Unreal gives the user a huge number of texture options. Some of which, as user interface designers, we are unlikely to use but are still worth knowing about.
Here we'll cover some of the texture-related issues that you might encounter as a UI programmer in Unreal.
Unreal 5.1 Update
As of Unreal Engine 5.1, mip maps are now supported on all textures!
Mip maps are now supported on non-power-of-two textures.
Texture Sizes
The size of the texture affects its compression, mipmap generation support and streaming support.
Compression
Generally UI textures are not compressed, as DXT5 compression in particular can cause some artifacts that can ruin the clean lines of some UI styles. However depending on your need to reduce your memory footprint (and whether your UIs aesthetic is compatible with it), you may want to enable compression.
DXT5 compression is only available for textures that are a multiple of 4. This is important to know, even if you are not planning on enabling compression for your UI textures as you may need to change your mind in the future.
Mipmap Generation
Mipmap scaling are not commonly used in UIs. But for some assets that could be shown at many different scales, like icons used in many parts of the UI, mipmap support may be useful.
Mipmap generation is only possible for textures that are a power of two.
Base Case
If the texture is not a power-of-two and not a multiple of 4, both compression and mipmap generation are disabled. The "Format" is a simple 32-bit image, B8G8R8A8.
Multiple of 4
If the texture is a multiple of 4 then it can be compressed with DXT5 compression. However mipmaps are not supported.
Power of Two
Power-of-two textures are supported by both compression and mipmap generation.
Manually Disabled Compression
With texture compression manually disabled for our 256px texture, the resource size increases from 85Kb to 341Kb.
Streaming Support
Streaming does not usually affect UI textures, but you should be aware that Unreal (as of 4.16) only supports streaming power-of-two textures.
Summary
Here's what I do:
- I make sure all my UI textures are multiples of 4.
- I turn on compression for most textures.
- For textures that I notice look gross with compression, I turn it off while being conscious of texture memory.
| Texture Size | Compression | Mipmaps | Streaming |
|---|---|---|---|
| Power-of-two | DXT5 Supported | Supported | Supported |
| Multiple of 4 | DXT5 Supported | Unsupported | Unsupported |
| Other | Unsupported | Unsupported | Unsupported |
