[Spice-devel] [PATCH] randr: set physical screen size to keep a constant 96 dpi

[Marc-André Lureau]

Some applications compute DPI based on physcial screen size.  Currently,
the width is reported to be 270mm, regardless of the resolution.  This
patch instead compute a physical screen size to have a constant DPI of
96. Of course, there are possible improvements to this approach (see
fixme), however, since that code is no longer executed with DRM driver,
I don't think we should invest more effort here (I guess DRM driver
relied on xrandr / gnome-settings-daemon to do the right thing, so
physical screen is updated)

https://bugzilla.redhat.com/show_bug.cgi?id=1066094
---
 src/vdagent-x11-randr.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/src/vdagent-x11-randr.c b/src/vdagent-x11-randr.c
index 5223f88..9bde7b9 100644
--- a/src/vdagent-x11-randr.c
+++ b/src/vdagent-x11-randr.c
@@ -767,13 +767,16 @@ void vdagent_x11_set_monitor_config(struct vdagent_x11 *x11,
     }
 
     if (primary_w != x11->width[0] || primary_h != x11->height[0]) {
+        const int dpi = 96; /* FIXME: read settings from desktop or get from client dpi? */
+        int fb_width_mm = (25.4 * primary_w) / dpi;
+        int fb_height_mm = (25.4 * primary_h) / dpi;
+
         if (x11->debug)
             syslog(LOG_DEBUG, "Changing screen size to %dx%d",
                    primary_w, primary_h);
         vdagent_x11_set_error_handler(x11, error_handler);
         XRRSetScreenSize(x11->display, x11->root_window[0], primary_w, primary_h,
-                         DisplayWidthMM(x11->display, 0),
-                         DisplayHeightMM(x11->display, 0));
+                         fb_width_mm, fb_height_mm);
         if (vdagent_x11_restore_error_handler(x11)) {
             syslog(LOG_ERR, "XRRSetScreenSize failed, not enough mem?");
             if (!fallback && curr) {
-- 
1.8.5.3