I just emailed to you from high gear before i saw this post,
Ok the "secret" is probably more of a trick, which i discovered yesterday. Normally gp4 uses alpha channels to determine reflectiveness but in a few special cases it uses the alpha channel to determine transparency or "opaqueness". One of these special cases is the new_steering_wheels_display stexture and cockpit_dash shape.
I created a window shape then edited it etc.
then i put it into the cockpit_dash shape.
Note:
.for some reason when its in the cockpit dash shape, it doesnt disply in the same place on screen as if its in the car_cockpit shape, so you will have to move it into position by trial and error
.the window has to be named the same as a component of the original cockpit_dash otherwise it wont show in game, ie cant call it window or something usefull like that.I used the warning_off object as this object is always visible, initially i mapped to one of the least used cockpit warning lights but then the window is only visible when the warning comes on. The original object that you mao it to can be left untouched just merge the new shape ,window, and the old one together, ie the warning_off still works as before.
.unfortunately you cant use a different texture with the cokpit_dash shape, and you cant use a different shape with the new_steering_wheels_displays texture. It has to be the new_steering_wheels_displays in the cockpit_dash shape otherwise the transparency wont work
.the transparency is fairly simple, Black is totally transparent and white is totally opaque, and of course shades of grey are somewhere in the middle.
.because the alph channel controlls visibility of the texture, it is easily possible to make tinted windows or put writing etc on the window.
.so yes i think it would be simple to use this trick for your gt mod for as many windows as you like,which by the way looks fantastic, god i hope you include decent lods as my computers fairly crappy.