Simple hair children: Make twist affected by vertex group

The idea is to give a control over direction of twist, and maybe amount of
twist as well. More concrete example: make braids on left and right side of
character head to be twisting opposite directions.

Now, tricky part: we need some negative values to flip direction, but weights
can not be negative. So we use same trick as displacement map and tangent normal
maps, where 0.5 is neutral, values below 0.5 are considered negative and values
above 0.5 are considered positive.

1 files changed, 15 insertions, 0 deletions

diff --git a/source/blender/makesrna/intern/rna_particle.c b/source/blender/makesrna/intern/rna_particle.c
index e9bbc981a13..caf120e0ea1 100644
--- a/source/blender/makesrna/intern/rna_particle.c
+++ b/source/blender/makesrna/intern/rna_particle.c
@@ -1313,6 +1313,7 @@ static void rna_ParticleVGroup_name_get_8(PointerRNA *ptr, char *value) { psys_v
 static void rna_ParticleVGroup_name_get_9(PointerRNA *ptr, char *value) { psys_vg_name_get__internal(ptr, value, 9); }
 static void rna_ParticleVGroup_name_get_10(PointerRNA *ptr, char *value) { psys_vg_name_get__internal(ptr, value, 10); }
 static void rna_ParticleVGroup_name_get_11(PointerRNA *ptr, char *value) { psys_vg_name_get__internal(ptr, value, 11); }
+static void rna_ParticleVGroup_name_get_12(PointerRNA *ptr, char *value) { psys_vg_name_get__internal(ptr, value, 12); }
 
 static int rna_ParticleVGroup_name_len_0(PointerRNA *ptr) { return psys_vg_name_len__internal(ptr, 0); }
 static int rna_ParticleVGroup_name_len_1(PointerRNA *ptr) { return psys_vg_name_len__internal(ptr, 1); }
@@ -1326,6 +1327,7 @@ static int rna_ParticleVGroup_name_len_8(PointerRNA *ptr) { return psys_vg_name_
 static int rna_ParticleVGroup_name_len_9(PointerRNA *ptr) { return psys_vg_name_len__internal(ptr, 9); }
 static int rna_ParticleVGroup_name_len_10(PointerRNA *ptr) { return psys_vg_name_len__internal(ptr, 10); }
 static int rna_ParticleVGroup_name_len_11(PointerRNA *ptr) { return psys_vg_name_len__internal(ptr, 11); }
+static int rna_ParticleVGroup_name_len_12(PointerRNA *ptr) { return psys_vg_name_len__internal(ptr, 12); }
 
 static void rna_ParticleVGroup_name_set_0(PointerRNA *ptr, const char *value) { psys_vg_name_set__internal(ptr, value, 0); }
 static void rna_ParticleVGroup_name_set_1(PointerRNA *ptr, const char *value) { psys_vg_name_set__internal(ptr, value, 1); }
@@ -1339,6 +1341,7 @@ static void rna_ParticleVGroup_name_set_8(PointerRNA *ptr, const char *value) {
 static void rna_ParticleVGroup_name_set_9(PointerRNA *ptr, const char *value) { psys_vg_name_set__internal(ptr, value, 9); }
 static void rna_ParticleVGroup_name_set_10(PointerRNA *ptr, const char *value) { psys_vg_name_set__internal(ptr, value, 10); }
 static void rna_ParticleVGroup_name_set_11(PointerRNA *ptr, const char *value) { psys_vg_name_set__internal(ptr, value, 11); }
+static void rna_ParticleVGroup_name_set_12(PointerRNA *ptr, const char *value) { psys_vg_name_set__internal(ptr, value, 12); }
 
 
 #else
@@ -3535,6 +3538,18 @@ static void rna_def_particle_system(BlenderRNA *brna)
 	RNA_def_property_ui_text(prop, "Vertex Group Field Negate", "Negate the effect of the field vertex group");
 	RNA_def_property_update(prop, 0, "rna_Particle_reset");
 
+	prop = RNA_def_property(srna, "vertex_group_twist", PROP_STRING, PROP_NONE);
+	RNA_def_property_string_funcs(prop, "rna_ParticleVGroup_name_get_12", "rna_ParticleVGroup_name_len_12",
+	                              "rna_ParticleVGroup_name_set_12");
+	RNA_def_property_ui_text(prop, "Vertex Group Twist", "Vertex group to control twist");
+	RNA_def_property_update(prop, 0, "rna_Particle_redo_child");
+
+	prop = RNA_def_property(srna, "invert_vertex_group_twist", PROP_BOOLEAN, PROP_NONE);
+	RNA_def_property_boolean_sdna(prop, NULL, "vg_neg", (1 << PSYS_VG_TWIST));
+	RNA_def_property_ui_text(prop, "Vertex Group Twist Negate",
+	                         "Negate the effect of the twist vertex group");
+	RNA_def_property_update(prop, 0, "rna_Particle_redo_child");
+
 	/* pointcache */
 	prop = RNA_def_property(srna, "point_cache", PROP_POINTER, PROP_NONE);
 	RNA_def_property_flag(prop, PROP_NEVER_NULL);