Does your TGA have an alpha channel or do you want your completely-rendered view to have an alpha value?
If it's the first (TGA + alpha channel), you should be able to render it fine, though you probably won't have the alpha preserved since the render-to-texture takes up the entirety of the image. As the TGA texture will no longer be available for pixel processing instructions, it seems like you wouldn't be able to preserve the alpha entirely. However, if you mean that the alpha channel values are either entirely transparent or entirely opaque (and not some value in-between) on your TGA file, you might be able to fake it by rendering the view on top of the opaque area of the image with the pos_x/pos_y and size_x/size_y properties to define a target square for your rendered VIEW object.
If you instead want your completely-rendered view to have an alpha value, you can either modify the alpha property of the VIEW object you're rendering or the alpha property of the ENTITY object you're rendering onto, depending on what type of effect you're looking for.
Hope this helped!
