BMesh: Add BM_face_calc_area_uv

1 files changed, 20 insertions, 0 deletions

diff --git a/source/blender/bmesh/intern/bmesh_polygon.c b/source/blender/bmesh/intern/bmesh_polygon.c
index 87903b3fd58..a3b0f72fbcf 100644
--- a/source/blender/bmesh/intern/bmesh_polygon.c
+++ b/source/blender/bmesh/intern/bmesh_polygon.c
@@ -30,6 +30,7 @@
 
 #include "DNA_listBase.h"
 #include "DNA_modifier_types.h"
+#include "DNA_meshdata_types.h"
 
 #include "MEM_guardedalloc.h"
 
@@ -262,6 +263,25 @@ float BM_face_calc_area_with_mat3(const BMFace *f, const float mat3[3][3])
 }
 
 /**
+ * get the area of UV face
+ */
+float BM_face_calc_area_uv(const BMFace *f, int cd_loop_uv_offset)
+{
+	/* inline 'area_poly_v2' logic, avoid creating a temp array */
+	const BMLoop *l_iter, *l_first;
+
+	l_iter = l_first = BM_FACE_FIRST_LOOP(f);
+	/* The Trapezium Area Rule */
+	float cross = 0.0f;
+	do {
+		const MLoopUV *luv = BM_ELEM_CD_GET_VOID_P(l_iter, cd_loop_uv_offset);
+		const MLoopUV *luv_next = BM_ELEM_CD_GET_VOID_P(l_iter->next, cd_loop_uv_offset);
+		cross += (luv_next->uv[0] - luv->uv[0]) * (luv_next->uv[1] + luv->uv[1]);
+	} while ((l_iter = l_iter->next) != l_first);
+	return fabsf(cross * 0.5f);
+}
+
+/**
  * compute the perimeter of an ngon
  */
 float BM_face_calc_perimeter(const BMFace *f)