Cleanup: ED_view3d_win_to_delta & ED_view3d_calc_zfac usage

- Rename ED_view3d_win_to_delta `mval` argument to `xy_delta` as it
  as it was misleading since this is an screen-space offset not a region
  relative cursor position (typical use of the name `mval`).
  Also rename the variable passed to this function which also used the
  term `mval` in many places.
- Re-order the output argument of ED_view3d_win_to_delta last.
  use an r_ prefix for return arguments.
- Document how the `zfac` argument is intended to be used.
- Split ED_view3d_calc_zfac into two functions as the `r_flip` argument
  was only used in some special cases.

1 files changed, 8 insertions, 9 deletions

diff --git a/source/blender/editors/transform/transform_generics.c b/source/blender/editors/transform/transform_generics.c
index 2b523461800..8987325145c 100644
--- a/source/blender/editors/transform/transform_generics.c
+++ b/source/blender/editors/transform/transform_generics.c
@@ -1146,7 +1146,7 @@ void calculateCenter(TransInfo *t)
 
         projectFloatView(t, axis, t->center2d);
 
-        /* rotate only needs correct 2d center, grab needs ED_view3d_calc_zfac() value */
+        /* Rotate only needs correct 2d center, grab needs #ED_view3d_calc_zfac() value. */
         if (t->mode == TFM_TRANSLATION) {
           copy_v3_v3(t->center_global, axis);
         }
@@ -1155,17 +1155,16 @@ void calculateCenter(TransInfo *t)
   }
 
   if (t->spacetype == SPACE_VIEW3D) {
-    /* ED_view3d_calc_zfac() defines a factor for perspective depth correction,
-     * used in ED_view3d_win_to_delta() */
+    /* #ED_view3d_calc_zfac() defines a factor for perspective depth correction,
+     * used in #ED_view3d_win_to_delta(). */
 
-    /* zfac is only used convertViewVec only in cases operator was invoked in RGN_TYPE_WINDOW
-     * and never used in other cases.
+    /* NOTE: `t->zfac` is only used #convertViewVec only in cases operator was invoked in
+     * #RGN_TYPE_WINDOW and never used in other cases.
      *
-     * We need special case here as well, since ED_view3d_calc_zfac will crash when called
-     * for a region different from RGN_TYPE_WINDOW.
-     */
+     * We need special case here as well, since #ED_view3d_calc_zfac will crash when called
+     * for a region different from #RGN_TYPE_WINDOW. */
     if (t->region->regiontype == RGN_TYPE_WINDOW) {
-      t->zfac = ED_view3d_calc_zfac(t->region->regiondata, t->center_global, NULL);
+      t->zfac = ED_view3d_calc_zfac(t->region->regiondata, t->center_global);
     }
     else {
       t->zfac = 0.0f;