Android 2D Texture Overrides

本页面将详细介绍 Android 特有的__纹理覆盖 (Texture Overrides)__。可在此处找到常规纹理覆盖的说明。

The information contained on this page assumes the reader has working knowledge of DXT and ETC Texture compression, OpenGL ES, and Android development.

有关纹理压缩和 OpenGL ES 的更多信息，请访问以下 Wikipedia 页面：

• DXT 纹理压缩 (DXT Texture compression)
• ETC (Ericsson Texture Compression)
• 有损压缩 (Lossy compression)
• OpenGL ES

If your app is installed on a device that doesn’t support the Texture compression format it uses, Unity decompresses the Textures to RGBA 32 and store them in the device’s memory, along with the compressed Textures, while the app is running. This leads to increased loading times and higher memory usage, because Unity must decompress the Textures and store two versions of the Textures used (compressed and uncompressed). This can also have a large impact on rendering performance, especially on older, slower devices.

Use ETC2 compression unless your app targets specific hardware like the Nvidia Tegra. ETC2 supports Textures with and without an alpha channel, and all OpenGL ES 3 devices support it. To avoid software decompression, follow these steps:

1. Open the Android Player settings (menu: Edit > Project Settings > Player Settings).
2. In the Other Settings section, remove OpenGL ES 2 from the Graphics APIs list. This sets the minimum graphics API to OpenGL ES 3.
3. In the Other Settings section, set the Minimum API Level to Android 4.4 ‘KitKat’ (API level 19).

To target OpenGL ES 2 and OpenGL ES 3 devices, you can create and publish two different APKs. Follow these steps:

1. Build an APK that targets OpenGL ES 3, using the Player settings in the screenshot above.
2. Build a separate APK that targets OpenGL ES 2. To do this, remove OpenGL ES 3 and Vulkan from the Graphics APIs section of the Player settings.
3. Publish both of these APKs to the Google Play Store. When a user downloads your app, the Google Play Store automatically installs the most relevant APK for their device.

有关发布多个 APK 文件的更多信息，请参阅 Android 开发者文档中的以下主题：

• 发布多个 APK
• Google Play 应用商店 APK 过滤。

在构建面向 OpenGL ES 2 的 APK 时，可使用 ETC1 纹理压缩。

The Texture compression format for OpenGL ES2-targeted APKs can be ETC1. Unity can use ETC1 for Textures with Alpha, provided they are placed on a sprite atlas (by specifying the packing tag) and the build is for Android. You can opt in for this by setting the Compress using ETC1 checkbox for the Texture. Unity then splits the resulting atlas into two Textures, each without alpha, and then combines them in the final parts of the render pipeline.

If you must store an alpha channel in a Texture, all hardware vendors support the RGBA 16 bit compression format.

• 2017–09–18 页面已修订

• Unity 2017.1 中的更新功能

• 在 Unity 2017.3 中更新了 Crunch 压缩格式