execute bisect immediately (without starting modal input) if the plane is already set or if there is no 3d view available.

source/blender/editors/mesh/editmesh_bisect.c

@@ -50,7 +50,7 @@
 
 #include "mesh_intern.h"  /* own include */
 
-
+static int mesh_bisect_exec(bContext *C, wmOperator *op);
 
 /* -------------------------------------------------------------------- */
 /* Model Helpers */
@@ -94,6 +94,7 @@ static bool mesh_bisect_interactive_calc(
 
 	/* cross both to get a normal */
 	cross_v3_v3v3(plane_no, co_a, co_b);
+	normalize_v3(plane_no);  /* not needed but nicer for user */
 
 	/* point on plane, can use either start or endpoint */
 	ED_view3d_win_to_3d(ar, co_ref, co_a_ss, plane_co);
@@ -110,6 +111,16 @@ static int mesh_bisect_invoke(bContext *C, wmOperator *op, const wmEvent *event)
 {
 	int ret;
 
+	/* if the properties are set or there is no rv3d,
+	 * skip model and exec immediately */
+
+	if ((CTX_wm_region_view3d(C) == NULL) ||
+	    (RNA_struct_property_is_set(op->ptr, "plane_co") &&
+	     RNA_struct_property_is_set(op->ptr, "plane_no")))
+	{
+		return mesh_bisect_exec(C, op);
+	}
+
 	ret = WM_gesture_straightline_invoke(C, op, event);
 	if (ret & OPERATOR_RUNNING_MODAL) {
 		View3D *v3d = CTX_wm_view3d(C);