Texture Support and Settings

Overview

This page details texture support both within the engine and hardware.

Texture Resolution

Unreal Engine 3 supports texture resolutions from 1x1 to 4096x4096.
Current DirectX video adapters and game consoles support various texture resolutions from 1x1 to 2048x2048 and up to 8192x8192. The highest texture resolution supported by a specific hardware device varies by manufacturer and model. The amount of available texture memory pool also varies by the hardware.
There are a number of features and settings in Unreal Engine 3 for managing the texture resolutions that are rendered for various areas such as world geometry or the user interface.

Engine Texture Resolution Limit

Unreal Engine 3 defaults to limiting the maximum number of texture mips to 13, which effectively limits the largest rendered texture to 4096 (1x1 to 4096x4096 is 13 mips). This has the side-effect that imported 8192 textures will only render up to mip1 of 4096. The constant MAX_TEXTURE_MIP_COUNT which defaults to 13 in the engine source files can be modified to a value of 14 to support 8192 texture rendering. This constant is defined in the following source files (as of QAMar09, be sure to verify on other QA versions).

Src\D3D10Drv\Src\D3D10Device.cpp
Src\D3D9Drv\Src\D3D9Device.cpp
Src\Engine\Inc\RHI.h
Src\Engine\Inc\UnTex.h
Src\Engine\Src\RHI.cpp
Src\Engine\Src\TextureCube.cpp

Compressed Texture Memory Requirements

DXT is a lossy compression based on packing pixels into 4x4 blocks with paletted colors and interpolated colors. This results in an 8:1 DXT1 and 4:1 DXT5 constant compression file size. Since video memory and texture pool resources are fixed for a specific platform and hardware, a balance must be struck between texture resolution and resource usage. The following table lists the texture memory requirements for DXT1 and DXT5 textures at various common resolutions with full mips (1x1 up to full native mip0). Note that the memory requirements are near-constant multiples of the texture resolution ratio, and that DXT5 textures require near-twice the memory of their DXT1 counterpart.
Since the resolution to compression ratio is a constant, to calculate the memory requirements for a texture resolution not listed here simply multiply the resolution ratios. For example, a 1024x512 texture would be one-half the memory requirements of a 1024x1024 texture.
The table data was compiled from textures created by ATI's Compressonator using Box-Filter mip generation and DirectX Texture Compression.

Normal Map Texture Formats

See the NormalMapFormats article for details on the normal map formats supported by Unreal Engine 3.

Engine Config TextureGroup Properties

The minimum and maximum LOD (mip) supported for specific game TextureGroups is defined in a number of engine configuration files.
The source set of configuration settings files is located in the UnrealEngine3\Engine\Config\BaseEngine.ini file under the [SystemSettings] section.
For developing games, the [My] Documents\My Games\[your_game]\Config\[your_game]Engine.ini file also contains a mirror set of the base properties in the Engine\Config\ folder and should be the copy that is normally modified for your game's specific settings.

Note that there are independant sets of TextureGroup entries for the Unreal Editor and in-game. These two sets are respectively located in the [SystemSettingsEditor] and [SystemSettings] sections in the config files.

The TextureGroup settings entries in the BaseEngine.ini file will look similar to this. Note that older QA versions may not include the MinMagFilter and MipFilter properties for each setting.

TEXTUREGROUP_World=(MinLODSize=1,MaxLODSize=4096,LODBias=0,MinMagFilter=aniso,MipFilter=point)
TEXTUREGROUP_WorldNormalMap=(MinLODSize=1,MaxLODSize=4096,LODBias=0,MinMagFilter=aniso,MipFilter=point)
TEXTUREGROUP_WorldSpecular=(MinLODSize=1,MaxLODSize=4096,LODBias=0,MinMagFilter=aniso,MipFilter=point)
TEXTUREGROUP_Character=(MinLODSize=1,MaxLODSize=4096,LODBias=0,MinMagFilter=aniso,MipFilter=point)
TEXTUREGROUP_CharacterNormalMap=(MinLODSize=1,MaxLODSize=4096,LODBias=0,MinMagFilter=aniso,MipFilter=point)
TEXTUREGROUP_CharacterSpecular=(MinLODSize=1,MaxLODSize=4096,LODBias=0,MinMagFilter=aniso,MipFilter=point)
TEXTUREGROUP_Weapon=(MinLODSize=1,MaxLODSize=4096,LODBias=0,MinMagFilter=aniso,MipFilter=point)
TEXTUREGROUP_WeaponNormalMap=(MinLODSize=1,MaxLODSize=4096,LODBias=0,MinMagFilter=aniso,MipFilter=point)
TEXTUREGROUP_WeaponSpecular=(MinLODSize=1,MaxLODSize=4096,LODBias=0,MinMagFilter=aniso,MipFilter=point)
TEXTUREGROUP_Vehicle=(MinLODSize=1,MaxLODSize=4096,LODBias=0,MinMagFilter=aniso,MipFilter=point)
TEXTUREGROUP_VehicleNormalMap=(MinLODSize=1,MaxLODSize=4096,LODBias=0,MinMagFilter=aniso,MipFilter=point)
TEXTUREGROUP_VehicleSpecular=(MinLODSize=1,MaxLODSize=4096,LODBias=0,MinMagFilter=aniso,MipFilter=point)
TEXTUREGROUP_Cinematic=(MinLODSize=1,MaxLODSize=4096,LODBias=0,MinMagFilter=aniso,MipFilter=point)
TEXTUREGROUP_Effects=(MinLODSize=1,MaxLODSize=4096,LODBias=0,MinMagFilter=linear,MipFilter=point)
TEXTUREGROUP_EffectsNotFiltered=(MinLODSize=1,MaxLODSize=4096,LODBias=0,MinMagFilter=aniso,MipFilter=point)
TEXTUREGROUP_Skybox=(MinLODSize=1,MaxLODSize=4096,LODBias=0,MinMagFilter=aniso,MipFilter=point)
TEXTUREGROUP_UI=(MinLODSize=1,MaxLODSize=4096,LODBias=0,MinMagFilter=aniso,MipFilter=point)
TEXTUREGROUP_LightAndShadowMap=(MinLODSize=1,MaxLODSize=4096,LODBias=0,MinMagFilter=aniso,MipFilter=point)
TEXTUREGROUP_RenderTarget=(MinLODSize=1,MaxLODSize=4096,LODBias=0,MinMagFilter=aniso,MipFilter=point)

The TextureGroup settings in the Engine.ini will usually look something like this. Note that the LOD settings are normally set to the range limits required by the game design and target platform.

TEXTUREGROUP_World=(MinLODSize=256,MaxLODSize=1024,LODBias=1)
TEXTUREGROUP_WorldNormalMap=(MinLODSize=256,MaxLODSize=1024,LODBias=1)
TEXTUREGROUP_WorldSpecular=(MinLODSize=256,MaxLODSize=1024,LODBias=1)
TEXTUREGROUP_Character=(MinLODSize=256,MaxLODSize=1024,LODBias=0)
TEXTUREGROUP_CharacterNormalMap=(MinLODSize=256,MaxLODSize=1024,LODBias=0)
TEXTUREGROUP_CharacterSpecular=(MinLODSize=256,MaxLODSize=1024,LODBias=0)
TEXTUREGROUP_Weapon=(MinLODSize=256,MaxLODSize=1024,LODBias=0)
TEXTUREGROUP_WeaponNormalMap=(MinLODSize=256,MaxLODSize=1024,LODBias=0)
TEXTUREGROUP_WeaponSpecular=(MinLODSize=256,MaxLODSize=1024,LODBias=0)
TEXTUREGROUP_Vehicle=(MinLODSize=512,MaxLODSize=1024,LODBias=0)
TEXTUREGROUP_VehicleNormalMap=(MinLODSize=512,MaxLODSize=1024,LODBias=0)
TEXTUREGROUP_VehicleSpecular=(MinLODSize=512,MaxLODSize=1024,LODBias=0)
TEXTUREGROUP_Cinematic=(MinLODSize=256,MaxLODSize=4096,LODBias=0)
TEXTUREGROUP_Effects=(MinLODSize=128,MaxLODSize=512,LODBias=1)
TEXTUREGROUP_Skybox=(MinLODSize=512,MaxLODSize=2048,LODBias=0)
TEXTUREGROUP_UI=(MinLODSize=512,MaxLODSize=1024,LODBias=1)
TEXTUREGROUP_LightAndShadowMap=(MinLODSize=512,MaxLODSize=4096,LODBias=0)
TEXTUREGROUP_RenderTarget=(MinLODSize=1,MaxLODSize=4096,LODBias=0)

PC AppCompat Buckets

AppCompat is used to override various SystemSettings based on objective and empirical evidence gathered at startup. When app compatibility is enabled (PC only), the system measures machine capability and then overwrites the Engine.ini values with preset values from one of 5 "buckets". See DefaultCompat.ini in UTGame for an example of this usage.

AppCompat is intended to only be checked ONCE when the game is first run (not the editor). It detects this by checking for the existence of an [AppCompat] section in [game]Engine.ini, which contains the previously computed scores for the machine. If AppCompat has already been applied once, it is not changed again to allow custom changes to be made by users without being overwritten every time.

AppCompat is specifically disabled for the editor so machine specs don't affect how assets are viewed on various machines during development. This is the reason for the split between SystemSettings and SystemSettingsEditor.

You can effectively disable AppCompat by supplying an empty DefaultCompat.ini for your game (see example in UTGame), which causes it to initialize all buckets from [SystemSettings] in Engine.ini. In this case, the system operates exactly as it did before AppCompat was introduced.

TEXTUREGROUP Properties

Each TextureGroup entry defines the texture properties for a specific texture set as used in the game rendering. Grouping textures into common sets allows for better control over the texture memory pool use by various game texture resources.

TextureGroup, LODGroup and LODBias

The TextureGroup and LODBias settings specified in the config ini files, along with the LODGroup and LODBias settings specified in the Texture Properties determine the final set of texture mips used for an individual texture.

An example TextureGroup entry in the Engine.ini may look like this:

TEXTUREGROUP_World=(MinLODSize=256,MaxLODSize=1024,LODBias=0,MinMagFilter=aniso,MipFilter=point,NumStreamedMips=3)

Any textures assigned to the TEXTUREGROUP_World LODGroup will use these settings to determine the mip range used for rendering.
The additional LODBias setting in the Texture Properties is additive with the LODBias specified in the config ini file TextureGroup.

The LODBias biases or offsets which mip is chosen for rendering. The LODBias is calculated before the LODGroup Min/Max range. The LODBias in the Texture Properties is added to the LODBias in the TextureGroup to determine the final LODBias value used.
An LODBias of 0 is the main (native) texture resolution. An LODBias of 1 is the first mip down for the texture, an LODBias of 2 is the second mip down, etc. For example, a 1024x1024 texture that has an LODBias of 1 results in the 512x512 mip being chosen for rendering.

The LODBias specified in the Texture Properties for each individual texture can be positive or negative, so that it can offset the TextureGroup's default LODBias to either higher or lower mip values.
For example, a TextureGroup LODBias of 0 and a Texture Properties LODBias of 0 would result in a final LODBias of 0.
A TextureGroup LODBias of 0 and a Texture Properties LODBias of 1 would result in a final LODBias of 1.
A TextureGroup LODBias of 1 and a Texture Properties LODBias of 1 would result in a final LODBias of 2.
A TextureGroup LODBias of 1 and a Texture Properties LODBias of -1 would result in a final LODBias of 0.

After the final LODBias is calculated, then the texture mip is checked to see that it fits into the TextureGroup's Min/Max LODSize range, and it is adjusted if necessary. This allows a simple config ini file change to effectively clamp a specific TextureGroup to within a set min/max LOD range. For example, a 1024x1024 texture with LODBias of 1 uses the 512x512 mip, if it is in the TEXTUREGROUP_World LODGroup as shown above, it is then checked to see if it fits within the TextureGroup's Minimum and Maximum LODSize range, which in this case is 256 and 1024.

Since each game title will have its own unique TextureGroup settings, artists and level designers should be aware of the MinLODSize and MaxLODSize for each group.
It would increase distributable package size with no rendering quality benefit if a game shipped with 2048 textures assigned to a TextureGroup with a MaxLODSize of 1024.

Texture Import Properties

For 24-bit RGB textures specify CompressionNoAlpha on import to produce a DXT1 texture.
For 32-bit ARGB textures leave CompressionNoAlpha unchecked to produce a DXT5 texture.

Specular and Opacity information is usually best placed into the Alpha Channel of a 32-bit DXT5 texture instead of using two 24-bit DXT1 textures. While two DXT1 textures are the same file size as one DXT5, in the engine a DXT5 uses one TextureSampler whereas two DXT1's will use two TextureSamplers. Video adapters commonly have 16 TextureSamplers (SM3 and SM4).
The Alpha Channel of a DXT5 texture is also better suited to hold grayscale data as it does not use the same style of lossy compression as the RGB planes.

If a texture must be larger than any specific TextureGroup maximum LOD value, be sure to choose a TextureGroup that supports the texture size natively and doesn't drop mips.

Be careful with using too many 2048 and larger textures, especially when targetting support for consoles. By overriding the default use of TextureGroups, you may impact the texture memory pool and cause issues on systems with less video memory, such as multiple scene textures forcefully dropping mips and looking "blurry".

Be sure to choose the appropriate additional settings when importing textures, such as choosing CompressionSettings of TC_NormalMap when importing NormalMap textures.

Texture Viewer Properties

The Texture Properties can be modified for each imported texture, and allow for changing such settings as LODGroup and LODBias.
Double-click on a texture in the generic browser, or right-click on a texture and choose Texture Viewer from the pop-up menu.