Zoom does not follow mouse correctly on external displays

[joeyhoer]

Environment: macOS 15.6.1 (likely affects other systems as well)

When using an external display, the zoom does not follow the mouse correctly along the Y axis. The X axis behaves correctly, while zoom is fixed vertically to the top of the display.

Steps to reproduce:

• Arrange an external display above the main display.
• Move the mouse across the external display while using zoom.

Observed behavior

• The zoomed area does not track the mouse properly along Y.

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Root cause

Look at the two following screenshots, and note the final value of the display name.

When the external display is arranged above the main display, the Y value is positive…

When the external display is arranged below the main display, the Y value is negative…

The get_monitor_info function extracts the monitor’s top-left coordinates from the display name using this regex:

x, y = found:match("(-?%d+),(-?%d+)")

OBS reports mouse positions relative to the main display's origin (top left):

• When the mouse is above the main display, the Y coordinate is negative.
• When the mouse is below the main display, the Y coordinate is positive.

This is the inverse behavior of how the monitor position is reported.

Later, the mouse position is calculated relative to the monitor using:

if monitor_info then
    mouse.x = mouse.x - monitor_info.x
    mouse.y = mouse.y - monitor_info.y
end

This subtraction assumes the monitor Y coordinate is positive relative to the main display, which is not true when the monitor is above the primary display.

Solution

Invert the Y value when parsing in get_monitor_info:

info.y = -tonumber(y, 10)

This aligns the monitor offset with OBS’s global mouse coordinates, fixing the vertical tracking on external displays.