Ace Combat 7: Skies Unknown

Texture Replacement Guide using Unreal Engine 4 Editor

Version 3.0c, last updated Mar. 31, 2022

By @Dantofu

This document is best read with View > Print layout disabled.

What’s New in 3.1:

• Added a cool front cover! Just scroll up!
• Added additional DXT compression visualization.
• Adjusted some text slightly for readability.

Table of Contents

1. Preface

2. Requirements

3. Starting Unreal Engine 4 Editor

4. Importing Diffuse Texture

5. Importing MREC Texture

6. Importing Normal Map Texture

7. Managing Multiple Assets

8. Naming the Assets

9. Cooking the Assets

10. Packing The Assets

11. Troubleshooting

i. Load Order

ii. Acquiring Textures

iv. DXT Compression Artifacting

v. DXT1 vs BC7

vi. White Artifacting in MREC

vii. Issue with Alpha Channel and UE4

viii. Closing and Credits

Update History

1. Preface

The purpose of this guide is to instruct prospective modders on using Unreal Engine 4 Editor to modify and replace textures in Ace Combat 7: Skies Unknown.

• This guide only covers getting texture replacements into the game. It is up to the readers to acquire and develop new texture designs using image editing softwares of their choice.

Other methods exist in achieving the same goal. @SuperOstrich has compiled several alternative guides to modding Ace Combat 7 textures using more lightweight tools, in addition to this guide itself.

The following outlines some key aspects to consider when using Unreal Engine 4 method:

Pros:

• Straightforward - Import and export of textures into final assets are done entirely in-editor.
• BC7 texture format - Improved image quality over standard textures by reducing compression artifacting, at the expense of increased file size.

• Despite improved quality, BC7 is not 100% lossless.

• Knowledge in UE4 Editor can apply to modding other games that utilize the same engine.

Cons:

• Large editor file size - Even though custom build reduces the overall size from 20GB to 7GB, it still takes up a large amount of disk space for texture replacement purposes alone.
• Lengthy editor loading times.
• Lower-end computers may struggle to run the editor.

2. Requirements

Unreal Engine 4 Editor (Version 4.18) - Lightweight custom build by VDINST_Rythus. Epic Games account, launcher or connection is not required for this build.

• Ace Combat 7 is built using UE4 version 4.18. Be sure to download this specific version instead of the latest (Versions 4.25 or 4.26) if using Epic Games Launcher!

UnrealPak (Alternative link) - Tool for mod packaging.

Custom Texture Filepaths - Contains edited material files, which allow unique MREC and Normal map textures to be used for every aircraft skin.

Sample textures - Contains sample F-15C Diffuse and MREC textures for this guide.

• Diffuse texture has been saved as JPG to reduce download size. In practice, always use lossless formats such as PNG or TGA.

3. Starting Unreal Engine 4 Editor

Download the .rar file provided in Section 2 - Requirements. Extract the .rar in the location of your choosing.

The UE4 Editor executable is located in the following:

Choose Blank in Template section.

Choose No Starter Content. They are not needed for this guide.

Set Folder path and project Name to your choosing.

Click Create Project.

This is the default window when starting a new UE4 Project.

Only the Content Browser (Highlighted in red box) matters for this guide.

Go to Edit > Project Settings. There is an option inside which needs to be changed to enable BC7 compression format.

Scroll down to Platforms > Windows tab.

Under Targeted RHIs you will see DirectX 11 (SM5) and DirectX 10 (SM4) ticked by default.

Untick DirectX 10 (SM4) to allow BC7 compression format.

• Leaving this ticked causes the texture editor to default to DXT1 compression format, even with BC7 selected in texture settings.

The settings are saved automatically, so close the Project Settings window once done.

4. Importing Diffuse Texture

Diffuse texture is an image that you see drawn on the surfaces of a 3D model.

Diffuse is also sometimes referred to as Base Color and Albedo.

• While technical differences exist between the terms, they serve the same function in providing the building blocks for photorealistic rendering.

If you have downloaded sample textures from Section 2 - Requirements, extract the contents.

To import textures, click on the Import button (Which opens the file browser).

• Alternatively, drag and drop an image file onto the Content Browser window.

UE4 Editor accepts various common image formats, and the full list can be found in UE4 official documentation. Recommended formats are PNG, TGA, and PSD due to their lossless quality.

• PSD may sometimes fail to import due to complexity (Too many layer effects, for example). In this case, export the PSD as PNG or TGA.

Double click on the icon to open Texture Settings.

UE4 Editor by default imports all images with Compression > Compression Settings selected to Default (DXT1/5, BC1/3 on DX11).

If the texture contains highly detailed designs and patterns (Such as character artwork), selecting BC7 (DX11, optional A) under the same settings page can help preserve quality at the expense of increased filesize.

Set Level of Detail > Texture Group to Character.

Avoid setting Texture Group to World (Default) or Vehicle. Doing so causes textures to be rendered at much lower resolution, even if the original image is saved at 4096x4096 resolution.

Alternatively, set Level of Detail > Mip Gen Settings to NoMipmaps to force the game to use maximum available texture resolution, no matter how far away the rendered object is.

• This is not recommended for textures used by NPC models, as numerous onscreen objects all using high-resolution textures can negatively impact performance.

Once everything is in order, click on Save at top-left to save the asset.

5. Importing MREC Texture

MREC stands for Metallic, Roughness, Emissions, and Custom data.

Each color channel in MREC texture image is used independently as image masks:

Each color channel’s values range from 0 (White color, full effect) to 255 (Black color, no effect) in determining lighting effects on that particular texture area. See the following table for summary:

Blue and Alpha Channels serve the same emissive function. The use of Alpha Channel depends on how the aircraft model is laid out.

• Emissive parts on tail fin, nose, and wing surfaces commonly use Alpha Channel.
• Emissive in cockpit instrument panels always uses Blue Channel.

If the imported texture contains Alpha Channel, the texture preview will initially show a largely transparent image. Go to View Settings and untick Alpha option to view the full texture.

Under Compression Settings, leave the option to Default (DXT1/5, BC1/3 on DX11).

• UE4 Editor automatically uses DXT5 if the texture contains Alpha Channel.

Under Level of Detail > Texture Group, pick CharacterSpecular.

Under Texture > sRGB, untick the checkbox.

• Leaving this enabled causes the aircraft to have a permanent wet-like shine.

Once everything is in order, click on Save at top-left to save the asset.

6. Importing Normal Map Texture

Skip this step if you do not intend to modify normal map texture.

• Editing normal maps is uncommon, and many texture mods do not include this.

Normal map fakes an appearance of 3D depth on a perfectly flat surface. Ace Combat 7 uses this to add minor details (Bolts, paneling, wiring) without having to 3D model each one, thus reducing model complexity.

As described earlier near the tail end of Section 4: Importing Diffuse Texture, if UE4 Editor detects an imported image that looks like a Normal map, the image will automatically be assigned the appropriate categories.

Under Level of Detail > Texture Group, pick CharacterNormalMap.

Compression Settings should have been auto-assigned to Normalmap (DXT5, BC5 on DX11).

sRGB setting should have been automatically unticked.

Once everything is in order, click on Save at top-left to save the asset.

7. Managing Multiple Assets

If you find yourself managing multiple texture assets and would like to modify several at a time instead of having to edit them one by one, Unreal Engine 4 Editor comes with Bulk Edit function.

For better organization, assets can be filtered in Content Browser prior to opening the bulk editor.

After selecting textures you wish to edit, right click on one of the highlighted textures and on the drop down menu go to: Asset Actions > Bulk Edit via Property Matrix.

Another window will open, containing texture info on the textures you have selected.

Settings page found on regular texture editor will be displayed on the right sidebar.

Selected assets will be highlighted in yellow, and changes applied using the right sidebar will be applied to every highlighted asset.

• Some changes, such as toggling sRGB with a large number of assets selected, takes longer to be applied. UE4 Editor may appear frozen until the process is complete.

Information can be added to the asset table column by clicking on the blue pin next to the texture settings option.

Likewise, information on the asset table column can be removed by right clicking on the column and clicking Remove.

More assets can be added to the Bulk Editor by going to File > Open Asset.

Changes made in the bulk editor can be saved by going to File > Save All.

8. Naming the Assets

To reduce storage space requirements, Ace Combat 7 reuses MREC and Normal map across its aircraft Skins. As such, replacing one such MREC would affect every playable and NPC skins that use the same texture.

This can lead to undesirable effects, where Skins that don’t use modded Diffuse texture will still have the modded MREC applied to it.

Which Diffuse, MREC, and Normal map textures get applied to a Skin is determined by the Skin’s material file. Each aircraft Skin contains one material file that controls texture filepaths.

Modding the Skin’s material files allow the use of custom texture filepaths, and thus allow use of MREC and Normal map textures that are not reused by any other Skins.

Extract Custom Texture Filepaths listed in Section 2 - Requirements. These files will be used to reference the proper asset names and filepaths needed for the mods to load correctly.

Since the sample textures does not modify Normal map texture, navigate to the following:

Skin material files start at 00 for Skin#1, based on array index formatting:

        01 for Skin#2

        02 for Skin#3

        ...and so on.

Every playable aircraft comes with 6 Skins, plus additional skins for Downloadable Content (DLC):

        00 - Osea

        01 - Erusea

        02 - Special

        03 - Osea variant (Trigger under Mage Squadron)

        04 - Osea variant (Trigger under Spare Squadron)

        05 - Osea variant (Trigger under Strider Squadron)

        06 and over - DLC

Material files with an alphabet letter appended (00a, 00b…) denote texture variants used by Non-Playable Character (NPC) aircraft.

Opening f15c-Filetree.txt shows how to name asset files. For this guide, sample textures will replace Skin #2.

Going back to UE4 Editor, name the asset files based on the list shown in the text file:

• Diffuse - f15c_01_D
• MREC - f15c_01xMREC

Unsaved assets will have an asterisk (*) in the lower-left-corner of the Content Viewer. Ensure sure that every imported asset is saved before continuing.

Either right click on the asset to save it, or click Save All button to save every unsaved asset in the project (It will show a window listing every unsaved asset prior to saving).

9. Cooking the Assets

To cook assets into game files, open the File menu and click Cook Content for Windows.

These windows will show at the bottom-right of the monitor display:

Once the cooking completes, the files will be saved in the following directory:

Where [Project Name] is the project name you have given at Section 3: Starting Unreal Engine 4 Editor:

The folder contains three files per asset:

• uasset - Contains the texture metadata.
• ubulk - Contains the textures with full resolution along with several Mip Map levels.
• uexp - Contains the last Mip Map levels of the texture.

If the texture is saved with NoMipmaps under Mip Gen Settings, then the asset will only generate the following:

• uasset - Contains the texture metadata.
• uexp - Contains a single, full-resolution texture. Ubulk is not generated.

10. Packing The Assets

Extract UnrealPak included in Section 2 - Requirements.

Ace Combat 7 uses Nimbus as its root directory (The starting folder).

• Nimbus is also its Project Name. Recall back to starting a new project in Section 3 - Starting UE4 Editor, where you had to give the project a name, which also became the project’s root directory.

For sample F-15C textures that replace Skin #2, place these items:

• uasset/ubulk/uexp files f15c_01_D and f15c_01xMREC generated from UE4 Editor
• uasset+uexp files f15c_01_Inst from Custom Texture Filepaths (MREC Only folder)

Into the following directory:

Where [ModName] is the name unrealpak will use when generating a pak file. Set [ModName] to whatever name you prefer; the resulting pak file can be renamed as well.

Once the cooked asset files are in place, drag and drop [ModName] folder to UnrealPak-Without-Compression.bat.

A command line window will open upon execution. Once completed, [ModName].pak will appear in the same folder.

Add “_P” at the end of the mod's filename, so that it becomes [ModName]_P.pak. The suffix allows the mod to load if the assets are replacing DLC content.

• The mod folder can also be renamed as such prior to packing.

Return to Ace Combat 7 filepath containing its pak files, and create ~mods folder inside so the filepath reads as follows:

Move [ModName]_P.pak inside ~mods folder.

Launch Ace Combat 7.

If everything went correctly, F-15C’s Skin #2 will load the modded Diffuse and MREC textures.

Congratulations, the new texture is now ready for release!

11. Troubleshooting

Here are some common texture modding issues and where to start looking:

i. Load Order

Ace Combat 7 loads content starting in ACE COMBAT 7\Game\Content\Paks.

However, filenames can be changed to affect the load order.

The tilde “~” prefix on mods folder name tells the game to load content in following order:

1. Pak files in the current folder (Paks)
2. Pak files in the “~” folder (~mods)

The game also loads pak files in alphabetical order:

1. Pak files in subfolders:

1. Alect
2. Garbo

2. Pak files in the current folder:

1. Pirates.pak
2. Solvalou.pak

3. ~Pak files in the current folder:

1. ~Bowl.pak

4. Pak files in ~subfolders

1. ~Bolka
2. ~Phoenix

If there are multiple pak files that load the same asset, the last pak file to be loaded will be in the game, overwriting the previous iteration.

There can be as many subfolders as desired, allowing for thorough mod organization.

ii. Acquiring Textures

Ace Combat 7’s aircraft textures have been extracted and uploaded on multiple sources:

• Aircraft models + textures (MEGA)
• Aircraft textures from all Ace Combat titles (OneDrive)

A community-led repository containing texture templates for easy modding can be found on ModDB and Nexus.

Gildor’s umodel allows file exploration of virtually any game that uses Unreal Engine, including Ace Combat 7.

Simply link the game directory in Path to game files, click OK, and enter https://ace7.acecombat.jp/special/ when prompted for AES Encryption Key.

Although umodel has functions to read and export game content, Ace Combat 7 obfuscates its uasset and uexp files, rendering the files unreadable for umodel.

Information stored in cooked assets can still be opened and edited using a hex editor, allowing changes to material properties in other games.

File obfuscation also prevents crucial model animation and material data from being exported, presenting a major barrier against modding aircraft and animations in Ace Combat 7.

Fortunately, original textures are contained in ubulk files, which have been left untouched. Ubulk files are simply texture images without header information, and can easily be edited into readable formats.

• Textures stored exclusively in uexp files however, remain unreadable due to said asset obfuscation.

@SuperOstrich has provided a guide on extracting Ace Combat 7 textures using umodel and hex editor.

Alternatively, @lotsbiss has uploaded a Texture Tool that can read any ubulk textures, automatically apply the correct DDS format, and export it in the desired location.

• Lotsbiss is also the author of popular TLS and EML performance mods.

iv. DXT Compression Artifacting

Ace Combat 7 features cutscenes that often produce close-up shots of the aircraft’s vertical fin, focusing on its tail design.

You may have noticed that on some aircrafts that have emblems drawn directly on the aircraft texture (Instead of a separate texture applied through emblem customization), the design appears jagged when viewed up close.

Opening game textures and zooming in on certain areas will reveal the same blocky effects. They are more pronounced on emblems where contrasting colors and complex details are drawn within a small image space.

This is caused by DXT compression, which helps maintain memory and space efficiency at the expense of some quality loss.

DXT1 (Diffuse) and DXT5 (MREC) both feature similar levels of quality loss as a result of its compression format.

Nathan Reed’s article presents a comprehensive explanation of compression formats.

In summary, DXT divides the overall image into 4x4 pixel blocks with a max of 4 colors per block.

The 4x4 pixel blocks can contain up to 16 unique colors. Those 16 colors are then reduced to 4 colors or less during compression.

The 4 colors must conform to a linear color gradient. DXT compression will try to interpolate the original 16 colors to produce the most ideal gradient.

• Colors in adjacent blocks have no influence on how the gradient is produced.

A block containing 16 colors with identical hue/saturations will retain its original appearance more closely than 16 colors with multiple contrasting hue/saturations.

For example, take these three 4x4 pixel blocks. First two blocks both contain 16 unique colors. Third block contains only 4 unique colors.

The same three 4x4 pixel blocks after DXT compression:

• The first block keeps its green gradient relatively intact.
• However, the second block looks nothing like the original—mixing cyan+yellow and purple+grey together to form an acceptable gradient.
• Although the third block had only 4 colors, the color extremities forces DXT compression to again mix green+grey and blue+red to form an acceptable gradient.

Here is another example with three 4x4 pixel blocks. This time, all three blocks contain only 4 unique colors. The second block is identical to the first block, except for a single shade of light green.

The same three 4x4 pixel blocks after DXT compression:

• The first block is nearly identical to the original, because its 4 colors already conforms to an acceptable gradient.
• The second block interpolates the light green color into its gradient.
• The third block mixes its three blue color shades together to form an acceptable gradient between red and blue.

There are some ways to reduce the amount of artifacting:

1. Greyscale / Low-visibility color layout - Reduces color complexity
2. Thicker outlines - Provides buffer area for artifacting

However, both options can clash with original design choices. In addition, focusing too much on artifacting can consume unnecessary development resources, when the quality loss often goes unnoticed to players in a fast-paced gameplay environment.

Despite its lossy nature, DXT1/5 compression formats are still widely used in the game industry for its efficient memory usage, whose benefits often outweigh the cost in image quality.

v. DXT1 vs BC7

BC7 is a recently-introduced texture compression format, which has not yet received DXT-equivalent designation (Where DXT1 = BC1, DXT5 (MREC) = BC3, and DXT5 (Normal) = BC5).

Pros:

• Very little loss in quality. BC7 is almost indistinguishable from the original image.

Cons:

• Increased filesize - From 10.6MB to 21.3MB for 4k textures.
• Useful only with Diffuse textures - BC7 MREC produces unwanted lighting effects when emissive effects are active (Takeoff+Landing / Refueling), even with zero blue/alpha color values in the original texture.

Nonetheless, BC7 offers an excellent solution for modders seeking to preserve their more complex texture designs, whether it be intricate patterns or detailed artwork images.

Optimization is still an important part of game development, and should be considered in the modding aspect as well. If your texture design looks good after lossy compression, then DXT formats can help minimize package filesize—which in turn reduce storage costs.

vi. White Artifacting in MREC

The white outline in the above image occurs when there is a hard edge between Metallic and Roughness values in MREC texture.

The artifacting is an inherent characteristic of Metallic-Roughness workflow required by Unreal Engine 4. There is no way to completely eliminate the white outline through textures alone.

vii. Issue with Alpha Channel and UE4

If you intend to introduce custom emissive patterns using MREC texture’s Alpha Channel, then this information may be useful to know.

Unreal Engine 4 Editor has an active bug where designs overlapping each other in Alpha and RGB channels suffer from very poor DXT artifacting. This bug still applies to the current version (4.26).

A workaround exists using SuperOstrich’s texture replacement guide via python script:

1. Generate ubulk file following the guide above.
2. Generate uasset/ubulk/uexp files from UE4 Editor.
3. Replace UE4 Editor’s ubulk file with Python-generated ubulk file.
4. Package UE4 Editor’s uasset/uexp file and Python’s ubulk file together.

Newer versions of GIMP come with the DDS plugin pre-installed. Use the same export options shown in the guide (Compression > DXT5, Mipmaps > Generate Mipmaps)—the remaining options can be left at default.

viii. Closing and Credits

I’d like to give thanks to @VDINST_Rythus on Twitter for his initial research towards Ace Combat 7 modding, and Xentax forums for discovering the .pak decryption key that enabled texture extraction.

Thanks to FluffyQuack for the UnrealPak tools.

And to the Ace Community community, for their continued support, discourse, and encouragement.

And to Project Aces and Kazutoki Kono, for delivering the finest Ace Combat experience yet.

Update History

3.0c (2022/02/15)

• Updated UE4 Editor link in Section 2 - Requirements… again. The package is now back on my MEGA drive.

3.0b (2021/08/04)

• Updated links in Section 2 - Requirements. Unreal Engine 4 Editor now links to the OneDrive folder maintained by VDINST_Rythus, which is updated periodically.

3.0 (2021/03/28)

• Rearranged and rewrote almost every part of the guide under a new writing style.
• Added requirements - Custom filepaths for MREC and Normal map textures.
• Added requirements - Sample textures that can be used to follow this guide.
• Added main section - Importing normal map texture.
• Added main section - Managing multiple assets using bulk editor.
• Added info section - White artifacting in MREC.
• Added info section - Issue with Alpha Channel and UE4 Editor.
• 3.0a: Added emphasis that BC7 is not 100% lossless.

2.0 (2020/03/21)

• Rewrote Section 5.
• Packing The Assets using UnrealPak method.
• Python method has been removed.

1.0f (2020/03/04)

• Fixed UE4 Editor build link again, and uploaded the build on another site to prevent further broken links.

• The build also comes with unrealpak, a packaging tool that removes u4pak and Python dependency. I will update the guide later when I have time, but for now please consult the included readme and source thread for usage.

1.0e (2020/02/09)

• Fixed UE4 Editor build link to newer version.

1.0d (2019/11/25)

• Expanded troubleshooting section to include u4pak script not executing.
• Added reference to F-22A Raptor and Eurofighter Typhoon in regards to DLC content loading.

1.0c (2019/10/03)

• Clarified Texture Group settings.
• References to “Vehicle” Texture Group settings have been removed. This was causing textures to load at much lower resolution than intended.

1.0b (2019/09/09)

• Minor update to iv. DXT vs BC7 section with new information.

1.0 (2019/08/10)

• Initial release.