UV: support snapping on non-uniform grids

Part of a wider set of changes to Grid and Pixel snapping in the
UV Editor.

This change fixes snapping behavior for non-uniform grids, either
manually specified Fixed grids, or pixel grids where the underlying
image is non-square.

See a24fc6bbc1ae for visual changes.

Maniphest Tasks: T78391

Differential Revision: https://developer.blender.org/D16275

4 files changed, 30 insertions, 28 deletions

diff --git a/source/blender/editors/transform/transform.c b/source/blender/editors/transform/transform.c
index 93e99f97387..34e5b78c48f 100644
--- a/source/blender/editors/transform/transform.c
+++ b/source/blender/editors/transform/transform.c
@@ -60,8 +60,6 @@
  * and being able to set it to zero is handy. */
 /* #define USE_NUM_NO_ZERO */
 
-static void initSnapSpatial(TransInfo *t, float r_snap[2]);
-
 bool transdata_check_local_islands(TransInfo *t, short around)
 {
   if (t->options & (CTX_CURSOR | CTX_TEXTURE_SPACE)) {
@@ -1723,7 +1721,7 @@ void saveTransform(bContext *C, TransInfo *t, wmOperator *op)
   }
 }
 
-static void initSnapSpatial(TransInfo *t, float r_snap[2])
+static void initSnapSpatial(TransInfo *t, float r_snap[2], float r_snap_y[2])
 {
   if (t->spacetype == SPACE_VIEW3D) {
     if (t->region->regiondata) {
@@ -1737,18 +1735,15 @@ static void initSnapSpatial(TransInfo *t, float r_snap[2])
     View2D *v2d = &t->region->v2d;
     int grid_size = SI_GRID_STEPS_LEN;
     float zoom_factor = ED_space_image_zoom_level(v2d, grid_size);
-    float grid_steps[SI_GRID_STEPS_LEN];
+    float grid_steps_x[SI_GRID_STEPS_LEN];
     float grid_steps_y[SI_GRID_STEPS_LEN];
 
-    ED_space_image_grid_steps(sima, grid_steps, grid_steps_y, grid_size);
+    ED_space_image_grid_steps(sima, grid_steps_x, grid_steps_y, grid_size);
     /* Snapping value based on what type of grid is used (adaptive-subdividing or custom-grid). */
-    r_snap[0] = ED_space_image_increment_snap_value(grid_size, grid_steps, zoom_factor);
+    r_snap[0] = ED_space_image_increment_snap_value(grid_size, grid_steps_x, zoom_factor);
     r_snap[1] = r_snap[0] / 2.0f;
-
-    /* TODO: Implement snapping for custom grid sizes with `grid_steps[0] != grid_steps_y[0]`.
-     * r_snap_y[0] = ED_space_image_increment_snap_value(grid_size, grid_steps_y, zoom_factor);
-     * r_snap_y[1] = r_snap_y[0] / 2.0f;
-     */
+    r_snap_y[0] = ED_space_image_increment_snap_value(grid_size, grid_steps_y, zoom_factor);
+    r_snap_y[1] = r_snap_y[0] / 2.0f;
   }
   else if (t->spacetype == SPACE_CLIP) {
     r_snap[0] = 0.125f;
@@ -1903,7 +1898,7 @@ bool initTransform(bContext *C, TransInfo *t, wmOperator *op, const wmEvent *eve
 
   initSnapping(t, op); /* Initialize snapping data AFTER mode flags */
 
-  initSnapSpatial(t, t->snap_spatial);
+  initSnapSpatial(t, t->snap_spatial_x, t->snap_spatial_y);
 
   /* EVIL! posemode code can switch translation to rotate when 1 bone is selected.
    * will be removed (ton) */
diff --git a/source/blender/editors/transform/transform.h b/source/blender/editors/transform/transform.h
index e2bab378cad..95686f12fe2 100644
--- a/source/blender/editors/transform/transform.h
+++ b/source/blender/editors/transform/transform.h
@@ -555,7 +555,9 @@ typedef struct TransInfo {
   /** Snapping Gears. */
   float snap[2];
   /** Spatial snapping gears(even when rotating, scaling... etc). */
-  float snap_spatial[2];
+  float snap_spatial_x[2];
+  /** Spatial snapping in the Y coordinate, for non-uniform grid in UV Editor. */
+  float snap_spatial_y[2];
   /** Mouse side of the current frame, 'L', 'R' or 'B' */
   char frame_side;
 
diff --git a/source/blender/editors/transform/transform_mode_translate.c b/source/blender/editors/transform/transform_mode_translate.c
index 8f6ec7bd98f..91388ecd661 100644
--- a/source/blender/editors/transform/transform_mode_translate.c
+++ b/source/blender/editors/transform/transform_mode_translate.c
@@ -590,7 +590,7 @@ void initTranslation(TransInfo *t)
   t->num.flag = 0;
   t->num.idx_max = t->idx_max;
 
-  copy_v2_v2(t->snap, t->snap_spatial);
+  copy_v2_v2(t->snap, t->snap_spatial_x);
 
   copy_v3_fl(t->num.val_inc, t->snap[0]);
   t->num.unit_sys = t->scene->unit.system;
diff --git a/source/blender/editors/transform/transform_snap.c b/source/blender/editors/transform/transform_snap.c
index 3f9cca55138..553202b5798 100644
--- a/source/blender/editors/transform/transform_snap.c
+++ b/source/blender/editors/transform/transform_snap.c
@@ -519,10 +519,12 @@ void applyGridAbsolute(TransInfo *t)
     return;
   }
 
-  float grid_size = (t->modifiers & MOD_PRECISION) ? t->snap_spatial[1] : t->snap_spatial[0];
+  float grid_size_x = (t->modifiers & MOD_PRECISION) ? t->snap_spatial_x[1] : t->snap_spatial_x[0];
+  float grid_size_y = (t->modifiers & MOD_PRECISION) ? t->snap_spatial_y[1] : t->snap_spatial_y[0];
+  float grid_size_z = grid_size_x;
 
-  /* early exit on unusable grid size */
-  if (grid_size == 0.0f) {
+  /* Early exit on unusable grid size. */
+  if (grid_size_x == 0.0f || grid_size_y == 0.0f || grid_size_z == 0.0f) {
     return;
   }
 
@@ -548,11 +550,9 @@ void applyGridAbsolute(TransInfo *t)
         copy_v3_v3(iloc, td->ob->obmat[3]);
       }
 
-      mul_v3_v3fl(loc, iloc, 1.0f / grid_size);
-      loc[0] = roundf(loc[0]);
-      loc[1] = roundf(loc[1]);
-      loc[2] = roundf(loc[2]);
-      mul_v3_fl(loc, grid_size);
+      loc[0] = roundf(iloc[0] / grid_size_x) * grid_size_x;
+      loc[1] = roundf(iloc[1] / grid_size_y) * grid_size_y;
+      loc[2] = roundf(iloc[2] / grid_size_z) * grid_size_z;
 
       sub_v3_v3v3(tvec, loc, iloc);
       mul_m3_v3(td->smtx, tvec);
@@ -1654,8 +1654,12 @@ bool snapNodesTransform(
 /** \name snap Grid
  * \{ */
 
-static void snap_grid_apply(
-    TransInfo *t, const int max_index, const float grid_dist, const float loc[3], float r_out[3])
+static void snap_grid_apply(TransInfo *t,
+                            const int max_index,
+                            const float grid_dist_x,
+                            const float grid_dist_y,
+                            const float loc[3],
+                            float r_out[3])
 {
   BLI_assert(max_index <= 2);
   snap_target_grid_ensure(t);
@@ -1672,7 +1676,7 @@ static void snap_grid_apply(
   }
 
   for (int i = 0; i <= max_index; i++) {
-    const float iter_fac = grid_dist * asp[i];
+    const float iter_fac = ((i == 1) ? grid_dist_y : grid_dist_x) * asp[i];
     r_out[i] = iter_fac * roundf((in[i] + center_global[i]) / iter_fac) - center_global[i];
   }
 }
@@ -1697,14 +1701,15 @@ bool transform_snap_grid(TransInfo *t, float *val)
     return false;
   }
 
-  float grid_dist = (t->modifiers & MOD_PRECISION) ? t->snap[1] : t->snap[0];
+  float grid_dist_x = (t->modifiers & MOD_PRECISION) ? t->snap_spatial_x[1] : t->snap_spatial_x[0];
+  float grid_dist_y = (t->modifiers & MOD_PRECISION) ? t->snap_spatial_y[1] : t->snap_spatial_y[0];
 
   /* Early bailing out if no need to snap */
-  if (grid_dist == 0.0f) {
+  if (grid_dist_x == 0.0f || grid_dist_y == 0.0f) {
     return false;
   }
 
-  snap_grid_apply(t, t->idx_max, grid_dist, val, val);
+  snap_grid_apply(t, t->idx_max, grid_dist_x, grid_dist_y, val, val);
   t->tsnap.snapElem = SCE_SNAP_MODE_GRID;
   return true;
 }