# Real-time translucency effect

While rendering my scene with OpenGL, I sometimes add an overlay which contains information, settings and a few draggable items. Currently, the overlay has a slightly transparent background to make text easily readable while still allowing the scene to shine through and to let the user see the scene behind/through the overlay.

I would like to replace the transparent background with a translucent background, which (as far as I know) requires the clear image of the scene to be heavily blurred*. And especially on mobile devices (e.g. iPad) with high resolutions and limited processing power, lots of texture lookups and real-time rendering don't work well together.

Is there a way to make real-time translucency feasible on mobile devices like the iPad? Or is there a way to avoid the need to heavily blur the scene in every frame?

Edit:

As suggested in the comments, here is an image I just found in the Wikipedia that describes the difference between transparency (right column) and translucency (middle column).

(Image source: Wikipedia)

*I know there is the two-pass blur (first blur in one and then in the other direction) to reduce texture lookups. But for translucency this still requires quite a large number of texture lookups.

• I'm not sure I'm understanding you. Slightly transparent == translucent. So you're already using translucency. Could you clarify what you're trying to do? Fully transparent background? (Aka, clear/invisible) Or translucent background? (Aka, you can see some stuff behind it, but covered with the background color) – RichieSams Aug 10 '15 at 19:44
• @RichieSams Currently I use a simple black background with an applied alpha transparency. So the scene can be seen, but is still sharp, which distracts the readability of the text. Thus I would like to change the simple alpha transparency to translucency. A real-world example maybe is the difference between looking through colored respectively iced glass. – Nero Aug 10 '15 at 20:07
• @Nero In graphics, "translucent" doesn't usually imply "frosted" or "iced", so I suggest making what your looking for clearer in your question, since I was also quite confused by it. – yuriks Aug 10 '15 at 20:22
• @yuriks translucent: (of a substance) allowing light, but not detailed shapes, to pass through. Translucent generally has the meaning used in the question, so this seems clear. – trichoplax Aug 13 '15 at 10:58