Sculpt: Pose Squash and Stretch deform mode

This implements squash and stretch as a deform mode for the Pose Brush.
It is similar to scale, but it applies different scale values in different
axis. To achieve this, the pivot local space of the transform needs to
be aligned to the segment when using this deform mode to apply the scale
in the correct direction.

Reviewed By: sergey

Differential Revision: https://developer.blender.org/D7934

source/blender/blenkernel/BKE_paint.h

@@ -239,7 +239,7 @@ typedef struct SculptPoseIKChainSegment {
   float initial_orig[3];
   float initial_head[3];
   float len;
-  float scale;
+  float scale[3];
   float rot[4];
   float *weights;
 

source/blender/editors/sculpt_paint/sculpt_pose.c

@@ -146,14 +146,14 @@ static void pose_solve_translate_chain(SculptPoseIKChain *ik_chain, const float
   }
 }
 
-static void pose_solve_scale_chain(SculptPoseIKChain *ik_chain, const float scale)
+static void pose_solve_scale_chain(SculptPoseIKChain *ik_chain, const float scale[3])
 {
   SculptPoseIKChainSegment *segments = ik_chain->segments;
   const int tot_segments = ik_chain->tot_segments;
 
   for (int i = 0; i < tot_segments; i++) {
     /* Assign the scale to each segment. */
-    segments[i].scale = scale;
+    copy_v3_v3(segments[i].scale, scale);
   }
 }
 
@@ -645,9 +645,10 @@ static void pose_ik_chain_origin_heads_init(SculptPoseIKChain *ik_chain,
     }
     copy_v3_v3(ik_chain->segments[i].orig, origin);
     copy_v3_v3(ik_chain->segments[i].initial_orig, origin);
+    copy_v3_v3(ik_chain->segments[i].head, head);
     copy_v3_v3(ik_chain->segments[i].initial_head, head);
     ik_chain->segments[i].len = len_v3v3(head, origin);
-    ik_chain->segments[i].scale = 1.0f;
+    copy_v3_fl(ik_chain->segments[i].scale, 1.0f);
   }
 }
 
@@ -656,7 +657,9 @@ static int pose_brush_num_effective_segments(const Brush *brush)
   /* Scaling multiple segments at the same time is not supported as the IK solver can't handle
    * changes in the segment's length. It will also required a better weight distribution to avoid
    * artifacts in the areas affected by multiple segments. */
-  if (brush->pose_deform_type == BRUSH_POSE_DEFORM_SCALE_TRASLATE) {
+  if (ELEM(brush->pose_deform_type,
+           BRUSH_POSE_DEFORM_SCALE_TRASLATE,
+           BRUSH_POSE_DEFORM_SQUASH_STRETCH)) {
     return 1;
   }
   return brush->pose_ik_segments;
@@ -987,6 +990,19 @@ static void sculpt_pose_do_translate_deform(SculptSession *ss, Brush *brush)
   pose_solve_translate_chain(ik_chain, ss->cache->grab_delta);
 }
 
+/* Calculate a scale factor based on the grab delta. */
+static float sculpt_pose_get_scale_from_grab_delta(SculptSession *ss, const float ik_target[3])
+{
+  SculptPoseIKChain *ik_chain = ss->cache->pose_ik_chain;
+  float plane[4];
+  float segment_dir[3];
+  sub_v3_v3v3(segment_dir, ik_chain->segments[0].initial_head, ik_chain->segments[0].initial_orig);
+  normalize_v3(segment_dir);
+  plane_from_point_normal_v3(plane, ik_chain->segments[0].initial_head, segment_dir);
+  const float segment_len = ik_chain->segments[0].len;
+  return segment_len / (segment_len - dist_signed_to_plane_v3(ik_target, plane));
+}
+
 static void sculpt_pose_do_scale_deform(SculptSession *ss, Brush *brush)
 {
   float ik_target[3];
@@ -998,14 +1014,8 @@ static void sculpt_pose_do_scale_deform(SculptSession *ss, Brush *brush)
   /* Solve the IK for the first segment to include rotation as part of scale. */
   pose_solve_ik_chain(ik_chain, ik_target, brush->flag2 & BRUSH_POSE_IK_ANCHORED);
 
-  /* Calculate a scale factor based on the grab delta. */
-  float plane[4];
-  float segment_dir[3];
-  sub_v3_v3v3(segment_dir, ik_chain->segments[0].initial_head, ik_chain->segments[0].initial_orig);
-  normalize_v3(segment_dir);
-  plane_from_point_normal_v3(plane, ik_chain->segments[0].initial_head, segment_dir);
-  const float segment_len = ik_chain->segments[0].len;
-  const float scale = segment_len / (segment_len - dist_signed_to_plane_v3(ik_target, plane));
+  float scale[3];
+  copy_v3_fl(scale, sculpt_pose_get_scale_from_grab_delta(ss, ik_target));
 
   /* Write the scale into the segments. */
   pose_solve_scale_chain(ik_chain, scale);
@@ -1055,6 +1065,45 @@ static void sculpt_pose_do_scale_translate_deform(SculptSession *ss, Brush *brus
   }
 }
 
+static void sculpt_pose_do_squash_stretch_deform(SculptSession *ss, Brush *UNUSED(brush))
+{
+  float ik_target[3];
+  SculptPoseIKChain *ik_chain = ss->cache->pose_ik_chain;
+
+  copy_v3_v3(ik_target, ss->cache->true_location);
+  add_v3_v3(ik_target, ss->cache->grab_delta);
+
+  float scale[3];
+  scale[2] = sculpt_pose_get_scale_from_grab_delta(ss, ik_target);
+  scale[0] = scale[1] = sqrtf(1.0f / scale[2]);
+
+  /* Write the scale into the segments. */
+  pose_solve_scale_chain(ik_chain, scale);
+}
+
+static void sculpt_pose_align_pivot_local_space(float r_mat[4][4],
+                                                ePaintSymmetryFlags symm,
+                                                ePaintSymmetryAreas symm_area,
+                                                SculptPoseIKChainSegment *segment,
+                                                const float grab_location[3])
+{
+  float segment_origin_head[3];
+  float symm_head[3];
+  float symm_orig[3];
+
+  copy_v3_v3(symm_head, segment->head);
+  copy_v3_v3(symm_orig, segment->orig);
+
+  SCULPT_flip_v3_by_symm_area(symm_head, symm, symm_area, grab_location);
+  SCULPT_flip_v3_by_symm_area(symm_orig, symm, symm_area, grab_location);
+
+  sub_v3_v3v3(segment_origin_head, symm_head, symm_orig);
+  normalize_v3(segment_origin_head);
+
+  copy_v3_v3(r_mat[2], segment_origin_head);
+  ortho_basis_v3v3_v3(r_mat[0], r_mat[1], r_mat[2]);
+}
+
 /* Main Brush Function. */
 void SCULPT_do_pose_brush(Sculpt *sd, Object *ob, PBVHNode **nodes, int totnode)
 {
@@ -1077,6 +1126,9 @@ void SCULPT_do_pose_brush(Sculpt *sd, Object *ob, PBVHNode **nodes, int totnode)
     case BRUSH_POSE_DEFORM_SCALE_TRASLATE:
       sculpt_pose_do_scale_translate_deform(ss, brush);
       break;
+    case BRUSH_POSE_DEFORM_SQUASH_STRETCH:
+      sculpt_pose_do_squash_stretch_deform(ss, brush);
+      break;
   }
 
   /* Flip the segment chain in all symmetry axis and calculate the transform matrices for each
@@ -1101,17 +1153,38 @@ void SCULPT_do_pose_brush(Sculpt *sd, Object *ob, PBVHNode **nodes, int totnode)
       SCULPT_flip_v3_by_symm_area(
           symm_initial_orig, symm, symm_area, ss->cache->orig_grab_location);
 
-      /* Create the transform matrix and store it in the segment. */
-      unit_m4(ik_chain->segments[i].pivot_mat[symm_it]);
-      quat_to_mat4(ik_chain->segments[i].trans_mat[symm_it], symm_rot);
-      mul_m4_fl(ik_chain->segments[i].trans_mat[symm_it], ik_chain->segments[i].scale);
+      float pivot_local_space[4][4];
+      unit_m4(pivot_local_space);
+
+      /* Align the segment pivot local space to the Z axis. */
+      if (brush->pose_deform_type == BRUSH_POSE_DEFORM_SQUASH_STRETCH) {
+        sculpt_pose_align_pivot_local_space(pivot_local_space,
+                                            symm,
+                                            symm_area,
+                                            &ik_chain->segments[i],
+                                            ss->cache->orig_grab_location);
+        unit_m4(ik_chain->segments[i].trans_mat[symm_it]);
+      }
+      else {
+        quat_to_mat4(ik_chain->segments[i].trans_mat[symm_it], symm_rot);
+      }
+
+      /* Apply segement scale to the transform. */
+      for (int scale_i = 0; scale_i < 3; scale_i++) {
+        mul_v3_fl(ik_chain->segments[i].trans_mat[symm_it][scale_i],
+                  ik_chain->segments[i].scale[scale_i]);
+      }
 
       translate_m4(ik_chain->segments[i].trans_mat[symm_it],
                    symm_orig[0] - symm_initial_orig[0],
                    symm_orig[1] - symm_initial_orig[1],
                    symm_orig[2] - symm_initial_orig[2]);
+
+      unit_m4(ik_chain->segments[i].pivot_mat[symm_it]);
       translate_m4(
           ik_chain->segments[i].pivot_mat[symm_it], symm_orig[0], symm_orig[1], symm_orig[2]);
+      mul_m4_m4_post(ik_chain->segments[i].pivot_mat[symm_it], pivot_local_space);
+
       invert_m4_m4(ik_chain->segments[i].pivot_mat_inv[symm_it],
                    ik_chain->segments[i].pivot_mat[symm_it]);
     }

source/blender/makesdna/DNA_brush_types.h

@@ -334,6 +334,7 @@ typedef enum eBrushClothForceFalloffType {
 typedef enum eBrushPoseDeformType {
   BRUSH_POSE_DEFORM_ROTATE_TWIST = 0,
   BRUSH_POSE_DEFORM_SCALE_TRASLATE = 1,
+  BRUSH_POSE_DEFORM_SQUASH_STRETCH = 2,
 } eBrushPoseDeformType;
 
 typedef enum eBrushPoseOriginType {

source/blender/makesrna/intern/rna_brush.c

@@ -1963,6 +1963,7 @@ static void rna_def_brush(BlenderRNA *brna)
   static const EnumPropertyItem brush_pose_deform_type_items[] = {
       {BRUSH_POSE_DEFORM_ROTATE_TWIST, "ROTATE_TWIST", 0, "Rotate/Twist", ""},
       {BRUSH_POSE_DEFORM_SCALE_TRASLATE, "SCALE_TRANSLATE", 0, "Scale/Translate", ""},
+      {BRUSH_POSE_DEFORM_SQUASH_STRETCH, "SQUASH_STRETCH", 0, "Squash/Stretch", ""},
       {0, NULL, 0, NULL, NULL},
   };