curve twist

* added new twist method - "Tangent", suggested by Martin.
  the nice thing about this is its stable no matter how you rotate the data, rotation is local to each segment.
* added smooth option that smooths the twisting (before applying user twist), to workaround Z-Up and Tangent's ugly curve twisting. Id prefer not to have this however it makes tangent much nicer. Possibly tangent can be improved some other way and this can be removed.
  A smooth value of 1.0 will iterate over and smooth the twisting by the resolution value of the spline.
* Minimum-Twist method now corrects for cyclic twist by taking the roll difference between first and last, then increasingly counter rotate each segment over the entire curve. Previously it calculated from both directions and blended them.

details
* BevPoints use quats rather then 3x3 matrix.
* added BevPoint direction "dir" and tangent "tan" used only for 3D curves.
* don't calculate BevPoint->cosa, BevPoint->sina for 3D curves.
* split bevel tilt calculation into functions.
* nurbs curves currently don't generate tangents and wont work with tangent twist method.
* some of the use of quats should be optimized.
* smoothing is not animation safe, the higher the smoothing the higher the likelyhood of flipping.

1 files changed, 20 insertions, 4 deletions

diff --git a/source/blender/makesrna/intern/rna_curve.c b/source/blender/makesrna/intern/rna_curve.c
index 91628bab376..d09546231d5 100644
--- a/source/blender/makesrna/intern/rna_curve.c
+++ b/source/blender/makesrna/intern/rna_curve.c
@@ -664,6 +664,12 @@ static void rna_def_curve(BlenderRNA *brna)
 	StructRNA *srna;
 	PropertyRNA *prop;
 	
+	static EnumPropertyItem curve_twist_mode_items[] = {
+			{CU_TWIST_Z_UP, "Z_UP", 0, "Z-Up", "Use Z-Up axis to calculate the curve twist at each point"},
+			{CU_TWIST_MINIMUM, "MINIMUM", 0, "Minimum", "Use the least twist over the entire curve"},
+			{CU_TWIST_TANGENT, "TANGENT", 0, "Tangent", "Use the tangent to calculate twist"},
+			{0, NULL, 0, NULL, NULL}};
+
 	srna= RNA_def_struct(brna, "Curve", "ID");
 	RNA_def_struct_ui_text(srna, "Curve", "Curve datablock storing curves, splines and NURBS.");
 	RNA_def_struct_ui_icon(srna, ICON_CURVE_DATA);
@@ -782,12 +788,22 @@ static void rna_def_curve(BlenderRNA *brna)
 	RNA_def_property_boolean_sdna(prop, NULL, "flag", CU_BACK);
 	RNA_def_property_ui_text(prop, "Back", "Draw filled back for extruded/beveled curves.");
 	RNA_def_property_update(prop, 0, "rna_Curve_update_data");
-	
-	prop= RNA_def_property(srna, "use_twist_correction", PROP_BOOLEAN, PROP_NONE);
-	RNA_def_property_boolean_sdna(prop, NULL, "flag", CU_NO_TWIST);
-	RNA_def_property_ui_text(prop, "Minimal Twist", "Correct for twisting.");
+
+	prop= RNA_def_property(srna, "twist_mode", PROP_ENUM, PROP_NONE);
+	RNA_def_property_enum_sdna(prop, NULL, "twist_mode");
+	RNA_def_property_enum_items(prop, curve_twist_mode_items);
+	RNA_def_property_ui_text(prop, "Twist Method", "The type of tilt calculation for 3D Curves.");
+	RNA_def_property_update(prop, 0, "rna_Curve_update_data");
+
+	// XXX - would be nice to have a better way to do this, only add for testing.
+	prop= RNA_def_property(srna, "twist_smooth", PROP_FLOAT, PROP_NONE);
+	RNA_def_property_float_sdna(prop, NULL, "twist_smooth");
+	RNA_def_property_ui_range(prop, 0, 100.0, 0.1, 0);
+	RNA_def_property_ui_text(prop, "Twist Smooth", "Smoothing iteration for tangents");
 	RNA_def_property_update(prop, 0, "rna_Curve_update_data");
 
+
+
 	prop= RNA_def_property(srna, "retopo", PROP_BOOLEAN, PROP_NONE);
 	RNA_def_property_boolean_sdna(prop, NULL, "flag", CU_RETOPO);
 	RNA_def_property_ui_text(prop, "Retopo", "Turn on the re-topology tool.");