设置细节层次

As an example, we will use the tubes_constructor_chrome_1120.fbx model from the Oil Refinery demo (available in UNIGINE SDK Browser). This FBX consists of several meshes, each of which represents an element of the tubes constructor.例如，我们将使用炼油厂演示中的 tubes_constructor_chrome_1120.fbx 模型（在 UNIGINE SDK 浏览器中可用）。这个 FBX 由几个网格组成，每个网格代表管道构造器的一个元素。

Perform the following in a 3D editor:在 3D 编辑器中执行以下操作：

1. Create several meshes for different LODs of your model: a detailed mesh for the closest LOD and a number of less detailed meshes for farther LODs.为模型的不同 LOD 创建多个网格：为最近的 LOD 创建一个详细的网格，为更远的 LOD 创建一些不太详细的网格。

   注意

   When naming the meshes, add a postfix to specify the LOD each mesh represents. For example: _lod_0 for the 1st LOD, _lod_1 for the 2nd LOD, etc. 在命名网格时，添加一个后缀来指定每个网格所代表的 LOD。例如：_lod_0 表示第 1 个 LOD，_lod_1 表示第 2 个 LOD，等等。

   For example, for each mesh representing an element of the tubes constructor (10 meshes), there are 3 meshes representing LODs:例如，对于表示管构造器元素的每个网格（10 个网格），有 3 个网格表示 LOD：

   

2. Export the meshes as an .fbx file.导出网格作为 .fbx 文件。

To import the model into UNIGINE, drag and drop the previously exported FBX file to the Asset Browser and perform the following to automatically create LODs based on the name postfixes:要将模型导入 UNIGINE，请将之前导出的 FBX 文件拖放到 Asset Browser 并执行以下操作以根据名称后缀自动创建 LOD：

1. Choose Combine By Postfixes in the Use LODs drop-down list.在 Use LODs 下拉列表中选择 Combine By Postfixes。
2. Specify the maximum number of LODs stored in the FBX container (in our case, 3).指定存储在 FBX 容器中的 LOD 的最大数量（在我们的示例中为 3）。

3. For each LOD, define a postfix that will be used to group objects in an FBX file into a corresponding LOD.对于每个 LOD，定义一个后缀，用于将 FBX 文件中的对象分组到相应的 LOD。

   注意

   The postfix must be the same as the one used when creating objects in a 3D editor.后缀必须与使用的后缀相同在 3D 编辑器中创建对象.

   For the tubes constructor model, the following postfixes should be specified:对于 tube 构造函数模型，应指定以下后缀：

   

   Names of generated surfaces will be as follows: material_name + LOD_postfix.

4. Specify the minimum and maximum visibility distances for each LOD. Maximum visibility distance of each LOD should be equal to the minimum visibility distance of the next LOD. Maximum visibility distance of the last LOD should be equal to inf.指定每个 LOD 的最小和最大可见距离。每个 LOD 的最大可见距离应等于下一个 LOD 的最小可见距离。最后一个 LOD 的最大可见距离应等于 inf。

   

   • For _lod_0, leave the default Min distance and set the Max distance at 5 units. It means that no matter how close the camera comes to the mesh, the surfaces will still be visible.对于 _lod_0，保留默认的 Min 距离并将 Max 距离设置为 5 单位。这意味着无论相机离网格有多近，表面仍然可见。
   • For _lod_1, set the Min and Max distances at 5 and 30 units. It means that when the camera is 5 units away from the mesh, the first LOD surfaces won't be visible and the second LOD surfaces will be shown over the distance of 30 units.对于 _lod_1，将 Min 和 Max 距离设置为 5 和 30 单位。这意味着当相机距离网格 5 单位时，第一个 LOD 表面将不可见，而第二个 LOD 表面将显示在 30 单位的距离上。
   • For _lod_2, set the Min distance at 30 units and leave the default Max distance. After 30 units, the second LOD surfaces won't be visible and the third LOD surfaces will be shown.对于 _lod_2，将 Min 距离设置为 30 单位，并保留默认的 Max 距离。在 30 单位之后，第二个 LOD 表面将不可见，而将显示第三个 LOD 表面。

5. Specify the minimum and maximum fade distances for each LOD:指定每个 LOD 的最小和最大渐变距离：

   

   • For _lod_0, leave the default Min distance and set the Max distance to 10 units. It will prolong the distance over which the LOD surfaces are still visible and provide smooth fading.对于 _lod_0，保留默认的 Min 距离并将 Max 距离设置为 10 单位。它将延长 LOD 表面仍然可见的距离并提供平滑的淡入淡出。
   • For _lod_1, set the Min distance to 10 units. After 5 up to 15 units, the second LOD surfaces will smoothly fade in. The Max distance set to 20 units. After 30 up to 50 units, the second LOD surfaces will smoothly fade out.对于 _lod_1，将 Min 距离设置为 10 单位。在 5 到 15 单位之后，第二个 LOD 表面将平滑淡入。Max 距离设置为 20 单位。在 30 到 50 个单位之后，第二个 LOD 表面将平滑淡出。
   • For _lod_2, set the Min distance to 20 units and leave the default Max distance. The third LOD surfaces will start to smoothly fade in from 30 to 50 units.对于 _lod_2，将 Min 距离设置为 20 单位并保留默认的 Max 距离。第三个 LOD 表面将从 30 单位平滑淡入到 50 单位。

In the result, the FBX container with 10 meshes will be imported. Each mesh will have 3 surfaces representing LODs.结果，将导入具有 10 个网格的 FBX 容器。每个网格将有 3 个表示 LOD 的表面。

Meshes of the Imported FBX导入的 FBX 的网格

注意

When working with large scenes, you cannot know for sure how many LODs some model will have. So, it is recommended to specify more LODs in the importer: in this case, you won't have to set up LODs manually, if the model contains more LODs than the previously imported one. For example, if you set up 10 LODs in the importer, you can import models with up to 10 LODs.在处理大型场景时，您无法确定某个模型将具有多少 LOD。因此，建议在导入器中指定更多的 LOD：在这种情况下，如果模型包含的 LOD 比之前导入的更多，则无需手动设置 LOD。例如，如果您在导入器中设置了 10 个 LOD，则最多可以导入具有 10 个 LOD 的模型。

Add an exported model into the world as described here. All LODs will be already created and set up according to the specified import values:将导出的模型添加到世界中这里描述.所有 LOD 都将根据指定的导入值创建和设置：

Imported Tubes Constructor with LODs带 LOD 的导入管构造器

FBX Added to the WorldFBX 添加到世界

If required, adjust the LODs surfaces in the Node tab of the Parameters window:如果需要，在 Parameters 窗口的 Node 选项卡中调整 LOD 表面：

• Configure the Min and Max Parent settings. In this tutorial, we use the default values of 1.配置 Min and Max Parent 设置。在本教程中，我们使用默认值 1。

Try to move the camera forward/backward to check how LODs are switched:尝试向前/向后移动相机以检查 LOD 的切换方式：

LODs SwitchingLOD 切换

For each LOD surface, you should specify a visibility distance and a fade distance. For setting up the LOD surfaces, do the following:对于每个 LOD 表面，您应该指定可见距离和淡入淡出距离。要设置 LOD 表面，请执行以下操作：

1. Open the World Hierarchy window, and choose the added node.打开世界等级窗口，然后选择添加的节点。

2. In the Surfaces group of the Node tab (the Parameters window), choose the first LOD surface:在 Node 选项卡（Parameters 窗口）的 Surfaces 组中，选择第一个 LOD 曲面：

   

   • Set its Maximum Visibility distance to 5. It means that when the camera is 5 units away from mesh, the first LOD surfaces won't be visible.将其 Maximum Visibility 距离设置为 5。这意味着当相机距离网格 5 个单位时，第一个 LOD 表面将不可见。
   • Leave the Minimum Visibility distance at -inf. It means that no matter how close the camera comes to the mesh, the surfaces will still be visible.将 Minimum Visibility 距离保留为 -inf。这意味着无论相机离网格有多近，表面仍然可见。
   • Set the Maximum Fade distance to 10 units. It will extend the distance over which the LOD surfaces are still visible and provide smooth fading.将 Maximum Fade 距离设置为 10 单位。它将延长 LOD 表面仍然可见的距离并提供平滑的淡入淡出。

   

   注意

   You can disable other LOD surfaces to see the result of the current LOD surface settings.您可以禁用其他 LOD 表面以查看当前 LOD 表面设置的结果。

3. Choose the second LOD surfaces and:选择第二个 LOD曲面并：

   • Set the Minimum Visibility distance of the second LOD surfaces to start exactly where the Maximum Visible distance of the first LOD surfaces ends: at 5 units. It means that when the first LOD surfaces begin to fade out, the second LOD surfaces will be shown.将第二个 LOD 曲面的 Minimum Visibility 距离设置为恰好从第一个 LOD 曲面的 Maximum Visible 距离结束的位置开始：以 5 为单位。这意味着当第一个 LOD 表面开始淡出时，将显示第二个 LOD 表面。
   • Set the Maximum Visibility distance at 30 units. After 30 units, the second LOD surfaces begin to fade out and the third LOD surfaces will be shown.将 Maximum Visibility 距离设置为30个单位。 30 个单位后，第二个 LOD 表面开始淡出，并显示第三个 LOD 表面。
   • Set the Minimum Fade distance to 10 units. After 5 up to 15 units, the second LOD surfaces will smoothly fade in.将 Minimum Fade 距离设置为 10 单位。在 5 到 15 个单位之后，第二个 LOD 表面将平滑淡入。
   • Set the Maximum Fade distance to 20 units. After 30 up to 50 units, the second LOD surfaces will smoothly fade out.将 Maximum Fade 距离设置为 20 单位。在 30 到 50 个单位之后，第二个 LOD 表面将平滑淡出。

   

4. Choose the third LOD surfaces and:
   • Set the Minimum Visibility distance to 30 units. It means that when the second LOD surfaces begin to disappear, the third LOD surfaces will be shown.Set the Minimum Visibility distance to 30 units. It means that when the second LOD surfaces begin to disappear, the third LOD surfaces will be shown.
   • Set the Maximum Visibility distance at 300 units. After 300 units the third LOD surfaces totally disappear.Set the Maximum Visibility distance at 300 units. After 300 units the third LOD surfaces totally disappear.
   • Set the Minimum Fade distance to 20 units. The third LOD surfaces will start to smoothly fade in from 30 to 50 units.Set the Minimum Fade distance to 20 units. The third LOD surfaces will start to smoothly fade in from 30 to 50 units.

   • Set the Maximum Fade distance to 50 units. After 300 units, the mesh will begin to smoothly fade out.Set the Maximum Fade distance to 50 units. After 300 units, the mesh will begin to smoothly fade out.

     注意

     If you want to leave the last LOD surface always visible, set the Maximum Visibility distance to inf.If you want to leave the last LOD surface always visible, set the Maximum Visibility distance to inf.

   

   Set the Minimum Visibility distance to 30 units. It means that when the second LOD surfaces begin to disappear, the third LOD surfaces will be shown.Set the Maximum Visibility distance at 300 units. After 300 units the third LOD surfaces totally disappear.Set the Minimum Fade distance to 20 units. The third LOD surfaces will start to smoothly fade in from 30 to 50 units.Set the Maximum Fade distance to 50 units. After 300 units, the mesh will begin to smoothly fade out.If you want to leave the last LOD surface always visible, set the Maximum Visibility distance to inf.选择第三个 LOD表面并且：
   • Set the Minimum Visibility distance to 30 units. It means that when the second LOD surfaces begin to disappear, the third LOD surfaces will be shown.将 Minimum Visibility距离设置为 30 单位。这意味着当第二个 LOD 表面开始消失时，将显示第三个 LOD 表面。
   • Set the Maximum Visibility distance at 300 units. After 300 units the third LOD surfaces totally disappear.将 Maximum Visibility距离设置为 300 单位。 300 个单位后，第三个 LOD 表面完全消失。
   • Set the Minimum Fade distance to 20 units. The third LOD surfaces will start to smoothly fade in from 30 to 50 units.将 Minimum Fade距离设置为 20 单位。第三个 LOD 表面将开始从 30 到 50 个单位平滑淡入。

   • Set the Maximum Fade distance to 50 units. After 300 units, the mesh will begin to smoothly fade out.将 Maximum Fade距离设置为 50 单位。 300 个单位后，网格将开始平滑淡出。

     注意

     If you want to leave the last LOD surface always visible, set the Maximum Visibility distance to inf.如果要让最后一个 LOD 表面始终可见，请将最大可见距离设置为 inf。

   

You should specify the same settings for each surface of the same LOD (if any). Different surfaces from one level of details should have the same settings to appear and disappear simultaneously.您应该为同一 LOD（如果有）的每个表面指定相同的设置。一个细节层次的不同表面应该具有相同的设置以同时出现和消失。

Another important parameters of the LODs are Min Parent and Max Parent.LOD 的另一个重要参数是 Min Parent and Max Parent。

These parameters enable you to specify to which surface or node up in the hierarchy the minimum and maximum visibility distances will be measured. Use the default values of 1. In this case, all surfaces of the mesh will be switched simultaneously, because their distances will be measured not to surfaces themselves, but to the bounding box of the whole mesh.这些参数使您能够指定将测量最小和最大可见距离到层次结构中的哪个表面或节点。使用默认值 1。在这种情况下，网格的所有表面将同时切换，因为它们的距离不是测量到表面本身，而是测量到整个网格的边界框。

Read here about these parameters.读这里关于这些参数。