wayland: Handle min/max sizes in fixed-size windows with viewports

Wayland is sometimes at-odds with clients that want to enforce an aspect ratio or min/max window size, as certain window states have dimensions that either must be obeyed (maximized), or will give terrible results if they aren't (tiled). Use a viewport and a masking subsurface to handle cases where surfaces are unable to match the exact window size.

The changes made to accommodate this also catches some additional windowing related edge-cases, simplifies synchronization, and prevents commits before a buffer has been attached to the surface.

wayland-protocols/single-pixel-buffer-v1.xml

@@ -0,0 +1,76 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<protocol name="single_pixel_buffer_v1">
+  <copyright>
+    Copyright © 2022 Simon Ser
+
+    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="single pixel buffer factory">
+    This protocol extension allows clients to create single-pixel buffers.
+
+    Compositors supporting this protocol extension should also support the
+    viewporter protocol extension. Clients may use viewporter to scale a
+    single-pixel buffer to a desired size.
+
+    Warning! The protocol described in this file is currently in the testing
+    phase. Backward compatible changes may be added together with the
+    corresponding interface version bump. Backward incompatible changes can
+    only be done by creating a new major version of the extension.
+  </description>
+
+  <interface name="wp_single_pixel_buffer_manager_v1" version="1">
+    <description summary="global factory for single-pixel buffers">
+      The wp_single_pixel_buffer_manager_v1 interface is a factory for
+      single-pixel buffers.
+    </description>
+
+    <request name="destroy" type="destructor">
+      <description summary="destroy the manager">
+        Destroy the wp_single_pixel_buffer_manager_v1 object.
+
+        The child objects created via this interface are unaffected.
+      </description>
+    </request>
+
+    <request name="create_u32_rgba_buffer">
+      <description summary="create a 1×1 buffer from 32-bit RGBA values">
+        Create a single-pixel buffer from four 32-bit RGBA values.
+
+        Unless specified in another protocol extension, the RGBA values use
+        pre-multiplied alpha.
+
+        The width and height of the buffer are 1.
+
+        The r, g, b and a arguments valid range is from UINT32_MIN (0)
+        to UINT32_MAX (0xffffffff).
+        
+        These arguments should be interpreted as a percentage, i.e.
+        - UINT32_MIN = 0% of the given color component
+        - UINT32_MAX = 100% of the given color component
+      </description>
+      <arg name="id" type="new_id" interface="wl_buffer"/>
+      <arg name="r" type="uint" summary="value of the buffer's red channel"/>
+      <arg name="g" type="uint" summary="value of the buffer's green channel"/>
+      <arg name="b" type="uint" summary="value of the buffer's blue channel"/>
+      <arg name="a" type="uint" summary="value of the buffer's alpha channel"/>
+    </request>
+  </interface>
+</protocol>