chickadee » physics

Physics

Documentation

A high-level wrapper for Chipmunk2D.

Author

Richard van Roy

Requirements

Vectors

Creation

(create-vect x y) procedure

Creates a new vector.

Properties

(vect-x vect) procedure
(vect-y vect) procedure

Methods

(vect-=? vect-a vect-b) procedure

Check if two vectors are equal.

(vect-add vect-a vect-b) procedure

Adds two vectors.

(vect-sub vect-a vect-b) procedure

Substracts two vectors

(vect-neg vect) procedure

Negate a vector.

(vect-mult vect scalar) procedure

Scalar multiplication

(vect-dot vect-a vect-b) procedure

Vector dot product.

(vect-cross vect-a vect-b) procedure

2D vector cross product analog. The cross product of 2D vectors results in a 3D vector with only a z component. This function returns the value along the z-axis.

(vect-perp vect) procedure

Returns a perpendicular vector. (90 degree rotation)

(vect-rperp vect) procedure

Returns a perpendicular vector. (-90 degree rotation)

(vect-project vect-a vect-b) procedure

Returns the vector projection of vect-a onto vect-b.

(vect-rotate vect-a vect-b) procedure

Uses complex multiplication to rotate vect-a by vect-b. Scaling will occur if vect-a is not a unit vector.

(vect-unrotate vect-a vect-b) procedure

Inverse of (vect-rotate).

(vect-length vect) procedure

Returns the length of v.

(vect-length-squared vect) procedure

Returns the squared length of v. Faster than (vect-length) when you only need to compare lengths.

(vect-lerp vect-a vect-b t) procedure

Linearly interpolate between vect-a and vect-b.

(vect-lerpconst vect-a vect-b t) procedure

Linearly interpolate between vect-a towards vect-b by distance d.

(vect-slerp vect-a vect-b t) procedure

Spherical linearly interpolate between vect-a and vect-b.

(vect-slerpconst vect-a vect-b angle) procedure

Spherical linearly interpolate between vect-a towards vect-b by no more than angle angle in radians.

(vect-normalize vect) procedure

Returns a normalized copy of v. As a special case, it returns (vect-zero) when called on (vect-zero).

(vect-clamp vect length) procedure

Clamp v to length length.

(vect-dist vect-a vect-b) procedure

Returns the distance between vect-a and vect-b.

(vect-dist-squared vect-a vect-b) procedure

Returns the squared distance between vect-a and vect-b. Faster than (cpvdist) when you only need to compare distances.

(vect-near? vect-a vect-b distance) procedure

Returns true if the distance between vect-a and vect-b is less than distance.

Conversions

(angle->vect angle) procedure

Returns the unit length vector for the given angle (in radians).

(vect->angle vect) procedure

Returns the angular direction vect is pointing in (in radians).

Axis Aligned Bounding Boxes

Creation

(create-bb left-bottom right-top) procedure

Creates a new Axis Aligned Bounding Box

Properties

(bb-left-bottom bb) procedure
(bb-right-top bb) procedure

Methods

(bb-intersects? bb-a bb-b) procedure

Returns true if the bounding boxes intersect.

(bb-contains-bb? bb other) procedure

Returns true if bb completely contains other.

(bb-contains-vect? bb vect) procedure

Returns true if bb contains vect.

(bb-merge bb-a bb-b) procedure

Return the minimal bounding box that contains both bb-a and bb-b.

(bb-expand bb vect) procedure

Return the minimal bounding box that contains both bb and vect.

(bb-center bb) procedure

Return the center of bb.

(bb-area bb) procedure

Return the area of bb.

(bb-merged-area bb-a bb-b) procedure

Merges bb-a and bb-b then returns the area of the merged bounding box.

(bb-seqment-query bb vect-a vect-b) procedure

Returns the fraction along the segment query the bounding box is hit. Returns infinity if it doesn’t hit.

(bb-intersects-seqment bb vect-a vect-b) procedure

Returns true if the segment defined by endpoints vect-a and vect-b intersect bb.

(bb-clamp-vect bb vect) procedure

Returns a copy of vect clamped to the bounding box.

(bb-wrap-vect bb vect) procedure

Returns a copy of vect wrapped to the bounding box.

Bodies

Creation

(create-body mass inertia) procedure

Returns a new body. mass and inertia are the mass and moment of inertia for the body. Guessing the mass for a body is usually fine, but guessing a moment of inertia can lead to a very poor simulation.

(create-static-body) procedure

Create additional static bodies with infinite mass and moment of inertia.

Properties

(body-mass body) procedure
(set! (body-mass body) value) setter

Mass of the body.

(body-moment body) procedure
(set! (body-moment body) value) setter

Moment of inertia (MoI or sometimes just moment) of the body. The moment is like the rotational mass of a body. See below for function to help calculate the moment.

(body-position body) procedure
(set! (body-position body) value) setter

Position of the center of gravity of the body. When changing the position you may also want to call (space-reindex-shapes-for-body) to update the collision detection information for the attached shapes if plan to make any queries against the space.

(body-velocity body) procedure
(set! (body-velocity body) value) setter

Linear velocity of the center of gravity of the body.

(body-force body) procedure
(set! (body-force body) value) setter

Force applied to the center of gravity of the body.

(body-angle body) procedure
(set! (body-angle body) value) setter

Rotation of the body in radians. When changing the rotation you may also want to call (space-reindex-shapes-for-body) to update the collision detection information for the attached shapes if plan to make any queries against the space.

(body-angle-velocity body) procedure
(set! (body-angle-velocity body) value) setter

The angular velocity of the body in radians per second.

(body-torque body) procedure
(set! (body-torque body) value) setter

The torque applied to the body.

(body-rotation body) procedure

The rotation vector for the body. Can be used with (vect-rotate) or (vect-unrotate) to perform fast rotations.

(body-velocity-limit body) procedure
(set! (body-velocity-limit body) value) setter

Velocity limit of the body. Defaults to infinity unless you set it specifically. Can be used to limit falling speeds, etc.

(body-angularvelocity-limit body) procedure
(set! (body-angular-velocity-limit body) value) setter

Angular velocity limit of the body in radians per second. Defaults to infinity unless you set it specifically.

(body-space body) procedure

Get the space that body has been added to.

(body-userdata body) procedure
(set! (body-userdata body) value) setter

Userdata can be set to any object and is not used internally.

Sleeping Functions

(body-sleeping? body) procedure

Returns #t if body is sleeping.

(body-activate body) procedure

Reset the idle timer on a body. If it was sleeping, wake it and any other bodies it was touching.

(body-sleep body) procedure

Forces a body to fall asleep immediately even if it’s in midair. Cannot be called from a callback.

(body-activate-static body [filter-shape]) procedure

Similar in function to (body-activate). Activates all bodies touching body. If filter-shape is set, then only bodies touching through it will be awoken.

(body-sleep-with-group body [group]) procedure

When objects in Chipmunk sleep, they sleep as a group of all objects that are touching or jointed together. When an object is woken up, all of the objects in it’s group are woken up. this function allows you group sleeping objects together. It acts identically to (body-sleep) if you don't pass a group by starting a new group. If you pass a sleeping body for group, body will be awoken when group is awoken. You can use this to initialize levels and start stacks of objects in a pre-sleeping state.

Iterators

(body-each-shape body proc) procedure

This functions calls proc on every shape inside this body.

proc should have the following form:

(lambda (shape) ...)
(body-each-constraint body proc) procedure

This functions calls proc on every constraint inside this body.

proc should have the following form:

(lambda (constraint) ...)
(body-each-arbiter body proc) procedure

This functions calls proc on every arbiter inside this body.

proc should have the following form:

(lambda (arbiter) ...)

Moment of Inertia and Area Helper Functions

Use the following functions to approximate the moment of inertia for your body, adding the results together if you want to use more than one.

(moment-for-circle mass radius-a radius-b offset) procedure

Calculate the moment of inertia for a hollow circle, radius-a and radius-b are the inner and outer diameters in no particular order. (A solid circle has an inner diameter of 0)

(moment-for-seqment mass vect-a vect-b) procedure

Calculate the moment of inertia for a line segment. The endpoints vect-a and vect-b are relative to the body.

(moment-for-polygon vertices offset) procedure

Calculate the moment of inertia for a solid polygon shape assuming it’s center of gravity is at it’s centroid. The offset is added to each vertex.

(moment-for-box width height) procedure

Calculate the moment of inertia for a solid box centered on the body.

(area-for-circle radius-a radius-b) procedure

Area of a hollow circle.

(area-for-segment vect-a vect-b radius) procedure

Area of a beveled segment. (Will always be zero if radius is zero)

(area-for-polygon vertices) procedure

Signed area of a polygon shape. Returns a negative number for polygons with a backwards winding.

Coordinate Conversion Functions

Many things are defined in coordinates local to a body meaning that the (0,0) is at the center of gravity of the body and the axis rotate along with the body.

(body-local->world body vect) procedure

Convert from body local coordinates to world space coordinates.

(body-world->local body vect) procedure

Convert from world space coordinates to body local coordinates.

Applying Forces and Torques

People are sometimes confused by the difference between a force and an impulse. An impulse is basically a very large force applied over a very short period of time, like a ball hitting a wall or cannon firing. Chipmunk treats impulses as if they occur instantaneously by simply adding directly to the velocity of an object. Both impulses and forces are affected the mass of an object. Double the mass of the object and halve the effect.

(body-reset-forces body) procedure

Zero both the forces and torques currently applied to the body.

(body-apply-force body f r) procedure

Add the force f to body at a relative offset r from the center of gravity.

(body-apply-impulse body i j) procedure

Add the impulse j to body at a relative offset r from the center of gravity.

Note: Both the (body-apply-force) and (body-apply-impulse) functions take a force or impulse in absolute coordinates and applies it at a relative offset in absolute coordinates. (The offset is relative to the center of gravity, but is not rotated with the body)

Misc functions

(body-static? body) procedure

Returns #t if body is a static body. Either (space-static-body) or a body created with (create-static-body).

(body-roque? body) procedure

Returns #t if body has never been added to a space.

Collision Shapes

Properties

(shape-body shape) procedure
(set! (shape-body shape) value) setter

The rigid body the shape is attached to. Can only be set when the shape is not added to a space.

(shape-bb shape) procedure
(set! (shape-bb shape) value) setter

The bounding box of the shape. Only guaranteed to be valid after (shape-cache-bb) or (space-step) is called. Moving a body that a shape is connected to does not update it’s bounding box. For shapes used for queries that aren’t attached to bodies, you can also use (shape-update).

(shape-sensor shape) procedure
(set! (shape-sensor shape) value) setter

A boolean value if this shape is a sensor or not. Sensors only call collision callbacks, and never generate real collisions.

(shape-elasticity shape) procedure
(set! (shape-elasticity shape) value) setter

Elasticity of the shape. A value of 0.0 gives no bounce, while a value of 1.0 will give a “perfect” bounce. However due to inaccuracies in the simulation using 1.0 or greater is not recommended however. The elasticity for a collision is found by multiplying the elasticity of the individual shapes together.

(shape-friction shape) procedure
(set! (shape-friction shape) value) setter

Friction coefficient. Chipmunk uses the Coulomb friction model, a value of 0.0 is frictionless. The friction for a collision is found by multiplying the friction of the individual shapes together.

(shape-surface-velocity shape) procedure
(set! (shape-surface-velocity shape) value) setter

The surface velocity of the object. Useful for creating conveyor belts or players that move around. This value is only used when calculating friction, not resolving the collision.

(shape-collision-type shape) procedure
(set! (shape-collision-type shape) value) setter

You can assign types to Chipmunk collision shapes that trigger callbacks when objects of certain types touch.

(shape-group shape) procedure
(set! (shape-group shape) value) setter
High-level interface procedure

TODO

(shape-layers shape) procedure
(set! (shape-layers shape) value) setter
High-level interface procedure

TODO

(shape-space shape) procedure

Get the space that shape has been added to.

(shape-userdata shape) procedure
(set! (shape-userdata shape) value) setter

This can be set to any value.

Misc Functions

(shape-cache-bb shape) procedure

Synchronizes shape with the body its attached to.

(shape-update shape position rotation) procedure

Sets the position and rotation of the shape.

(reset-id-counter) procedure

Chipmunk keeps a counter so that every new shape is given a unique hash value to be used in the spatial index. Because this affects the order in which the collisions are found and handled, you can reset the shape counter every time you populate a space with new shapes. If you don’t, there might be (very) slight differences in the simulation.

Circles

Creation
(create-circle body radius offset) procedure

body is the body to attach the circle to, offset is the offset from the body’s center of gravity in body local coordinates.

Properties
(circle-offset cirlce-shape) procedure
(circle-radius cirlce-shape) procedure

Segments

Creation
(create-segment-shape body vect-a vect-b radius) procedure

body is the body to attach the segment to, vect-a and vect-b are the endpoints, and radius is the thickness of the segment.

Properties
(segment-shape-a segment-shape) procedure
(segment-shape-b segment-shape) procedure
(segment-shape-normal segment-shape) procedure
(segment-shape-radius segment-shape) procedure

Polygons

Creation
(create-polygon-shape body vertices offset [radius]) procedure

body is the body to attach the poly to, vertices is an list of vectors defining a convex hull with a clockwise winding, offset is the offset from the body’s center of gravity in body local coordinates. An assertion will be thrown the vertexes are not convex or do not have a clockwise winding.

Properties
(polygon-shape-vertex-count polygon-shape) procedure
(polygon-shape-vertices polygon) procedure
(polygon-shape-radius) procedure
Helper Functions
(valid-polygon? vertices) procedure

Check if a vertex array is convex and with the correct winding.

(centroid-for-polygon vertices) procedure

Calculate the centroid for a polygon.

(centroid-for-polygon vertices) procedure

Center a polygon to (0,0). Subtracts the centroid from each vertex.

Convex Hull Helper Functions

TODO

Boxes

TODO

Space

Creation

(create-space) procedure

Properties

(space-iterations space) procedure
(set! (space-iterations space) value) setter

Iterations allow you to control the accuracy of the solver. Defaults to 10.

(space-gravity space) procedure
(set! (space-gravity space) value) setter

Global gravity applied to the space. Defaults to (vect-zero). Can be overridden on a per body basis by writing custom integration functions.

(space-damping space) procedure
(set! (space-damping space) value) setter

Amount of simple damping to apply to the space. A value of 0.9 means that each body will lose 10% of it’s velocity per second. Defaults to 1. Like gravity can be overridden on a per body basis.

(space-idle-speed-treshold space) procedure
(set! (space-idle-speed-treshold space) value) setter

Speed threshold for a body to be considered idle. The default value of 0 means to let the space guess a good threshold based on gravity.

(space-sleep-time-treshold space) procedure
(set! (space-sleep-time-treshold space) value) setter

Time a group of bodies must remain idle in order to fall asleep. The default value of INFINITY disables the sleeping feature.

(space-collision-slop space) procedure
(set! (space-collision-slop space) value) setter

Amount of overlap between shapes that is allowed. It’s encouraged to set this as high as you can without noticable overlapping as it improves the stability. It defaults to 0.1.

(space-collision-bias space) procedure
(set! (space-collision-bias space) value) setter

Chipmunk allows fast moving objects to overlap, then fixes the overlap over time. Overlapping objects are unavoidable even if swept collisions are supported, and this is an efficient and stable way to deal with overlapping objects. The bias value controls what percentage of overlap remains unfixed after a second and defaults to ~0.2%. Valid values are in the range from 0 to 1, but using 0 is not recommended for stability reasons. The default value is calculated as (vect-pow((- 1.0 0.1) 60.0) meaning that Chipmunk attempts to correct 10% of error ever 160th of a second. 'Note<procedure> Very very few games will need to change this value.</procedure>

(space-collision-persistence space) procedure
(set! (space-collision-persistence space) value) setter

The number of frames the space keeps collision solutions around for. Helps prevent jittering contacts from getting worse. This defaults to 3 and very very very few games will need to change this value.

(space-current-time-step space) procedure

Retrieves the current (if you are in a callback from (space-step)) or most recent (outside of a (space-step) call) timestep.

(space-locked?) procedure

Returns true when in a callback meaning that you cannot add''remove objects from the space. Can be used to choose to create a post-step callback instead.

(space-userdata space) procedure
(set! (space-userdata space) value) setter

This can be set to any value.

(space-static-body space) procedure

A dedicated static body for the space. You don’t have to use it, but because it’s memory is managed automatically with the space it’s very convenient. You can set its user data pointer to something helpful if you want for callbacks.

(space-bodies space) procedure

Returns a list of all bodies added to this space.

(space-shapes space) procedure

Returns a list of all shapes added to this space.

(space-constraints space) procedure

Returns a list of all constraints added to this space.

Operations

Note: It is not possible to add/remove something to/from a space inside callbacks other then post-step.

(space-add-shape space shape) procedure
(space-add-static-shape space shape) procedure
(space-remove-shape space shape) procedure
(space-has-shape? space shape) procedure
(space-add-body space body) procedure
(space-remove-body space body) procedure
(space-has-body? space body) procedure
(space-add-constraint space constraint) procedure
(space-remove-constraint space constraint) procedure
(space-has-constraint? space constraint) procedure

Iterators

(space-each-body space func) procedure

This functions calls proc on every body inside this space.

proc should have the following form:

(lambda (body) ...)
(space-each-shape space func) procedure

This functions calls proc on every shape inside this space.

proc should have the following form:

(lambda (shape) ...)
(space-each-constraint space func) procedure

This functions calls proc on every constraint inside this space.

proc should have the following form:

(lambda (constraint) ...)

Simulating the Space

(space-step space) procedure

Update the space for the given time step. Using a fixed time step is highly recommended.

Enabling and Tuning the Spatial Hash

If you have thousands of objects that are all approximately the same size, the spatial hash may be for you.

(space-use-spatital-hash space dim count) procedure

Switch the space to use a spatial hash instead of the bounding box tree.

Collision Handlers

(space-on-collision-begin space) procedure
(set! (space-on-collision-begin space) func) setter

Two shapes just started touching for the first time this step. Return true from the callback to process the collision normally or false to cause Chipmunk to ignore the collision entirely. If you return false, the /presolve/ and /postsolve/ callbacks will never be run, but you will still recieve a separate event when the shapes stop overlapping.

func must have the form:

(lambda (arbiter space data) ...) -> boolean

Return #t from the callback to process the collision normally or #f to cause Chipmunk to ignore the collision entirely. If you return #f, the (presolve) and (postSolve) callbacks will never be run, but you will still recieve a separate event when the shapes stop overlapping.

(space-on-collision-presolve space) procedure
(set! (space-on-collision-presolve space) func) setter

Two shapes are touching during this step. Return #f from the callback to make Chipmunk ignore the collision this step or #t to process it normally. Additionally, you may override collision values using /(set! arbiter-fricion ...)/ /(set! arbiter-elasticity ...)/ or /(set! arbiter-surface-velocity ...)/ to provide custom friction, elasticity, or surface velocity values.

func must have the form:

(lambda (arbiter space data) ...)
(space-on-collision-postsolve space) procedure
(set! (space-on-collision-postsolve space) func) setter

Two shapes are touching and their collision response has been processed. You can retrieve the collision impulse or kinetic energy at this time if you want to use it to calculate sound volumes or damage amounts.

func must have the form:

(lambda (arbiter space data) ...)
(space-on-collision-seperate space) procedure
(set! (space-on-collision-seperate space) func) setter

Two shapes have just stopped touching for the first time this step. To ensure that (begin) and (separate) are always called in balanced pairs, it will also be called when removing a shape while its in contact with something or when deallocating the space.

func must have the form:

(lambda (arbiter space data) ...) -> boolean
(space-add-collision-handler space type-a type-b begin presolve postsolve seperate [data]) procedure

Adds callback functions for collision types type-a and type-b see previous sections for the forms of the callback functions.

(space-remove-collision-handler space type-a type-b) procedure

Remove a collision handler for a given collision type pair.

(space-add-poststep-callback space func key [data]) procedure

Register a default collision handler to be used when no specific collision handler is found. The space is given a default handler when created that returns #t for all collisions in (begin) and (presolve) and does nothing in the (postsolve) and (separate) callbacks.

Constraints

Properties

(constraint-a constraint) procedure
(constraint-b constraint) procedure

Getters for the two bodies the constraint is attached to.

(constraint-max-force constraint) procedure
(set! (constraint-max-force constraint) value) setter

The maximum force that the constraint can use to act on the two bodies. Defaults to infinity.

(constraint-error-bias constraint) procedure
(set! (constraint-error-bias constraint) value) setter

The percentage of joint error that remains unfixed after a second. This works exactly the same as the collision bias property of a space, but applies to fixing error (stretching) of joints instead of overlapping collisions.

(constraint-max-bias constraint) procedure
(set! (constraint-max-bias constraint) value) setter

The maximum speed at which the constraint can apply error correction. Defaults to infinity.

(constraint-space constraint) procedure

Get the space that constraint has been added to.

(constraint-impulse constraint) procedure

The most recent impulse that constraint applied. To convert this to a force, divide by the timestep passed to (space-step). You can use this to implement breakable joints to check if the force they attempted to apply exceeded a certain threshold.

(space-userdata space) procedure
(set! (space-userdata space) value) setter

This can be set to any value.

(constraint-userdata constraint) procedure
(set! (constraint-userdata constraint) value) setter

This can be set to any value.

Pin Joints

Creation

<procedure>(create-pin-joint body-a body-b anchor-a anchor-b)<procedure> a and b are the two bodies to connect, and anchor-a and anchor-b are the anchor points on those bodies. The distance between the two anchor points is measured when the joint is created. If you want to set a specific distance, use the setter function to override it

Properties
(constraint-anchor-a constraint) procedure
(set! (constraint-anchor-a constraint) value) setter
(constraint-anchor-b constraint) procedure
(set! (constraint-anchor-b constraint) value) setter
(constraint-distance constraint) procedure
(set! (constraint-distance constraint) value) setter

Slide Joints

Creation
(create-slide-joint body-a body-b anchor-a anchor-b min max) procedure

a and b are the two bodies to connect, anchor-a and anchor-b are the anchor points on those bodies, and min and max'' define the allowed distances of the anchor points.

Properties
(constraint-anchor-a constraint) procedure
(set! (constraint-anchor-a constraint) value) setter
(constraint-anchor-b constraint) procedure
(set! (constraint-anchor-b constraint) value) setter
(constraint-min constraint) procedure
(set! (constraint-min constraint) value) setter
(constraint-max constraint) procedure
(set! (constraint-max constraint) value) setter

Pivot Joints

Creation
(create-pivot-joint-with-pivot body-a body-b pivot) procedure
(create-pivot-joint-with-anchors body-a body-b anchor-a anchor-b) procedure

a and b are the two bodies to connect, and pivot is the point in world coordinates of the pivot. Because the pivot location is given in world coordinates, you must have the bodies moved into the correct positions already. Alternatively you can specify the joint based on a pair of anchor points, but make sure you have the bodies in the right place as the joint will fix itself as soon as you start simulating the space.

Properties
(constraint-anchor-a constraint) procedure
(set! (constraint-anchor-a constraint) value) setter
(constraint-anchor-b constraint) procedure
(set! (constraint-anchor-b constraint) value) setter

Groove Joints

Creation
(create-groove-joint body-a body-b groove-a groove-b anchor-b) procedure

The groove goes from 'groove-a to groove-b on body-a, and the pivot is attached to anchor-b on body-b''. All coordinates are body local.

Properties
(constraint-anchor constraint) procedure
(set! (constraint-anchor constraint) value) setter
(constraint-groove-a constraint) procedure
(set! (constraint-groove-a constraint) value) setter
(constraint-groove-b constraint) procedure
(set! (constraint-groove-b constraint) value) setter

Damped Spring

Creation
(create-damped-spring body-a body-b anchor-a anchor-b rest-length stiffness damping) procedure

Defined much like a slide joint. rest-length is the distance the spring wants to be, stiffness is the spring constant (Young’s modulus), and damping is how soft to make the damping of the spring.

Properties
(constraint-anchor-a constraint) procedure
(set! (constraint-anchor-a constraint) value) setter
(constraint-anchor-b constraint) procedure
(set! (constraint-anchor-b constraint) value) setter
(constraint-rest-length constraint) procedure
(set! (constraint-rest-length constraint) value) setter
(constraint-stiffness constraint) procedure
(set! (constraint-stiffness constraint) value) setter
(constraint-damping constraint) procedure
(set! (constraint-damping constraint) value) setter

Damped Rotary Spring

Creation
(create-damped-rotary-spring body-a body-b anchor-a anchor-b rest-angle stiffness damping) procedure

Like a damped spring, but works in an angular fashion. rest-angle is the relative angle in radians that the bodies want to have, stiffness and damping work basically the same as on a damped spring.

Properties
(constraint-length constraint) procedure
(set! (constraint-length constraint) value) setter
(constraint-stiffness constraint) procedure
(set! (constraint-stiffness constraint) value) setter
(constraint-damping constraint) procedure
(set! (constraint-damping constraint) value) setter

Rotary Limit Joint

Creation
(create-rotary-limit-joint body-a body-b min max) procedure

Constrains the relative rotations of two bodies. min and max are the angular limits in radians. It is implemented so that it’s possible to for the range to be greater than a full revolution.

Properties
(constraint-min constraint) procedure
(set! (constraint-min constraint) value) setter
(constraint-max constraint) procedure
(set! (constraint-max constraint) value) setter

Ratchet Joint

Creation
(create-ratchet-joint body-a body-b ratchet phase) procedure

Works like a socket wrench. ratchet is the distance between “clicks”, phase is the initial offset to use when deciding where the ratchet angles are.

Properties
(constraint-angle constraint) procedure
(set! (constraint-angle constraint) value) setter
(constraint-phase constraint) procedure
(set! (constraint-phase constraint) value) setter
(constraint-ratchet constraint) procedure
(set! (constraint-ratchet constraint) value) setter

Gear Joint

Creation
(create-gear-joint body-a body-b phase ratio) procedure

Keeps the angular velocity ratio of a pair of bodies constant. 'ratio' is always measured in absolute terms. It is currently not possible to set the ratio in relation to a third body’s angular velocity. 'phase' is the initial angular offset of the two bodies.

Properties
(constraint-phase constraint) procedure
(set! (constraint-phase constraint) value) setter
(constraint-ratio constraint) procedure
(set! (constraint-ratio constraint) value) setter

Simple Motor

Creation
(create-simple-motor body-a body-b rate) procedure

Keeps the relative angular velocity of a pair of bodies constant. rate is the desired relative angular velocity. You will usually want to set an force (torque) maximum for motors as otherwise they will be able to apply a nearly infinite torque to keep the bodies moving.

Properties
(constraint-rate constraint) procedure
(set! (constraint-rate constraint) value) setter

Queries

TODO Documentation TODO Make something nice for passing layers

(space-nearest-point-query space point max-distance layers group [data]) procedure
(space-segment-query space start end layers group [data]) procedure
(space-bb-query space bb layers group func data) procedure

TODO Make data optional

(space-shape-query space shape func [data]) procedure

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