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.

6 files changed, 47 insertions, 42 deletions

diff --git a/source/blender/editors/space_view3d/view3d_edit.c b/source/blender/editors/space_view3d/view3d_edit.c
index d6bc7ded92e..5adce170e06 100644
--- a/source/blender/editors/space_view3d/view3d_edit.c
+++ b/source/blender/editors/space_view3d/view3d_edit.c
@@ -832,13 +832,13 @@ void ED_view3d_cursor3d_position(bContext *C,
     return;
   }
 
-  ED_view3d_calc_zfac(rv3d, cursor_co, &flip);
+  ED_view3d_calc_zfac_ex(rv3d, cursor_co, &flip);
 
   /* Reset the depth based on the view offset (we _know_ the offset is in front of us). */
   if (flip) {
     negate_v3_v3(cursor_co, rv3d->ofs);
     /* re initialize, no need to check flip again */
-    ED_view3d_calc_zfac(rv3d, cursor_co, NULL /* &flip */);
+    ED_view3d_calc_zfac(rv3d, cursor_co);
   }
 
   if (use_depth) { /* maybe this should be accessed some other way */
diff --git a/source/blender/editors/space_view3d/view3d_navigate.c b/source/blender/editors/space_view3d/view3d_navigate.c
index 21e0459f346..d1e7f6ffb12 100644
--- a/source/blender/editors/space_view3d/view3d_navigate.c
+++ b/source/blender/editors/space_view3d/view3d_navigate.c
@@ -396,7 +396,7 @@ ViewOpsData *viewops_data_create(bContext *C, const wmEvent *event, enum eViewOp
   {
     float tvec[3];
     negate_v3_v3(tvec, rv3d->ofs);
-    vod->init.zfac = ED_view3d_calc_zfac(rv3d, tvec, NULL);
+    vod->init.zfac = ED_view3d_calc_zfac(rv3d, tvec);
   }
 
   vod->reverse = 1.0f;
@@ -559,7 +559,7 @@ void viewmove_apply(ViewOpsData *vod, int x, int y)
   else {
     float dvec[3];
 
-    ED_view3d_win_to_delta(vod->region, event_ofs, dvec, vod->init.zfac);
+    ED_view3d_win_to_delta(vod->region, event_ofs, vod->init.zfac, dvec);
 
     sub_v3_v3(vod->rv3d->ofs, dvec);
 
diff --git a/source/blender/editors/space_view3d/view3d_navigate_ndof.c b/source/blender/editors/space_view3d/view3d_navigate_ndof.c
index 6b77f464773..1ce9bdcb211 100644
--- a/source/blender/editors/space_view3d/view3d_navigate_ndof.c
+++ b/source/blender/editors/space_view3d/view3d_navigate_ndof.c
@@ -48,7 +48,7 @@ static float view3d_ndof_pan_speed_calc_ex(RegionView3D *rv3d, const float depth
   float speed = rv3d->pixsize * NDOF_PIXELS_PER_SECOND;
 
   if (rv3d->is_persp) {
-    speed *= ED_view3d_calc_zfac(rv3d, depth_pt, NULL);
+    speed *= ED_view3d_calc_zfac(rv3d, depth_pt);
   }
 
   return speed;
diff --git a/source/blender/editors/space_view3d/view3d_navigate_zoom.c b/source/blender/editors/space_view3d/view3d_navigate_zoom.c
index 8eb8fffaa31..5f6f9fde324 100644
--- a/source/blender/editors/space_view3d/view3d_navigate_zoom.c
+++ b/source/blender/editors/space_view3d/view3d_navigate_zoom.c
@@ -125,18 +125,18 @@ static void view_zoom_to_window_xy_3d(ARegion *region, float dfac, const int zoo
     float dvec[3];
     float tvec[3];
     float tpos[3];
-    float mval_f[2];
+    float xy_delta[2];
 
     float zfac;
 
     negate_v3_v3(tpos, rv3d->ofs);
 
-    mval_f[0] = (float)(((zoom_xy[0] - region->winrct.xmin) * 2) - region->winx) / 2.0f;
-    mval_f[1] = (float)(((zoom_xy[1] - region->winrct.ymin) * 2) - region->winy) / 2.0f;
+    xy_delta[0] = (float)(((zoom_xy[0] - region->winrct.xmin) * 2) - region->winx) / 2.0f;
+    xy_delta[1] = (float)(((zoom_xy[1] - region->winrct.ymin) * 2) - region->winy) / 2.0f;
 
     /* Project cursor position into 3D space */
-    zfac = ED_view3d_calc_zfac(rv3d, tpos, NULL);
-    ED_view3d_win_to_delta(region, mval_f, dvec, zfac);
+    zfac = ED_view3d_calc_zfac(rv3d, tpos);
+    ED_view3d_win_to_delta(region, xy_delta, zfac, dvec);
 
     /* Calculate view target position for dolly */
     add_v3_v3v3(tvec, tpos, dvec);
diff --git a/source/blender/editors/space_view3d/view3d_navigate_zoom_border.c b/source/blender/editors/space_view3d/view3d_navigate_zoom_border.c
index 4e909151ce4..f834efe4a7b 100644
--- a/source/blender/editors/space_view3d/view3d_navigate_zoom_border.c
+++ b/source/blender/editors/space_view3d/view3d_navigate_zoom_border.c
@@ -125,7 +125,7 @@ static int view3d_zoom_border_exec(bContext *C, wmOperator *op)
       negate_v3_v3(new_ofs, p);
     }
     else {
-      float mval_f[2];
+      float xy_delta[2];
       float zfac;
 
       /* We can't use the depth, fallback to the old way that doesn't set the center depth */
@@ -134,12 +134,12 @@ static int view3d_zoom_border_exec(bContext *C, wmOperator *op)
       {
         float tvec[3];
         negate_v3_v3(tvec, new_ofs);
-        zfac = ED_view3d_calc_zfac(rv3d, tvec, NULL);
+        zfac = ED_view3d_calc_zfac(rv3d, tvec);
       }
 
-      mval_f[0] = (rect.xmin + rect.xmax - vb[0]) / 2.0f;
-      mval_f[1] = (rect.ymin + rect.ymax - vb[1]) / 2.0f;
-      ED_view3d_win_to_delta(region, mval_f, dvec, zfac);
+      xy_delta[0] = (rect.xmin + rect.xmax - vb[0]) / 2.0f;
+      xy_delta[1] = (rect.ymin + rect.ymax - vb[1]) / 2.0f;
+      ED_view3d_win_to_delta(region, xy_delta, zfac, dvec);
       /* center the view to the center of the rectangle */
       sub_v3_v3(new_ofs, dvec);
     }
diff --git a/source/blender/editors/space_view3d/view3d_project.c b/source/blender/editors/space_view3d/view3d_project.c
index 2cf9ac0a52e..85d239507ce 100644
--- a/source/blender/editors/space_view3d/view3d_project.c
+++ b/source/blender/editors/space_view3d/view3d_project.c
@@ -276,7 +276,7 @@ float ED_view3d_pixel_size_no_ui_scale(const RegionView3D *rv3d, const float co[
   return mul_project_m4_v3_zfac(rv3d->persmat, co) * rv3d->pixsize;
 }
 
-float ED_view3d_calc_zfac(const RegionView3D *rv3d, const float co[3], bool *r_flip)
+float ED_view3d_calc_zfac_ex(const RegionView3D *rv3d, const float co[3], bool *r_flip)
 {
   float zfac = mul_project_m4_v3_zfac(rv3d->persmat, co);
 
@@ -299,10 +299,15 @@ float ED_view3d_calc_zfac(const RegionView3D *rv3d, const float co[3], bool *r_f
   return zfac;
 }
 
+float ED_view3d_calc_zfac(const RegionView3D *rv3d, const float co[3])
+{
+  return ED_view3d_calc_zfac_ex(rv3d, co, NULL);
+}
+
 float ED_view3d_calc_depth_for_comparison(const RegionView3D *rv3d, const float co[3])
 {
   if (rv3d->is_persp) {
-    return ED_view3d_calc_zfac(rv3d, co, NULL);
+    return ED_view3d_calc_zfac(rv3d, co);
   }
   return -dot_v3v3(rv3d->viewinv[2], co);
 }
@@ -436,8 +441,8 @@ bool view3d_get_view_aligned_coordinate(ARegion *region,
 
   if (ret == V3D_PROJ_RET_OK) {
     const float mval_f[2] = {(float)(mval_cpy[0] - mval[0]), (float)(mval_cpy[1] - mval[1])};
-    const float zfac = ED_view3d_calc_zfac(rv3d, fp, NULL);
-    ED_view3d_win_to_delta(region, mval_f, dvec, zfac);
+    const float zfac = ED_view3d_calc_zfac(rv3d, fp);
+    ED_view3d_win_to_delta(region, mval_f, zfac, dvec);
     sub_v3_v3(fp, dvec);
 
     return true;
@@ -584,57 +589,57 @@ bool ED_view3d_win_to_3d_on_plane_with_fallback(const ARegion *region,
 }
 
 void ED_view3d_win_to_delta(const ARegion *region,
-                            const float mval[2],
-                            float out[3],
-                            const float zfac)
+                            const float xy_delta[2],
+                            const float zfac,
+                            float r_out[3])
 {
   RegionView3D *rv3d = region->regiondata;
   float dx, dy;
 
-  dx = 2.0f * mval[0] * zfac / region->winx;
-  dy = 2.0f * mval[1] * zfac / region->winy;
+  dx = 2.0f * xy_delta[0] * zfac / region->winx;
+  dy = 2.0f * xy_delta[1] * zfac / region->winy;
 
-  out[0] = (rv3d->persinv[0][0] * dx + rv3d->persinv[1][0] * dy);
-  out[1] = (rv3d->persinv[0][1] * dx + rv3d->persinv[1][1] * dy);
-  out[2] = (rv3d->persinv[0][2] * dx + rv3d->persinv[1][2] * dy);
+  r_out[0] = (rv3d->persinv[0][0] * dx + rv3d->persinv[1][0] * dy);
+  r_out[1] = (rv3d->persinv[0][1] * dx + rv3d->persinv[1][1] * dy);
+  r_out[2] = (rv3d->persinv[0][2] * dx + rv3d->persinv[1][2] * dy);
 }
 
-void ED_view3d_win_to_origin(const ARegion *region, const float mval[2], float out[3])
+void ED_view3d_win_to_origin(const ARegion *region, const float mval[2], float r_out[3])
 {
   RegionView3D *rv3d = region->regiondata;
   if (rv3d->is_persp) {
-    copy_v3_v3(out, rv3d->viewinv[3]);
+    copy_v3_v3(r_out, rv3d->viewinv[3]);
   }
   else {
-    out[0] = 2.0f * mval[0] / region->winx - 1.0f;
-    out[1] = 2.0f * mval[1] / region->winy - 1.0f;
+    r_out[0] = 2.0f * mval[0] / region->winx - 1.0f;
+    r_out[1] = 2.0f * mval[1] / region->winy - 1.0f;
 
     if (rv3d->persp == RV3D_CAMOB) {
-      out[2] = -1.0f;
+      r_out[2] = -1.0f;
     }
     else {
-      out[2] = 0.0f;
+      r_out[2] = 0.0f;
     }
 
-    mul_project_m4_v3(rv3d->persinv, out);
+    mul_project_m4_v3(rv3d->persinv, r_out);
   }
 }
 
-void ED_view3d_win_to_vector(const ARegion *region, const float mval[2], float out[3])
+void ED_view3d_win_to_vector(const ARegion *region, const float mval[2], float r_out[3])
 {
   RegionView3D *rv3d = region->regiondata;
 
   if (rv3d->is_persp) {
-    out[0] = 2.0f * (mval[0] / region->winx) - 1.0f;
-    out[1] = 2.0f * (mval[1] / region->winy) - 1.0f;
-    out[2] = -0.5f;
-    mul_project_m4_v3(rv3d->persinv, out);
-    sub_v3_v3(out, rv3d->viewinv[3]);
+    r_out[0] = 2.0f * (mval[0] / region->winx) - 1.0f;
+    r_out[1] = 2.0f * (mval[1] / region->winy) - 1.0f;
+    r_out[2] = -0.5f;
+    mul_project_m4_v3(rv3d->persinv, r_out);
+    sub_v3_v3(r_out, rv3d->viewinv[3]);
   }
   else {
-    negate_v3_v3(out, rv3d->viewinv[2]);
+    negate_v3_v3(r_out, rv3d->viewinv[2]);
   }
-  normalize_v3(out);
+  normalize_v3(r_out);
 }
 
 bool ED_view3d_win_to_segment_clipped(struct Depsgraph *depsgraph,