Laptop as external monitor for desktop via DP/USB-C?

Question

So with Windows 10's "Project to This PC" Miracast stuff, I can use my laptop as a third monitor for my desktop. However, this is laggy, not the highest quality, and requires an active connection. If I had a hard-wired connection between the two systems, the effect would be much better.

My desktop's 1050 Ti has a DisplayPort output, and my laptop has multiple Thunderbolt 3-enabled USB-C ports. Theoretically, I can use this to output video from my desktop to my laptop, then simply transpose the video over my display on the laptop, creating a low-latency connection.

I have no idea if something like this exists (or if anything remotely similar to this has popped up). Anyone have any ideas?

Solution 1

Theoretically, I can use this to output video from my desktop to my laptop, then simply transpose the video over my display on the laptop, creating a low-latency connection.

Theoretically, this is possible, but it would require two pieces of dedicated hardware on your laptop: (1) The ability to receive DisplayPort signals, instead of having the graphics card send them, and (2) the ability to overlay received data onto your display.

I've never heard about such hardware on a laptop. Apple doesn't really provide details on the hardware, so even if your hardware could do that (unlikely), you can't write drivers for it.

So, that won't work.

Solution 2

and my laptop has multiple Thunderbolt 3-enabled USB-C ports. Theoretically, I can use this to output video from my desktop to my laptop

No, you can't output DP into your laptop's USB. Mostly because the laptop USBs are USB hosts, and secondly the USB ports can't "input" DP signals even if they are multi-functional TB/DP/USB ports, and the DP is an output. But you can output virtual display card over USB, which can be displayed on special USB displays.

To turn your laptop into "USB display" you need the laptop to be a USB DEVICE, and a special device. I don't know if your XPS 9370 suppports DRP modes (formerly known as OTG), but even if it can, it must implement the AV-class of USB devices with image rendering capability. While image rendering on laptop screen should be a relative no-brainier, the implementation of AV-Class on standard OTG device controller is very questionable. See some more details here.

Solution 3

If you principally need to use a USB-C, this will require a USB Graphics Controller driver (WDDM). Try the solution from Fresco Logic: LCI Proxy driver (Github). Or use the classic options from DisplayLink via USB.

If you need a result and wi-fi is quite satisfied - a complete solution to the issue is SPACEDESK app.

Spacedesk even listed all similar solutions (see SIMILAR PRODUCTS).

Comments

[confetti]

I'm not sure but I don't think your laptop's GPU would support a video input. Usually, GPUs only output stuff. You would have to somehow create the cable from your desktop directly to the laptop's monitor, which isn't impossible but requires hardware modification and you wouldn't be able to fit all that in your laptop's case, so you won't be able to close it up anymore. (That's depending on how your laptop is connected to the display internally and might be impossible alltogether. But driverboards for most laptop LCD's exist, so sacrificing the laptop, it should be possible but far form ideal)

[Isaac Corbrey]

@confetti My laptop is a Dell XPS 9370, all of the USB-C ports carry data. Would it be possible to emulate a monitor at the laptop end while catching the display data to the laptop?

[confetti]

Handling video as an input requires specific chipsets on the hardware side, which I don't think any laptop comes with.

[Isaac Corbrey]

@confetti That's unfortunate. Thanks anyway!

[confetti]

cnet.com/forums/discussions/… - I've found this. But you can expect a very bad quality from that, and I'm sure your PC doesn't have a VGA output. You could use a DP to analog adapter but things are getting really expensive here and the quality you can expect is similar to a ten year old TV.

[confetti]

Apparently the Dell Alienware M18x has an HDMI Audio/Video input, and apparently it's the only one on the entire market.

[Isaac Corbrey]

Interesting. I'll have to see how that's supposed to work

[confetti]

There are also a bunch of video capture cards for HDMI to USB, but those are around $90.

[Isaac Corbrey]

Honestly, I think that if I get a DP to USB-C cable, there should be some software solution for something like this. Maybe I can write it lol

[confetti]

There are two types of this kinda cable, and both include a very specific chipset. One is for outputs, if your laptop supports DP via USB-C then those are cheap since they are passive adapters. But if you need one for input you need one with a chipset that allows this, basically a "capture card". They do what you want and come with the software you need, but like I said they are expensive

[Isaac Corbrey]

RIP. Well, maybe I can figure out a better wireless solution with Miracast.

[confetti]

I've never used miracast in my life, but what I use for this thing is VNC. I have a 4K resolution that is being streamed in high quality over VNC to my laptop and I have barely any latency. I wouldn't use it for gaming but anything else works fine. Edit: NVM I just realize you're looking for an additional monitor rather than mirroring it. This is possible too using VNC, but AFAIK only on Linux.

[Isaac Corbrey]

Maybe that would work better. How are you emulating the extra monitor?

[confetti]

Yeah, see my edit, I forgot about that. On Linux that's very simple but I don't know about Windows.

[Isaac Corbrey]

Hmm. I think I've looked at this before, but I'm not sure. There's gotta be some good solution to this.

[Isaac Corbrey]

I mean, external GPUs are a thing. Surely I can utilize that tech to accomplish this

[dirkt]

@IsaacCorbrey: The external GPU is using the Thunderbolt PCIe connection. So yes, you can use Thunderbolt to DMA stuff into your framebuffer (which is actually a security vulnerability). No, you can't do this with DisplayPort signals, you'll need a PCIe device at the other end. Yes, you can make a device that reads DisplayPort signals, and uses PCIe to DMA the data in, but I am not aware of such a device.

[Att Righ]

There are apps like duet display for android and ipad that can do a reasonable job of using a tablet as a second display via usb. They don't use specialist hardware.