPRINTF_RLEN(numstr, conv_float, len_v3v3(v1, v2));
 
           DRW_text_cache_add(dt, co, numstr, numstr_len, 0, edge_tex_sep, txt_flag, col);
@@ -502,15 +497,9 @@ void DRW_text_edit_mesh_measure_stats(const ARegion *region,
         vmid *= 1.0f / float(n);
         vmid = blender::math::transform_point(ob->object_to_world(), vmid);
 
-        const size_t numstr_len = unit->system ?
+        const size_t numstr_len =
-                                      BKE_unit_value_as_string(
+            unit->system ? BKE_unit_value_as_string_scaled(
-                                          numstr,
+                               numstr, sizeof(numstr), area, 3, B_UNIT_AREA, unit, false) :
-                                          sizeof(numstr),
-                                          double(area * unit->scale_length * unit->scale_length),
-                                          3,
-                                          B_UNIT_AREA,
-                                          unit,
-                                          false) :
                            SNPRINTF_RLEN(numstr, conv_float, area);
 
         DRW_text_cache_add(dt, vmid, numstr, numstr_len, 0, 0, txt_flag, col);

source/blender/editors/mesh/editmesh_bevel.cc

@@ -133,13 +133,8 @@ static void edbm_bevel_update_status_text(bContext *C, wmOperator *op)
   }
   else {
     double offset_val = double(RNA_float_get(op->ptr, "offset"));
-    BKE_unit_value_as_string(offset_str,
+    BKE_unit_value_as_string_scaled(
-                             NUM_STR_REP_LEN,
+        offset_str, NUM_STR_REP_LEN, offset_val, 3, B_UNIT_LENGTH, &sce->unit, true);
-                             offset_val * sce->unit.scale_length,
-                             3,
-                             B_UNIT_LENGTH,
-                             &sce->unit,
-                             true);
   }
 
   PropertyRNA *prop;

source/blender/editors/mesh/editmesh_knife.cc

@@ -514,13 +514,8 @@ static void knifetool_draw_visible_distances(const KnifeTool_OpData *kcd)
     SNPRINTF(numstr, "%.*f", distance_precision, cut_len);
   }
   else {
-    BKE_unit_value_as_string(numstr,
+    BKE_unit_value_as_string_scaled(
-                             sizeof(numstr),
+        numstr, sizeof(numstr), cut_len, distance_precision, B_UNIT_LENGTH, unit, false);
-                             double(cut_len * unit->scale_length),
-                             distance_precision,
-                             B_UNIT_LENGTH,
-                             unit,
-                             false);
   }
 
   BLF_enable(blf_mono_font, BLF_ROTATION);

source/blender/editors/object/object_remesh.cc

@@ -320,13 +320,8 @@ static void voxel_size_edit_draw(const bContext *C, ARegion * /*region*/, void *
   short strdrawlen = 0;
   Scene *scene = CTX_data_scene(C);
   const UnitSettings *unit = &scene->unit;
-  BKE_unit_value_as_string(str,
+
-                           VOXEL_SIZE_EDIT_MAX_STR_LEN,
+  BKE_unit_value_as_string_scaled(str, sizeof(str), cd->voxel_size, -3, B_UNIT_LENGTH, unit, true);
-                           double(cd->voxel_size * unit->scale_length),
-                           -3,
-                           B_UNIT_LENGTH,
-                           unit,
-                           true);
   strdrawlen = BLI_strlen_utf8(str);
 
   immUnbindProgram();

source/blender/editors/space_view3d/view3d_gizmo_ruler.cc

@@ -215,13 +215,7 @@ static void ruler_item_as_string(
       BLI_snprintf(numstr, numstr_size, "%.*f", prec, ruler_len);
     }
     else {
-      BKE_unit_value_as_string(numstr,
+      BKE_unit_value_as_string(numstr, numstr_size, ruler_len, prec, B_UNIT_LENGTH, unit, false);
-                               numstr_size,
-                               double(ruler_len * unit->scale_length),
-                               prec,
-                               B_UNIT_LENGTH,
-                               unit,
-                               false);
     }
   }
 }

source/blender/editors/transform/transform_mode_shrink_fatten.cc

@@ -114,10 +114,10 @@ static void applyShrinkFatten(TransInfo *t)
   }
   else {
     /* Default header print. */
-    if (unit != nullptr) {
+    if (unit->system != USER_UNIT_NONE) {
       char unit_str[64];
-      BKE_unit_value_as_string(
+      BKE_unit_value_as_string_scaled(
-          unit_str, sizeof(unit_str), distance * unit->scale_length, 4, B_UNIT_LENGTH, unit, true);
+          unit_str, sizeof(unit_str), distance, 4, B_UNIT_LENGTH, unit, true);
       fmt::format_to(fmt::appender(str), "{}", unit_str);
     }
     else {

source/blender/editors/transform/transform_mode_translate.cc

@@ -187,9 +187,8 @@ static void translate_dist_to_str(char *r_str,
                                   const float val,
                                   const UnitSettings *unit)
 {
-  if (unit) {
+  if (unit && (unit->system != USER_UNIT_NONE)) {
-    BKE_unit_value_as_string(
+    BKE_unit_value_as_string_scaled(r_str, r_str_maxncpy, val, 4, B_UNIT_LENGTH, unit, false);
-        r_str, r_str_maxncpy, val * unit->scale_length, 4, B_UNIT_LENGTH, unit, false);
   }
   else {
     /* Check range to prevent string buffer overflow. */

source/blender/makesdna/DNA_scene_types.h

@@ -1801,7 +1801,13 @@ typedef struct ToolSettings {
 /** Display/Editing unit options for each scene. */
 typedef struct UnitSettings {
 
-  /** Maybe have other unit conversions? */
+  /* Maybe have other unit conversions? */
+  /**
+   * Spatial scale.
+   * - This must not be used when `system == USER_UNIT_NONE`.
+   * - Typically the scale should be applied using #BKE_unit_value_scale
+   *   which supports different kinds of users and checks a none unit system.
+   */
   float scale_length;
   /** Imperial, metric etc. */
   char system;