Fix T77819: Snap Incremental does not match grid in all cases

The behavior of the incremental snap did not take into account the
relative dimensions of the window, which resulted in a different behavior
if the area height was greater than the width.

source/blender/editors/gpencil/gpencil_edit.c

@@ -2737,12 +2737,12 @@ static bool gpencil_snap_poll(bContext *C)
 static int gpencil_snap_to_grid(bContext *C, wmOperator *UNUSED(op))
 {
   bGPdata *gpd = ED_gpencil_data_get_active(C);
-  RegionView3D *rv3d = CTX_wm_region_data(C);
+  ARegion *region = CTX_wm_region(C);
   View3D *v3d = CTX_wm_view3d(C);
   Scene *scene = CTX_data_scene(C);
   Depsgraph *depsgraph = CTX_data_ensure_evaluated_depsgraph(C);
   Object *obact = CTX_data_active_object(C);
-  const float gridf = ED_view3d_grid_view_scale(scene, v3d, rv3d, NULL);
+  const float gridf = ED_view3d_grid_view_scale(scene, v3d, region, NULL);
 
   LISTBASE_FOREACH (bGPDlayer *, gpl, &gpd->layers) {
     /* only editable and visible layers are considered */

source/blender/editors/include/ED_view3d.h

@@ -693,7 +693,7 @@ void ED_view3d_grid_steps(const struct Scene *scene,
                           float *r_grid_steps);
 float ED_view3d_grid_view_scale(struct Scene *scene,
                                 struct View3D *v3d,
-                                struct RegionView3D *rv3d,
+                                struct ARegion *region,
                                 const char **r_grid_unit);
 
 void ED_scene_draw_fps(const struct Scene *scene, int xoffset, int *yoffset);

source/blender/editors/space_view3d/view3d_draw.c

@@ -949,15 +949,16 @@ void ED_view3d_grid_steps(const Scene *scene,
  * Currently the simulation is only done when RV3D_VIEW_IS_AXIS. */
 float ED_view3d_grid_view_scale(Scene *scene,
                                 View3D *v3d,
-                                RegionView3D *rv3d,
+                                ARegion *region,
                                 const char **r_grid_unit)
 {
   float grid_scale;
+  RegionView3D *rv3d = region->regiondata;
   if (!rv3d->is_persp && RV3D_VIEW_IS_AXIS(rv3d->view)) {
     /* Decrease the distance between grid snap points depending on zoom. */
     /* `0.38` was a value visually obtained in order to get a snap distance
      * that matches previous versions Blender.*/
-    float min_dist = 0.38f * (rv3d->dist / v3d->lens);
+    float min_dist = 16.0f / (region->sizex * rv3d->winmat[0][0]);
     float grid_steps[STEPS_LEN];
     ED_view3d_grid_steps(scene, v3d, rv3d, grid_steps);
     /* Skip last item, in case the 'mid_dist' is greater than the largest unit. */
@@ -1468,12 +1469,13 @@ static void draw_selected_name(
 }
 
 static void draw_grid_unit_name(
-    Scene *scene, RegionView3D *rv3d, View3D *v3d, int xoffset, int *yoffset)
+    Scene *scene, ARegion *region, View3D *v3d, int xoffset, int *yoffset)
 {
+  RegionView3D *rv3d = region->regiondata;
   if (!rv3d->is_persp && RV3D_VIEW_IS_AXIS(rv3d->view)) {
     const char *grid_unit = NULL;
     int font_id = BLF_default();
-    ED_view3d_grid_view_scale(scene, v3d, rv3d, &grid_unit);
+    ED_view3d_grid_view_scale(scene, v3d, region, &grid_unit);
 
     if (grid_unit) {
       char numstr[32] = "";
@@ -1558,7 +1560,7 @@ void view3d_draw_region_info(const bContext *C, ARegion *region)
 
     if (v3d->gridflag & (V3D_SHOW_FLOOR | V3D_SHOW_X | V3D_SHOW_Y | V3D_SHOW_Z)) {
       /* draw below the viewport name */
-      draw_grid_unit_name(scene, rv3d, v3d, xoffset, &yoffset);
+      draw_grid_unit_name(scene, region, v3d, xoffset, &yoffset);
     }
 
     DRW_draw_region_engine_info(xoffset, &yoffset, VIEW3D_OVERLAY_LINEHEIGHT);

source/blender/editors/space_view3d/view3d_snap.c

@@ -73,14 +73,14 @@ static int snap_sel_to_grid_exec(bContext *C, wmOperator *UNUSED(op))
   ViewLayer *view_layer_eval = DEG_get_evaluated_view_layer(depsgraph);
   Object *obact = CTX_data_active_object(C);
   Scene *scene = CTX_data_scene(C);
-  RegionView3D *rv3d = CTX_wm_region_data(C);
+  ARegion *region = CTX_wm_region(C);
   View3D *v3d = CTX_wm_view3d(C);
   TransVertStore tvs = {NULL};
   TransVert *tv;
   float gridf, imat[3][3], bmat[3][3], vec[3];
   int a;
 
-  gridf = ED_view3d_grid_view_scale(scene, v3d, rv3d, NULL);
+  gridf = ED_view3d_grid_view_scale(scene, v3d, region, NULL);
 
   if (OBEDIT_FROM_OBACT(obact)) {
     ViewLayer *view_layer = CTX_data_view_layer(C);
@@ -657,11 +657,11 @@ void VIEW3D_OT_snap_selected_to_active(wmOperatorType *ot)
 static int snap_curs_to_grid_exec(bContext *C, wmOperator *UNUSED(op))
 {
   Scene *scene = CTX_data_scene(C);
-  RegionView3D *rv3d = CTX_wm_region_data(C);
+  ARegion *region = CTX_wm_region(C);
   View3D *v3d = CTX_wm_view3d(C);
   float gridf, *curs;
 
-  gridf = ED_view3d_grid_view_scale(scene, v3d, rv3d, NULL);
+  gridf = ED_view3d_grid_view_scale(scene, v3d, region, NULL);
   curs = scene->cursor.location;
 
   curs[0] = gridf * floorf(0.5f + curs[0] / gridf);

source/blender/editors/transform/transform.c

@@ -1626,11 +1626,9 @@ void saveTransform(bContext *C, TransInfo *t, wmOperator *op)
 static void initSnapSpatial(TransInfo *t, float r_snap[2])
 {
   if (t->spacetype == SPACE_VIEW3D) {
-    RegionView3D *rv3d = t->region->regiondata;
-
-    if (rv3d) {
+    if (t->region->regiondata) {
       View3D *v3d = t->area->spacedata.first;
-      r_snap[0] = ED_view3d_grid_view_scale(t->scene, v3d, rv3d, NULL) * 1.0f;
+      r_snap[0] = ED_view3d_grid_view_scale(t->scene, v3d, t->region, NULL) * 1.0f;
       r_snap[1] = r_snap[0] * 0.1f;
     }
   }