I'm running the Linux version on a 1366x768 laptop. The resolution of the game is set to 1366x768 in the menu.

The file .local/share/DotEMU/Another World/AnotherWorldUserDef.xml has
<resolutionWidth>1366</resolutionWidth><resolutionHeight>768</resolutionHeight>

The menu fills the screen but the game itself have black bars on both sides.

In the game's folder there is a file ../AnotherWorld/game/layout_1024x768.xml with the following content:

<layout>
<item name="a" locked="no">
<state name="default">
<srcFile><![CDATA[ingame_UI_atlas_hires.png]]></srcFile>
<srcRect x="128" y="768" w="128" h="128" />
</state>
<state name="pressed">
<srcFile><![CDATA[ingame_UI_atlas_hires.png]]></srcFile>
<srcRect x="128" y="896" w="128" h="128" />
</state>
<dstRect x="816" y="584" w="128" h="128" />
</item>
<item name="b" locked="no">
<state name="default">
<srcFile><![CDATA[ingame_UI_atlas_hires.png]]></srcFile>
<srcRect x="256" y="768" w="128" h="128" />
</state>
<state name="pressed">
<srcFile><![CDATA[ingame_UI_atlas_hires.png]]></srcFile>
<srcRect x="256" y="896" w="128" h="128" />
</state>
<dstRect x="944" y="616" w="96" h="96" />
</item>
<item name="c" locked="no">
<state name="default">
<srcFile><![CDATA[ingame_UI_atlas_hires.png]]></srcFile>
<srcRect x="768" y="0" w="128" h="128" />
</state>
<state name="pressed">
<srcFile><![CDATA[ingame_UI_atlas_hires.png]]></srcFile>
<srcRect x="768" y="128" w="128" h="128" />
</state>
<dstRect x="720" y="616" w="96" h="96" />
</item>
<item name="dpad" locked="no">
<state name="default">
<srcFile><![CDATA[ingame_UI_atlas_hires.png]]></srcFile>
<srcRect x="0" y="0" w="256" h="256" />
</state>
<state name="down">
<srcFile><![CDATA[ingame_UI_atlas_hires.png]]></srcFile>
<srcRect x="256" y="256" w="256" h="256" />
</state>
<state name="down-left">
<srcFile><![CDATA[ingame_UI_atlas_hires.png]]></srcFile>
<srcRect x="512" y="512" w="256" h="256" />
</state>
<state name="down-right">
<srcFile><![CDATA[ingame_UI_atlas_hires.png]]></srcFile>
<srcRect x="256" y="512" w="256" h="256" />
</state>
<state name="left">
<srcFile><![CDATA[ingame_UI_atlas_hires.png]]></srcFile>
<srcRect x="256" y="0" w="256" h="256" />
</state>
<state name="right">
<srcFile><![CDATA[ingame_UI_atlas_hires.png]]></srcFile>
<srcRect x="512" y="0" w="256" h="256" />
</state>
<state name="up">
<srcFile><![CDATA[ingame_UI_atlas_hires.png]]></srcFile>
<srcRect x="0" y="256" w="256" h="256" />
</state>
<state name="up-left">
<srcFile><![CDATA[ingame_UI_atlas_hires.png]]></srcFile>
<srcRect x="0" y="512" w="256" h="256" />
</state>
<state name="up-right">
<srcFile><![CDATA[ingame_UI_atlas_hires.png]]></srcFile>
<srcRect x="512" y="256" w="256" h="256" />
</state>
<dstRect x="24" y="584" w="160" h="160" />
</item>
<item name="load" locked="no">
<state name="default">
<srcFile><![CDATA[ingame_UI_atlas_hires.png]]></srcFile>
<srcRect x="512" y="768" w="128" h="128" />
</state>
<state name="pressed">
<srcFile><![CDATA[ingame_UI_atlas_hires.png]]></srcFile>
<srcRect x="512" y="896" w="128" h="128" />
</state>
<dstRect x="927" y="100" w="96" h="96" />
</item>
</layout>

As you can see "1024" is nowhere to potentially change to 1366 and save as layout_1366x768.xml that might get picked up and applied. Just guessing here.

There is also a layout_custom.xml which is empty (<layout></layout>).

Any ideas how to get rid of the black bars and have the game actually fill the full screen like the menu does?