[PATCH 2/2] protocol: Support scaled outputs and surfaces
Jason Ekstrand
jason at jlekstrand.net
Thu May 16 08:05:13 PDT 2013
On May 16, 2013 8:44 AM, <alexl at redhat.com> wrote:
>
> From: Alexander Larsson <alexl at redhat.com>
>
> This adds the wl_surface.set_buffer_scale request, and a wl_output.scale
> event. These together lets us support automatic upscaling of "old"
> clients on very high resolution monitors, while allowing "new" clients
> to take advantage of this to render at the higher resolution when the
> surface is displayed on the scaled output.
>
> It is similar to set_buffer_transform in that the buffer is stored in
> a transformed pixels (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.
>
> Additionally this adds a "scaled" flag to the wl_output.mode flags
> so that clients know which resolutions are native and which are scaled.
>
> Also, in places where the documentation was previously not clear as to
> what coordinate system was used this was fleshed out.
>
> It also adds a scaling_factor event 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.
This looks better.
I still think we can solve this problem better if the clients, instead of
providing some sort of pre-scaled buffer that matches the output's
arbitrary scale factor, simply told the compositor which output they
rendered for. Then everything will be in that outputs coordinates. If the
surface ever lands on a different output, the compositor can scale
everything relative to the selected output. Surfaces which do not specify
an output would just get scaled by the factor. This has three advantages.
1. Everything is still pixel-perfect and there are no input rounding errors.
2. There is no confusion about things like subsurface positioning and
clients can place subsurfaces at any pixel, not just multiples of the scale
factor. (Sub surfaces would have to inherent their "drawing on X monitor"
setting from the parent to keep everything sane.)
3. Since surfaces are scaled relative to their preferred output, the user
can specify arbitrary scaling factors for each output and are not
restricted to integers.
I proposed this in more detail in a previous email but no one bothered to
respond to it.
Thanks,
--Jason Ekstrand
> ---
> protocol/wayland.xml | 107
++++++++++++++++++++++++++++++++++++++++++++-------
> 1 file changed, 93 insertions(+), 14 deletions(-)
>
> diff --git a/protocol/wayland.xml b/protocol/wayland.xml
> index d3ae149..acfb140 100644
> --- a/protocol/wayland.xml
> +++ b/protocol/wayland.xml
> @@ -173,7 +173,7 @@
> </event>
> </interface>
>
> - <interface name="wl_compositor" version="2">
> + <interface name="wl_compositor" version="3">
> <description summary="the compositor singleton">
> A compositor. This object is a singleton global. The
> compositor is in charge of combining the contents of multiple
> @@ -709,7 +709,7 @@
>
> The x and y arguments specify the locations of the upper left
> corner of the surface relative to the upper left corner of the
> - parent surface.
> + parent surface, in surface local coordinates.
>
> The flags argument controls details of the transient behaviour.
> </description>
> @@ -777,6 +777,10 @@
> in any of the clients surfaces is reported as normal, however,
> clicks in other clients surfaces will be discarded and trigger
> the callback.
> +
> + The x and y arguments specify the locations of the upper left
> + corner of the surface relative to the upper left corner of the
> + parent surface, in surface local coordinates.
> </description>
>
> <arg name="seat" type="object" interface="wl_seat" summary="the
wl_seat whose pointer is used"/>
> @@ -860,6 +864,9 @@
>
> The client is free to dismiss all but the last configure
> event it received.
> +
> + The width and height arguments specify the size of the window
> + in surface local coordinates.
> </description>
>
> <arg name="edges" type="uint"/>
> @@ -876,11 +883,16 @@
> </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.
>
> + The size of a surface (and relative positions on it) is described
> + in surface local coordinates, which may differ from the buffer
> + local coordinates of the pixel content, in case a buffer_transform
> + or a buffer_scale is used.
> +
> Surfaces are also used for some special purposes, e.g. as
> cursor images for pointers, drag icons, etc.
> </description>
> @@ -895,20 +907,25 @@
> <description summary="set the surface contents">
> Set a buffer as the content of this surface.
>
> + The new size of the surface is calculated based on the buffer
> + size transformed by the inverse buffer_transform and the
> + inverse buffer_scale. This means that the supplied buffer
> + must be an integer multiple of the buffer_scale.
> +
> The x and y arguments specify the location of the new pending
> - buffer's upper left corner, relative to the current buffer's
> - upper left corner. In other words, the x and y, and the width
> - and height of the wl_buffer together define in which directions
> - the surface's size changes.
> + buffer's upper left corner, relative to the current buffer's upper
> + left corner, in surface local coordinates. In other words, the
> + x and y, combined with the new surface size define in which
> + directions the surface's size changes.
>
> Surface contents are double-buffered state, see wl_surface.commit.
>
> The initial surface contents are void; there is no content.
> wl_surface.attach assigns the given wl_buffer as the pending
> wl_buffer. wl_surface.commit makes the pending wl_buffer the new
> - surface contents, and the size of the surface becomes the size of
> - the wl_buffer, as described above. After commit, there is no
> - pending buffer until the next attach.
> + surface contents, and the size of the surface becomes the size
> + calculated from the wl_buffer, as described above. After commit,
> + there is no pending buffer until the next attach.
>
> Committing a pending wl_buffer allows the compositor to read the
> pixels in the wl_buffer. The compositor may access the pixels at
> @@ -945,6 +962,8 @@
>
> Damage is double-buffered state, see wl_surface.commit.
>
> + The damage rectangle is specified in surface local coordinates.
> +
> The initial value for pending damage is empty: no damage.
> wl_surface.damage adds pending damage: the new pending damage
> is the union of old pending damage and the given rectangle.
> @@ -996,6 +1015,8 @@
> behaviour, but marking transparent content as opaque will result
> in repaint artifacts.
>
> + The opaque region is specified in surface local coordinates.
> +
> The compositor ignores the parts of the opaque region that fall
> outside of the surface.
>
> @@ -1023,6 +1044,8 @@
> surface in the server surface stack. The compositor ignores the
> parts of the input region that fall outside of the surface.
>
> + The input region is specified in surface local coordinates.
> +
> Input region is double-buffered state, see wl_surface.commit.
>
> wl_surface.set_input_region changes the pending input region.
> @@ -1100,7 +1123,7 @@
> according to the output transform, thus permiting the compositor
to
> use certain optimizations even if the display is rotated. Using
> hardware overlays and scanning out a client buffer for fullscreen
> - surfaces are examples of such optmizations. Those optimizations
are
> + surfaces are examples of such optimizations. Those optimizations
are
> highly dependent on the compositor implementation, so the use of
this
> request should be considered on a case-by-case basis.
>
> @@ -1110,6 +1133,30 @@
> </description>
> <arg name="transform" type="int"/>
> </request>
> +
> + <!-- Version 3 additions -->
> +
> + <request name="set_buffer_scale" since="3">
> + <description summary="sets the buffer scaling factor">
> + This request sets an optional scaling factor on how the compositor
> + interprets the contents of the buffer attached to the window.
> +
> + 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. Its
> + intended that you pick the same buffer scale as the scale of the
> + output that the surface is displayed on.This means the compositor
> + can avoid scaling when rendering the surface on that output.
> +
> + Note that if the scale is larger than 1, then you have to attach
> + a buffer that is larger (by a factor of scale in each dimension)
> + than the desired surface size.
> + </description>
> + <arg name="scale" type="uint"/>
> + </request>
> </interface>
>
> <interface name="wl_seat" version="1">
> @@ -1197,7 +1244,8 @@
> The parameters hotspot_x and hotspot_y define the position of
> the pointer surface relative to the pointer location. Its
> top-left corner is always at (x, y) - (hotspot_x, hotspot_y),
> - where (x, y) are the coordinates of the pointer location.
> + where (x, y) are the coordinates of the pointer location, in
surface
> + local coordinates.
>
> On surface.attach requests to the pointer surface, hotspot_x
> and hotspot_y are decremented by the x and y parameters
> @@ -1548,6 +1596,8 @@
> summary="indicates this is the current mode"/>
> <entry name="preferred" value="0x2"
> summary="indicates this is the preferred mode"/>
> + <entry name="scaled" value="0x4"
> + summary="indicates that this is a scaled mode"/>
> </enum>
>
> <event name="mode">
> @@ -1559,10 +1609,15 @@
> again if an output changes mode, for the mode that is now
> current. In other words, the current mode is always the last
> mode that was received with the current flag set.
> +
> + The size of a mode is given relative to the global compositor
> + space. This is not necessarily the native size of the display,
> + as the output might be scaled, as described in wl_output.scale.
> + In this case the scaled flag will be set.
> </description>
> <arg name="flags" type="uint" summary="bitfield of mode flags"/>
> - <arg name="width" type="int" summary="width of the mode in
pixels"/>
> - <arg name="height" type="int" summary="height of the mode in
pixels"/>
> + <arg name="width" type="int" summary="width of the mode in global
coordinates"/>
> + <arg name="height" type="int" summary="height of the mode in
global coordinates"/>
> <arg name="refresh" type="int" summary="vertical refresh rate in
mHz"/>
> </event>
>
> @@ -1575,6 +1630,30 @@
> atomic, even if they happen via multiple events.
> </description>
> </event>
> +
> + <event name="scale" since="2">
> + <description summary="output scaling properties">
> + This event contains scaling geometry information
> + that is not in the geometry event. It may be sent after
> + binding the output object or if the output scale changes
> + later. If it is not sent, the client should assume a
> + scale of 1.
> +
> + A scale larger than 1 means that the compositor will
> + automatically scale surface buffers by this amount
> + when rendering. This is used for very high resolution
> + displays where applications rendering at the native
> + resolution would be too small to be legible.
> +
> + It is intended that scaling aware clients track the
> + current output of a surface, and if it is on a scaled
> + output it should use wl_surface.set_buffer_scale with
> + the scale of the output. That way the compositor can
> + avoid scaling the surface, and the client can supply
> + a higher detail image.
> + </description>
> + <arg name="factor" type="uint" summary="scaling factor of output"/>
> + </event>
> </interface>
>
> <interface name="wl_region" version="1">
> --
> 1.8.1.4
>
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