Environment: Substance 3D Painter 12.1.3, Windows 11 22631, RTX 5080 (NVIDIA 610.62 / 610.74 / 616.56 — identical on all three), Wacom Cintiq 22 as primary display, Windows Ink enabled per Adobe's pen guide. Reproduces since 12.1.0.
Symptom: during a normal painting session the viewport stops updating permanently. Menus, panels and the layer stack keep working; Windows never flags the app as unresponsive. F, view toggles, resize, dock re-attach, minimize/restore do not recover it. Only a restart does.
Conditions (several dozen occurrences over two months):
- Only while using the pen. Never with the mouse — zero occurrences in mouse-only sessions.
- Almost always during camera navigation (Alt+drag), not during strokes.
- Often preceded by a sudden camera jump. Worse after Alt+Tab and back.
Evidence collected on one instrumented occurrence (2026-09-07 20:10):
- Minidumps (6 total): the "SAL Render Thread" is parked in std::condition_variable wait (ntdll!NtWaitForAlertByThreadId → RtlSleepConditionVariableSRW → msvcp140!_Cnd_wait → Painter). No mutex deadlock, process otherwise idle, no driver frames.
- Vulkan api_dump layer: Painter uses two swapchains (one per viewport); rendering is on-demand. Last vkQueuePresentKHR at 20:10:23.8, none afterwards.
- Qt QPA event log (windows:verbose=2): all 61 WM_POINTERDOWN have matching WM_POINTERUP; the last Alt press has its SYSKEYUP; WM_CAPTURECHANGED appears only after the user alt-tabbed away post-stall. ~21,000 further input messages arrive after the last pen-up and are processed — input is not lost.
- GetGUIThreadInfo at capture: hwndCapture = 0.
So: input reaches the app normally, but after a pen-driven camera move the viewport stops issuing frame requests and the render thread never wakes. Driver, OS input, and WinTab are ruled out (Painter uses Windows Ink since 2019.3).
Already tried without effect: SVT hardware acceleration off, TDR delay 60, NVIDIA present-method/vsync profiles, 12.1.0→12.1.3, Adobe's recommended pen settings.
Happy to provide the dumps, api_dump captures and event logs. Is there an internal ticket for this? A community thread from 2023 (Huion pen display freeze) mentions a backlog item that couldn't be reproduced consistently — the pen-only / camera-navigation condition above may be the missing reproduction key.
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