wayland: implement HIDPI support

The wayland protocol exposes scaling done by the compositor to
compensate for small window sizes on small high DPI displays. If the
program ignores the scaling done, what'll happen is the compositor is
going to ask the program to be scaled down by N times the window size and
then it'll upscale the program's surface by N times. The scaling
algorithm seems to be bilinear so the scaling is quite obvious.

This commit sets up callbacks to listen for the scaling factor of each
output and, on rescale events, notifies the compositor that the
surface's scale is what the compositor asked for and changes the
player's surface to the appropriate size, causing no scaling to be done
by the compositor.

Compositors not supporting this interface will ignore the callbacks and do
nothing, keeping program behaviour the same. For compositors supporting
and using this interface (mutter), this will fix the rendering to be pixel
precise as it should be.

Both the opengl wayland backend and the wayland vo have been fixed to support
this. Verified to not break either on weston and mutter.

Signed-off-by: Rostislav Pehlivanov <atomnuker@gmail.com>

1 files changed, 1 insertions, 0 deletions

diff --git a/video/out/wayland_common.h b/video/out/wayland_common.h
index d23b2f24c7..ec3f72ce67 100644
--- a/video/out/wayland_common.h
+++ b/video/out/wayland_common.h
@@ -41,6 +41,7 @@ struct vo_wayland_output {
     uint32_t flags;
     int32_t width;
     int32_t height;
+    int32_t scale;
     int32_t refresh_rate; // fps (mHz)
     const char *make;
     const char *model;