I want to start off by saying that I'm quite new to this, and have just been learning through experimentation. Here is the summary of my problem:

I want to use the advinterp2x scaler/shader with Openxcom. Openxcom allows you to add your own custom GLSL shaders, but they need to be in a file format that has an extension of ".OpenGL.shader". From what I have been finding, this should be possible, because that both DOSBox and Openxcom are open source. How can I accomplish this?

One thing that I have come across is that DOSBox-x has a "glshaders" folder that stores most of it's shaders in a .glsl file format. However, the advinterp2x shader file is completely empty. DOSBox-x seems to call advinterp2x as well as a few other shaders as "built-in shaders" and it seems like it stores them somewhere else, so that was a bit of a dead end.

Thanks very much for any responses and assistance.