Pose Brush: Option to disable the IK anchor point

The IK chain was using an anchor point by default as it makes sense for
posing, but for creating curved shapes it is useful to be able to
disable it.

Reviewed By: jbakker

Differential Revision: https://developer.blender.org/D6584

release/scripts/startup/bl_ui/properties_paint_common.py

@@ -620,6 +620,7 @@ def brush_settings(layout, context, brush, popover=False):
             layout.prop(brush, "pose_offset")
             layout.prop(brush, "pose_smooth_iterations")
             layout.prop(brush, "pose_ik_segments")
+            layout.prop(brush, "use_pose_ik_anchored")
             layout.separator()
         
         if brush.sculpt_tool == 'SCRAPE':

source/blender/blenkernel/intern/brush.c

@@ -1000,6 +1000,7 @@ void BKE_brush_sculpt_reset(Brush *br)
     case SCULPT_TOOL_POSE:
       br->pose_smooth_iterations = 4;
       br->pose_ik_segments = 1;
+      br->flag2 |= BRUSH_POSE_IK_ANCHORED;
       br->flag &= ~BRUSH_ALPHA_PRESSURE;
       br->flag &= ~BRUSH_SPACE;
       br->flag &= ~BRUSH_SPACE_ATTEN;

source/blender/blenloader/intern/versioning_280.c

@@ -4440,5 +4440,12 @@ void blo_do_versions_280(FileData *fd, Library *UNUSED(lib), Main *bmain)
         br->pose_ik_segments = 1;
       }
     }
+
+    /* Pose brush keep anchor point. */
+    for (Brush *br = bmain->brushes.first; br; br = br->id.next) {
+      if (br->sculpt_tool == SCULPT_TOOL_POSE) {
+        br->flag2 |= BRUSH_POSE_IK_ANCHORED;
+      }
+    }
   }
 }

source/blender/editors/sculpt_paint/sculpt.c

@@ -3576,7 +3576,9 @@ static void sculpt_flip_quat_by_symm_area(float quat[3],
   }
 }
 
-static void pose_solve_ik_chain(SculptPoseIKChain *ik_chain, const float initial_target[3])
+static void pose_solve_ik_chain(SculptPoseIKChain *ik_chain,
+                                const float initial_target[3],
+                                const bool use_anchor)
 {
   SculptPoseIKChainSegment *segments = ik_chain->segments;
   int tot_segments = ik_chain->tot_segments;
@@ -3615,13 +3617,15 @@ static void pose_solve_ik_chain(SculptPoseIKChain *ik_chain, const float initial
   }
 
   /* Move back the whole chain to preserve the anchor point. */
-  float anchor_diff[3];
-  sub_v3_v3v3(
-      anchor_diff, segments[tot_segments - 1].initial_orig, segments[tot_segments - 1].orig);
+  if (use_anchor) {
+    float anchor_diff[3];
+    sub_v3_v3v3(
+        anchor_diff, segments[tot_segments - 1].initial_orig, segments[tot_segments - 1].orig);
 
-  for (int i = 0; i < tot_segments; i++) {
-    add_v3_v3(segments[i].orig, anchor_diff);
-    add_v3_v3(segments[i].head, anchor_diff);
+    for (int i = 0; i < tot_segments; i++) {
+      add_v3_v3(segments[i].orig, anchor_diff);
+      add_v3_v3(segments[i].head, anchor_diff);
+    }
   }
 }
 
@@ -3742,8 +3746,8 @@ static void do_pose_brush(Sculpt *sd, Object *ob, PBVHNode **nodes, int totnode)
     copy_v3_v3(ik_target, ss->cache->true_location);
     add_v3_v3(ik_target, ss->cache->grab_delta);
 
-    /* Solve the IK positions */
-    pose_solve_ik_chain(ik_chain, ik_target);
+    /* Solve the IK positions. */
+    pose_solve_ik_chain(ik_chain, ik_target, brush->flag2 & BRUSH_POSE_IK_ANCHORED);
   }
 
   /* Flip the segment chain in all symmetry axis and calculate the transform matrices for each

source/blender/makesdna/DNA_brush_types.h

@@ -458,6 +458,7 @@ typedef enum eBrushSamplingFlags {
 typedef enum eBrushFlags2 {
   BRUSH_MULTIPLANE_SCRAPE_DYNAMIC = (1 << 0),
   BRUSH_MULTIPLANE_SCRAPE_PLANES_PREVIEW = (1 << 1),
+  BRUSH_POSE_IK_ANCHORED = (1 << 2),
 } eBrushFlags2;
 
 typedef enum {

source/blender/makesrna/intern/rna_brush.c

@@ -2099,6 +2099,12 @@ static void rna_def_brush(BlenderRNA *brna)
       prop, "Show Cursor Preview", "Preview the scrape planes in the cursor during the stroke");
   RNA_def_property_update(prop, 0, "rna_Brush_update");
 
+  prop = RNA_def_property(srna, "use_pose_ik_anchored", PROP_BOOLEAN, PROP_NONE);
+  RNA_def_property_boolean_sdna(prop, NULL, "flag2", BRUSH_POSE_IK_ANCHORED);
+  RNA_def_property_ui_text(
+      prop, "Keep Anchor Point", "Keep the position of the last segmend in the IK chain fixed");
+  RNA_def_property_update(prop, 0, "rna_Brush_update");
+
   prop = RNA_def_property(srna, "invert_to_scrape_fill", PROP_BOOLEAN, PROP_NONE);
   RNA_def_property_boolean_sdna(prop, NULL, "flag", BRUSH_INVERT_TO_SCRAPE_FILL);
   RNA_def_property_ui_text(prop,