On X11, if RANDR based scale factor is higher than 20 reset it to 1

Some video drivers could set display metrics to odd values, which can result in
extra large scale factors (e.g. winit is sending 720 for 5k screen on nvidia
binary drivers), so let's just drop them to prevent clients from using them.
The value 20 was picked, because the DPR for 8k @ 5 inch is ~18.36.

Fixes #1983.

CHANGELOG.md

@@ -16,6 +16,7 @@
 - On Wayland, bump `smithay-client-toolkit` to 0.15.1.
 - On Wayland, implement `request_user_attention` with `xdg_activation_v1`.
 - On X11, emit missing `WindowEvent::ScaleFactorChanged` when the only monitor gets reconnected.
+- On X11, if RANDR based scale factor is higher than 20 reset it to 1
 
 # 0.25.0 (2021-05-15)
 

src/platform_impl/linux/x11/util/randr.rs

@@ -27,7 +27,11 @@ pub fn calc_dpi_factor(
     // Quantize 1/12 step size
     let dpi_factor = ((ppmm * (12.0 * 25.4 / 96.0)).round() / 12.0).max(1.0);
     assert!(validate_scale_factor(dpi_factor));
-    dpi_factor
+    if dpi_factor <= 20. {
+        dpi_factor
+    } else {
+        1.
+    }
 }
 
 impl XConnection {