javascript
/
three.js
oglindă de https://github.com/tazdij/three.js.git


			
				
					
						
						
							12345678910111213141516171819202122232425262728293031323334353637383940414243444546474849505152535455565758596061626364
							<!DOCTYPE html>
<html lang="en">
	<head>
		<meta charset="utf-8">
		<script src="../../list.js"></script>
		<script src="../../page.js"></script>
		<link type="text/css" rel="stylesheet" href="../../page.css" />
	</head>
	<body>
		<h1>[name]</h1>

		<p>
		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.
		</p>

		<h2>Convenience properties and *matrixAutoUpdate*</h2>

		There are two ways to update an object's transformation:
		<ol>
			<li>
				Modify the object's *position*, *quaternion*, and *scale* properties, then ask Three.js to recompute the object's matrix from these properties:
				<code>
				object.position = start_position;
				object.quaternion = quaternion;
				object.updateMatrix();
				</code>
				Calling the *updateMatrix* method forces the object's matrix to be recomputed from *position*, *quaternion*, and *scale*. You can also set 
				<code>
				object.matrixAutoUpdate = true;
				</code>
				in lieu of calling *updateMatrix*. This will force the matrix to be recomputed every frame; for static objects, you should therefore set 
				<code>
				object.matrixAutoUpdate = false;
				</code>
			</li>
			<li>
				Modify the object's matrix directly. The [page:Matrix4] class has various methods for modifying the matrix:
				<code>
				object.matrix.setRotationFromQuaternion(quaternion);
				object.matrix.setPosition(start_position);
				object.matrixAutoUpdate = false;
				</code>
				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.
			</li>
		</ol>

		<h2>Object and world matrices</h2>
		<p>
		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].
		</p>
		<p>
		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]().
		</p>

		<h2>Rotation and Quaternion</h2>
		<p>
		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].
		</p>
		<p>
		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.
		</p>

	</body>
</html>