UD-3900 install - project duplicate display to second screen no longers fills the entire screen


#1

I set up my laptop computer (running Windows 8.1) and its peripheral devices using my new UD-3900 this week. Overall, things seems to work fine–except for one issue:

Before installing the DisplayLink drivers, I could duplicate the laptop screen display (resolution 1600 X 900) to my external 24" monitor (resolution 1920 X 1080) and the display on the second screen would automatically adjust to fill the entire screen. It appeared to scale to utilize the extra space.

Since the install, when I duplicate the laptop screen, it is like an exact duplicate of the smaller laptop screen on the larger external screen; there is an ~2 inch black border around the display on the second screen. When I switch the Windows setting to devices>project>second screen only, the resolution does adjust properly to the correct resolution of the larger screen (the PC screen of the laptop at this point is blank.)

This is not a major problem, but I did prefer the way it worked before the driver install. It’s just an extra procedure to go through before I can get to work. Also, I’m afraid that I will forget to reset the setting to “PC screen only” or “duplicate” display before I shut down, and possibly finding myself to trying login without a working laptop screen. (I’m not sure if this would happen, but I’d prefer not to find out.)

Any suggestions?


#2

Hi Brenden,

Thanks for posting. I haven’t seen any reports of this type of behavior previously, so I ran it by our display engineering guru for his insight, pasted below:


Windows’ default behavior is to set the exact same mode on both monitors when two displays are set to duplicate. A monitor that is larger or has a different aspect ratio will take that signal and display it using scalers inside the monitor. Most of those scalers will preserve pixel aspect ratio, which means black borders somewhere if the two displays have different aspect ratios.

In this case, it looks like perhaps the primary GPU on the laptop is doing some special work to modify Windows’ default behavior (without Windows knowing). When both monitors are off the same GPU, it looks like it’s doing some more work in the GPU to scale to fill the entire second monitor by processing the pixels before they leave the second output and using a more sophisticated scaling method than the monitor has itself. That would require scaling more in the X or Y direction, which would distort the image a little, but it’s a tradeoff to avoid black borders. Apple does something similar in most Mac systems, and leverage that fact to produce display (Cinema displays) without any scalers at all – when directly Mac connected, they can set any mode, but when connected any other way, only the native resolution or exactly half it show as available.

Unfortunately, this kind of hardware scaling in the GPU is otherwise unusual and DisplayLink devices don’t have this kind of ability or option. They always pass the pixels on to the display 1-1 without any modification or scaling.

So ultimately I think it’s likely that there’s not much that can be done to alleviate the black borders if running in clone mode, and running the attached display as either a standalone or as an extended desktop would be the best available workarounds for using the full screen real estate.

Regarding changing the display configuration settings prior to shutdown, there’s generally not a need to do this in the vast majority of cases. Once the system boots back into Windows the previous display configuration is usually restored. (I’ve encountered one or two cases where this functionality didn’t work correctly, but it’s definitely a rare exception.)

By all means feel free to email us directly at support@plugable.com if needed.

Thanks!
Gary


#3