wayland: use correct rounding in logical->physical conversions

rust-windowing / winit

Window handling library in pure Rust

https://docs.rs/winit/

Apache License 2.0

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wayland: use correct rounding in logical->physical conversions #3955

Open mahkoh opened 1 month ago

mahkoh commented 1 month ago

/// A wp-fractional-scale scale.
///
/// This type implements the `physical_size = round_half_up(logical_size * scale)`
/// operation with infinite precision as required by the protocol.
#[derive(Copy, Clone, Debug, Eq, PartialEq)]
pub struct Scale {
        scale: u64,
}

[x] Tested on all platforms changed
[ ] Added an entry to the changelog module if knowledge of this change could be valuable to users
[ ] Updated documentation to reflect any user-facing changes, including notes of platform-specific behavior
[ ] Created or updated an example program if it would help users understand this functionality
[ ] Updated feature matrix, if new features were added or implemented

kchibisov commented 1 month ago

While I don't mind changing the algorithm is unspecified, which we brought before here https://gitlab.freedesktop.org/wayland/wayland-protocols/-/issues/132

What winit does is what majority of compositors do (probably not yours since you've sent the patch), so we error the same.

Unless upstream issue progresses, I don't see why this new rounding is correct when there's no specification of what is correct.

mahkoh commented 1 month ago

See https://gitlab.freedesktop.org/wayland/wayland-protocols/-/merge_requests/309/diffs

What winit does is what majority of compositors do (probably not yours since you've sent the patch)

Actually my compositor also uses f64 just like winit. A mistake for sure.

kchibisov commented 1 month ago

See https://gitlab.freedesktop.org/wayland/wayland-protocols/-/merge_requests/309/diffs

You should've have linked it right away in the PR description.

Will wait until it merges and then I'll merge it here as well once review is done.