foot/fractional-scale-v1.xml

<?xml version="1.0" encoding="UTF-8"?>
<protocol name="fractional_scale_v1">
  <copyright>
    Copyright © 2022 Kenny Levinsen

    Permission is hereby granted, free of charge, to any person obtaining a
    copy of this software and associated documentation files (the "Software"),
    to deal in the Software without restriction, including without limitation
    the rights to use, copy, modify, merge, publish, distribute, sublicense,
    and/or sell copies of the Software, and to permit persons to whom the
    Software is furnished to do so, subject to the following conditions:

    The above copyright notice and this permission notice (including the next
    paragraph) shall be included in all copies or substantial portions of the
    Software.

    THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
    IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
    FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
    THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
    LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
    FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
    DEALINGS IN THE SOFTWARE.
  </copyright>

  <description summary="Protocol for requesting fractional surface scales">
    This protocol allows a compositor to suggest for surfaces to render at
    fractional scales.

    A client can submit scaled content by utilizing wp_viewport. This is done by
    creating a wp_viewport object for the surface and setting the destination
    rectangle set to the surface size before the scale factor is applied.

    If the surface is not a subsurface, then the buffer size is calculated by
    multiplying the surface size by the intended scale, rounding the result
    halfway away from zero.

    If the surface is a subsurface, then the calculation must account for the
    surface position when rounding the buffer size. First, add the subsurface
    position relative to its parent to the surface size, multiplying them by the
    intended scale and rounding the result halfway away from zero. Second, take
    the subsurface position relative to its parent, multiplying it by the
    intended scale and rounding the result halfway away from zero. Finally,
    subtract the result of the second calculation from the first calculation to
    get the buffer size.

    The wl_surface buffer scale should remain set to 1 in both cases.

    In the compositor, final subsurface positions are calculated by multiplying
    the position of the subsurface relative to its parent by the intended scale,
    and rounding the result halfway away from zero. The positions of the parent
    surfaces, calculated using the same mechanism, are then recursively added to
    the result. This ensures that position and size rounding is not affected by
    the movement of parent surfaces.

    If a surface has a surface-local size of 100 px by 50 px and wishes to
    submit buffers with a scale of 1.5, then a buffer of 150px by 75 px should
    be used and the wp_viewport destination rectangle should be 100 px by 50 px.
  </description>

  <interface name="wp_fractional_scale_manager_v1" version="1">
    <description summary="fractional surface scale information">
      A global interface for requesting surfaces to use fractional scales.
    </description>

    <request name="destroy" type="destructor">
      <description summary="unbind the surface scale interface">
        Informs the server that the client will not be using this protocol
        object anymore. This does not affect any other objects,
        wp_fractional_scale_v1 objects included.
      </description>
    </request>

    <enum name="error">
      <entry name="fractional_scale_exists" value="0"
        summary="the surface already has a fractional_scale object associated"/>
    </enum>

    <request name="get_fractional_scale">
      <description summary="extend surface interface for scale information">
        Create an add-on object for the the wl_surface to let the compositor
        request fractional scales. If the given wl_surface already has a
        wp_fractional_scale_v1 object associated, the fractional_scale_exists
        protocol error is raised.
      </description>
      <arg name="id" type="new_id" interface="wp_fractional_scale_v1"
           summary="the new surface scale info interface id"/>
      <arg name="surface" type="object" interface="wl_surface"
           summary="the surface"/>
    </request>
  </interface>

  <interface name="wp_fractional_scale_v1" version="1">
    <description summary="fractional scale interface to a wl_surface">
      An additional interface to a wl_surface object which allows the compositor
      to inform the client of the preferred scale.
    </description>

    <request name="destroy" type="destructor">
      <description summary="remove surface scale information for surface">
        The associated wl_surface's fractional scale object is destroyed.
      </description>
    </request>

    <event name="preferred_scale">
      <description summary="notify of new preferred scale">
        Notification of a new preferred scale for this surface that the
        compositor suggests that the client should use.
      </description>
      <arg name="scale" type="fixed" summary="the new preferred scale"/>
    </event>
  </interface>
</protocol>