"Error: cannot implicitly convert expression (_param_0) of type luigi.gui.Widget to luigi.gui.Button"
The above error appeared because of a line of code like this:
b31b.clicked ~= (Button b){
onApplyTexture();
};
All error messages should print file an line numbers, preferably in the form:
<filename>(<linenumber>): Error: <the message>
This makes it easier for IDEs and text editors to automatically take the user to the line that generated the error.