Transform: Remove current 'Snap Base' in 'Set Snap Base' mode

The current `Snap Base` was available and displayed to allow snapping
to `Edge Perpendicular`.

However, the usefulness of perpendicular snapping in `Set Snap Base`
mode is questionable and can sometimes cause inconvenience.

Also, removing the current `Snap Base` indicator (the `X` drawing)
makes the intention of the operation more apparent.

Therefore, this commit removes both the indicator and the effect of the
current `Snap Base` in `Set Snap Base` mode.

Pull Request: https://projects.blender.org/blender/blender/pulls/108776

source/blender/editors/transform/transform.c

@@ -581,7 +581,7 @@ static bool transform_modal_item_poll(const wmOperator *op, int value)
         return false;
       }
       if (value == TFM_MODAL_ADD_SNAP) {
-        if (!validSnap(t)) {
+        if (!(t->tsnap.status & SNAP_TARGET_FOUND)) {
           return false;
         }
       }

source/blender/editors/transform/transform.h

@@ -143,6 +143,8 @@ typedef enum {
 
   /** Do not display Xform gizmo even though it is available. */
   T_NO_GIZMO = 1 << 24,
+
+  T_DRAW_SNAP_SOURCE = 1 << 25,
 } eTFlag;
 ENUM_OPERATORS(eTFlag, T_NO_GIZMO);
 

source/blender/editors/transform/transform_mode_snapsource.c

@@ -61,12 +61,9 @@ static void snapsource_end(TransInfo *t)
   t->mouse.post = customdata->mouse_prev.post;
   t->mouse.use_virtual_mval = customdata->mouse_prev.use_virtual_mval;
 
-  transform_gizmo_3d_model_from_constraint_and_mode_set(t);
-
   MEM_freeN(customdata);
 
-  t->tsnap.snap_source_fn = NULL;
-
+  transform_gizmo_3d_model_from_constraint_and_mode_set(t);
   tranform_snap_source_restore_context(t);
 }
 
@@ -74,6 +71,9 @@ static void snapsource_confirm(TransInfo *t)
 {
   BLI_assert(t->modifiers & MOD_EDIT_SNAP_SOURCE);
   getSnapPoint(t, t->tsnap.snap_source);
+  t->tsnap.snap_source_fn = NULL;
+  t->tsnap.status |= SNAP_SOURCE_FOUND;
+  t->flag |= T_DRAW_SNAP_SOURCE;
 
   int mval[2];
 #ifndef RESET_TRANSFORMATION
@@ -180,23 +180,12 @@ void transform_mode_snap_source_init(TransInfo *t, wmOperator *UNUSED(op))
 
   t->mode_info = &TransMode_snapsource;
   t->tsnap.target_operation = SCE_SNAP_TARGET_ALL;
-
-  if ((t->tsnap.status & SNAP_SOURCE_FOUND) == 0) {
-    if (t->tsnap.snap_source_fn) {
-      /* Calculate the current snap source for perpendicular snap. */
-      t->tsnap.snap_source_fn(t);
-    }
-    if ((t->tsnap.status & SNAP_SOURCE_FOUND) == 0) {
-      /* Fallback. */
-      copy_v3_v3(t->tsnap.snap_source, t->center_global);
-      t->tsnap.status |= SNAP_SOURCE_FOUND;
-    }
-  }
+  t->tsnap.status &= ~SNAP_SOURCE_FOUND;
 
   if ((t->tsnap.mode & ~(SCE_SNAP_MODE_INCREMENT | SCE_SNAP_MODE_GRID)) == 0) {
     /* Initialize snap modes for geometry. */
     t->tsnap.mode &= ~(SCE_SNAP_MODE_INCREMENT | SCE_SNAP_MODE_GRID);
-    t->tsnap.mode |= SCE_SNAP_MODE_GEOM & ~SCE_SNAP_MODE_FACE_NEAREST;
+    t->tsnap.mode |= SCE_SNAP_MODE_GEOM;
   }
 
   if (t->data_type == &TransConvertType_Mesh) {

source/blender/editors/transform/transform_snap.cc

@@ -174,12 +174,10 @@ void drawSnapping(const bContext *C, TransInfo *t)
     return;
   }
 
-  const bool draw_source = (t->spacetype == SPACE_VIEW3D) &&
-                           (t->tsnap.status & SNAP_SOURCE_FOUND) &&
-                           ((t->tsnap.mode & SCE_SNAP_MODE_EDGE_PERPENDICULAR) ||
-                            t->tsnap.snap_source_fn == nullptr);
+  const bool draw_source = (t->tsnap.status & SNAP_SOURCE_FOUND) && (t->flag & T_DRAW_SNAP_SOURCE);
+  const bool draw_target = (t->tsnap.status & (SNAP_TARGET_FOUND | SNAP_MULTI_POINTS));
 
-  if (!(draw_source || validSnap(t))) {
+  if (!(draw_source || draw_target)) {
     return;
   }
 
@@ -767,6 +765,10 @@ static void initSnappingMode(TransInfo *t)
     t->tsnap.mode &= ~(SCE_SNAP_MODE_FACE_RAYCAST | SCE_SNAP_MODE_FACE_NEAREST);
   }
 
+  if (t->tsnap.mode & SCE_SNAP_MODE_EDGE_PERPENDICULAR) {
+    t->flag |= T_DRAW_SNAP_SOURCE;
+  }
+
   setSnappingCallback(t);
 
   if (t->spacetype == SPACE_VIEW3D) {
@@ -1388,7 +1390,7 @@ eSnapMode snapObjectsTransform(
   snap_object_params.use_occlusion_test = true;
   snap_object_params.use_backface_culling = (t->tsnap.flag & SCE_SNAP_BACKFACE_CULLING) != 0;
 
-  float *target = (t->tsnap.status & SNAP_SOURCE_FOUND) ? t->tsnap.snap_source : t->center_global;
+  float *prev_co = (t->tsnap.status & SNAP_SOURCE_FOUND) ? t->tsnap.snap_source : nullptr;
   return ED_transform_snap_object_project_view3d(t->tsnap.object_context,
                                                  t->depsgraph,
                                                  t->region,
@@ -1397,7 +1399,7 @@ eSnapMode snapObjectsTransform(
                                                  &snap_object_params,
                                                  nullptr,
                                                  mval,
-                                                 target,
+                                                 prev_co,
                                                  dist_px,
                                                  r_loc,
                                                  r_no);

source/blender/editors/transform/transform_snap_object.cc

@@ -3294,8 +3294,10 @@ static eSnapMode transform_snap_context_project_view3d_mixed_impl(SnapObjectCont
     }
   }
 
-  if ((snap_to_flag & SCE_SNAP_MODE_FACE_NEAREST) && ELEM(nullptr, prev_co, init_co)) {
-    /* No location to work with #SCE_SNAP_MODE_FACE_NEAREST. */
+  if (prev_co == nullptr) {
+    snap_to_flag &= ~(SCE_SNAP_MODE_EDGE_PERPENDICULAR | SCE_SNAP_MODE_FACE_NEAREST);
+  }
+  else if (init_co == nullptr) {
     snap_to_flag &= ~SCE_SNAP_MODE_FACE_NEAREST;
   }