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Clarify behavior of buffer transformations

Julian Orth requested to merge mahkoh/wayland:jorth/transform into main

The new text describes how

  • Weston
  • Mutter
  • Plasma
  • Sway 1.8
  • Jay

behave.

Sway 1.9 flipped the behavior of 90 degree and 270 degree set_buffer_transform requests. mpv also changed the behavior of its vo_wayland_dmabuf backend which makes it only work correctly on sway 1.9.

It seems that the previous text was open to interpretation or at least caused some amount of confusion.

Consider the following example:

image

  • The user has rotated his display 90 degrees clockwise.
  • The compositor will rotate surface space 90 degrees counter-clockwise during compositing. It reports wl_output::transform = 90.
  • The client has rotated its buffer 90 degrees counter-clockwise relative to its surface. It sets wl_surface::set_buffer_transform = 90.
  • During compositing, the compositor does not have to apply any rotation to the buffer.
Edited by Julian Orth

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