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Add pick parenting markdeep doc
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docs/interface/raypick/pick-parenting.md.html
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docs/interface/raypick/pick-parenting.md.html
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<meta charset="utf-8">
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**Pick Parenting**
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# What is a pick?
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A pick calculates spatial information about the world on on the client.
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Picks are immutable to allow efficient use by scripts. There are currently four types of picks:
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- Ray pick - Finds the first intersected object along a straight path
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- Parabola pick - Finds the first intersected object along a parabolic path
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- Stylus pick - Finds the distance between a point and a list of whitelisted objects
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- Collision pick - Uses a volume to check for collisions in the physics engine
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With the exception of collision picks, all picks use the visible appearance of the object to check for collisions.
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# What is parenting?
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Parenting allows an object's position, orientation, and scale (where applicable) to be calculated to another object. This collection of state defines the transform of the object.
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Pick parenting allows the pick's transform to be calculated relative to another object, without creating a new pick.
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# What can be parented to what?
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Child type: | Entity | My Avatar | Other Avatar | 3D Overlay | Pick^1 | Pointer^1
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---------------|----------|-------------|----------------|--------------|----------|---------------
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Entity | yes | no | no | yes | yes | yes
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My Avatar | yes | no | no | yes | yes | yes
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Other Avatar | yes | no | no | yes | yes | yes
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3D Overlay | yes | no | no | yes | yes | yes
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Pick | no | no | no | no | yes | yes
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Pointer | no | no | no | no | no | no
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The Mouse | no | no | no | no | yes | yes
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- ^1 Excluding stylus, which can only be parented to My Avatar's hands
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# How pick parenting works
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This section describes what happens when picks are parented to things.
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Since pointers use picks to calculate their results, the rules below
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also apply when pointers are parented to things.
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## Parent transform exposed
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The way a pick is moved/rescaled depends on its parent. In particular,
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parenting to a pick actually parents to the pick's result, which
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has no notion of scale. A pick can also be transformed relative to
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a joint on a model, such as an avatar's hand.
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Parent type: | Entity/Avatar | 3D Overlay | Pick
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--------------------------|-----------------|--------------|--------
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Has position | yes | yes | yes
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Has orientation | yes | yes | no
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Has scale | yes | yes | no
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Can have joints | yes | no | no
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## Entity or overlay parent
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Parenting a pick to an entity or overlay works similarly to
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parenting entities to other things. However, unlike entities,
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picks with scale will rescale their dimensions when
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their parent rescales.
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************************************************************************
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* May have a joint, otherwise parent to the parent's origin *
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* | *
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* scale ^ +--+------+ ^ --+ orientation *
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* determined / / | /| |orientation \ offset *
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* from / / v / | | v *
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* dimensions / / o /..|...................... ^ *
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* +-> +---------+ | ------------. . / *
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* | | | / position +----> */ <----+ *
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* | | | / offset child *
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* | | |/ ^ transform*
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* v +---------+ / <---+ *
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* . +-> dimensions *
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* . . . . . . . . . . . . . . | relative *
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* . . . v to parent *
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************************************************************************
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!!! WARNING
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Skew is not supported for collision picks. Scaling a parent entity or
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overlay non-uniformly can lead to inaccurate shapes for the child
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collision pick.
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## Avatar parent
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A pick parented to an avatar behaves like a wearable. It will maintain
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its position relative to some point on the avatar's body. If the pick
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has scale (currently only collision picks), then the pick will rescale
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when the avatar rescales.
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****************************************************************
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* Avatar .---. hand ^ -. *
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* | | | joint / | *
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* '-----> | | \ /orientation | *
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* '-+-' +-> o | *
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* | / ^ position |relative *
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* +---------' +----- |avatar *
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* | |scale *
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* | if not a joint, |factor *
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* | parent to the |(default: 1) *
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* | avatar's origin | *
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* |\ | |uniform scale *
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* | \ | | ^ *
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* | \ | | +-> *
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* | o \ <-+ -' v *
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****************************************************************
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***************************************************************
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* orientation offset *
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* <-----+ *
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* ^ \ *
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* \ *
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* \ child *
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* Avatar .---. hand .......... * <-- transform *
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* | | | joint . ^ | *
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* '-----> | | \ . / v *
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* '-+-' +-> o ---------+ ^ *
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* | / position +-> scale *
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* +---------' offset v relative *
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* | to avatar *
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***************************************************************
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## Pick parent
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Picks can also be parented to other picks.
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When this is done, the child pick is actually parented to
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the parent pick's result, not the pick itself.
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A pick parented to another pick will have its position changed,
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but not its orientation or scale.
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### Ray pick parent
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**********************************
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* position *
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* o *
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* \ \ orientation *
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* \ \ *
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* \ v . . . . *
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* \ . *
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* \ . result transform *
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* * <-- no scale *
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* . no orientation *
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* . *
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**********************************
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### Parabola pick parent
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**************************************************************
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* .------. acceleration *
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* + + | ^ *
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* speed x ^ / \ . | | *
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* orientation / / \ . v | *
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* / / * y axis to rotate *
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* | . ^ acceleration with *
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* o . | *
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* position result transform *
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* no scale *
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* no orientation *
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**************************************************************
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### Stylus pick parent
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********************************************
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* *
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* *
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* . *
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* . *
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* . *
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* .---. avatar * *
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* | | hand / ^. *
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* | | \ / \ . *
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* '-+-' +-> o \ *
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* | / result transform *
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* +---------' no scale *
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* | no orientation *
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********************************************
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### Collision pick parent
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********************************************
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* *
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* .---. *
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* | | <-- collision pick *
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* | | *
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* | *<-+--- result transform at *
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* | | collision pick position *
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* | | no scale *
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* . . . '---' . . no orientation *
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* *
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********************************************
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# Effect of scale on picks
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Scale affects the position and shape of picks, which in turn affects the pick result.
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Scale currently does not affect the max distance of a pick.
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## Ray and stylus pick scaling
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Rescaling the parent of a ray pick or stylus pick can result in a translation of the pick.
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***************************************
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* before after *
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* *
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* pick *
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* pick +--------------+ ^ *
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* ^ | |/ *
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* +-----+/ | o *
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* | o | | *
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* | | | | *
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* +-----+ | | *
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* parent | | *
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* +--------------+ *
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* parent *
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* *
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***************************************
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## Parabola pick scaling
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***************************************************************************
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* before after after *
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* (scaleWithParent (scaleWithParent *
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* is false) is true) *
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* *
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* .----. *
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* + + *
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* .--. / \ *
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* + + / \ *
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* .--. / \ / \ *
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* + + /pick \ /pick \ *
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* / \ +-------o +-------o *
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* /pick \ | | | | *
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* +---o | | | | *
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* | | | | | | *
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* +---+ +-------+ +-------+ *
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* parent parent parent *
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***************************************************************************
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## Collision pick scaling
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Collision picks use the full transform of their parent (position, orientation, and scale/dimensions).
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When first created, a collision pick's transform is defined in world space.
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As the parent rescales, the collision pick rescales proportionally.
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The collision pick's threshold also rescales. The change is proportional to the largest
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dimension of the parent. So, if the largest dimension of the parent was 3.0 and is now 6.0,
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the threshold doubles.
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************************************************************
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* *
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* before after *
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* *
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* pick *
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* +------------+ *
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* | | *
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* | ........ | *
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* | . . | *
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* | . . | *
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* | . . | *
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* pick | . . | *
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* +-----+ | ........ +___ *
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* |.....| | | theshold *
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* |. .| theshold +------------+--- *
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* |.....|___ | *
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* +-----+--- <-+ *
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* +----------+ *
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* +---+ / \ *
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* +-----+ +--------------+ *
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* parent parent *
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* *
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************************************************************
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<style class="fallback">body{visibility:hidden}</style><script>markdeepOptions={tocStyle:'medium'};</script>
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<link rel="stylesheet" href="../../markdeep_apidoc.css?">
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<!-- Markdeep: --><style class="fallback">body{visibility:hidden;white-space:pre;font-family:monospace}</style><script src="../../markdeep.min.js"></script><script>window.alreadyProcessedMarkdeep||(document.body.style.visibility="visible")</script>
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