Spline IK: support changing individual bone length via Y scaling.

Previously Spline IK provided only two choices: either scale the
length of the bone chain to fit the length of the curve, or don't
scale the bone in the Y dimension at all (ignoring effects of
actually fitting to the curve due to curvature and curve object
scale).

This patch adds a new option to use the pre-IK Y scale of the
bones to adjust their length when fitted to the curve, allowing
individual posing control over the length of the segments.

Reviewers: brecht

Differential Revision: https://developer.blender.org/D4687

release/scripts/startup/bl_ui/properties_constraint.py

@@ -794,9 +794,9 @@ class ConstraintButtonsPanel:
 
         col = layout.column()
         col.label(text="Chain Scaling:")
-        col.prop(con, "use_y_stretch")
         col.prop(con, "use_curve_radius")
 
+        layout.prop(con, "y_scale_mode")
         layout.prop(con, "xz_scale_mode")
 
         if con.xz_scale_mode == 'VOLUME_PRESERVE':

source/blender/blenkernel/intern/armature_update.c

@@ -230,7 +230,7 @@ static bool splineik_evaluate_init(tSplineIK_Tree *tree, tSplineIk_EvalState *st
 	unit_m4(state->locrot_offset);
 
 	/* Apply corrections for sensitivity to scaling. */
-	if ((ikData->flag & CONSTRAINT_SPLINEIK_SCALE_LIMITED) && (tree->totlength != 0.0f)) {
+	if ((ikData->yScaleMode != CONSTRAINT_SPLINEIK_YS_FIT_CURVE) && (tree->totlength != 0.0f)) {
 		/* get the current length of the curve */
 		/* NOTE: this is assumed to be correct even after the curve was resized */
 		float splineLen = cache->path->totdist;
@@ -262,6 +262,12 @@ static void splineik_evaluate_bone(tSplineIK_Tree *tree, Object *ob, bPoseChanne
 	float curveLen = tree->points[index] - tree->points[index + 1];
 	float pointStart = state->curve_position;
 	float baseScale = 1.0f;
+
+	if (ikData->yScaleMode == CONSTRAINT_SPLINEIK_YS_ORIGINAL) {
+		/* Carry over the bone Y scale to the curve range. */
+		baseScale = len_v3v3(poseHead, poseTail) / pchan->bone->length;
+	}
+
 	float pointEnd = pointStart + curveLen * baseScale * state->curve_scale;
 
 	state->curve_position = pointEnd;

source/blender/blenkernel/intern/constraint.c

@@ -3959,6 +3959,8 @@ static void splineik_new_data(void *cdata)
 	data->bulge = 1.0;
 	data->bulge_max = 1.0f;
 	data->bulge_min = 1.0f;
+
+	data->yScaleMode = CONSTRAINT_SPLINEIK_YS_FIT_CURVE;
 }
 
 static void splineik_id_looper(bConstraint *con, ConstraintIDFunc func, void *userdata)

source/blender/blenloader/intern/versioning_280.c

@@ -3140,6 +3140,23 @@ void blo_do_versions_280(FileData *fd, Library *UNUSED(lib), Main *bmain)
 	}
 
 	{
+		if (!DNA_struct_elem_find(fd->filesdna, "bSplineIKConstraint", "short", "yScaleMode")) {
+			for (Object *ob = bmain->objects.first; ob; ob = ob->id.next) {
+				if (ob->pose) {
+					for (bPoseChannel *pchan = ob->pose->chanbase.first; pchan; pchan = pchan->next) {
+						for (bConstraint *con = pchan->constraints.first; con; con = con->next) {
+							if (con->type == CONSTRAINT_TYPE_SPLINEIK) {
+								bSplineIKConstraint *data = (bSplineIKConstraint *)con->data;
+								if ((data->flag & CONSTRAINT_SPLINEIK_SCALE_LIMITED) == 0) {
+									data->yScaleMode = CONSTRAINT_SPLINEIK_YS_FIT_CURVE;
+								}
+							}
+						}
+					}
+				}
+			}
+		}
+
 		/* Versioning code until next subversion bump goes here. */
 	}
 }

source/blender/makesdna/DNA_constraint_types.h

@@ -231,6 +231,9 @@ typedef struct bSplineIKConstraint {
 	short flag;
 	/** Method used for determining the x & z scaling of the bones. */
 	short xzScaleMode;
+	/** Method used for determining the y scaling of the bones. */
+	short yScaleMode;
+	short _pad[3];
 
 		/* volume preservation settings */
 	float		bulge;
@@ -879,8 +882,10 @@ typedef enum eSplineIK_Flags {
 	CONSTRAINT_SPLINEIK_BOUND			= (1 << 0),
 	/* root of chain is not influenced by the constraint */
 	CONSTRAINT_SPLINEIK_NO_ROOT			= (1 << 1),
+#ifdef DNA_DEPRECATED
 	/* bones in the chain should not scale to fit the curve */
 	CONSTRAINT_SPLINEIK_SCALE_LIMITED	= (1 << 2),
+#endif
 	/* evenly distribute the bones along the path regardless of length */
 	CONSTRAINT_SPLINEIK_EVENSPLITS		= (1 << 3),
 	/* don't adjust the x and z scaling of the bones by the curve radius */
@@ -903,6 +908,16 @@ typedef enum eSplineIK_XZScaleModes {
 	CONSTRAINT_SPLINEIK_XZS_VOLUMETRIC		= 3,
 } eSplineIK_XZScaleModes;
 
+/* bSplineIKConstraint->yScaleMode */
+typedef enum eSplineIK_YScaleModes {
+	/* no y scaling */
+	CONSTRAINT_SPLINEIK_YS_NONE        = 0,
+	/* bones in the chain should be scaled to fit the length of the curve */
+	CONSTRAINT_SPLINEIK_YS_FIT_CURVE   = 1,
+	/* bones in the chain should take their y scales from the original scaling */
+	CONSTRAINT_SPLINEIK_YS_ORIGINAL    = 2,
+} eSplineIK_YScaleModes;
+
 /* bArmatureConstraint -> flag */
 typedef enum eArmature_Flags {
 	/** use dual quaternion blending */

source/blender/makesrna/intern/rna_constraint.c

@@ -2262,6 +2262,15 @@ static void rna_def_constraint_spline_ik(BlenderRNA *brna)
 		{0, NULL, 0, NULL, NULL},
 	};
 
+	static const EnumPropertyItem splineik_y_scale_mode[] = {
+		{CONSTRAINT_SPLINEIK_YS_NONE, "NONE", 0, "None", "Don't scale in the Y axis"},
+		{CONSTRAINT_SPLINEIK_YS_FIT_CURVE, "FIT_CURVE", 0, "Fit Curve",
+	                                       "Scale the bones to fit the entire length of the curve"},
+		{CONSTRAINT_SPLINEIK_YS_ORIGINAL, "BONE_ORIGINAL", 0, "Bone Original",
+		                                  "Use the original Y scale of the bone"},
+		{0, NULL, 0, NULL, NULL},
+	};
+
 	srna = RNA_def_struct(brna, "SplineIKConstraint", "Constraint");
 	RNA_def_struct_ui_text(srna, "Spline IK Constraint", "Align 'n' bones along a curve");
 	RNA_def_struct_sdna_from(srna, "bSplineIKConstraint", "data");
@@ -2308,11 +2317,6 @@ static void rna_def_constraint_spline_ik(BlenderRNA *brna)
 	                         "Ignore the relative lengths of the bones when fitting to the curve");
 	RNA_def_property_update(prop, NC_OBJECT | ND_CONSTRAINT, "rna_Constraint_update");
 
-	prop = RNA_def_property(srna, "use_y_stretch", PROP_BOOLEAN, PROP_NONE);
-	RNA_def_property_boolean_negative_sdna(prop, NULL, "flag", CONSTRAINT_SPLINEIK_SCALE_LIMITED);
-	RNA_def_property_ui_text(prop, "Y Stretch", "Stretch the Y axis of the bones to fit the curve");
-	RNA_def_property_update(prop, NC_OBJECT | ND_CONSTRAINT, "rna_Constraint_update");
-
 	prop = RNA_def_property(srna, "use_curve_radius", PROP_BOOLEAN, PROP_NONE);
 	RNA_def_property_boolean_negative_sdna(prop, NULL, "flag", CONSTRAINT_SPLINEIK_NO_CURVERAD);
 	RNA_def_property_ui_text(prop, "Use Curve Radius",
@@ -2328,6 +2332,15 @@ static void rna_def_constraint_spline_ik(BlenderRNA *brna)
 	                         "Method used for determining the scaling of the X and Z axes of the bones");
 	RNA_def_property_update(prop, NC_OBJECT | ND_CONSTRAINT, "rna_Constraint_update");
 
+	/* y scaling mode */
+	prop = RNA_def_property(srna, "y_scale_mode", PROP_ENUM, PROP_NONE);
+	RNA_def_property_enum_sdna(prop, NULL, "yScaleMode");
+	RNA_def_property_enum_items(prop, splineik_y_scale_mode);
+	RNA_def_property_ui_text(prop, "Y Scale Mode",
+	                         "Method used for determining the scaling of the Y axis of the bones, "
+	                         "on top of the shape and scaling of the curve itself");
+	RNA_def_property_update(prop, NC_OBJECT | ND_CONSTRAINT, "rna_Constraint_update");
+
 	/* volume presevation for "volumetric" scale mode */
 	prop = RNA_def_property(srna, "bulge", PROP_FLOAT, PROP_NONE);
 	RNA_def_property_range(prop, 0.0, 100.f);