source/blender/editors/io/io_stl_ops.cc

@@ -33,6 +33,7 @@
 #  include "IO_stl.hh"
 #  include "io_stl_ops.hh"
 #  include "io_utils.hh"
+#  include <intern/unit_type.cc>
 
 static int wm_stl_export_invoke(bContext *C, wmOperator *op, const wmEvent * /*event*/)
 {
@@ -52,6 +53,7 @@ static int wm_stl_export_execute(bContext *C, wmOperator *op)
   RNA_string_get(op->ptr, "filepath", export_params.filepath);
   export_params.forward_axis = eIOAxis(RNA_enum_get(op->ptr, "forward_axis"));
   export_params.up_axis = eIOAxis(RNA_enum_get(op->ptr, "up_axis"));
+  export_params.file_unit_type = UnitType(RNA_enum_get(op->ptr, "file_unit_type"));
   export_params.global_scale = RNA_float_get(op->ptr, "global_scale");
   export_params.apply_modifiers = RNA_boolean_get(op->ptr, "apply_modifiers");
   export_params.export_selected_objects = RNA_boolean_get(op->ptr, "export_selected_objects");
@@ -91,8 +93,20 @@ static void wm_stl_export_draw(bContext *C, wmOperator *op)
           sub, ptr, "export_selected_objects", UI_ITEM_NONE, IFACE_("Selection Only"), ICON_NONE);
     }
 
-    uiItemR(sub, ptr, "global_scale", UI_ITEM_NONE, IFACE_("Scale"), ICON_NONE);
-    uiItemR(sub, ptr, "use_scene_unit", UI_ITEM_NONE, IFACE_("Scene Unit"), ICON_NONE);
+    uiItemR(sub, ptr, "file_unit_type", UI_ITEM_NONE, IFACE_("File Unit"), ICON_NONE);
+    /* The scale input field should only be enabled, if unit type is set to CUSTOM */
+    uiLayout *subScale = uiLayoutColumn(sub, true);
+    PropertyRNA *prop = RNA_struct_find_property(ptr, "file_unit_type");
+    int selected_file_unit_type = RNA_property_enum_get(ptr, prop);
+    if (selected_file_unit_type == IO_UNIT_TYPE_CUSTOM) {
+      uiLayoutSetEnabled(subScale, true);
+    }
+    else {
+      uiLayoutSetEnabled(subScale, false);
+    }
+    uiItemR(subScale, ptr, "global_scale", UI_ITEM_NONE, IFACE_("Scale"), ICON_NONE);
+    uiItemR(subScale, ptr, "use_scene_unit", UI_ITEM_NONE, IFACE_("Scene Unit"), ICON_NONE);
+
     uiItemR(sub, ptr, "forward_axis", UI_ITEM_NONE, IFACE_("Forward"), ICON_NONE);
     uiItemR(sub, ptr, "up_axis", UI_ITEM_NONE, IFACE_("Up"), ICON_NONE);
   }
@@ -169,7 +183,26 @@ void WM_OT_stl_export(wmOperatorType *ot)
                         "Export only objects from this collection (and its children)");
   RNA_def_property_flag(prop, PROP_HIDDEN);
 
-  RNA_def_float(ot->srna, "global_scale", 1.0f, 1e-6f, 1e6f, "Scale", "", 0.001f, 1000.0f);
+  prop = RNA_def_enum(
+      ot->srna,
+      "file_unit_type",
+      io_unit_type,
+      IO_UNIT_TYPE_METER,
+      "File Unit",
+      "Unit used for the output file as STL is a unitless file format. Usually "
+      "millimieters is assumed by most programs, however blender uses meters.\nThe choice depends "
+      "on the modelling scale, e.g. for 1m in blender to be perceived as 1m (equal to 1000mm) by "
+      "most other applications, set this option to 'Millimeters'");
+  RNA_def_property_update_runtime(prop, io_ui_unit_type_export_update);
+  RNA_def_float(ot->srna,
+                "global_scale",
+                1.0f,
+                1e-6f,
+                1e6f,
+                "Scale",
+                "Scale value used when 'File Unit' is set to 'CUSTOM'",
+                0.001f,
+                1000.0f);
   RNA_def_boolean(ot->srna,
                   "use_scene_unit",
                   false,
@@ -242,8 +275,21 @@ static void ui_stl_import_settings(const bContext *C, uiLayout *layout, PointerR
 
   if (uiLayout *panel = uiLayoutPanel(C, layout, "STL_import_general", false, IFACE_("General"))) {
     uiLayout *col = uiLayoutColumn(panel, false);
-    uiItemR(col, ptr, "global_scale", UI_ITEM_NONE, nullptr, ICON_NONE);
-    uiItemR(col, ptr, "use_scene_unit", UI_ITEM_NONE, nullptr, ICON_NONE);
+
+    uiItemR(col, ptr, "file_unit_type", UI_ITEM_NONE, IFACE_("File Unit"), ICON_NONE);
+    /* The scale input field should only be enabled, if unit type is set to CUSTOM */
+    uiLayout *subScale = uiLayoutColumn(col, true);
+    PropertyRNA *prop = RNA_struct_find_property(ptr, "file_unit_type");
+    int selected_file_unit_type = RNA_property_enum_get(ptr, prop);
+    if (selected_file_unit_type == IO_UNIT_TYPE_CUSTOM) {
+      uiLayoutSetEnabled(subScale, true);
+    }
+    else {
+      uiLayoutSetEnabled(subScale, false);
+    }
+    uiItemR(subScale, ptr, "global_scale", UI_ITEM_NONE, IFACE_("Scale"), ICON_NONE);
+    uiItemR(subScale, ptr, "use_scene_unit", UI_ITEM_NONE, IFACE_("Scene Unit"), ICON_NONE);
+
     uiItemR(col, ptr, "forward_axis", UI_ITEM_NONE, IFACE_("Forward Axis"), ICON_NONE);
     uiItemR(col, ptr, "up_axis", UI_ITEM_NONE, nullptr, ICON_NONE);
   }
@@ -284,7 +330,23 @@ void WM_OT_stl_import(wmOperatorType *ot)
                                  FILE_DEFAULTDISPLAY,
                                  FILE_SORT_DEFAULT);
 
-  RNA_def_float(ot->srna, "global_scale", 1.0f, 1e-6f, 1e6f, "Scale", "", 0.001f, 1000.0f);
+  prop = RNA_def_enum(ot->srna,
+                      "file_unit_type",
+                      io_unit_type,
+                      IO_UNIT_TYPE_METER,
+                      "File Unit",
+                      "Unit used in the input file as STL is a unitless file format. Usually "
+                      "millimieters is assumed by most programs, however blender uses meters");
+  RNA_def_property_update_runtime(prop, io_ui_unit_type_import_update);
+  RNA_def_float(ot->srna,
+                "global_scale",
+                1.0f,
+                1e-6f,
+                1e6f,
+                "Scale",
+                "Scale value used when 'File Unit' is set to 'CUSTOM'",
+                0.001f,
+                1000.0f);
   RNA_def_boolean(ot->srna,
                   "use_scene_unit",
                   false,

source/blender/io/common/CMakeLists.txt

@@ -19,6 +19,7 @@ set(SRC
   intern/orientation.cc
   intern/path_util.cc
   intern/subdiv_disabler.cc
+  intern/unit_type.cc
 
   IO_abstract_hierarchy_iterator.h
   IO_dupli_persistent_id.hh
@@ -27,6 +28,7 @@ set(SRC
   IO_path_util_types.hh
   IO_subdiv_disabler.hh
   IO_types.hh
+  IO_unit_type.hh
   intern/dupli_parent_finder.hh
 )
 

source/blender/io/common/IO_unit_type.hh

@@ -0,0 +1,35 @@
+/* SPDX-FileCopyrightText: 2024 Blender Authors
+ *
+ * SPDX-License-Identifier: GPL-2.0-or-later */
+
+#pragma once
+
+struct EnumPropertyItem;
+struct Main;
+struct PointerRNA;
+struct Scene;
+
+enum UnitType {
+  IO_UNIT_TYPE_METER = 0,
+  IO_UNIT_TYPE_DECIMETER = 1,
+  IO_UNIT_TYPE_CENTIMETER = 2,
+  IO_UNIT_TYPE_MILLIMIETER = 3,
+  IO_UNIT_TYPE_INCH = 4,
+  IO_UNIT_TYPE_SCENE_LENGTH = 5,
+  IO_UNIT_TYPE_CUSTOM = 6
+};
+
+typedef struct {
+  UnitType unit_type;
+  float factor;
+} UnitFactor;
+
+const UnitFactor io_units_factor[] = {{IO_UNIT_TYPE_METER, 1.0},
+                                      {IO_UNIT_TYPE_DECIMETER, 0.1},
+                                      {IO_UNIT_TYPE_CENTIMETER, 0.01},
+                                      {IO_UNIT_TYPE_MILLIMIETER, 0.0010},
+                                      {IO_UNIT_TYPE_INCH, 0.0254}};
+
+float get_scene_unit_scale_factor(bool asExport, Scene *scene);
+void io_ui_unit_type_import_update(Main *main, Scene *scene, PointerRNA *ptr);
+void io_ui_unit_type_export_update(Main *main, Scene *scene, PointerRNA *ptr);

source/blender/io/common/intern/unit_type.cc

@@ -0,0 +1,111 @@
+/* SPDX-FileCopyrightText: 2024 Blender Authors
+ *
+ * SPDX-License-Identifier: GPL-2.0-or-later */
+
+#include "BKE_main.hh"
+#include "DNA_scene_types.h"
+#include "RNA_access.hh"
+#include "RNA_types.hh"
+
+#include "IO_unit_type.hh"
+
+const EnumPropertyItem io_unit_type[] = {
+    {IO_UNIT_TYPE_METER,
+     "Meter",
+     0,
+     "Meter",
+     "Meter is used by blender and thus will persist the blender scale"},
+    {IO_UNIT_TYPE_DECIMETER, "Decimeter", 0, "Decimeter", ""},
+    {IO_UNIT_TYPE_CENTIMETER, "Centimeter", 0, "Centimeter", ""},
+    {IO_UNIT_TYPE_MILLIMIETER, "Millimeter", 0, "Millimeter", ""},
+    {IO_UNIT_TYPE_INCH, "Inch", 0, "Inch", ""},
+    {IO_UNIT_TYPE_SCENE_LENGTH,
+     "Scene Unit Length",
+     0,
+     "Scene Unit Length",
+     "Use the scene unit, as defined in the scene settings by taking scene scale and scene unit "
+     "length into account."},
+    {IO_UNIT_TYPE_CUSTOM, "CUSTOM", 0, "CUSTOM", "Use the scale factor provided below"},
+    {0, nullptr, 0, nullptr, nullptr}};
+
+static float lookup_factor_meter_to_scene_unit(Scene *scene)
+{
+  /* Returns the factor used to convert the scene unit length to meter. */
+
+  char scene_unit = scene->unit.length_unit;
+  if (scene->unit.system == USER_UNIT_METRIC) {
+    switch (scene_unit) {
+      case '\0':  // kilometer
+        return 1000.0;
+      case '\x3':  // meter
+        return 1.0;
+      case '\x5':  // centimeter
+        return 0.01;
+      case '\x6':  // millimeter
+        return 0.001;
+      case '\a':  // micrometer
+        return 1e-6;
+    }
+  }
+  else if (scene->unit.system == USER_UNIT_IMPERIAL) {
+    switch (scene_unit) {
+      case '\x2':  // mile
+        return 1609.34;
+      case '\x4':  // feet
+        return 0.3047992424196;
+      case '\x5':  // inch
+        return 0.025399936868299999304;
+      case '\x6':  // thou
+        return 2.54e-5;
+    }
+  }
+  return 1.0;
+}
+
+float get_scene_unit_scale_factor(bool as_export, Scene *scene)
+{
+  /* Returns the scale factor needed to convert from the set scene unit to meters. */
+  float scene_unit_scale = scene->unit.scale_length;
+  scene_unit_scale = lookup_factor_meter_to_scene_unit(scene) / scene_unit_scale;
+  return as_export ? (1.0 / scene_unit_scale) : (scene_unit_scale);
+}
+
+static void calculate_io_scale_factor(bool as_export, Scene *scene, PointerRNA *ptr)
+{
+  /* Calulates the scale factor for io depending on file unit selection, scene unit type and scale.
+   */
+
+  int unit = RNA_enum_get(ptr, "file_unit_type");
+
+  if (unit == IO_UNIT_TYPE_CUSTOM) {
+    return;
+  }
+
+  // determine the io scale factor
+  float scale_factor = 1.0;
+  if (unit == IO_UNIT_TYPE_SCENE_LENGTH) {
+    // using scene unit
+    scale_factor = get_scene_unit_scale_factor(as_export, scene);
+  }
+  else {
+    // using file unit
+    scale_factor = as_export ? (scale_factor / io_units_factor[unit].factor) :
+                               (scale_factor * io_units_factor[unit].factor);
+  }
+
+  RNA_float_set(ptr, "global_scale", scale_factor);
+}
+
+void io_ui_unit_type_export_update(Main * /*main*/, Scene *scene, PointerRNA *ptr)
+{
+  /* Set the selected scale factor value to scale input field. */
+
+  calculate_io_scale_factor(true, scene, ptr);
+}
+
+void io_ui_unit_type_import_update(Main * /*main*/, Scene *scene, PointerRNA *ptr)
+{
+  /* Set the selected scale factor value to scale input field. */
+
+  calculate_io_scale_factor(false, scene, ptr);
+}

source/blender/io/stl/IO_stl.hh

@@ -14,6 +14,8 @@
 
 #include "IO_orientation.hh"
 
+#include "IO_unit_type.hh"
+
 struct Mesh;
 struct bContext;
 struct ReportList;
@@ -37,6 +39,7 @@ struct STLExportParams {
   eIOAxis forward_axis;
   eIOAxis up_axis;
   float global_scale;
+  UnitType file_unit_type;
   bool export_selected_objects;
   bool use_scene_unit;
   bool apply_modifiers;