# nDisplay: -dx12 -quad\_buffer\_stereo outputs mono when the display is a multi-GPU NVIDIA Mosaic (works on DX11, and on a single-GPU surface with the same build) **URL:** \ **Category:** Issues and Bug Reporting (Unreal Engine)\ **Tags:** stereo-rendering, stereoscopic, ndisplay, unreal-engine, open, dx12\ **Created:** [August 3, 2026, 2:56pm UTC](https://forums.unrealengine.com/t/ndisplay-dx12-quad-buffer-stereo-outputs-mono-when-the-display-is-a-multi-gpu-nvidia-mosaic-works-on-dx11-and-on-a-single-gpu-surface-with-the-same-build/2740364 "2026-08-03T14:56:59Z")\ **Posts on this page:** 2\ **Page:** 1
**Author:** ![raphaelsc-fl](https://d3kjluh73b9h9o.cloudfront.net/original/4X/2/8/5/28502927f1d97ba1051b3b47ccfe17233bf41ef0.png) [@raphaelsc-fl](https://forums.unrealengine.com/u/raphaelsc-fl)\ **Post date:** [August 3, 2026, 2:56pm UTC](https://forums.unrealengine.com/t/ndisplay-dx12-quad-buffer-stereo-outputs-mono-when-the-display-is-a-multi-gpu-nvidia-mosaic-works-on-dx11-and-on-a-single-gpu-surface-with-the-same-build/2740364/1 "2026-08-03T14:56:59Z")
### Summary On a machine whose display output is an NVIDIA Mosaic spanning two GPUs, running an nDisplay cluster node with -dx12 -quad\_buffer\_stereo produces a mono image. Both eyes are rendered - the frame rate halves as expected for stereo - but there is no depth on screen, and no error or warning appears in the log. Two controlled comparisons narrow this considerably: Same machine, only the RHI changes. -dx11 -quad\_buffer\_stereo displays correct stereo on that machine. That is our live production configuration and runs daily - same GPUs, same Mosaic, same driver, same OS, same projectors, same driver stereo mode (On-board DIN connector), 120 Hz active shutter-glasses stereo. Same engine build, only the display topology changes. The identical build (5.7.3-50162420+++UE5+Release-5.7) produces correct DX12 stereo on a second machine whose output is a single-GPU surface. WORKING MACHINE - displays correct stereo: Engine build: 5.7.3-50162420 Output surface: single GPU, 7680x2160 GPU: NVIDIA Quadro RTX 6000 (Turing) Driver: 596.72 and 582.53 (both tested, both stereo) OS: Windows 11 25H2 Cluster: 1 node and 2 nodes (both tested, both stereo) RHI / feature level: D3D12 SM6 FAILING MACHINE - displays mono: Engine build: 5.7.3-50162420 (identical) Output surface: NVIDIA Mosaic spanning 2 GPUs, 6467x3830 GPU: NVIDIA RTX PRO 6000 Blackwell Driver: 582.53 OS: Windows 11 24H2 Cluster: 2 nodes RHI / feature level: D3D12 SM6 So neither factor alone is sufficient - this looks like an interaction between the D3D12 presentation path and this display topology. Note this is not Unreal’s multi-GPU feature. -MaxGPUCount is not passed, so the engine renders on a single GPU in both cases. The two-GPU aspect is entirely in the Mosaic / scan-out layer, which the engine never sees. Questions we would like answered: (1) both RHIs request a structurally identical stereo swapchain and the engine hands Present a correct 2-slice buffer on D3D12, yet only the D3D11 output actually displays as stereo on this machine - does the D3D12 present path need anything additional that D3D11 receives implicitly, or is this entirely a driver responsibility? (2) Is nDisplay quad-buffer stereo on D3D12 known to work with a Mosaic surface spanning multiple GPUs - has that been validated? (3) The same symptom has been reported since 5.0.3 in [nDisplay stereoscopic rendering dx12](https://forums.unrealengine.com/t/ndisplay-stereoscopic-rendering-dx12/624582) with no response - is there a known issue tracked internally, or should this go through UDN? ### What Type of Bug are you experiencing? Rendering (Graphics / Niagara) ### Steps to Reproduce 1. Configure an NVIDIA Mosaic display surface that spans two GPUs, with quad-buffer stereo enabled in the driver. Our stereo display mode is On-board DIN connector; the venue runs 120 Hz active shutter-glasses stereo. 2. Launch an nDisplay cluster node against that surface: .uproject -game -dc\_cluster -dc\_cfg=.ndisplay -dc\_node= -dx12 -quad\_buffer\_stereo -windowed with a borderless window covering the Mosaic surface, ray tracing disabled, and no -MaxGPUCount (so the engine renders on a single GPU). 3. View the output through the active stereo glasses. Relaunch identically but with -dx11 in place of -dx12, changing nothing else, and compare. ### Expected Result Stereo output under -dx12 -quad\_buffer\_stereo - as produced by -dx11 -quad\_buffer\_stereo on the same machine and display, and as produced by -dx12 -quad\_buffer\_stereo on a machine with a single-GPU output surface running the identical engine build. ### Observed Result DX12: mono. Both eyes are rendered - the frame rate halves as expected for stereo - but the displayed image has no depth. No error or warning is logged. DX11, same machine, same session, only the flag changed: correct stereo. Further observations from our investigation: - Not the driver version. We installed the failing machine’s driver (582.53) on the working machine. Still stereo. - Not the cluster size. A 2-node cluster on the working machine still gives stereo. - Not a swapchain creation failure. The log lines “was not able to create stereo SwapChain” and “Backbuffer does not support stereo rendering.” never appear on either machine - so the stereo swapchain is created and nDisplay sees an array-typed backbuffer. - Both RHIs request a structurally identical stereo swapchain - “Stereo = TRUE”, “DXGI\_SWAP\_EFFECT\_FLIP\_DISCARD”, “BufferCount = 2” - and Present is a plain “SwapChain1-\>Present” in both, with nothing stereo-specific. - The engine delivers a correct stereo buffer on D3D12. We instrumented nDisplay on a separate workstation to tag the left eye red and the right eye green immediately before their copies into the backbuffer, then read back slice 0 and slice 1 of the real presented swapchain buffer. On D3D12 slice 0 = red and slice 1 = green, identical to the D3D11 path that displays correctly. The driver stereo configuration on the failing machine is demonstrably correct: the same Mosaic and the same On-board DIN connector stereo mode deliver correct stereo every day under D3D11. This is not a case of stereo being misconfigured in the control panel. ### Affects Versions 5.7 ### Platform(s) Windows ---
**Author:** ![Bug-Reporter](https://d1ap1mz92jnks1.cloudfront.net/user_avatar/forums.unrealengine.com/bug-reporter/32/997076_2.png) [@Bug-Reporter](https://forums.unrealengine.com/u/Bug-Reporter)\ **Post date:** [October 7, 2026, 8:00pm UTC](https://forums.unrealengine.com/t/ndisplay-dx12-quad-buffer-stereo-outputs-mono-when-the-display-is-a-multi-gpu-nvidia-mosaic-works-on-dx11-and-on-a-single-gpu-surface-with-the-same-build/2740364/4 "2026-10-07T20:00:27Z")
UE-390126 has been added to our ‘To Do’ list. Someone’s been assigned this task.