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.

4 files changed, 18 insertions, 20 deletions

diff --git a/source/blender/editors/transform/transform.c b/source/blender/editors/transform/transform.c
index b006b13d217..67b0d5c85ac 100644
--- a/source/blender/editors/transform/transform.c
+++ b/source/blender/editors/transform/transform.c
@@ -177,8 +177,8 @@ void convertViewVec(TransInfo *t, float r_vec[3], double dx, double dy)
       r_vec[1] = dy;
     }
     else {
-      const float mval_f[2] = {(float)dx, (float)dy};
-      ED_view3d_win_to_delta(t->region, mval_f, r_vec, t->zfac);
+      const float xy_delta[2] = {(float)dx, (float)dy};
+      ED_view3d_win_to_delta(t->region, xy_delta, t->zfac, r_vec);
     }
   }
   else if (t->spacetype == SPACE_IMAGE) {
diff --git a/source/blender/editors/transform/transform_constraints.c b/source/blender/editors/transform/transform_constraints.c
index 64ef170a13f..81b35e4539b 100644
--- a/source/blender/editors/transform/transform_constraints.c
+++ b/source/blender/editors/transform/transform_constraints.c
@@ -1041,8 +1041,7 @@ static void setNearestAxis3d(TransInfo *t)
    * and to overflow the short integers.
    * The formula used is a bit stupid, just a simplification of the subtraction
    * of two 2D points 30 pixels apart (that's the last factor in the formula) after
-   * projecting them with ED_view3d_win_to_delta and then get the length of that vector.
-   */
+   * projecting them with #ED_view3d_win_to_delta and then get the length of that vector. */
   zfac = mul_project_m4_v3_zfac(t->persmat, t->center_global);
   zfac = len_v3(t->persinv[0]) * 2.0f / t->region->winx * zfac * 30.0f;
 
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;
diff --git a/source/blender/editors/transform/transform_mode_vert_slide.c b/source/blender/editors/transform/transform_mode_vert_slide.c
index 0afc527d4a8..77c5707d814 100644
--- a/source/blender/editors/transform/transform_mode_vert_slide.c
+++ b/source/blender/editors/transform/transform_mode_vert_slide.c
@@ -146,9 +146,9 @@ static void calcVertSlideMouseActiveEdges(struct TransInfo *t, const int mval[2]
    * by finding the closest edge in local-space.
    * However this skews the outcome with non-uniform-scale. */
 
-  /* first get the direction of the original mouse position */
+  /* First get the direction of the original mouse position. */
   sub_v2_v2v2(dir, imval_fl, mval_fl);
-  ED_view3d_win_to_delta(t->region, dir, dir, t->zfac);
+  ED_view3d_win_to_delta(t->region, dir, t->zfac, dir);
   normalize_v3(dir);
 
   for (i = 0, sv = sld->sv; i < sld->totsv; i++, sv++) {
@@ -425,18 +425,18 @@ void drawVertSlide(TransInfo *t)
       /* direction from active vertex! */
       if ((t->mval[0] != t->mouse.imval[0]) || (t->mval[1] != t->mouse.imval[1])) {
         float zfac;
-        float mval_ofs[2];
+        float xy_delta[2];
         float co_orig_3d[3];
         float co_dest_3d[3];
 
-        mval_ofs[0] = t->mval[0] - t->mouse.imval[0];
-        mval_ofs[1] = t->mval[1] - t->mouse.imval[1];
+        xy_delta[0] = t->mval[0] - t->mouse.imval[0];
+        xy_delta[1] = t->mval[1] - t->mouse.imval[1];
 
         mul_v3_m4v3(
             co_orig_3d, TRANS_DATA_CONTAINER_FIRST_OK(t)->obedit->obmat, curr_sv->co_orig_3d);
-        zfac = ED_view3d_calc_zfac(t->region->regiondata, co_orig_3d, NULL);
+        zfac = ED_view3d_calc_zfac(t->region->regiondata, co_orig_3d);
 
-        ED_view3d_win_to_delta(t->region, mval_ofs, co_dest_3d, zfac);
+        ED_view3d_win_to_delta(t->region, xy_delta, zfac, co_dest_3d);
 
         invert_m4_m4(TRANS_DATA_CONTAINER_FIRST_OK(t)->obedit->imat,
                      TRANS_DATA_CONTAINER_FIRST_OK(t)->obedit->obmat);