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64 lines
3.3 KiB
HTML
64 lines
3.3 KiB
HTML
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<!DOCTYPE html>
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<html lang="en">
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<head>
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<meta charset="utf-8">
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<script src="../../list.js"></script>
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<script src="../../page.js"></script>
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<link type="text/css" rel="stylesheet" href="../../page.css" />
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</head>
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<body>
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<h1>[name]</h1>
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<p>
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Three.js uses *matrices* to encode 3D transformations---translations (position), rotations, and scaling. Every instance of [page:Object3D] has a [page:Object3D.matrix matrix] which stores that object's position, rotation, and scale. This page describes how to update an object's transformation.
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</p>
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<h2>Convenience properties and *matrixAutoUpdate*</h2>
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There are two ways to update an object's transformation:
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<ol>
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<li>
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Modify the object's *position*, *quaternion*, and *scale* properties, then ask Three.js to recompute the object's matrix from these properties:
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<code>
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object.position = start_position;
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object.quaternion = quaternion;
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object.updateMatrix();
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</code>
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Calling the *updateMatrix* method forces the object's matrix to be recomputed from *position*, *quaternion*, and *scale*. You can also set
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<code>
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object.matrixAutoUpdate = true;
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</code>
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in lieu of calling *updateMatrix*. This will force the matrix to be recomputed every frame; for static objects, you should therefore set
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<code>
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object.matrixAutoUpdate = false;
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</code>
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</li>
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<li>
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Modify the object's matrix directly. The [page:Matrix4] class has various methods for modifying the matrix:
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<code>
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object.matrix.setRotationFromQuaternion(quaternion);
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object.matrix.setPosition(start_position);
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object.matrixAutoUpdate = false;
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</code>
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Note that *matrixAutoUpdate* <emph>must</emph> be set to *false* in this case, and you should make sure <emph>not</emph> to call *updateMatrix*. Calling *updateMatrix* will clobber the manual changes made to the matrix, recalculating the matrix from *position*, *scale*, and so on.
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</li>
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</ol>
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<h2>Object and world matrices</h2>
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<p>
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An object's [page:Object3D.matrix matrix] stores the object's transformation <emph>relative</emph> to the object's [page:Object3D.parent parent]; to get the object's transformation in <emph>world</emph> coordinates, you must access the object's [page:Object3D.matrixWorld].
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</p>
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<p>
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When either the parent or the child object's transformation changes, you can request that the child object's [page:Object3D.matrixWorld matrixWorld] be updated by calling [page:Object3D.updateMatrixWorld updateMatrixWorld]().
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</p>
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<h2>Rotation and Quaternion</h2>
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<p>
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Three.js provides two ways of representing 3D rotations: [page:Euler Euler angles] and [page:Quaternion Quaternions], as well as methods for converting between the two. Euler angles are subject to a problem called "gimbal lock," where certain configurations can lose a degree of freedom (preventing the object from being rotated about one axis). For this reason, object rotations are <emph>always</emph> stored in the object's [page:Object3D.quaternion quaternion].
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</p>
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<p>
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Previous versions of the library included a *useQuaternion* property which, when set to false, would cause the object's [page:Object3D.matrix matrix] to be calculated from an Euler angle. This practice is deprecated---instead, you should use the [page:Object3D.setRotationFromEuler setRotationFromEuler] method, which will update the quaternion.
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</p>
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</body>
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</html>
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