[PATCH] protocol: Add buffer_scale to wl_surface and wl_output

[alexl at redhat.com]

From: Alexander Larsson <alexl at redhat.com>

This adds wl_surface_set_buffer_scale() to set the buffer scale of a
surface.

It is similar to set_buffer_transform that the buffer is stored in a
way that has been transformed (in this case scaled). This means that
if an output is scaled we can directly use the pre-scaled buffer with
additional data, rather than having to scale it.

It also adds a geometry2 event with a scale member to wl_output that
specifies the scaling of an output.

This is meant to be used for outputs with a very high DPI to tell the
client that this particular output has subpixel precision. Coordinates
in other parts of the protocol, like input events, relative window
positioning and output positioning are still in the compositor space
rather than the scaled space. However, input has subpixel precision
so you can still get input at full resolution.

This setup means global properties like mouse acceleration/speed,
pointer size, monitor geometry, etc can be specified in a "mostly
similar" resolution even on a multimonitor setup where some monitors
are low dpi and some are e.g. retina-class outputs.
---
 protocol/wayland.xml | 41 +++++++++++++++++++++++++++++++++++++++--
 1 file changed, 39 insertions(+), 2 deletions(-)

diff --git a/protocol/wayland.xml b/protocol/wayland.xml
index 3bce022..e5744c7 100644
--- a/protocol/wayland.xml
+++ b/protocol/wayland.xml
@@ -876,7 +876,7 @@
     </event>
   </interface>
 
-  <interface name="wl_surface" version="2">
+  <interface name="wl_surface" version="3">
     <description summary="an onscreen surface">
       A surface is a rectangular area that is displayed on the screen.
       It has a location, size and pixel contents.
@@ -1110,6 +1110,30 @@
       </description>
       <arg name="transform" type="int"/>
     </request>
+
+    <!-- Version 3 additions -->
+
+    <request name="set_buffer_scale" since="3">
+      <description summary="sets the buffer scale">
+	This request sets an optional scaling factor on how the compositor
+	interprets the contents of the buffer attached to the surface. A
+	value larger than 1, like e.g. 2 means that the buffer is 2 times the
+	size of the surface.
+
+	Buffer scale is double-buffered state, see wl_surface.commit.
+
+	A newly created surface has its buffer scale set to 1.
+
+	The purpose of this request is to allow clients to supply higher resolution
+	buffer data for use on high-resolution outputs where the output itself
+	has a scaling factor set. For instance, a laptop with a high DPI
+	internal screen and an low DPI external screen would have two outputs
+	with different scaling, and a wl_surface rendered on the scaled output
+	would normally be scaled up. To avoid this upscaling the app can supply
+	a pre-scaled version with more detail by using set_buffer_scale.
+      </description>
+      <arg name="scale" type="fixed"/>
+    </request>
    </interface>
 
   <interface name="wl_seat" version="1">
@@ -1467,7 +1491,7 @@
     </event>
   </interface>
 
-  <interface name="wl_output" version="1">
+  <interface name="wl_output" version="2">
     <description summary="compositor output region">
       An output describes part of the compositor geometry.  The
       compositor works in the 'compositor coordinate system' and an
@@ -1520,6 +1544,8 @@
 	The geometry event describes geometric properties of the output.
 	The event is sent when binding to the output object and whenever
 	any of the properties change.
+
+        Some additional properties were later added, see wl_output.geometry2.
       </description>
       <arg name="x" type="int"
 	   summary="x position within the global compositor space"/>
@@ -1565,6 +1591,17 @@
       <arg name="height" type="int" summary="height of the mode in pixels"/>
       <arg name="refresh" type="int" summary="vertical refresh rate in mHz"/>
     </event>
+
+    <event name="geometry2" since="2">
+      <description summary="additional properties of the output">
+	This event contains additional geometric information
+        that are not in the geometry event. Whenever it is sent
+        it will be followed by a geometry event. This way you can
+        tell by the time the geometry event is recieved whether a
+        geometry2 event will be seen or not.
+      </description>
+      <arg name="scale" type="fixed" summary="scaling factor of output"/>
+    </event>
   </interface>
 
   <interface name="wl_region" version="1">
-- 
1.8.1.4