fix: Correct buffer scaling when using fractional scale protocol - #28
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When wp_fractional_scale_manager_v1 is active, the compositor expects the buffer scale to be 1, with scaling handled via wp_viewport. Previously, we were mistakenly applying the integer output scale (e.g. 2x) to the buffer, resulting in a logical size mismatch and rendering errors on compositors like Niri.
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Description
This PR fixes an issue where the application would render with incorrect dimensions on Wayland compositors using fractional scaling (in my case Niri).
The Problem
When the
wp_fractional_scale_manager_v1protocol is active, the application is responsible for rendering at the exact physical pixel size, and the Wayland surface buffer scale should be set to 1.Previously, the application was correctly using
wp_viewportfor sizing but was also setting thewl_surfacebuffer scale to the integer scale factor provided bywl_output(e.g., setting it to2on a 1.25x scale output).This "double scaling" caused the compositor to interpret the buffer as having half the intended logical size (e.g., 3840 physical pixels / scale 2 = 1920 logical pixels), resulting in mismatched window geometry and errors such as:
wp_viewport: source rectangle extends outside of the content areaThe Fix
The fix ensures that
wl_surface.setBufferScaleis explicitly set to1whenever thewp_fractional_scale_manager_v1is available and in use. The existing logic for integer-only scaling remains unchanged to prevent regressions on compositors that do not support fractional scaling.Verification