Set App Icon from Pixels #135

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1. tonsky

   added

   Platform: X11

   Platform: Windows

   Platform: macOS

   Java

   DesignAPI design is needed before implementationAPI design is needed before implementation

   on Aug 25, 2021
2. dzaima commented on Sep 24, 2024

   

   dzaima

   on Sep 24, 2024

   Last edited by dzaima

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   Currently looking into this, as part of trying to get general app icons for Linux. For that, there are, as far as I can tell, two approaches:

   • have a globally-installed the-app.desktop file describing the program and its icon location (and the app setting a WM_CLASS hint to associate to it); seems impossible to make work via just setIcon, but would be good to have as a WindowX11-only thing for those wanting to do proper X11 application association;
   • set via pixels; this could be bound to setIcon, but means something has to decode the png (or whatever file format).

   I have both WM_CLASS configuring and icon-from-pixels configuring for X11 here via a temporary interface, using Skija to decode the png in the dashboard example. (the class isn't used by the example, but e.g. an OS-global icon theme could now set a custom icon for it)
3. tonsky commented on Sep 27, 2024

   

   tonsky

   on Sep 27, 2024

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   Both look good, make a PR?

   I understand that setting icon is more of a packaging problem and probably can’t be easily solved by just doing API calls, but where it can work I don’t see why not have it
4. chirontt commented on Jun 19, 2026

   

   chirontt

   on Jun 19, 2026

   Last edited by chirontt

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   The above code is working for X11, but what about other platforms such as Mac and Windows?

   Currently the Window class contains only one method: to load the icon from a physical file in the file system:
   

   JWM/shared/java/Window.java

   Line 205 in b921797

   public abstract Window setIcon(File icon);

   The above method won't work if the icon is a resource in an application's jar file; in that case, the icon is just a stream of bytes embedded in the jar file. I suggest JWM should add a new method for such use case:

       public abstract Window setIcon(byte[] icon);

   Browsing the dashboard example application, the paths to the physical icons are hard-coded in the application's code:
   

   JWM/examples/dashboard/java/Example.java

   Lines 82 to 87 in b921797

   	case WINDOWS -> {
   	window.setIcon(new File("examples/dashboard/resources/windows.ico"));
   	}
   	case MACOS -> {
   	window.setIcon(new File("examples/dashboard/resources/macos.icns"));
   	}

   which allows only one place to run the application in order to properly load the physical icon file. This is too limited/restrictive.

   Instead, the code can be enhanced to use the above new setIcon(byte[]) method:

               case WINDOWS -> {
                   window.setIcon(loadIconResource("windows.ico"));
               }
               case MACOS -> {
                   window.setIcon(loadIconResource("macos.icns"));
               }

   where loadIconResource is a utility method that returns the icon resource as a stream of bytes:

       byte[] loadIconResource(String icon) {
           // load the icon from a physical file, or from a resource in the classpath, etc.
       }
5. tonsky commented on Jun 20, 2026

   

   tonsky

   on Jun 20, 2026

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   If OS API allows for that (e.g. it doesn’t require you to point at file on disk) then I am all in for byte[]
6. chirontt commented on Jun 22, 2026

   

   chirontt

   on Jun 22, 2026

   Last edited by chirontt

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   I don't know about Mac or X11, but I think the X11 case is already solved in this thread/commits.

   For Windows, Java doesn't have a built-in way to parse the .ico file, so we need to use native Windows APIs. Assuming the byte[] array are raw bytes from a .ico file, we can use the following Win32 functions exported by user32.dll:

   • LookupIconIdFromDirectoryEx: Inspects raw icon bits and returns the exact integer resource identifier (offset) for the icon version that best fits your display resolution.

   • CreateIconFromResourceEx: Builds the HICON handle from the raw resource bits once the correct offset is identified.

   I've done some prototype code with the above 2 functions and they work fine, although I use Java FFM to prototype, not JNI C header.

   But I'm not sure what JWM can do with the given Windows HICON handle. How can JWM use the handle to "set the icon" to the window?
7. tonsky commented on Jun 22, 2026

   

   tonsky

   on Jun 22, 2026

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   I don’t know :) But I also think changing icon of a running application is a very narrow use-case
8. chirontt commented on Jun 26, 2026

   

   chirontt

   on Jun 26, 2026

   Last edited by chirontt

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   what JWM can do with the given Windows HICON handle. How can JWM use the handle to "set the icon" to the window?

   PR #310

   With this PR, I can now create a dashboard native image using GraalVM.
9. tonsky

   added a commit that references this issue on Jun 28, 2026

   Merge branch 'windows_icon_in_bytes' #310 #135

   8d67d73