Three.js（二）LOD源码注释

最新推荐文章于 2024-09-27 10:00:00 发布

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最新推荐文章于 2024-09-27 10:00:00 发布

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本文详细解析了Three.js中的LOD(Level of Detail)组件源码。介绍了如何通过LOD组件根据观察者与对象间的距离自动调整场景中模型的细节级别，以实现优化渲染性能的目的。文章还展示了LOD组件的主要功能，包括添加不同级别的细节对象、根据距离选择合适的细节层级以及更新显示的细节等级。

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//对lod的源码进行了注释
/**
* @author mikael emtinger / http://gomo.se/
* @author alteredq / http://alteredqualia.com/
* @author mrdoob / http://mrdoob.com/
*/
//  目录src/objects/LOD.js
<script>
	THREE.LOD = function () 
	{
		THREE.Object3D.call( this );
		this.objects = [];
	};


	THREE.LOD.prototype = Object.create( THREE.Object3D.prototype );
	//添加细节
	THREE.LOD.prototype.addLevel = function ( object, distance ) 
	{
		if ( distance === undefined ) 
			distance = 0;//未定义距离时为0
		distance = Math.abs( distance );//取距离的绝对值
		//将各个细节的距离进行从小到大的排序
		for ( var l = 0; l < this.objects.length; l ++ ) 
		{
			if ( distance < this.objects[ l ].distance ) 
			{
				break;
			}
		}

		this.objects.splice( l, 0, { distance: distance, object: object } );//?objects.splice
		this.add( object );

	};
	//根据距离返回对应层次的对象
	THREE.LOD.prototype.getObjectForDistance = function ( distance ) 
	{
		//排序由小到大遍历
		for ( var i = 1, l = this.objects.length; i < l; i ++ )
		{
			if ( distance < this.objects[ i ].distance )
			{

				break;
			}
		}
		return this.objects[ i - 1 ].object;
	};
	//更新显示的层次
	THREE.LOD.prototype.update = function () 
	{
	
		var v1 = new THREE.Vector3();//点1
		var v2 = new THREE.Vector3();//点2
		return function ( camera ) 
		{
			//当细节层次不为1时
			if ( this.objects.length > 1 ) 
			{
				v1.setFromMatrixPosition( camera.matrixWorld );//相机的矩阵
				v2.setFromMatrixPosition( this.matrixWorld );//LOD的矩阵
				var distance = v1.distanceTo( v2 );//相机到LOD的距离
				this.objects[ 0 ].object.visible = true;//第一层（细节最详细）的可见性为true
				//向细节不详细的层次距离遍历
				for ( var i = 1, l = this.objects.length; i < l; i ++ ) 
				{
					//距离小的详细程度高的可见度为false
					if ( distance >= this.objects[ i ].distance ) 
					{
						this.objects[ i - 1 ].object.visible = false;
						this.objects[ i ].object.visible = true;
					} 
					//到达对应的详细程度的距离区间后跳出
					else 
					{
						break;
					}
				}	
				//对应级别向后的可见度为false
				for( ; i < l; i ++ ) 
				{
					this.objects[ i ].object.visible = false;
				}
			}
		};
	}();

	THREE.LOD.prototype.clone = function ( object ) 
	{	
		//未定义时声明lod
		if ( object === undefined ) 
			object = new THREE.LOD();
		//将LOD复制到object中
		THREE.Object3D.prototype.clone.call( this, object); 
		//依次添加每个细节到object中
		for ( var i = 0, l = this.objects.length; i < l; i ++ )
		{
			var x = this.objects[i].object.clone();
			x.visible = i === 0;
			object.addLevel( x, this.objects[i].distance );
		}
		return object;
	};
</script>