We reccommend you to use a professional vector drawing software to create your icon like Inkscape (open source) or Adobe Illustrator. Create a new document with a size of 512x512 pixels and unleash your creativity :)
We are going to use some linux libraries to transform and convert our icon from
png to the good extensions allowed by the goblin builder.
We have to generate 3 types of icon for all platforms :
They will be placed in the folder
${yourWorkingDirectory}/app/{appName}/icons. It’s important to rename all
files to icon or the goblin builder will not find the icon for your app
!
To achieve that, we are going to install 2 libraries from linux :
sudo apt install icnsutils imagemagick
If you are on windows, you can use the linux subsystem to install and use these libraries.
A simple way to convert your icon from .png to .icns is to use the command
png2icns from library icnsutils :
png2icns icon.icns your-icon.png
You can also convert your icon from .png to .ico by using the command
convert from imagemagick. Small detail here, we specify all intermediate sizes
of the icon :
convert -define icon:auto-resize="256,128,96,64,48,32,16" your-icon.png icon.ico