/*************************************************************************/ /* physics_2d_server.h */ /*************************************************************************/ /* This file is part of: */ /* GODOT ENGINE */ /* http://www.godotengine.org */ /*************************************************************************/ /* Copyright (c) 2007-2017 Juan Linietsky, Ariel Manzur. */ /* */ /* Permission is hereby granted, free of charge, to any person obtaining */ /* a copy of this software and associated documentation files (the */ /* "Software"), to deal in the Software without restriction, including */ /* without limitation the rights to use, copy, modify, merge, publish, */ /* distribute, sublicense, and/or sell copies of the Software, and to */ /* permit persons to whom the Software is furnished to do so, subject to */ /* the following conditions: */ /* */ /* The above copyright notice and this permission notice shall be */ /* included in all copies or substantial portions of the Software. */ /* */ /* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, */ /* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF */ /* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.*/ /* IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY */ /* CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, */ /* TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE */ /* SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE. */ /*************************************************************************/ #ifndef PHYSICS_2D_SERVER_H #define PHYSICS_2D_SERVER_H #include "object.h" #include "reference.h" #include "resource.h" class Physics2DDirectSpaceState; class Physics2DDirectBodyState : public Object { OBJ_TYPE( Physics2DDirectBodyState, Object ); protected: static void _bind_methods(); public: virtual Vector2 get_total_gravity() const=0; // get gravity vector working on this body space/area virtual float get_total_linear_damp() const=0; // get density of this body space/area virtual float get_total_angular_damp() const=0; // get density of this body space/area virtual float get_inverse_mass() const=0; // get the mass virtual real_t get_inverse_inertia() const=0; // get density of this body space virtual void set_linear_velocity(const Vector2& p_velocity)=0; virtual Vector2 get_linear_velocity() const=0; virtual void set_angular_velocity(real_t p_velocity)=0; virtual real_t get_angular_velocity() const=0; virtual void set_transform(const Matrix32& p_transform)=0; virtual Matrix32 get_transform() const=0; virtual void set_sleep_state(bool p_enable)=0; virtual bool is_sleeping() const=0; virtual int get_contact_count() const=0; virtual Vector2 get_contact_local_pos(int p_contact_idx) const=0; virtual Vector2 get_contact_local_normal(int p_contact_idx) const=0; virtual int get_contact_local_shape(int p_contact_idx) const=0; virtual RID get_contact_collider(int p_contact_idx) const=0; virtual Vector2 get_contact_collider_pos(int p_contact_idx) const=0; virtual ObjectID get_contact_collider_id(int p_contact_idx) const=0; virtual Object* get_contact_collider_object(int p_contact_idx) const; virtual int get_contact_collider_shape(int p_contact_idx) const=0; virtual Variant get_contact_collider_shape_metadata(int p_contact_idx) const=0; virtual Vector2 get_contact_collider_velocity_at_pos(int p_contact_idx) const=0; virtual real_t get_step() const=0; virtual void integrate_forces(); virtual Physics2DDirectSpaceState* get_space_state()=0; Physics2DDirectBodyState(); }; class Physics2DShapeQueryResult; //used for script class Physics2DShapeQueryParameters : public Reference { OBJ_TYPE(Physics2DShapeQueryParameters, Reference); friend class Physics2DDirectSpaceState; RID shape; Matrix32 transform; Vector2 motion; float margin; Set exclude; uint32_t layer_mask; uint32_t object_type_mask; protected: static void _bind_methods(); public: void set_shape(const RES& p_shape); void set_shape_rid(const RID& p_shape); RID get_shape_rid() const; void set_transform(const Matrix32& p_transform); Matrix32 get_transform() const; void set_motion(const Vector2& p_motion); Vector2 get_motion() const; void set_margin(float p_margin); float get_margin() const; void set_layer_mask(int p_layer_mask); int get_layer_mask() const; void set_object_type_mask(int p_object_type_mask); int get_object_type_mask() const; void set_exclude(const Vector& p_exclude); Vector get_exclude() const; Physics2DShapeQueryParameters(); }; class Physics2DDirectSpaceState : public Object { OBJ_TYPE( Physics2DDirectSpaceState, Object ); Dictionary _intersect_ray(const Vector2& p_from, const Vector2& p_to,const Vector& p_exclude=Vector(),uint32_t p_layers=0,uint32_t p_object_type_mask=TYPE_MASK_COLLISION); Array _intersect_point(const Vector2& p_point,int p_max_results=32,const Vector& p_exclude=Vector(),uint32_t p_layers=0,uint32_t p_object_type_mask=TYPE_MASK_COLLISION); Array _intersect_shape(const Ref &p_shape_query,int p_max_results=32); Array _cast_motion(const Ref &p_shape_query); Array _collide_shape(const Ref &p_shape_query,int p_max_results=32); Dictionary _get_rest_info(const Ref &p_shape_query); protected: static void _bind_methods(); public: enum ObjectTypeMask { TYPE_MASK_STATIC_BODY=1<<0, TYPE_MASK_KINEMATIC_BODY=1<<1, TYPE_MASK_RIGID_BODY=1<<2, TYPE_MASK_CHARACTER_BODY=1<<3, TYPE_MASK_AREA=1<<4, TYPE_MASK_COLLISION=TYPE_MASK_STATIC_BODY|TYPE_MASK_CHARACTER_BODY|TYPE_MASK_KINEMATIC_BODY|TYPE_MASK_RIGID_BODY }; struct RayResult { Vector2 position; Vector2 normal; RID rid; ObjectID collider_id; Object *collider; int shape; Variant metadata; }; virtual bool intersect_ray(const Vector2& p_from, const Vector2& p_to,RayResult &r_result,const Set& p_exclude=Set(),uint32_t p_layer_mask=0xFFFFFFFF,uint32_t p_object_type_mask=TYPE_MASK_COLLISION)=0; struct ShapeResult { RID rid; ObjectID collider_id; Object *collider; int shape; Variant metadata; }; virtual int intersect_point(const Vector2& p_point,ShapeResult *r_results,int p_result_max,const Set& p_exclude=Set(),uint32_t p_layer_mask=0xFFFFFFFF,uint32_t p_object_type_mask=TYPE_MASK_COLLISION,bool p_pick_point=false)=0; virtual int intersect_shape(const RID& p_shape, const Matrix32& p_xform,const Vector2& p_motion,float p_margin,ShapeResult *r_results,int p_result_max,const Set& p_exclude=Set(),uint32_t p_layer_mask=0xFFFFFFFF,uint32_t p_object_type_mask=TYPE_MASK_COLLISION)=0; virtual bool cast_motion(const RID& p_shape, const Matrix32& p_xform,const Vector2& p_motion,float p_margin,float &p_closest_safe,float &p_closest_unsafe, const Set& p_exclude=Set(),uint32_t p_layer_mask=0xFFFFFFFF,uint32_t p_object_type_mask=TYPE_MASK_COLLISION)=0; virtual bool collide_shape(RID p_shape, const Matrix32& p_shape_xform,const Vector2& p_motion,float p_margin,Vector2 *r_results,int p_result_max,int &r_result_count, const Set& p_exclude=Set(),uint32_t p_layer_mask=0xFFFFFFFF,uint32_t p_object_type_mask=TYPE_MASK_COLLISION)=0; struct ShapeRestInfo { Vector2 point; Vector2 normal; RID rid; ObjectID collider_id; int shape; Vector2 linear_velocity; //velocity at contact point Variant metadata; }; virtual bool rest_info(RID p_shape, const Matrix32& p_shape_xform,const Vector2& p_motion,float p_margin,ShapeRestInfo *r_info, const Set& p_exclude=Set(),uint32_t p_layer_mask=0xFFFFFFFF,uint32_t p_object_type_mask=TYPE_MASK_COLLISION)=0; Physics2DDirectSpaceState(); }; class Physics2DShapeQueryResult : public Reference { OBJ_TYPE( Physics2DShapeQueryResult, Reference ); Vector result; friend class Physics2DDirectSpaceState; protected: static void _bind_methods(); public: int get_result_count() const; RID get_result_rid(int p_idx) const; ObjectID get_result_object_id(int p_idx) const; Object* get_result_object(int p_idx) const; int get_result_object_shape(int p_idx) const; Physics2DShapeQueryResult(); }; class Physics2DTestMotionResult; class Physics2DServer : public Object { OBJ_TYPE( Physics2DServer, Object ); static Physics2DServer * singleton; virtual bool _body_test_motion(RID p_body, const Vector2& p_motion, float p_margin=0.08, const Ref& p_result=Ref()); virtual bool _body_test_motion_from(RID p_body, const Matrix32 &p_from, const Vector2& p_motion, float p_margin=0.08, const Ref& p_result=Ref()); protected: static void _bind_methods(); public: static Physics2DServer * get_singleton(); enum ShapeType { SHAPE_LINE, ///< plane:"plane" SHAPE_RAY, ///< float:"length" SHAPE_SEGMENT, ///< float:"length" SHAPE_CIRCLE, ///< float:"radius" SHAPE_RECTANGLE, ///< vec3:"extents" SHAPE_CAPSULE, SHAPE_CONVEX_POLYGON, ///< array of planes:"planes" SHAPE_CONCAVE_POLYGON, ///< Vector2 array:"triangles" , or Dictionary with "indices" (int array) and "triangles" (Vector2 array) SHAPE_CUSTOM, ///< Server-Implementation based custom shape, calling shape_create() with this value will result in an error }; virtual RID shape_create(ShapeType p_shape)=0; virtual void shape_set_data(RID p_shape, const Variant& p_data)=0; virtual void shape_set_custom_solver_bias(RID p_shape, real_t p_bias)=0; virtual ShapeType shape_get_type(RID p_shape) const=0; virtual Variant shape_get_data(RID p_shape) const=0; virtual real_t shape_get_custom_solver_bias(RID p_shape) const=0; //these work well, but should be used from the main thread only virtual bool shape_collide(RID p_shape_A, const Matrix32& p_xform_A,const Vector2& p_motion_A,RID p_shape_B, const Matrix32& p_xform_B, const Vector2& p_motion_B,Vector2 *r_results,int p_result_max,int &r_result_count)=0; /* SPACE API */ virtual RID space_create()=0; virtual void space_set_active(RID p_space,bool p_active)=0; virtual bool space_is_active(RID p_space) const=0; enum SpaceParameter { SPACE_PARAM_CONTACT_RECYCLE_RADIUS, SPACE_PARAM_CONTACT_MAX_SEPARATION, SPACE_PARAM_BODY_MAX_ALLOWED_PENETRATION, SPACE_PARAM_BODY_LINEAR_VELOCITY_SLEEP_TRESHOLD, SPACE_PARAM_BODY_ANGULAR_VELOCITY_SLEEP_TRESHOLD, SPACE_PARAM_BODY_TIME_TO_SLEEP, SPACE_PARAM_CONSTRAINT_DEFAULT_BIAS, }; virtual void space_set_param(RID p_space,SpaceParameter p_param, real_t p_value)=0; virtual real_t space_get_param(RID p_space,SpaceParameter p_param) const=0; // this function only works on fixed process, errors and returns null otherwise virtual Physics2DDirectSpaceState* space_get_direct_state(RID p_space)=0; virtual void space_set_debug_contacts(RID p_space,int p_max_contacts)=0; virtual Vector space_get_contacts(RID p_space) const=0; virtual int space_get_contact_count(RID p_space) const=0; //missing space parameters /* AREA API */ //missing attenuation? missing better override? enum AreaParameter { AREA_PARAM_GRAVITY, AREA_PARAM_GRAVITY_VECTOR, AREA_PARAM_GRAVITY_IS_POINT, AREA_PARAM_GRAVITY_DISTANCE_SCALE, AREA_PARAM_GRAVITY_POINT_ATTENUATION, AREA_PARAM_LINEAR_DAMP, AREA_PARAM_ANGULAR_DAMP, AREA_PARAM_PRIORITY }; virtual RID area_create()=0; virtual void area_set_space(RID p_area, RID p_space)=0; virtual RID area_get_space(RID p_area) const=0; enum AreaSpaceOverrideMode { AREA_SPACE_OVERRIDE_DISABLED, AREA_SPACE_OVERRIDE_COMBINE, AREA_SPACE_OVERRIDE_COMBINE_REPLACE, // Combines, then discards all subsequent calculations AREA_SPACE_OVERRIDE_REPLACE, AREA_SPACE_OVERRIDE_REPLACE_COMBINE // Discards all previous calculations, then keeps combining }; virtual void area_set_space_override_mode(RID p_area, AreaSpaceOverrideMode p_mode)=0; virtual AreaSpaceOverrideMode area_get_space_override_mode(RID p_area) const=0; virtual void area_add_shape(RID p_area, RID p_shape, const Matrix32& p_transform=Matrix32())=0; virtual void area_set_shape(RID p_area, int p_shape_idx,RID p_shape)=0; virtual void area_set_shape_transform(RID p_area, int p_shape_idx, const Matrix32& p_transform)=0; virtual int area_get_shape_count(RID p_area) const=0; virtual RID area_get_shape(RID p_area, int p_shape_idx) const=0; virtual Matrix32 area_get_shape_transform(RID p_area, int p_shape_idx) const=0; virtual void area_remove_shape(RID p_area, int p_shape_idx)=0; virtual void area_clear_shapes(RID p_area)=0; virtual void area_attach_object_instance_ID(RID p_area,ObjectID p_ID)=0; virtual ObjectID area_get_object_instance_ID(RID p_area) const=0; virtual void area_set_param(RID p_area,AreaParameter p_param,const Variant& p_value)=0; virtual void area_set_transform(RID p_area, const Matrix32& p_transform)=0; virtual Variant area_get_param(RID p_parea,AreaParameter p_param) const=0; virtual Matrix32 area_get_transform(RID p_area) const=0; virtual void area_set_collision_mask(RID p_area,uint32_t p_mask)=0; virtual void area_set_layer_mask(RID p_area,uint32_t p_mask)=0; virtual void area_set_monitorable(RID p_area,bool p_monitorable)=0; virtual void area_set_pickable(RID p_area,bool p_pickable)=0; virtual void area_set_monitor_callback(RID p_area,Object *p_receiver,const StringName& p_method)=0; virtual void area_set_area_monitor_callback(RID p_area,Object *p_receiver,const StringName& p_method)=0; /* BODY API */ //missing ccd? enum BodyMode { BODY_MODE_STATIC, BODY_MODE_KINEMATIC, BODY_MODE_RIGID, BODY_MODE_CHARACTER //BODY_MODE_SOFT ?? }; virtual RID body_create(BodyMode p_mode=BODY_MODE_RIGID,bool p_init_sleeping=false)=0; virtual void body_set_space(RID p_body, RID p_space)=0; virtual RID body_get_space(RID p_body) const=0; virtual void body_set_mode(RID p_body, BodyMode p_mode)=0; virtual BodyMode body_get_mode(RID p_body) const=0; virtual void body_add_shape(RID p_body, RID p_shape, const Matrix32& p_transform=Matrix32())=0; virtual void body_set_shape(RID p_body, int p_shape_idx,RID p_shape)=0; virtual void body_set_shape_transform(RID p_body, int p_shape_idx, const Matrix32& p_transform)=0; virtual void body_set_shape_metadata(RID p_body, int p_shape_idx, const Variant& p_metadata)=0; virtual int body_get_shape_count(RID p_body) const=0; virtual RID body_get_shape(RID p_body, int p_shape_idx) const=0; virtual Matrix32 body_get_shape_transform(RID p_body, int p_shape_idx) const=0; virtual Variant body_get_shape_metadata(RID p_body, int p_shape_idx) const=0; virtual void body_set_shape_as_trigger(RID p_body, int p_shape_idx,bool p_enable)=0; virtual bool body_is_shape_set_as_trigger(RID p_body, int p_shape_idx) const=0; virtual void body_remove_shape(RID p_body, int p_shape_idx)=0; virtual void body_clear_shapes(RID p_body)=0; virtual void body_attach_object_instance_ID(RID p_body,uint32_t p_ID)=0; virtual uint32_t body_get_object_instance_ID(RID p_body) const=0; enum CCDMode { CCD_MODE_DISABLED, CCD_MODE_CAST_RAY, CCD_MODE_CAST_SHAPE, }; virtual void body_set_continuous_collision_detection_mode(RID p_body,CCDMode p_mode)=0; virtual CCDMode body_get_continuous_collision_detection_mode(RID p_body) const=0; virtual void body_set_layer_mask(RID p_body, uint32_t p_mask)=0; virtual uint32_t body_get_layer_mask(RID p_body) const=0; virtual void body_set_collision_mask(RID p_body, uint32_t p_mask)=0; virtual uint32_t body_get_collision_mask(RID p_body) const=0; // common body variables enum BodyParameter { BODY_PARAM_BOUNCE, BODY_PARAM_FRICTION, BODY_PARAM_MASS, ///< unused for static, always infinite BODY_PARAM_INERTIA, // read-only: computed from mass & shapes BODY_PARAM_GRAVITY_SCALE, BODY_PARAM_LINEAR_DAMP, BODY_PARAM_ANGULAR_DAMP, BODY_PARAM_MAX, }; virtual void body_set_param(RID p_body, BodyParameter p_param, float p_value)=0; virtual float body_get_param(RID p_body, BodyParameter p_param) const=0; //state enum BodyState { BODY_STATE_TRANSFORM, BODY_STATE_LINEAR_VELOCITY, BODY_STATE_ANGULAR_VELOCITY, BODY_STATE_SLEEPING, BODY_STATE_CAN_SLEEP, }; virtual void body_set_state(RID p_body, BodyState p_state, const Variant& p_variant)=0; virtual Variant body_get_state(RID p_body, BodyState p_state) const=0; //do something about it virtual void body_set_applied_force(RID p_body, const Vector2& p_force)=0; virtual Vector2 body_get_applied_force(RID p_body) const=0; virtual void body_set_applied_torque(RID p_body, float p_torque)=0; virtual float body_get_applied_torque(RID p_body) const=0; virtual void body_add_force(RID p_body, const Vector2& p_offset, const Vector2& p_force)=0; virtual void body_apply_impulse(RID p_body, const Vector2& p_offset, const Vector2& p_impulse)=0; virtual void body_set_axis_velocity(RID p_body, const Vector2& p_axis_velocity)=0; //fix virtual void body_add_collision_exception(RID p_body, RID p_body_b)=0; virtual void body_remove_collision_exception(RID p_body, RID p_body_b)=0; virtual void body_get_collision_exceptions(RID p_body, List *p_exceptions)=0; virtual void body_set_max_contacts_reported(RID p_body, int p_contacts)=0; virtual int body_get_max_contacts_reported(RID p_body) const=0; virtual void body_set_one_way_collision_direction(RID p_body,const Vector2& p_direction)=0; virtual Vector2 body_get_one_way_collision_direction(RID p_body) const=0; virtual void body_set_one_way_collision_max_depth(RID p_body,float p_max_depth)=0; virtual float body_get_one_way_collision_max_depth(RID p_body) const=0; //missing remove virtual void body_set_contacts_reported_depth_treshold(RID p_body, float p_treshold)=0; virtual float body_get_contacts_reported_depth_treshold(RID p_body) const=0; virtual void body_set_omit_force_integration(RID p_body,bool p_omit)=0; virtual bool body_is_omitting_force_integration(RID p_body) const=0; virtual void body_set_force_integration_callback(RID p_body,Object *p_receiver,const StringName& p_method,const Variant& p_udata=Variant())=0; virtual bool body_collide_shape(RID p_body, int p_body_shape,RID p_shape, const Matrix32& p_shape_xform,const Vector2& p_motion,Vector2 *r_results,int p_result_max,int &r_result_count)=0; virtual void body_set_pickable(RID p_body,bool p_pickable)=0; struct MotionResult { Vector2 motion; Vector2 remainder; Vector2 collision_point; Vector2 collision_normal; Vector2 collider_velocity; ObjectID collider_id; RID collider; int collider_shape; Variant collider_metadata; }; virtual bool body_test_motion(RID p_body,const Vector2& p_motion,float p_margin=0.001,MotionResult *r_result=NULL)=0; virtual bool body_test_motion_from(RID p_body,const Matrix32& p_from,const Vector2& p_motion,float p_margin=0.001,MotionResult *r_result=NULL)=0; /* JOINT API */ enum JointType { JOINT_PIN, JOINT_GROOVE, JOINT_DAMPED_SPRING }; enum JointParam { JOINT_PARAM_BIAS, JOINT_PARAM_MAX_BIAS, JOINT_PARAM_MAX_FORCE, }; virtual void joint_set_param(RID p_joint, JointParam p_param, real_t p_value)=0; virtual real_t joint_get_param(RID p_joint,JointParam p_param) const=0; virtual RID pin_joint_create(const Vector2& p_anchor,RID p_body_a,RID p_body_b=RID())=0; virtual RID groove_joint_create(const Vector2& p_a_groove1,const Vector2& p_a_groove2, const Vector2& p_b_anchor, RID p_body_a,RID p_body_b)=0; virtual RID damped_spring_joint_create(const Vector2& p_anchor_a,const Vector2& p_anchor_b,RID p_body_a,RID p_body_b=RID())=0; enum PinJointParam { PIN_JOINT_SOFTNESS }; virtual void pin_joint_set_param(RID p_joint, PinJointParam p_param, real_t p_value)=0; virtual real_t pin_joint_get_param(RID p_joint, PinJointParam p_param) const=0; enum DampedStringParam { DAMPED_STRING_REST_LENGTH, DAMPED_STRING_STIFFNESS, DAMPED_STRING_DAMPING }; virtual void damped_string_joint_set_param(RID p_joint, DampedStringParam p_param, real_t p_value)=0; virtual real_t damped_string_joint_get_param(RID p_joint, DampedStringParam p_param) const=0; virtual JointType joint_get_type(RID p_joint) const=0; /* QUERY API */ enum AreaBodyStatus { AREA_BODY_ADDED, AREA_BODY_REMOVED }; /* MISC */ virtual void free(RID p_rid)=0; virtual void set_active(bool p_active)=0; virtual void init()=0; virtual void step(float p_step)=0; virtual void sync()=0; virtual void flush_queries()=0; virtual void end_sync()=0; virtual void finish()=0; enum ProcessInfo { INFO_ACTIVE_OBJECTS, INFO_COLLISION_PAIRS, INFO_ISLAND_COUNT, INFO_STEP_TIME, INFO_BROAD_PHASE_TIME }; virtual int get_process_info(ProcessInfo p_info)=0; Physics2DServer(); ~Physics2DServer(); }; class Physics2DTestMotionResult : public Reference { OBJ_TYPE( Physics2DTestMotionResult, Reference ); Physics2DServer::MotionResult result; bool colliding; friend class Physics2DServer; protected: static void _bind_methods(); public: Physics2DServer::MotionResult* get_result_ptr() const { return const_cast(&result); } //bool is_colliding() const; Vector2 get_motion() const; Vector2 get_motion_remainder() const; Vector2 get_collision_point() const; Vector2 get_collision_normal() const; Vector2 get_collider_velocity() const; ObjectID get_collider_id() const; RID get_collider_rid() const; Object* get_collider() const; int get_collider_shape() const; Physics2DTestMotionResult(); }; VARIANT_ENUM_CAST( Physics2DServer::ShapeType ); VARIANT_ENUM_CAST( Physics2DServer::SpaceParameter ); VARIANT_ENUM_CAST( Physics2DServer::AreaParameter ); VARIANT_ENUM_CAST( Physics2DServer::AreaSpaceOverrideMode ); VARIANT_ENUM_CAST( Physics2DServer::BodyMode ); VARIANT_ENUM_CAST( Physics2DServer::BodyParameter ); VARIANT_ENUM_CAST( Physics2DServer::BodyState ); VARIANT_ENUM_CAST( Physics2DServer::CCDMode ); VARIANT_ENUM_CAST( Physics2DServer::JointParam ); VARIANT_ENUM_CAST( Physics2DServer::JointType ); VARIANT_ENUM_CAST( Physics2DServer::DampedStringParam ); //VARIANT_ENUM_CAST( Physics2DServer::ObjectType ); VARIANT_ENUM_CAST( Physics2DServer::AreaBodyStatus ); VARIANT_ENUM_CAST( Physics2DServer::ProcessInfo ); #endif