[macOS] Canvas appears pixelated/aliased when using scaled monitor resolution

[syntask]

Description
On macOS, when using an external 4K monitor set to a scaled resolution, there is a rendering mismatch between the UI and the canvas. The UI elements (menus, toolbars, and icons) are rendered sharply at HiDPI, but the canvas area (the actual image) appears pixelated/aliased. It seems the canvas surface is not correctly adopting the system's backing scale factor, resulting in a low-resolution render that is then stretched to fit the space.

To Reproduce

1. Connect a 4K monitor to a Mac.
2. In macOS System Settings > Displays, set the resolution to a scaled resolution (e.g. 1920 x 1080).
3. Open Pinta and create or open an image.
4. Observe the canvas area: the image appears pixelated, even at 100% zoom, while the surrounding Pinta UI remains crisp.

Additional Info

• Switching the monitor to its native (non-scaled) 2160p resolution fixes the canvas pixelation, but makes the UI too small for use on my 27" monitor.
• Adjusting Pinta’s internal zoom (e.g., to 50% or 100%) does not fix the pixelation.

Version

• Operating System: macOS 26.2
• Pinta Version: 3.1.1