Add tangent space computation/access from RNA (i.e. python).

This simply mimics code used for loopnormals, to enable py scripts to generate and access (temporary)
a tangent 3D vector and bitangent sign for each loop. Together with the split normals, this allow
to recreate a complete tangent space for normal mapping (bitangent = bitangent_sign * cross(normal, tangent)).

Expects all faces to be tri or quads.

Reviewed By: Brecht, campbellbarton

Differential Revision: https://developer.blender.org/D185

1 files changed, 40 insertions, 0 deletions

diff --git a/source/blender/makesrna/intern/rna_mesh_api.c b/source/blender/makesrna/intern/rna_mesh_api.c
index 34f21046a92..76097b04c99 100644
--- a/source/blender/makesrna/intern/rna_mesh_api.c
+++ b/source/blender/makesrna/intern/rna_mesh_api.c
@@ -34,6 +34,8 @@
 
 #include "RNA_define.h"
 
+#include "DNA_customdata_types.h"
+
 #include "BLI_sys_types.h"
 
 #include "BLI_utildefines.h"
@@ -100,6 +102,32 @@ static void rna_Mesh_free_normals_split(Mesh *mesh)
 	CustomData_free_layers(&mesh->ldata, CD_NORMAL, mesh->totloop);
 }
 
+static void rna_Mesh_calc_tangents(Mesh *mesh, ReportList *reports, const char *uvmap)
+{
+	float (*r_looptangents)[4];
+
+	if (CustomData_has_layer(&mesh->ldata, CD_MLOOPTANGENT)) {
+		r_looptangents = CustomData_get_layer(&mesh->ldata, CD_MLOOPTANGENT);
+		memset(r_looptangents, 0, sizeof(float[4]) * mesh->totloop);
+	}
+	else {
+		r_looptangents = CustomData_add_layer(&mesh->ldata, CD_MLOOPTANGENT, CD_CALLOC, NULL, mesh->totloop);
+		CustomData_set_layer_flag(&mesh->ldata, CD_MLOOPTANGENT, CD_FLAG_TEMPORARY);
+	}
+
+	/* Compute loop normals if needed. */
+	if (!CustomData_has_layer(&mesh->ldata, CD_NORMAL)) {
+		rna_Mesh_calc_normals_split(mesh, (float)M_PI);
+	}
+
+	BKE_mesh_loop_tangents(mesh, uvmap, r_looptangents, reports);
+}
+
+static void rna_Mesh_free_tangents(Mesh *mesh)
+{
+	CustomData_free_layers(&mesh->ldata, CD_MLOOPTANGENT, mesh->totloop);
+}
+
 static void rna_Mesh_calc_smooth_groups(Mesh *mesh, int use_bitflags, int *r_poly_group_len,
                                         int **r_poly_group, int *r_group_total)
 {
@@ -141,6 +169,18 @@ void RNA_api_mesh(StructRNA *srna)
 	func = RNA_def_function(srna, "free_normals_split", "rna_Mesh_free_normals_split");
 	RNA_def_function_ui_description(func, "Free split vertex normals");
 
+	func = RNA_def_function(srna, "calc_tangents", "rna_Mesh_calc_tangents");
+	RNA_def_function_flag(func, FUNC_USE_REPORTS);
+	RNA_def_function_ui_description(func,
+	                                "Compute tangents and bitangent signs, to be used together with the split normals "
+	                                "to get a complete tangent space for normal mapping "
+	                                "(split normals are also computed if not yet present)");
+	parm = RNA_def_string(func, "uvmap", "", MAX_CUSTOMDATA_LAYER_NAME, "",
+	                      "Name of the UV map to use for tangent space computation");
+
+	func = RNA_def_function(srna, "free_tangents", "rna_Mesh_free_tangents");
+	RNA_def_function_ui_description(func, "Free tangents");
+
 	func = RNA_def_function(srna, "calc_tessface", "ED_mesh_calc_tessface");
 	RNA_def_function_ui_description(func, "Calculate face tessellation (supports editmode too)");