macOS: Mouse confined to main display when streaming a secondary monitor

Start in src/platform/macos/macos_backend.cpp at the MacosInputState::display initialization near line 384 and the coordinate clamping in post_mouse() near line 684. Reproduce with a secondary streamed display and verify that mouse coordinates cover the selected display without changing the macOS main display.

Describe the Bug

When streaming a secondary monitor (set in Sunshine config), keyboard input and mouse clicks work, but the cursor cannot move normally across the streamed display. It moves vertically along the left edge and appears pinned horizontally at x=0.

Switching between Moonlight’s relative and absolute mouse modes does not resolve the issue. I want to stream the secondary monitor without making it the macOS main display.

Expected Behavior

The cursor should be able to reach the entire streamed secondary display without changing which monitor is the macOS main display.

Actual behavior

Keyboard input and clicks reach the host. Mouse positioning is incorrect; in testing, the cursor becomes pinned to the streamed display’s left edge while still moving vertically.

Additional Context

Environment

• Sunshine: 2026.906.222525
• Commit: LizardByte/sunshine@cb72dffa3233c5815cd5ba88f09f049dd679ba75
• Installation: Homebrew, running as a user service
• Host: macOS Sonoma 14.8.5, Apple Silicon
• Client: Moonlight on macOS
• Capture: macOS screen capture
• Encoder: VideoToolbox

Suspected cause

The bundled libvirtualhid revision with my build of Sunshine is 6fdb8bd4de3b68d96c30e5303ac2ebb333c09746.

Its macOS backend initializes MacosInputState::display using CGMainDisplayID(). In post_mouse(), it clamps both mouse coordinates to CGDisplayBounds(state_->display). Both relative and absolute motion paths use this function.

This appears to constrain injected mouse movement to the main display rather than allowing movement on the selected secondary display.

Main-display initialization
https://github.com/LizardByte/libvirtualhid/blob/6fdb8bd4de3b68d96c30e5303ac2ebb333c09746/src/platform/macos/macos_backend.cpp#L384

Mouse coordinate clamping
https://github.com/LizardByte/libvirtualhid/blob/6fdb8bd4de3b68d96c30e5303ac2ebb333c09746/src/platform/macos/macos_backend.cpp#L684